HK1050450B - Method and apparatus for high rate packet data transmission - Google Patents

Description

Method and apparatus for high rate packet data transmission

This application is a divisional application of an invention patent application having an application date of 1998, 3/11, and an application number of 98810951.4, which is the same name as the present application.

Background

I. Field of the invention

The present invention relates to data communication. More particularly, the present invention relates to a novel and improved method and apparatus for high rate packet data transmission.

Description of the Prior Art

Modern communication systems are required to support a variety of applications. One such communication system IS a Code Division Multiple Access (CDMA) system that conforms to the TIA/EIA/IS-95 mobile station-base station compatibility standard for dual-mode wideband spread spectrum cellular systems, hereinafter referred to as the IS-95 standard. CDMA systems allow voice and data communications between users over terrestrial links. The use of CDMA techniques in multiple access communication systems is disclosed in U.S. patent No. 4,901,307, entitled "spread spectrum multiple access communication system using satellite or terrestrial repeaters," and U.S. patent No. 5,103,459, entitled "system and method for generating waveforms in a CDMA cellular telephone system," both assigned to the assignee of the present invention and incorporated herein by reference.

In this specification, a base station refers to hardware with which each mobile station communicates. A cell refers to a hardware or geographic coverage area, depending on the scope of the term used. A sector is a portion of a cell. Since the sectors of the CDMA system have the property of a cell, the teaching material described in the term cell can be easily extended to a sector.

In a CDMA system, communication between users is conducted through one or more base stations. A first user at one mobile station communicates with a second user at a second mobile station by transmitting data on the reverse link to the base station. The base station receives the data and may route the data to another base station. Data is transmitted to the second mobile station on the forward link of the same base station, or a second base station. The forward link refers to transmissions from the base station to the mobile station and the reverse link refers to transmissions from the mobile station to the base station. In an IS-95 system, separate frequencies are allocated for the forward and reverse links.

During communication, the mobile station communicates with at least one base station. During soft handoff, a CDMA mobile station may communicate with multiple base stations simultaneously. Soft handoff is the process of establishing a link with a new base station before disconnecting the link with the previous base station. Soft handoff minimizes the probability of dropped calls. Methods and systems for communicating with a mobile station via more than one base station during a soft handoff are disclosed in U.S. patent No. 5,267,261, entitled "soft handoff to assist a mobile station in a CDMA telephone system," which is assigned to the assignee of the present invention and is incorporated herein by reference. Soft handoff is the process by which communication occurs over multiple sectors, which are served by the same base station. Pending U.S. patent application No. 08/763,498 entitled "method and apparatus for soft handoff between sectors of a common base station," filed 11/1996, which is assigned to the assignee of the present invention and is incorporated herein by reference, describes the soft handoff process in detail.

The growing demand for wireless data applications has made the demand for extremely efficient wireless data communication systems increasingly important. The IS-95 standard IS capable of transmitting traffic data and voice data on the forward and reverse links. A method of transmitting traffic data in fixed size code channel frames is described in detail in U.S. patent No. 5,504,773, entitled "method and apparatus for transmitting data formatting," which is assigned to the assignee of the present invention and is incorporated herein by reference. According to the IS-95 standard, traffic data or voice data IS divided into code channel frames that are 20 milliseconds wide, with data rates as high as 14.4 Kbps.

A notable difference between voice services and data services is the fact that the former imposes precise and fixed delay requirements. Typically, the one-way delay of the total speech frame must be less than 100 milliseconds. In contrast, data delay can be a variable parameter for optimizing the efficiency of a data communication system. In particular, more efficient error correction code techniques may be applied which require significantly more delay than what can be tolerated by voice services. An efficient encoding scheme for data is disclosed in U.S. patent No. 08/743,688 entitled "soft decision output decoder for decoding convolutionally encoded codewords", filed 11/6 1996, which is assigned to the assignee of the present invention and is incorporated herein by reference.

Another notable difference between voice services and data services is that the former requires a fixed and common grade of service (GOS) for all users. Typically, for digital systems, voice services are provided, which translates into a fixed and equal transmission rate for all users, and a maximum tolerable value for the error rate of the speech frames. In contrast, for data services, there may be different GOS from user to user and may be a parameter optimized to increase the overall efficiency of the data communication system. The GOS for a data communication is typically determined as the total delay incurred in transmitting a predetermined amount of data, hereinafter referred to as a data packet.

Another notable difference between voice services and data services is that the former require a reliable communication link, which in the exemplary CDMA communication system is provided by soft handoff. Soft handoff results in redundant transmissions from two or more base stations to improve reliability. However, data transmission does not require this additional reliability, since received data packets with errors can be retransmitted. For data services, the transmit power used to support soft handoff may be more efficiently used to transmit additional data.

The parameters that measure the quality and effectiveness of a data communication system are the transmission delay required to transmit a data packet and the average throughput rate of the system. In data communications, the transmission delay does not have identical pulses, unlike it is in voice communications, but it is an important measure of the quality of the communication system. The average throughput rate is a measure of the efficiency of the data transmission capability of the communication system.

It is well known that in cellular systems, the signal-to-noise-and-interference ratio C/I for any given user is a function of the user's location within the coverage area. In order to maintain a given level of service, TDMA and FDMA systems are classified into types of frequency reuse, i.e., not all frequency channels and/or time slots are used in each base station. In a CDMA system, the same frequency assignment is reused in each cell of the system, thus improving overall efficiency. The resulting C/I of any given user's mobile station determines the information rate that can be supported by this particular link from the base station to the user's mobile station. Given the particular modulation and error correction method used for transmission, the present invention seeks to optimize data transmission to achieve a given level of performance at the required C/I level. In order to idealise a cellular system with a hexagonal cell profile and apply a common frequency in each cell, the resulting C/I distribution within the ideal cell can be calculated.

The C/I achieved by any given user is a function of the path loss, which for terrestrial cellular systems is given by r³To r⁵And increases where r is the distance to the radiation source. Furthermore, path loss is subject to random variables due to man-made and natural obstructions in the radio wave path. These random variables are typically modularized as a log-normal shaded random process with an 8dB standard deviation. For a base station antenna with omni-directionality, the resulting C/I distribution for an ideal hexagonal cell profile is r⁴The propagation law, and the shading process with 8dB standard deviation, is shown in figure 10.

The resulting C/I distribution can only be obtained if the mobile station is served by the best base station at any instant in time and at any location (the base station that gets the largest C/I value is defined as the best base station regardless of the physical location for each base station). Due to the random nature of the path loss as described above, the signal having the largest C/I value may be one whose distance from the mobile station is not the smallest physical distance. In contrast, if only the base station of the minimum distance is communicated, the C/I can be substantially reduced. It is therefore most advantageous for the mobile station to communicate back and forth to the best serving base station at all times, thus resulting in the best C/I value. It can also be observed that in the ideal module described above and as shown in fig. 10, the range of C/I values obtained is such that the difference between the maximum and minimum values can be as large as 10,000. In practical implementations, the range is typically limited to about 1: 100 or 20 dB. Since the following relationship is maintained, it is possible for the base station serving the mobile station to have an information bit rate of up to the change factor of 100.

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Wherein R is_bRepresenting the information rate for a particular mobile station, W being the total bandwidth occupied by the spread spectrum signal, E_b/I_oIs the energy per bit at the interference density required to achieve a given performance level. For example, if the spread spectrum signal occupies a bandwidth W of 1.2288MHz, and reliable communication requires an average E_b/I_oEqual to 3dB, a mobile station that gets a C/I value of 3dB for the best base station can communicate at a data rate of up to 1.2288 Mbps. On the other hand, if the mobile station experiences significant interference from neighboring base stations and can only achieve a C/I of-7 dB, reliable communication cannot be supported at rates greater than 122.88 Kbps. Thus, a communication system designed to optimize average throughput will attempt to serve each remote user from the best serving base station at the highest data rate R that can reliably support the remote user_bThe above. The data communication system of the present invention takes advantage of the above-noted characteristics and optimizes the data throughput from the CDMA base station to the mobile station.

Summary of The Invention

The present invention is a new and improved method and apparatus for high rate packet data transmission in a CDMA system. The present invention improves the efficiency of a CDMA system by providing a means to transmit data on the forward and reverse links. Each mobile station communicates with one or more base stations and monitors the control channel for the duration of the communication with the base stations. The base station may use the control channel to transmit small amounts of data, paging messages addressed to a given mobile station, and broadcast messages to all mobile stations. The paging message informs the mobile station that the base station is to transmit a large amount of data to the mobile station.

It is an object of the present invention to improve the application of forward and reverse link capacity in a data communication system. Upon receiving a paging message from one or more base stations, the mobile station measures the signal-to-noise-and-interference ratio (C/I) of the forward link signal (e.g., forward link pilot signal) at each time slot and addresses the best base station using a set of parameters, which may include present and previous C/I measurements. In the exemplary embodiment, the mobile station sends a request for transmission at the highest data rate on a dedicated Data Request (DRC) channel to the selected base station on each slot, the measured C/I reliably supporting the highest data rate. The selected base station transmits data in data packets at a data rate that does not exceed the data rate received from the mobile station on the DRC channel. By transmitting from the best base station on each slot, improved throughput and transmission delay is obtained.

It is another object of the present invention to improve performance by transmitting to a mobile station at a data rate requested by the mobile station at a peak transmit power for the duration of one or more time slots from a selected base station. In the exemplary CDMA communication system, the base station operates at a predetermined full power (e.g., 3dB) from the available transmit power to count the variables in use. Therefore, the average transmission power is half of the peak power. However, in the present invention, since high speed data transmission is scheduled and power is not generally shared (e.g., in the middle of transmission), there is no need to deviate from the available transmit power.

It is yet another object of the present invention to enhance efficiency by allowing a base station to transmit data packets to each mobile station in a variable number of slots. The ability to transmit from time slot to time slot from different base stations enables the data communication system of the present invention to quickly adapt to changes in the operating environment. Furthermore, it is possible in the present invention to transmit data packets on non-contiguous time slots, because the sequence numbers are used to identify data units within the data packets.

It is yet another object of the present invention to increase flexibility by forwarding data packets addressed to a given mobile station from a central controller to all base stations that are members of an active set of mobile stations. In the present invention, data transmission may occur from any base station in the active set of mobile stations on each time slot. Since each base station includes a queue containing data to be transmitted to the mobile station, efficient forward link transmission can occur with minimal processing delay.

It is yet another object of the present invention to provide a mechanism for retransmission of data units that are received in error. In an example embodiment, each data packet includes a predetermined number of data units, each data unit being identified by a sequence number. When one or more data units are received incorrectly, the mobile station sends a Negative Acknowledgement (NACK) on the reverse link data channel indicating the sequence number of the missing data unit for retransmission from the base station. The base station receives the NACK message and can retransmit the received data unit with errors.

It is yet another object of the present invention to enable a mobile station to select the best candidate base station for communication in accordance with the procedures described in U.S. patent application No. 08/790,497 entitled "method and apparatus for soft handoff in a wireless communication system", filed on 29/1/1997, which is assigned to the assignee of the present invention and incorporated herein by reference. In an example embodiment, a base station may be added to the active set of a mobile station if the received pilot signal is above a predetermined increase threshold and removed from the active set of the mobile station if the pilot signal is below a predetermined decrease threshold. In another embodiment, a base station may be added to the active set if the additional energy of the base station (e.g., as measured by the pilot signal) and the energy of base stations already in the active set exceed predetermined thresholds. With this further embodiment, no base station is added to the active set that transmits energy comprising a small amount of the total energy received at the mobile station.

It is yet another object of the present invention for the mobile station to transmit a data rate request on the DRC channel in such a manner that only selected base stations among the base stations in communication with the mobile station can resolve the DRC message, thereby ensuring that the forward link transmission on any given time slot is from the selected base station. In the exemplary embodiment, each base station communicating with the mobile station is assigned a unique walsh code. The mobile station covers the DRC message with the walsh code corresponding to the selected base station. The DRC message may be covered with other codes, although orthogonal codes are typically applied and walsh codes are preferred.

Brief Description of Drawings

The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein,

fig. 1 is a diagram of a data communication system of the present invention, which includes a plurality of cells, a plurality of base stations, and a plurality of mobile stations.

FIG. 2 is an exemplary block diagram of a subsystem of the data communication system of the present invention;

3A-3B are block diagrams of exemplary forward link structures of the present invention;

FIG. 4A is a diagram of an exemplary forward link frame structure of the present invention;

4B-4C are diagrams illustrating an example forward traffic channel and a power control channel, respectively;

FIG. 4D is a diagram of a punctured packet of the present invention;

4E-4G are diagrams of two example data packet formats and control channel containers, respectively;

FIG. 5 is an example timing diagram illustrating high rate packet transmission on the forward link;

FIG. 6 is a block diagram of an exemplary reverse link architecture of the present invention;

FIG. 7A is a diagram of an exemplary reverse link frame structure of the present invention;

FIG. 7B is a diagram of an example reverse link access channel;

fig. 8 is an example timing diagram illustrating high rate packet transmission on the reverse link;

FIG. 9 is an exemplary state diagram illustrating a change in the operational state of a mobile station;

fig. 10 is a graph of the Cumulative Distribution Function (CDF) of the C/I distribution in an ideal hexagonal honeycomb profile.

Detailed description of the preferred embodiments

According to an exemplary embodiment of the data communication system of the present invention, a forward link data transmission occurs from a base station to a mobile station at or near a maximum data rate (see fig. 1), which may be supported by the forward link and system. Reverse link data communication may occur from one mobile station to one or more base stations. The calculation of the maximum data rate for forward link transmission will be described in detail below. The data is divided into data packets, each of which is transmitted over one or more time slots. On each time slot, the base station may direct data transmissions to any of the mobile stations in communication with the base station.

Initially, the mobile station establishes communication with the base station using a predetermined access procedure. In the connected state, the mobile station can receive data and control messages from the base station and can transmit data and control messages to the base station. The mobile station then monitors the forward link for transmissions from the base stations in the mobile station's active set. The active set includes a series of base stations that communicate with the mobile stations. In particular, when received at the mobile station, the mobile station measures the signal-to-noise-and-interference ratio (C/I) of the forward link pilots from the base stations in the active set. If the received pilot signal is above a predetermined increase threshold or below a predetermined decrease threshold, the mobile station reports this to the base station. Subsequent messages from the base station direct the mobile station to add or remove the base station from its active set, respectively. Various operating states of the mobile station are described below.

If no data can be sent, the mobile station returns to the idle state and stops transmitting data rate information to each base station. When the mobile station is in the idle state, the mobile station monitors paging messages for control channels from one or more base stations in the active set.

If there is data to be sent to the mobile station, the data is sent by the central controller to all base stations in the active set and stored in a queue at each base station. Paging messages are then sent by one or more base stations to the mobile stations on the corresponding control channels. To ensure reception even when the mobile station transitions between base stations, the base station may transmit all such paging messages on several base stations simultaneously. The mobile station demodulates and decodes the signals on the one or more control channels to receive the paging message.

The paging message is decoded and for each slot, until the data transmission is complete, the mobile station measures the C/I of the forward link signals received at the mobile station from the base stations in the active set. The C/I of the forward link signal may be obtained by measuring the corresponding pilot signal. The mobile station then selects the best base station based on a set of parameters. The set of parameters may include present and previous C/I measurements and bit error rate or packet error rate. For example, the best base station may be selected based on the largest C/I measurement. The mobile station then identifies the best base station and sends a data request message (hereinafter referred to as a DRC message) on a data request channel (hereinafter referred to as a DRC channel) to the selected base station. The DRC message may include the requested data rate or, alternatively, an indication of the quality of the forward link channel (e.g., the C/I measurement itself, the bit error rate, or the packet error rate). In an example embodiment, the mobile station may direct the transmission of the DRC message to a designated base station through the use of a walsh code that uniquely defines the base station. The DRC message symbols are xored with a unique walsh code. Since each base station in the active set of the mobile station is defined by a unique walsh code, only the selected base station, which performs the same exclusive-or operation with the correct walsh code as that performed by the mobile station, can correctly decode the DRC message. The base station uses the rate control information from each mobile station to effectively transmit forward link data at the highest possible rate.

On each slot, the base station may select any paged mobile station for data transmission. The base station then determines the data rate at which to transmit data to the selected mobile station based on the most recent DRC message value received from the mobile station. In addition, the base station uniquely determines the transmission to a particular mobile station by using a spreading code that is unique to that mobile station. In an exemplary embodiment, the spreading code IS a long pseudo noise code (PN), which IS defined by the IS-95 standard.

The mobile station to which the data packet is intended receives the data transmission and decodes the data packet. Each data packet includes a plurality of data units. In the exemplary embodiment, the data unit includes 8 information bits, although different data bit sizes may be defined and are within the scope of the invention. In an exemplary embodiment, each data unit is associated with a sequence number, and the mobile station is able to identify lost transmissions or duplicate transmissions. In this process, the mobile station communicates the sequence number associated with the missing data unit over the reverse link data channel. The base station controller, having received the data message from the mobile station, then indicates to all base stations that communication is in progress with that particular mobile station, but that no data unit was received by the mobile station. The base station then schedules retransmission of such data units.

Each mobile station in the data communication system is capable of communicating with multiple base stations on the reverse link. In an exemplary embodiment, the data communication system of the present invention supports soft or softer handoff on the reverse link for several reasons. First, soft handoff does not consume additional capacity on the reverse link but rather allows the mobile station to transmit data at a minimum power level such that at least one base station can reliably decode the data. Second, the reception of reverse link signals by multiple base stations increases the reliability of the transmission and only requires additional hardware at the base stations.

In an exemplary embodiment, the forward link capacity of the data transmission system of the present invention is determined by the rate request of the mobile station. Additional gain in forward link capacity may be obtained by using directional antennas and adaptive spatial filters. An exemplary method and apparatus for providing directional transmission is disclosed in pending U.S. patent application No. 08/575,049 entitled "method and apparatus for determining a transmission data rate in a multi-user communication system," filed on 20.12.1995, and U.S. patent application No. 08/925,521 entitled "method and apparatus for providing orthogonal spot beams, sectors, and picocells (formerly known as picocells"), filed on 8.9.1997, both assigned to the assignee of the present invention and incorporated herein by reference.

I. Description of the System

Referring to the drawings, FIG. 1 illustrates an exemplary data communication system of the present invention, which includes a plurality of cells 2a-2 g. Each cell 2 is served by a respective base station 4. Mobile stations 6 are dispersed throughout the data communication system. In the exemplary embodiment, each mobile station 6 communicates with at most one base station 4 on the forward link at each time slot, but may communicate with one or more base stations 4 on the reverse link depending on whether the mobile station 6 is in soft handoff or not. For example, in time slot n, base station 4a transmits data only to mobile station 6a, base station 4b transmits data only to mobile station 6b, and base station 4c transmits data only to mobile station 6 c. In fig. 1, a solid line with arrows represents data transmission from the base station 4 to the mobile station 6. The dashed line with arrows indicates that the mobile station 6 is receiving a pilot signal from the base station 4, but has no data transmission. For simplicity, reverse link communications are not shown in fig. 1.

As shown in fig. 1, each base station 4 preferably transmits data to one mobile station 6 at any given moment. A mobile station 6, particularly a mobile station 6 located near a cell boundary, may receive pilot signals from multiple base stations 4. If the pilot signal is above a predetermined threshold, mobile station 6 may request that base station 4 be added to the active set of mobile station 6. In an example embodiment, mobile station 6 may receive data transmissions from zero or one member of the active set.

A block diagram illustrating the basic subsystems of the data communication system of the present invention is shown in fig. 2. The base station controller 10 is connected to the packet network interface 24, the PSTN 30, and all base stations 4 in the data communication system (only one base station 4 is shown for simplicity). Base station controller 10 coordinates communication between mobile station 6 and other users connected to packet network interface 24 and PSTN 30 in a data communication system. PSTN 30 is connected to users through a standard telephone network (not shown in fig. 2).

The base station controller 10 comprises a number of selector units 14, although only one is shown in fig. 2 for simplicity. A selector element 14 is assigned to control the communication between one or more base stations 4 and a mobile station 6. If no selector element 14 has been assigned to mobile station 6, call control processor 16 is notified that mobile station 6 must be called. Call control processor 16 then directs base station 4 to call mobile station 6.

Data source 20 includes data to be transmitted to mobile station 6. Data source 20 provides data to packet network interface 24. Packet network interface 24 receives the data and routes the data to selector element 14. The selector element 14 transmits data to each base station 4 in communication with the mobile station 6. Each base station 4 maintains a data queue 40 containing data to be transmitted to mobile stations 6.

In an example embodiment, on the forward link, the data packet relates to a predetermined amount of data independent of the data rate. The data packet is formatted and encoded with other control and code bits. If data transmission occurs over multiple walsh channels, the encoded packet is demultiplexed into parallel streams for each stream sent over the walsh channels.

Data is transmitted in data packets from the data queue 40 to the channel element 42. For each data packet, the channel element 42 inserts the necessary control fields. The data packet, control field, frame check sequence bits, and code tail bits comprise a formatted packet. Channel element 42 then encodes the one or more formatted packets and interleaves (or reorders) the symbols within the encoded packets. Second, the interleaved packet is scrambled with a scrambling sequence, covered with Walsh codes and covered with long PN codes and short PN codes_IAnd PN_QAnd (5) spreading codes. The spread data is quadrature modulated, filtered and amplified by the transmitter in the RF unit 44. The forward link signal is transmitted over the air through an antenna 46 on the forward link.

At mobile station 6, the forward link signal is received by antenna 60 and routed to a receiver in front end 62. The receiver filters, amplifies, quadrature demodulates, and quantizes the signal. The digitized signal is provided to a demodulator (DEMOD)64 where it is encoded with a long PN code and a short PN_IAnd PN_QCode despreading, decovering with walsh codes, and scrambling with the same scrambling sequence. The demodulated data is provided to a decoder 66 which performs the inverse signal processing functions to those performed in the base station 4, particularly the de-interleaving, decoding and frame check functions. The decoded data is provided to a data sink 68. As described above, the hardware supports the transmission of data, messages, voice, video, and other communications over the forward link.

System control and scheduling functions may be accomplished by a number of implementations. The location of the channel scheduler 48 depends on whether a centralized or distributed control/scheduling process is required. For example, for distributed processing, a channel scheduler may be placed within each base station 4. Conversely, for centralized processing, a channel scheduler may be located within the base station controller 10 and may be designed to coordinate the transmission of data by multiple base stations 4. Other implementations of the above described functions are contemplated and are within the scope of the present invention.

As shown in fig. 1, mobile stations 6 are spread throughout the data communication system and may communicate with zero or one base station 4 on the forward link. In the exemplary embodiment, channel scheduler 48 coordinates forward link data transmissions for one base station 4. In the exemplary embodiment, channel scheduler 48 is coupled to data queue 40 and channel element 42 within base station 4 and receives queue sizes and DRC messages from mobile stations 6, the queue sizes indicating the amount of data to send to mobile stations 6. The channel scheduler 48 schedules high rate data transmissions such that the system goals of maximum data throughput and minimum transmission delay are optimized.

In an example embodiment, data transmission is scheduled based in part on a quality of a communication link. An exemplary communication system for selecting a transmission rate based on link quality is disclosed in U.S. patent application No. 08/741,320 entitled "method and apparatus for providing high speed data communication in a cellular environment", filed 1996 on 11.9.9.78, which is assigned to the assignee of the present invention and incorporated herein by reference. In the present invention, the scheduling of data communication may be based on additional considerations such as the GOS of the user, the queue size, the type of data, the amount of delay that has been experienced, and the error rate of the data transmission. These considerations are described in detail in U.S. patent application No. 08/798,951 entitled "method and apparatus for forward link rate scheduling", filed on 11/2/1997, and U.S. patent application No. 08/914,928 entitled "method and apparatus for reverse link rate scheduling", filed on 20/8/1997, both assigned to the assignee of the present invention and incorporated herein by reference. Other factors in scheduling data transmissions may be considered and are within the scope of the present invention.

The data communication system of the present invention supports data and message transmission on the reverse link. Within mobile station 6, a controller 76 processes the data or message transmission by routing the data or message to encoder 72. The controller 76 may be implemented in a microcontroller, microprocessor, Digital Signal Processor (DSP) chip, or ASIC programmed to perform the functions described above.

In an exemplary embodiment, the encoder 72 encodes a message that conforms to the Blank and Burst (Blank and Burst) signaling data format described in the aforementioned U.S. Pat. No. 5,504,773. Encoder 72 then generates and adds a set of CRC bits, adds a set of code tail bits, encodes and adds bits to the data, and reorders the symbols within the encoded data. The interleaved data is provided to a Modulator (MOD) 74.

The adjuster 74 may be implemented in many embodiments. In an exemplary embodiment (see fig. 6), the data is covered with walsh codes, spread with long PN codes and further spread with short PN codes. The spread data is provided to a transmitter within front end 62. The transmitter modulates, filters, amplifies, and transmits the reverse link signal over the air, on a reverse link 52 through the antenna 46.

In the exemplary embodiment, mobile station 6 spreads the reverse link data according to a long PN code. Each reverse link channel is defined in terms of an instantaneous offset of a common long PN sequence. At two different offsets, the results of the modulated sequence are not correlated. The offset of mobile station 6 IS determined from the unique numerical identifier of mobile station 6, which in the exemplary embodiment of IS-95 mobile station 6 IS a mobile station specific identification number. Thus, each mobile station transmits on an uncorrelated reverse link channel determined based on its unique electronic serial number.

At the base station 4, the reverse link signal is received by an antenna 46 and provided to an RF unit 44. The RF unit 44 filters, amplifies, demodulates, and quantizes the signal and provides the digitized signal to the channel unit 42. The channel element 42 despreads the digitized signal with the short PN code and the long PN code. Channel element 42 also performs walsh code decovering and pilot and DRC acquisition. Channel element 42 then reorders the demodulated data, decodes the de-interleaved data and performs a CRC check function. The decoded data, e.g. data or messages, are provided to a selector unit 14. The selector unit 14 selects a route to route the data and messages to the appropriate destination. The channel unit 42 may also forward a quality indicator to the selector unit 14 to indicate the condition of the received data packet.

In an exemplary embodiment, mobile station 6 may be in one of 3 operating states. An example state diagram is shown in fig. 9, representing changes between various operating states of mobile station 6. In the access state 902, the mobile station 6 sends an access probe and waits for a channel assignment from the base station 4. The channel assignment includes resource allocation, such as power control channel and frequency allocation. If mobile station 6 is called and alerted of an incoming data transmission, or if mobile station 6 is transmitting data on the reverse link, mobile station 6 changes from access state 902 to connected state 904. In the connected state 904, mobile station 6 exchanges (e.g., transmits or receives) data and completes the handoff operation. Upon completion of the release process, mobile station 6 changes from connected state 904 to idle state 906. Mobile station 6 may also change from access state 902 to idle state 906 when denied a connection with base station 4. In idle state 906, mobile station 6 listens to overhead and paging messages and completes the idle handoff process by receiving and decoding messages on the forward control channel. By having the process begin, mobile station 6 may change to access state 902. The state diagram shown in fig. 9 is merely an example state definition shown for illustration. Other state diagrams may also be applied and are within the scope of the invention.

Forward Link data Transmission

In the exemplary embodiment, communication between mobile station 6 and base station 4 begins in a similar manner as used by CDMA systems. After call setup is completed, mobile station 6 monitors the control channel for paging information. While in the connected state, mobile station 6 begins transmission of a pilot signal on the reverse link.

An exemplary flow chart of the forward link high rate data transmission of the present invention is shown in fig. 15. If base station 4 has data to send to mobile station 6, base station 4 addresses mobile station 6 to send a paging message on a control channel at block 502. Paging messages may be sent from one or more base stations 4 depending on the handoff state of the mobile station 6. Upon receipt of the paging message, mobile station 6 begins the C/I measurement procedure at block 504. The C/I of the forward link signal is calculated from one or a combination of the following methods. Mobile station 6 then selects the requested data rate based on the best C/I measurement and transmits the DRC message on the DRC channel at block 506.

Within the same time slot, the base station 4 receives the DRC message at block 508. If the next time slot for the data transmission is available, base station 4 transmits data to mobile station 6 at the requested data rate at block 510. If the next slot is available, at block 514, base station 4 transmits the remaining packet and at block 516, mobile station 6 receives the data transmission.

In the present invention, a mobile station 6 may communicate with one or more base stations 4 simultaneously. The action taken by the mobile station is based on whether the mobile station 6 is in soft handoff or not. These two cases are discussed separately below.

No soft handover situation

In the absence of soft handoff, the mobile station 6 communicates with one of the base stations 4. Referring to fig. 2, data destined for a particular mobile station 6 is provided to a selector element 14, which has been assigned to control communication with the mobile station 6. The selector unit 14 forwards the data to a data queue 40 in the base station 4. The base station 4 queues the data and sends a paging message on the control channel. The base station 4 then monitors the reverse link DRC channel for a DRC message from the mobile station 6 and the base station 4 can retransmit the paging message until the DRC message is detected. After a predetermined number of retransmission attempts, the base station 4 may terminate the process or re-start a call to the mobile station.

In the exemplary embodiment, mobile station 6 transmits the requested data rate in the form of a DRC message to base station 4 on the DRC channel. In another embodiment, mobile station 6 transmits an indication of the quality of the forward link channel (e.g., a C/I measurement) to base station 4. In the exemplary embodiment, base station 4 decodes the 3-bit DRC message with soft decisions. In an exemplary embodiment, the DRC message is transmitted during the first half of each slot. The base station 4 then decodes the DRC message in the remaining half slot and composes the hardware for data transmission in the next following slot if the mobile station 6 has access to this slot for data transmission. If the next slot in succession is not available, the base station 4 waits for the next available slot and monitors the DRC channel for a new DRC message.

In a first embodiment, the base station 4 transmits at the requested data rate. This embodiment enables the mobile station 6 to have an important capability of selecting the decision of the data rate. Always transmitting at the requested rate has the advantage that the mobile station 6 knows which data rate to expect. Thus, mobile station 6 only demodulates and decodes the traffic channel in accordance with the requested data rate. The base station 4 need not send a message to the mobile station 6 indicating which data rate the base station 4 is using.

In the first embodiment, mobile station 6 continuously attempts to demodulate the data at the requested data rate after receiving the paging message. Mobile station 6 demodulates the forward traffic channel and provides soft decision symbols to the decoder. The decoder decodes the symbols and performs a frame check on the decoded packet to determine whether the packet was received correctly. The frame check will indicate a packet error if the received packet has errors or if the packet is intended for another mobile station 6. In another aspect of the first embodiment, the mobile station 6 demodulates the data on a slot-to-slot basis. In an exemplary embodiment, mobile station 6 is able to determine whether the data transmission directed to it is based on a preamble incorporated within each transmitted data packet, as described below. Thus, if the mobile station 6 determines that this is a directed transmission to another mobile station 6, it can terminate the decoding process. In each case, mobile station 6 sends a Negative Acknowledgement (NACK) message to base station 4 to confirm the incorrect receipt of the data unit. When a NACK is received, the received data unit with errors is retransmitted.

The transmission of the NACK message can be implemented in the same way as the transmission of Error Indication Bits (EIB) in a CDMA system. The implementation and use of EIB transmission is disclosed in U.S. patent application No. 5,568,483, entitled "method and apparatus for formatting Transmission data," which is assigned to the assignee of the present invention and incorporated herein by reference. On the other hand, a NACK may be sent in a message.

In a second embodiment, the base station 4 determines the data rate using input from the mobile station 6. Mobile station 6 completes the C/I measurements and sends an indication of the link quality (e.g., the C/I measurements) to base station 4. The base station 4 may adjust the requested data rate according to the resources available to the base station 4, such as queue size and available transmit power. The adjusted data rate may be sent to mobile station 6 prior to or in conjunction with data transmission at the adjusted data rate, or can be included in the encoding of the data packet. In the first case, the mobile station 6 receives the adjusted data rate prior to data transmission, and the mobile station 6 demodulates and decodes the received packet in the manner described in the first embodiment. In the second case, the adjusted data rate is transmitted to mobile station 6 concurrently with the data transmission, and mobile station 6 may demodulate the forward traffic channel and store the demodulated data. Upon receiving the adjusted data rate, mobile station 6 decodes the data according to the adjusted data rate. And in the third case, having the adjusted data rate included in the encoded data packet, mobile station 6 decodes all selected rates and inductively determines the transmission rate used to select the decoded data. The method and apparatus for performing rate determination is described in detail in U.S. patent application No. 08/730,863 entitled "method and apparatus for determining a received data rate in a variable rate communication system," filed on 18.10.1996 and U.S. patent application No. 08/908,866 entitled "method and apparatus for determining a received data rate in a variable rate communication system," filed on 8.8.1997, both assigned to the assignee of the present invention and incorporated herein by reference. In all cases described above, mobile station 6 transmits a NACK message if the result of the frame check is negative, as described above.

Unless otherwise noted, the discussion hereinafter follows in accordance with a first embodiment in which mobile station 6 sends a DRC message to base station 4 indicating the requested data rate. However, the inventive concepts described herein are equally applicable to the second embodiment in which mobile station 6 transmits an indication of link quality to the base station.

Handover situation

In a handoff scenario, mobile station 6 communicates with multiple base stations 4 on the reverse link. In the exemplary embodiment, data transmission on the forward link to a particular mobile station 6 occurs from one base station 4. However, mobile station 6 may receive pilot signals from multiple base stations 4 simultaneously. If the C/I measurement of base station 4 exceeds a predetermined threshold, base station 4 is added to the active set of mobile station 6. During the soft handoff direction message, the new base station 4 assigns the mobile station 6 to a Reverse Power Control (RPC) walsh channel as explained below. Each base station 4 and mobile station 6 in soft handoff monitors the reverse link transmissions and sends RPC bits on their respective RPC walsh channels.

Referring to fig. 2, the selector element 14 assigned to control the communication with the mobile station 6 forwards data to all base stations 4 in the active set of the mobile station 6. All base stations 4 that receive the data from selector element 14 send paging messages to mobile station 6 on their respective control channels. When the mobile station 6 is in the connected state, the mobile station 6 performs two functions. First, the mobile station 6 selects the best base station 4 based on a set of parameters (which may be the best C/I measurements). The mobile station 6 then selects a data rate corresponding to the C/I measurement and sends a DRC message to the selected base station 4. Mobile station 6 may direct the transmission of the DRC message to a particular base station 4 by covering the DRC message with a walsh cover assigned to the particular base station 4. Second, mobile station 6 attempts to demodulate the forward link signal based on the requested data rate at each subsequent time slot.

After sending the paging message, all base stations 4 in the active set monitor the DRC channel for DRC messages from the mobile station 6. Furthermore, because the DRC message is covered with walsh codes, selected base stations 4 assigned with the same walsh cover can decover the DRC message. Upon receiving the DRC message, the selected base station 4 transmits data to the mobile station 6 on the next available slot.

In the exemplary embodiment, base station 4 transmits data in the form of packets to mobile station 6, which includes a plurality of data units at the requested data rate. If mobile station 6 incorrectly receives the data unit, a NACK message is sent on the reverse link to all base stations 4 in the active set. In the exemplary embodiment, the base station 4 demodulates and decodes the NACK message and forwards it to the selector element 14 for processing. In processing the NACK message, the data unit is retransmitted using the procedure described above. In the exemplary embodiment, the selector unit 14 combines the NACK signals received from all base stations 4 into one NACK message and sends the NACK message to all base stations 4 in the active set.

In an example embodiment, mobile station 6 may check for changes in the best C/I measurements and dynamically request data transmissions from different base stations 4 on each time slot to improve efficiency. In the exemplary embodiment, since data transmission occurs from only one base station 4 at any given time slot, the other base stations 4 in the active set do not know what data units (if any) have been sent to the mobile station 6. In the exemplary embodiment, the transmitting base station 4 informs the selector unit 14 of the data transmission. The selector unit 14 then sends a message to all base stations in the active set. In the exemplary embodiment, the transmitted data is deemed to have been correctly received by mobile station 6. Thus, if mobile station 6 requests a data transmission from a different base station 4 in the active set, the new base station 4 sends the remaining data units. In the exemplary embodiment, the new base station 4 transmits according to the latest transmission update from the selector unit 14. On the other hand, the new base station 4 selects the next data unit to transmit using a prediction scheme based on metrics from the selector unit 14, such as average transmission rate and priority updates. These mechanisms minimize repeated re-transmission (causing loss of efficiency) of the same data by multiple base stations 4 on different time slots. If the received priority transmission is in error, the base station 4 may retransmit these data units outside the sequence because each data unit is identified by a unique sequence number as described below. In an exemplary embodiment, if a hole (or non-transmitted data unit) is generated (e.g., as a result of a handoff between one base station 4 to another base station 4), the lost data is considered as being received with errors. The mobile station 6 sends a NACK message corresponding to the missing data units and retransmits the data units.

In the exemplary embodiment, each base station 4 in the active set maintains a separate data queue 40 containing data to be transmitted to mobile station 6. The selected base station 4 transmits the data present in its data queue 40 in sequential order, except for retransmitted data units and signaling messages received with errors. In an example embodiment, after transmission, the transmitted data unit is removed from the queue 40.

V. other considerations for Forward Link data Transmission

An important consideration in the data communication system of the present invention is the accuracy of the C/I estimate, which is used to select the data rate for future transmission. In the exemplary embodiment, when base station 4 transmits a pilot signal, during a time interval, the C/I measurements are done on the pilot signal. In the exemplary embodiment, since only the pilot signal is transmitted during the pilot time interval, the effects of multipath and interference are minimized.

In other implementations of the invention, similar to the IS-95 system, the pilot signal IS transmitted continuously on orthogonal code channels, and the effects of multipath and interference distort the C/I measurements. Similarly, multipath and interference can also corrupt the C/I measurements when they are done on the data transmission instead of the pilot signal. In both cases, when one base station 4 transmits to one mobile station 6, the mobile station 6 can correctly measure the C/I of the forward link signal because there are no other interfering signals. However, when the mobile station 6 is in soft handoff and receives pilot signals from a plurality of base stations 4, the mobile station 6 cannot distinguish whether the base stations 4 are transmitting data. In the worst case, mobile station 6 may measure a high C/I on the first time slot, when no base station 4 is transmitting data to any mobile station 6, and receive a data transmission on the second time slot, when all base stations 4 are transmitting data on the same time slot. When all base stations 4 are idle, the C/I measurement on the first time slot gives a false alarm indication of the forward link signal quality on the second time slot, since the data communication system has changed state. In fact, the true C/I on the second slot may drop to a point where reliable decoding at the requested data rate is not possible.

The opposite extreme exists when the C/I is estimated by the mobile station 6 from the maximum interference. However, the actual transmission occurs only when the selected base station is transmitting. In this case, the C/I estimate and the selected data rate are conservative, and transmission occurs at a lower rate than can be reliably decoded, thus reducing transmission efficiency.

In practice, the C/I measurement is done on a continuous pilot signal or traffic signal, and by three embodiments, the C/I prediction on the second slot may be more accurate based on the C/I measurement on the first slot. In a first embodiment, the data transmission from the base station 4 is controlled such that the base station 4 does not constantly transition between transmission and idle states on successive time slots. This may be achieved by queuing sufficient data (e.g., a predetermined number of information bits) before transmitting the actual data to mobile station 6.

In the second embodiment, each base station 4 sends a forward activity bit (hereinafter FAC bit) indicating whether transmission will occur in the next half frame. The use of the FAC bit will be explained in detail below. The mobile station 6 completes the C/I measurement in view of the received FAC bit from each base station 4.

In the third embodiment, which corresponds to a scheme of transmitting a link quality indication to the base station 4 and uses a central scheduling scheme, scheduling information indicating which base station 4 transmits data on each time slot can be obtained by the channel scheduler 48. The channel scheduler 48 receives the C/I measurements from the mobile stations 6 and can adjust the C/I measurements based on its knowledge of the presence or absence of data transmissions from each of the base stations 4 in the data communication system. For example, mobile station 6 can measure the C/I on the first slot when no neighboring base station is transmitting. The measured C/I is provided to the channel scheduler 48. The channel scheduler 48 knows that the neighbouring base station 4 did not transmit on the first time slot and therefore the channel scheduler 48 did not schedule. When scheduling data transmission on the second time slot, the channel scheduler 48 knows whether one or more base stations 4 will transmit data. Channel scheduler 48 may adjust the C/I measured on the first time slot to take into account the additional interference mobile station 6 will receive in the second time slot due to the data transmission of the neighboring base station 4. On the other hand, if the C/I is measured on the first time slot when the neighboring base station 4 is transmitting, but none of these base stations transmit on the second time slot, the channel scheduler 48 may adjust the C/I measurement in view of the additional information.

Another important consideration is to minimize redundant retransmissions. Redundant retransmissions are a result of allowing mobile stations 6 to select data transmissions from different base stations 4 on consecutive time slots. If mobile station 6 measures nearly equal C/I for these base stations 4, the best C/I measurement may be switched between two or more base stations 4 on successive time slots. The transition may be triggered by a deviation in the C/I measurements and/or a change in the channel conditions. The transmission of data by different base stations 4 over successive time slots may cause a loss of efficiency.

The problem of switching can be solved by using hysteresis. Hysteresis may be implemented with a signal level scheme, a timing scheme, or a combination of signal level and timing. In the exemplary signal level scheme, the preferred C/I measurement for a different base station 4 in the active set is not selected unless it exceeds the C/I measurement of the base station 4 currently transmitting by at least a hysteresis amount. As an example, assume that at the first time slot, the lag is 10dB, the C/I measurement for the first base station 4 is 3.5dB, and the C/I measurement for the second base station 4 is 3.0 dB. On the next time slot, the second base station 4 is not selected unless its C/I measurement is at least 1.0dB higher than that of the first base station 4. Thus, if the C/I measurement of the first base station 4 is still 3.5dB on the next time slot, the second base station 4 is not selected unless its C/I measurement is at least 4.5 dB.

In the exemplary timing scheme, base station 4 transmits data packets to mobile station 6 for a predetermined number of time slots. The mobile station 6 is not allowed to select a different transmitting base station 4 within a predetermined number of time slots. Mobile station 6 constantly measures the C/I of base station 4 currently transmitting on each slot and selects a data rate based on the C/I measurements.

Yet another important consideration is the efficiency of data transfer. Referring to fig. 4E and 4F, each data packet format 410 and 430 includes data and extra overhead bits. In an example embodiment, the number of overhead bits is fixed for all data rates. At the highest data rate, the percentage of overhead relative to the packet size is small and efficient. At lower data rates, the extra overhead bits may comprise a larger percentage of the packet. Inefficiencies at lower data rates may be ameliorated by transmitting variable length data packets to mobile station 6. Variable length data packets may be transmitted separately over multiple time slots. Preferably, variable length data packets are sent to mobile station 6 on successive time slots to simplify processing. The present invention is directed to using various packet sizes for various supported data rates to improve overall transmission efficiency.

Forward link structure

In the exemplary embodiment, base station 4 transmits to a single mobile station 6 at the maximum power available to base station 4 and the maximum data rate supported by the data communication system at any given time slot. The maximum data rate that can be supported is dynamic and related to the C/I of the forward link signal as measured by the mobile station 6. Preferably, base station 4 transmits to only one mobile station 6 on any given time slot.

To facilitate data transmission, the forward link includes 4 time multiplexed channels: a pilot channel, a power control channel, a control channel, and a traffic channel. The function and implementation of each of these channels is explained below. In an example embodiment, each of the traffic and power control channels includes a number of orthogonal spread walsh channels. In the present invention, traffic data and paging messages are transmitted to mobile station 6 using a traffic channel. When used to transmit paging messages, the traffic channel is also referred to as the control channel in this description.

In an example embodiment, the bandwidth of the forward link is selected to be 1.2288 MHz. This bandwidth selection allows the use of existing hardware components designed for CDMA systems that conform to the IS-95 standard. However, the system of the present invention may be employed for different bandwidths to improve capacity and/or to meet system requirements. For example, a bandwidth of 5MHz may be applied to increase capacity. Further, the bandwidth of the forward and reverse links may be different (e.g., 5MHz bandwidth on the forward link and 1.2288MHz bandwidth on the reverse link) to more closely fit the link capacity as desired.

In an example embodiment, short PN_IAnd PN_QThe codes are of the same length 2¹⁵PN codes, which are specified by the IS-95 standard. At a chip rate of 1.2288MHz, the short PN sequence repeats every 26.67 milliseconds (26.67 milliseconds ═ 2)¹⁵/1.2288×10⁶). In the exemplary embodiment, all base stations 4 within the data communication system use the same short PN code. However, each base station 4 is identified by a unique offset of the basic short PN sequence. In an example embodiment, the offset is incremented by 64 chips. Other bandwidths and PN codes may be applied and are within the scope of the invention.

Forward link traffic channel

A block diagram of an exemplary forward link architecture of the present invention is shown in fig. 3A. The data is divided into data packets and provided to CRC encoder 112. For each data packet, CRC encoder 112 generates frame check bits (e.g., CRC parity bits) and inserts code tail bits. The formatted packet from CRC encoder 112 includes data, frame checksum tail bits, and other overhead bits as explained below. The formatted packets are provided to an encoder 114, which, in an exemplary embodiment, encoder 114 encodes the packets according to the encoding format disclosed in the aforementioned U.S. patent application No. 08/743,688. Other encoding formats may be used and are within the scope of the present invention. The encoded packet from encoder 114 is provided to interleaver 116, which reorders the code symbols in the packet. The interleaved packet is provided to puncturing unit 118, which removes a portion of the packet in a manner described below. The punctured packets are provided to a multiplier 120 which scrambles the data with a scrambling sequence from a scrambler 122. The puncturing unit 118 and the scrambler 122 are explained in detail below. The output from multiplier 120 includes the scrambled packet.

The scrambled packet is provided to a variable rate controller 130 which demultiplexes the packet into parallel in-phase and quadrature channels, where k is related to the data rate. In an example embodiment, the scrambled packets are first demultiplexed into in-phase (I) and quadrature (Q) streams. In an example embodiment, the I stream includes even-index symbols and the Q stream includes odd-index symbols. Each stream is further demultiplexed into kappa parallel channels such that the symbol rate of each channel is fixed for all data rates. The kappa channels of each stream are provided to a Walsh covering unit 132, which covers each channel with a Walsh function to provide orthogonal channels. The quadrature channel data is provided to a gain unit 134 which scales the data to maintain a constant total energy per chip (and thus constant output power) for all data rates. The scaled data from the gain unit 134 is provided to a Multiplexer (MUX)160 that multiplexes the data with a preamble. The preamble is discussed in detail below. The output from the MUX 160 is provided to a Multiplexer (MUX)162, which multiplexes traffic data, power control bits, and pilot data. The output of MUX162 includes I walsh channels and Q walsh channels.

A block diagram of an example adjuster for modulating data is shown in fig. 3B. The I Walsh channel and the Q Walsh channel are provided to adders 212a and 212b, respectively, which add the Walsh channels at k to provide signal I Walsh, respectively_sumAnd Q_sum′. Will I_sumAnd Q_sumThe signal is provided to a complex multiplier 214 which also receives the PN _ I and PN _ QX signals from multipliers 236a and 236b, respectively, and multiplies the two complex inputs according to the following equation:

(I_mult+jQ_mult)＝(I_sum+jQ_sum)·(PN_I+jPN_Q) (2)

＝(I_sum·PN_I-jQ_sum·PN_Q)+j(I_sum·PN_Q+jQ_sum·PN_I)

wherein, I_multAnd Q_multIs output from the complex multiplier 214 and j is a complex representation. Will I_multAnd Q_multThe signals are provided to filters 216a and 216b, respectively, which filter the signals. The filtered signals from filters 216a and 216b are provided to multipliers 218a and 218b, respectively, which sum the signals to an in-phase sinusoidal COS (w), respectively_Ct) and quadrature sinusoid SIN (w)_Ct) are multiplied. The I and Q modulated signals are provided to adder 220 which adds the signals to provide a forward modulated waveform s (t).

In an example embodiment, the data packet is spread with a long PN code and a short PN code. The long PN code scrambles the packet so that only the mobile station 6 to which the packet is assigned can descramble the packet. In the exemplary embodiment, the pilot and power control bits and control channel packets are spread with a short PN code rather than a long PN code to allow all mobile stations 6 to receive these bits. The long PN sequence is generated by long code generator 232 and provided to Multiplexer (MUX) 234. The long PN mask determines the offset of the long PN sequence and uniquely assigns it to the target mobile station 6. During the transmit data portion, long PN sequences are output from MUX 234, otherwise zeros are output (e.g., during the pilot and power control portions). The gated long PN sequence from MUX 234 and the short PNI and PNQ sequences from short code generator 238 are provided to multipliers 236a and 236b, respectively, which multiply the two sets of sequences to form the PN _ I and PN _ Q signals, respectively. The PN _ I and PN _ Q signals are provided to a complex multiplier 214.

The block diagram of the exemplary traffic channel shown in fig. 3A and 3B is one of a variety of structures that support data coding and modulation on the forward link. Other architectures, such as those used for forward link traffic channels in CDMA systems, which conform to the IS-95 standard, may be used and are within the scope of the present invention.

In the exemplary embodiment, the data rates supported by base station 4 are predetermined and each supported data rate is assigned a unique rate index. Mobile station 6 selects one of the supported data rates based on the C/I measurements. Since the requested data rate needs to be transmitted to the base station 4 to direct the base station 4 to transmit data at the requested data rate, a tradeoff is made between the number of data rates supported and the number of bits needed to identify the requested data rate. In an example embodiment, the number of supported data rates is 7, and a 3-bit rate index is used to identify the requested data rate. Table 1 shows an example definition of supported data rates. Different definitions of the supported data rates are envisaged and are within the scope of the invention.

In an example embodiment, the minimum data rate is 38.4Kbps and the maximum data rate is 2.4576 Mbps. The minimum data rate is selected based on the worst case C/I measurement in the system, the processing gain of the system, the design of the error correction code, and the required performance level. In an example embodiment, the supported data rates are selected such that the difference between successive supported data rates is 3 dB. This 3dB increment is a compromise between several factors including the accuracy of the C/I measurements available to mobile station 6, the loss (or inefficiency) caused by quantizing the data rate based on the C/I measurements, and the number of bits (or bit rate) required to transmit the requested data rate from mobile station 6 to base station 4. More supported data rates require more bits to identify the requested data rate, but allow more efficient use of the forward link because the quantization error between the calculated maximum data rate and the supported data rate is smaller. The present invention is directed to use any number of supported data rates and data rates other than those listed in table 1.

Table 1 traffic channel parameters

Parameter(s)	Data rate							Unit of
										38.4	76.8	153.6	307.2	614.4	1228.8	2457.6	Kbps
Data bits/packets	1024	1024	1024	1024	1024	2048	2048	Bit
									Packet length	26.67	13.33	6.67	3.33	1.67	1.67	0.83	Millisecond (ms)
Time slot/packet	16	8	4	2	1	1	0.5	Time slot
									Packet/transmission	1	1	1	1	1	1	2	Grouping
Time slot/transmission	16	8	4	2	1	1	1	Time slot
									Walsh symbol rate	153.6	307.2	614.41	1228.8	2457.6	2457.6	4915.2	Ksps
Walsh channel/QPSK phase	1	2	4	8	16	16	16	Channel with a plurality of channels
									Modulator rate	76.8	76.8	76.8	76.8	76.8	76.8	76.8	ksps
PN chip/data bit	32	16	8	4	2	1	0.5	Raising Yuan/bit
									PN chip rate	1228.8	1228.8	1228.8	1228.8	1228.8	1228.8	1228.8	Kcps
Modulation format	QPSK	QPSK	QPSK	QPSK	QPSK	QPSK	QAM1
									Rate index	0	1	2	3	4	5	6

Note: (1)16-QAM (Quadrature amplitude modulation) modulation

An exemplary diagram of the forward link frame structure of the present invention is shown in fig. 4A. The traffic channel transmission is divided into frames, which in the exemplary embodiment are defined as the length of the short PN sequence or 26.67 milliseconds. Each frame may carry control channel information (control channel frames) addressed to all mobile stations 6, traffic data addressed to a particular traffic channel or may be null (idle frames). The content of each frame is determined by a scheduler executed by the transmitting base station 4. In the exemplary embodiment, each frame includes 16 slots, each slot having a duration of 1.667 milliseconds. A time slot of 1.667 milliseconds is sufficient for mobile station 6 to complete the C/I measurement of the forward link signal. A 1.667 millisecond slot also represents a sufficient amount of time for an effective packet data transmission. In the exemplary embodiment, each slot is further divided into 4 quarter slots.

In the present invention, each data packet is transmitted over one or more time slots, as shown in table 1. In an exemplary embodiment, each forward link data packet includes 1024 or 2048 bits, and thus the number of slots required to transmit each data packet is related to the data rate and range, from 16 slots at 38.4Kbps rate to 1.2288Mbps rate and higher 1 slot.

An exemplary diagram of the forward link slot structure of the present invention is shown in fig. 4B. In the exemplary embodiment, each time slot includes 3 of 4 time multiplexed channels (traffic channel, control channel, pilot channel, and power control channel). In the exemplary embodiment, the pilot and power control channels are transmitted in two pilot and power control bursts (bursts) located at the same location in each slot. The pilot and power control bursts are described in detail below.

In an exemplary embodiment, the interleaved packets provided by interleaver 116 are punctured to accommodate the pilot and power control bursts. In an example embodiment, each interleaved packet includes 4096 code symbols and the first 512 code symbols are punctured, as shown in fig. 4D. The remaining code symbols are skewed in time to align with the traffic channel transmission time interval.

The data is randomized by scrambling the puncture code symbols prior to applying the orthogonal walsh cover. Randomization limits the peak-to-average envelope to the modulated waveform s (t). The scrambling sequence can be generated using a linear feedback shift register in a manner known in the art. In the exemplary embodiment, scrambler 122 is loaded in an LC state at the beginning of each slot. In the exemplary embodiment, the clock of scrambler 122 is synchronized to the clock of interleaver 116, but is stopped during pilot and power control.

In an exemplary embodiment, forward walsh channels (for traffic channels and power control channels) are orthogonally spread with 16-bit walsh cover at a fixed chip rate of 1.2288 Mcps. As shown in Table 1, the parallel-quadrature channel number per in-phase and quadrature signals, κ, is a function of the data rate. In an exemplary embodiment, for lower data rates, the in-phase and quadrature walsh covers are selected as orthogonal sets to minimize cross-talk to the demodulator phase estimation error. For example, for a 16 Walsh channel, an exemplary Walsh allocation for the in-phase signal is W₀To W₇For quadrature signals is W₈To W₁₅。

In an example embodiment, QPSK modulation is used for a data rate of 1.2288Mbps or lower. For QPSK modulation, each walsh channel includes 1 bit. In an example embodiment, at the highest data rate of 2.4576Mbps, 16-QAM is used and the scrambled data is demultiplexed into 32 parallel streams each 2 bits wide, 16 parallel streams for the in-phase signal and 16 parallel streams for the quadrature signal. In an example embodiment, the mapped QAM modulation inputs (0, 1,3, 2) are to modulation values (+3, +1, -3), respectively. Other modulation schemes such as m-array phase shift keying PSK may be envisaged and are within the scope of the present invention.

The in-phase and quadrature walsh channels are scaled prior to modulation to maintain a constant total transmit power independent of the data rate. The gain setting is normalized to a unit reference equivalent to unmodulated BPSK. The normalized channel gain G as a function of the number of walsh channels (or data rate) is shown in table 2. The average power per walsh channel (in-phase or quadrature) is also listed in table 2, so that the total normalized power is equal to one unit. Note that in practice the channel gain count for 16-QAM, the normalized energy per walsh chip is 1 for QPSK and 5 for 16-QAM.

Table 2 traffic channel orthogonal channel gain

In the present invention, a preamble is punctured into each traffic frame to help mobile station 6 synchronize with the first time slot of each variable rate transmission. In the exemplary embodiment, the preamble is an all-zero sequence that is spread with a long PN code for traffic frames but not a long PN code for control channel frames. In the exemplary embodiment, the preamble is unmodulated BPSK, which is covered W with Walsh₁Are spread orthogonally. Single positiveThe use of cross channels minimizes the peak-to-average envelope. In addition, a non-zero Walsh cover W is used₁Erroneous pilot detection can be minimized because the pilot covers W with active walsh for the traffic frame₀Spread and the pilot and preamble are not spread with the long PN code.

At the beginning of a packet, a preamble is multiplexed into the traffic channel, with the multiplexing period being a function of the data rate. The length of the preamble is such that the preamble overhead is approximately constant for all data rates when the probability of false alarm detection is minimal. A list of preambles as a function of data rate is shown in table 3.

TABLE 3 preamble parameters

	Preamble puncture duration
				Data Rate (Kbps)	Walsh code element	PN chip	Overhead
38.4	32	512	1.6％
				76.8	16	256	1.6％
153.6	8	128	1.6％
				307.2	4	64	1.6％
614.4	3	48	2.3％
				1228.8	4	64	3.1％
2457.6	2	32	3.1％

Forward link traffic frame format

In an example embodiment, each data packet is formatted with additional frame check bits, code tail bits, and other control fields. In this description, 8-bit groups are defined as 8 information bits and one data unit is one single 8-bit group and includes 8 information bits.

In an example embodiment, the forward link supports two data packet formats shown in fig. 4E and 4F. Packet format 410 includes 5 fields and packet format 430 includes 9 fields. Packet format 410 is used when a data packet to be sent to mobile station 6 includes enough data to completely fill in all available 8-bit groups in data field 418 field. Packet format 430 is used if the amount of data to be transmitted is less than the 8-bit set available in data field 418. The 8-bit groups unused by all zero PADDING are designated as PADDING (PADDING) field 446.

In an example embodiment, a Frame Check Sequence (FCS) field412 and 432 include CRC parity bits that are generated by CRC generator 112 (see fig. 3A) according to a predetermined generator polynomial. In an example embodiment, the CRC polynomial is g (x) x¹⁶+x¹²+x⁵+1, although other polynomials may be used and are within the scope of the invention. In an example embodiment, CRC bits are calculated over FMT, SEQ, LEN, DATA and PADDING fields. This provides error checking on all bits except for the code TAIL bits in TAIL fields 420 and 428 which are sent on the traffic channel of the forward link. In another embodiment, the value calculates a CRC bit on the DATA field. In the exemplary embodiment, FCS fields 412 and 432 include 16 CRC parity bits, although different numbers of parity bits provided by other CRC generators may be used and are within the scope of the invention. Although the FCS fields 412 and 432 of the present invention have been illustrated in the context of CRC parity bits, other frame check sequences may be used and are within the scope of the present invention. For example, a checksum may be calculated over the packet and provided in the FCS field.

In the exemplary embodiment, frame Format (FMT) fields 414 and 434 include a control bit that indicates whether the data frame includes only one data 8-bit group (packet format 410) or includes data and padding 8-bit groups and zero or more information (packet format 430). In an example embodiment, a low value of the FMT field 414 corresponds to the packet format 410. On the other hand, a high value of the FMT field 434 corresponds to the packet format 430.

Sequence number (SEQ) fields 416 and 442 identify the first data unit in data fields 418 and 444, respectively. The sequence number allows data to be sent out of order to the mobile station 6, for example for retransmission of packets that have been received with errors. The assignment of sequence numbers at the data unit level eliminates the need for a frame fragmentation protocol for retransmission. The sequence number also allows the mobile station 6 to detect duplicate data units. Upon receiving the FMT, SEQ and LEN fields, the mobile station 6 is able to determine which data units have been received on each time slot without using special signaling messages.

The number of bits allocated to represent the sequence number is based on the maximum number of data units that can be transmitted in a slot and the worst-case data retransmission delay. In an example embodiment, each data bit is defined by a 24-bit sequence number. At a 2.4576Mbps data rate, the maximum number of data units that can be transmitted per time slot is approximately 256. 8 bits are required to identify each data unit. Further, worse case data retransmission delays of less than 500 milliseconds may be calculated. The retransmission delay includes the time required for mobile station 6 to use for NACK messages, the time required for retransmission of data, and the time required for the number of retransmission attempts due to worse case burst errors. Thus, the 24 bits allow the mobile station 6 to positively identify the received data unit without any confusion. Depending on the size of the DATA field 418 and retransmission delay, the number of bits in the SEQ fields 416 and 442 may be increased or decreased. It is within the scope of the present invention to use different numbers of bits for SEQ fields 416 and 442.

When the DATA sent by base station 4 to mobile station 6 is less than the space available in DATA field 418, it is less than packet format 430. Packet format 430 allows base station 4 to send any number of data units to mobile station 6 up to the maximum number of data units available. In the exemplary embodiment, a high value of FMT field 434 indicates that base station 4 is transmitting packet format 430. Within packet format 430, LEN field 440 includes a value for the number of data units being transmitted in the packet. In an example embodiment, the LEN field 440 is 8 bits in length, as the DATA field 444 may range from 8 bits of groups of 0 to 255.

DATA fields 418 and 444 include DATA to be sent to mobile station 6. In an example embodiment, for packet format 410, each data packet includes 1024 bits, of which 992 are data bits. However, it is also within the scope of the invention that variable length data packets may be used to increase the number of information bits. For packet format 430, the size of the DATA field 444 is determined by the LEN field 440.

In an example embodiment, zero or more signaling messages may be sent in packet format 430. The signaling length (SIG LEN) field 436 includes the length of 8-bit groups of successive signaling messages. In an example embodiment, the SIG LEN field 436 is 8 bits in length. SIGNALING field 438 comprises a SIGNALING message. In the exemplary embodiment, each signaling message includes a message identification (MESSAGE ID) field, a message Length (LEN) field, and a message payload, as described below.

The PADDING field 446 includes PADDING 8-bit groups, which in the exemplary embodiment is set to 0 x 00 (hex). PADDING field 446 is used because the 8-bit groups of DATA that base station 4 will send to mobile station 6 may be less than the number of 8-bit groups available in DATA field 418. When this occurs, the paddding field 446 contains enough PADDING 8-bit groups to fill in the unused data fields. The PADDING field 446 is variable in length and varies depending on the length of the DATA field 444.

The last fields of packet formats 410 and 430 are tail fields 420 and 448, respectively. The tail fields 420 and 448 include zero (0 x 0) code tail bits that are used to force the encoder 114 (see fig. 3A) into a known state at the end of each data packet. The code tail bits allow the encoder 114 to simply divide the packets such that only bits from one packet are used in the encoding process. The code tail bits also allow a decoder within mobile station 6 to determine packet boundaries during the decoding process. The number of bits in the tail fields 420 and 448 is a function of the design of the encoder 114. In an exemplary embodiment, the tail fields 420 and 448 are of sufficient length to force the encoder 114 into a known state.

The two packet formats described above are example formats that may be used to facilitate the design and transmission of signaling messages. Various other packet formats may be established to meet the needs of a particular communication system. Also, the communication system may be designed to accommodate more than two packet formats, as described above.

IX. Forward Link control channel frame

In the present invention, the traffic channel is also used to transmit messages from base station 4 to mobile station 6. The types of messages sent include: (1) a handoff direction message, (2) a paging message (e.g., paging a mobile station 6 for which mobile station 6 there is data in the queue), (3) a short data packet for a particular mobile station 6, and (4) an ACK or NACK message for reverse link data transmission (described below). Other types of messages may also be sent on the control channel and are within the scope of the present invention. When the call setup phase is complete, mobile station 6 monitors the control channel for page messages and begins transmission of the reverse link pilot signal.

In an example embodiment, as shown in fig. 4A, the control channel and traffic data on the traffic channel are time multiplexed. The mobile station 6 identifies the control message by detecting a preamble, which has been covered with a predetermined PN code. In the exemplary embodiment, the control messages are sent at a fixed rate that is determined by the mobile station 6 during acquisition. In the preferred embodiment, the data rate of the control channel is 76.8 Kbps.

The control channel sends messages in a control channel container. A diagram of an example control channel container is shown in fig. 4G. In the example embodiment, each container includes a preamble 462, a control payload, and CRC parity bits 474. The control payload includes one or more messages and, if desired, padding bits 472. Each message includes a message identifier (MSG ID)464, a message Length (LEN)466, an optional Address (ADDR)468 (e.g., if the message is directed to a particular mobile station 6), and a message payload 470. In an example embodiment, the message is aligned to an 8-bit group boundary. The example control channel container shown in fig. 4G includes two broadcast messages intended for all mobile stations 6 and one message directed at a particular mobile station 6. MSG ID field 464 determines whether the message requires an address field (e.g., whether it is a broadcast or a specific message).

Forward link pilot channel

In the present invention, the forward link pilot channel provides a pilot signal that is used by mobile station 6 for initial acquisition, phase recovery, timing recovery, and proportional combining. These uses are similar to IS-95 compliant CDMA communication systems. In the exemplary embodiment, mobile station 6 also uses the pilot signals for C/I measurements.

Fig. 3A illustrates an exemplary block diagram of a forward link pilot channel of the present invention. The pilot data comprises an all 0 (or all 1) sequence that is provided to the multiplier 156. Walsh code W for multiplier 156₀The pilot data is covered. Due to Walsh code W₀Is an all 0 sequence and the output of multiplier 156 is pilot data. The pilot data is time multiplexed by the MUX162 and provided to the I walsh channel, which is passed through the short PN in the complex multiplier 214 (see fig. 3B)_IAnd (5) spreading codes. In the exemplary embodiment, pilot data is not spread with a long PN code, and MUX 234 does not gate the pilot signal during the pilot burst to allow reception by all mobile stations 6. Thus, the pilot signal is an unmodulated BPSK signal.

A schematic diagram of a pilot signal is shown in fig. 4B. In the exemplary embodiment, each slot includes two pilot bursts 306a and 306b that occur at the end of the first and third quarters of the slot. In an example embodiment, the duration of each pilot burst 306 is 64chips (TP ═ 64 chips). In the absence of traffic data or control channel data, the base station 4 transmits only pilot and power control bursts, resulting in a discontinuous waveform burst at a periodicity of 1200 Hz. The pilot modulation parameters are listed in table 4.

XI reverse link power control

In the present invention, forward link power control channels are used to send power control commands that are used to control the transmit power of reverse link transmissions from remote station 6. On the reverse link, each transmitting mobile station 6 acts as a source of interference to all other mobile stations 6 in the network. To minimize interference and maximize capacity on the reverse link, the transmit power of each mobile station 6 is controlled by two power control loops. In an exemplary embodiment, the power control loop is similar to that used in CDMA systems, which is disclosed in detail in U.S. patent application No. 5,056,109, entitled "method and apparatus for controlling transmission power in a CDMA cellular mobile telephone system," which is assigned to the assignee of the present invention and is incorporated herein by reference. Other power control mechanisms are also contemplated and are within the scope of the present invention.

The first power control loop adjusts the transmit power of mobile station 6 such that the reverse link signal remains at the set level. The quality of the signal is measured as the energy-per-bit-to-noise-plus-interference ratio Eb/Io of the reverse link signal received at the base station 4. The set level is referred to as the Eb/Io setpoint. The second power control loop adjusts the set point such that the required level of performance (as measured by the Frame Error Rate (FER)) is maintained. Power control on the reverse link is stringent because the transmit power of each mobile station 6 is the interference to other mobile stations 6 in the communication system. Minimization of reverse link transmit power reduces interference and increases reverse link capacity.

Within the first power control loop, the Eb/Io of the reverse link signal is measured at the base station 4. The base station 4 then compares the measured Eb/Io with a setpoint. If the measured Eb/Io is greater than the set point, the base station 4 sends a power control message to the mobile station 6 to increase the transmit power. In an example embodiment, the power control message is implemented with one power control bit. In the exemplary embodiment, a high value of the power control bit commands mobile station 6 to increase its transmit power, while a low value commands mobile station 6 to decrease its transmit power.

In the present invention, the power control bits for all mobile stations 6 with which each base station 4 is in communication are transmitted on a power control channel. In an exemplary embodiment, the power control channels include up to 32 orthogonal channels, which are spread with 16-bit walsh covers. Each walsh channel transmits one Reverse Power Control (RPC) bit or one FAC bit at periodic intervals. Each active mobile station 6 is assigned an RPC index that determines the walsh cover and QPSK modulation phase (e.g., in-phase or quadrature) for transmission of the RPC bit stream designated for that mobile station 6. In an example embodiment, the RPC index of 0 is reversed for the FAC bit.

An example block diagram of a power control channel is shown in fig. 3A. The RPC bits are provided to symbol repeater 150, which forwards each RPC bit a predetermined number of times. The forwarded RPC bits are provided to a walsh cover unit 152, which covers the bits with a walsh cover corresponding to the RPC index. The covered bits are provided to a gain unit 154 which scales the bits prior to modulation so as to maintain a constant total transmit power. In an example embodiment, the RPC Walsh channels are normalized so that the total RPC channel power is equal to the total available transmit power. The gain of the walsh channel can be made to vary as a function of time in order to efficiently apply the total transmit power of the base station while maintaining reliable RPC transmission to all active mobile stations 6. In the exemplary embodiment, the walsh channel gain for inactive mobile station 6 is set to zero. Using the estimate of the forward link quality measurement (the corresponding DRC channel from the mobile station 6) automated power control of the RPC walsh channel is possible. The scaled RPC bits from the gain unit 154 are provided to the MUX 162.

In an exemplary embodiment, RPC indices of 0 through 15 are assigned to Walsh covers W, respectively₀To W₁₅And is sent around the first pilot burst in the slot (RPC burst 304 in fig. 4C). Assigning RPC indices of 16 to 31 to Walsh covers W, respectively₀To W₁₅And is sent around the second pilot burst in the slot (RPC burst 308 in fig. 4C). In an exemplary embodiment, an even Walsh cover (e.g., W) modulated on an in-phase signal is used₀、W₂、W₄Etc.) and odd walsh covers modulated on orthogonal signals (e.g., W)₁、W₃、W₅Etc.) BPSK modulates the RPC bit. To reduce the peak-to-average envelope, it is desirable to balance the in-phase and quadrature power. Furthermore, to reduce cross-talk due to demodulator phase estimation errors, it is preferable to assign quadrature covers to the in-phase and quadrature signals.

In an example embodiment, up to 31 RPC bits may be sent on 31 RPC walsh channels in each slot. In the example embodiment, 15 RPC bits are sent on the first half of the slot and 16 RPC bits are sent on the second half of the slot. Adder 212 (see FIG. 3B) combines the RPC bits, and the combined waveform of the power control bits is shown in FIG. 4C.

A timing diagram of the power control channel is shown in fig. 4B. In the exemplary embodiment, the RPC bit rate is 600, or one RPC bit per slot. Each RPC bit is time multiplexed and transmitted over two RPC bursts (e.g., RPC bursts 304a and 304B), as shown in fig. 4B and 4C. In an example embodiment, the width of each RPC burst (TPC ═ 32 chips) is 32 PN chips (or 2 walsh chips) and the total width of the RPC bits is 64 PN chips (or 4 walsh chips). Other RPC bit rates can be obtained by varying the number of symbol repetitions. For example, an RPC bit rate of 1200bps (while supporting up to 63 mobile stations 6 or increasing the power control rate) can be achieved by sending a first set of 31 RPC bits over RPC bursts 304a and 304b and a second set of 32 RPC bits over RPC bursts 308a and 308 b. In this case, all walsh covers in the in-phase and quadrature signals are used. The modulation parameters for the RPC bits are summarized in table 4.

Table 4 pilot and power control modulation parameters

Parameter(s)	RPC	FAC	Pilot frequency	Unit of
					Rate of speed	600	75	1200	Hz
Modulation format	QPSK	QPSK	BPSK
					Duration of control bit	64	1024	64	PN chip
Forwarding	4	64	4	Code element

The power control channel has the characteristic of a burst because the number of mobile stations 6 communicating with each base station 4 may be less than the number of available RPC walsh channels. In this case, appropriate adjustment of the gain by gain unit 154 causes some of the RPC Walsh channels to be set to zero.

In the exemplary embodiment, the RPC bits are sent to mobile station 6 without being encoded or interleaved to reduce processing delay. Furthermore, erroneous reception of the power control bits is not detrimental to the data communication system of the present invention, since the power control loop can correct the error in the next time slot.

In the present invention, mobile station 6 may be in soft handoff with multiple base stations 4 on the reverse link. A method and apparatus for reverse power control of a mobile station 6 in soft handoff is disclosed in the aforementioned U.S. patent No. 5,056,109. The mobile station 6 in soft handoff monitors the RPC walsh channel for each base station 4 in the active set and combines the RPC bits according to the method disclosed in the aforementioned U.S. patent No. 5,056,109. In a first embodiment, the mobile station 6 performs a logical or of the down power command. If any of the received RPC bits commands the mobile station 6 to decrease transmit power, the mobile station 6 decreases transmit power. In a second embodiment, mobile station 6 in soft handoff may combine soft decisions of RPC bits before making a hard decision. Alternative embodiments are contemplated to process the received RPC bits, all of which are within the scope of the present invention.

In the present invention, the FAC bit indicates to mobile station 6 whether the traffic channel associated with the pilot channel will be transmitted on the next field. By broadcasting knowledge of the interference activity, the use of the FAC bit improves the C/I estimation of the mobile station 6 and thus improves the data rate request. In the exemplary embodiment, the FAC bit changes only at the boundary of a field and repeats in 8 consecutive slots, resulting in a bit rate of 75 bps. The parameters of the FAC bit are listed in table 4.

Using the FAC bit, mobile station 6 may calculate the C/I measurement as follows:

img id="idf0003" file="C0210601400391.GIF" wi="381" he="66" img-content="drawing" img-format="GIF"/

wherein (C/I)_iIs the C/I measurement of the ith forward link signal, Ci is the total received power of the ith forward link signal, C_jIs the received power of the jth forward link signal, I is the total interference if all base stations 4 are transmitting, α_jIs the FAC bit of the jth forward link signal, which may be either 0 or 1 depending on the FAC bit.

XII reverse link data transmission

In the present invention, the reverse link supports variable rate data transmission. Variable rate provides flexibility and allows mobile stations 6 to transmit at one of several data rates depending on the amount of data to be transmitted to base station 4. In the exemplary embodiment, mobile station 6 may transmit at a lower data rate at any time. In the exemplary embodiment, transmissions at higher data rates require grants by base station 4. This implementation minimizes reverse link transmission delay while providing efficient utilization of reverse link resources.

An exemplary illustration of the flow chart of the reverse link data transmission of the present invention is shown in fig. 8. Initially, at block 802, mobile station 6 executes an access probe to establish a lower rate data channel on the reverse link at time slot n, as described in the above-mentioned U.S. patent No. 5,289,527. In the same time slot, base station 4 demodulates the access probe at block 804 and receives the access message at block 804. At block 806, the base station 4 grants the request for the data channel, sends the grant on slot n +2 and assigns an RPC index on the control channel. At block 808, the mobile station receives the grant and is power controlled by base station 4 on time slot n + 2. Beginning at time slot n +3, mobile station 6 begins transmitting pilot signals and immediately accesses the lower rate data channel on the reverse link.

If mobile station 6 has traffic data and requires a high rate data channel, mobile station 6 may initiate the request at block 810. At block 812, base station 4 receives a high speed data request on time slot n + 3. At block 814, base station 4 transmits a grant on the control channel on time slot n + 5. At block 816, mobile station 6 receives the grant at time slot n +5 and begins high speed data transmission on the reverse link at block 818 at time slot n + 6.

Xiii reverse link structure

In the data communication system of the present invention, the reverse link transmission and the forward link transmission differ in some respects. On the forward link, data transmission typically occurs from one base station 4 to one mobile station 6. On the reverse link, however, each base station 4 may receive data transmissions from multiple mobile stations 6 simultaneously. In the exemplary embodiment, each mobile station 6 may transmit at one of several data rates, depending on the amount of data to be transmitted to base station 4. The system design reflects the asymmetric nature of data communications.

In an example embodiment, the time base unit on the reverse link is the same as the time base unit on the forward link. In an example embodiment, forward link and reverse link data transmissions occur over time slots that are 1.667 milliseconds in duration. However, since data transmission on the reverse link typically occurs at lower data rates, longer timing units may be used to improve efficiency.

In the exemplary embodiment, the reverse link supports two channels: a pilot/DRC channel and a data channel. The function and implementation of each of these channels is explained below. The pilot/DRC channel is used to transmit pilot signals and DRC messages and the data channel is used to transmit traffic data.

A diagram of an exemplary reverse link frame structure of the present invention is shown in fig. 7A. In the exemplary embodiment, the reverse link frame structure is similar to the forward link frame structure shown in FIG. 4A. However, on the reverse link, the pilot/DRC design and traffic data are transmitted on both the in-phase and quadrature channels.

In the exemplary embodiment, mobile station 6 transmits DRC messages on the pilot DRC channel on every slot whenever mobile station 6 is receiving a high-speed data transmission. On the other hand, when mobile station 6 is not receiving high speed data transmissions, the entire slot contains a pilot signal on the pilot/DRC channel. The receiving base station 4 uses the pilot signal for several functions: as an aid to initial acquisition, as a phase reference for the pilot/DRC and data channels and as a source for closed loop reverse link power control.

In an example embodiment, the bandwidth of the selected reverse link is 1.2288 MHz. This bandwidth selection allows the use of existing hardware designed for CDMA systems that conform to the IS-95 standard. However, other bandwidths may be applied to increase capacity and/or to meet system requirements. In an exemplary embodiment, the same long PN code and short PN as specified in the IS-95 standard are used_IAnd PN_QThe code spreads the reverse link signal. In an exemplary embodiment, the reverse link channel is transmitted using QPSK modulation. On the other hand, OQPSK modulation can be used to minimize peak-to-average amplitude variation of the modulated signal, which can result in improved performance. Can be provided withIt is contemplated that the use of different system bandwidths, PN codes, and modulation schemes are within the scope of the present invention.

In the exemplary embodiment, the transmit power of the reverse link transmission on the pilot/DRC channel and the data channel is controlled such that the E of the reverse link signal is measured at base station 4_b/I_oIs kept at a predetermined E_b/I_oAt set point, as described in the aforementioned U.S. patent No. 5,506,109. As described above, power control is maintained by the base station 4 in communication with the mobile station 6 and the commands are sent as RPC.

XIV. reverse link data channel

A block diagram of an exemplary reverse link architecture of the present invention is shown in fig. 6. The data is divided into data packets and provided to an encoder 612. For each data packet, encoder 612 generates CRC parity bits, inserts code tail bits, and encodes the data. In an exemplary embodiment, the encoder 612 encodes the packets according to the encoding format disclosed in the aforementioned U.S. patent application No. 08/743,688. Other encoding formats may also be used and are within the scope of the invention. The encoded packet from encoder 612 is provided to block interleaver 614, which reorders the code symbols in the packet. The interleaved packet is provided to multiplier 616 which covers the data with the walsh cover and provides the covered data to gain unit 618. Gain unit 618 scales the data to maintain a constant energy-per-bit Eb independent of the data rate. The scaled data from the gain unit 618 is provided to multipliers 650b and 650d, which spread the data with PN _ Q and PN _ I sequences, respectively. The expanded data from multipliers 650b and 650d are provided to filters 652b and 652d, respectively, which filter the data. The filtered signals from filters 652a and 652b are provided to adder 654a and the filtered signals from filters 652c and 652d are provided to adder 654 b. The adder 654 adds the signal from the data channel and the signal from the pilot/DRC channel. The outputs of adders 654a and 654b include IOUT and QOUT, respectively, using in-phase sinusoidal COS (w), respectively_Ct) and quadrature sinusoid SIN (w)_Ct) modulated (as in the forward link) and added (not shown in fig. 6). In an example embodiment, traffic data is transmitted on two in-phase and quadrature phases of a sinusoid.

In an example embodiment, data is spread with a long PN code and a short PN code. The long PN code scrambles the data so that the receiving base station 4 can identify the transmitting mobile station 6. The short PN codes spread the signal over the system frequency band. A long PN sequence is generated by long code generator 642 and provided to multiplier 646. Short PN generation by short code generator 644_IAnd PN_QThe sequences, also provided to multipliers 646a and 646b, respectively, are multiplied together to form the PN _ I and PN _ Q signals, respectively. The timing/control circuit 640 provides a timing reference.

The example block diagram of the data channel structure shown in fig. 6 is one of many structures that support data coding and modulation on the reverse link. For high rate data transmission, a structure employing multiple orthogonal channels similar to that used for the forward link may be used. Other architectures, such as those used for the reverse link traffic channel in a CDMA system conforming to the IS-95 standard, are also contemplated and are within the scope of the present invention.

In the exemplary embodiment, the reverse link data channel supports four data rates listed in Table 5. Additional data rates and different data rates may be supported and are within the scope of the invention. In an exemplary embodiment, the packet size for the reverse link is related to the data rate, as shown in table 5. As described in the above-mentioned us patent application No. 08/743,688, improved decoder performance for larger packet sizes may be obtained. Thus, different packet sizes than those listed in Table 5 may be applied to improve performance and are within the scope of the invention. In addition, parameters related to data rate independence may dictate packet size.

TABLE 5 Pilot and Power control modulation parameters

Parameter(s)	Data rate				Unit of
							9.6	19.2	38.4	76.8	Kbps
Frame duration	26.66	26.66	13.33	13.33	Millisecond (ms)
						Data packet length	245	491	491	1003	Bit
CRC length	16	16	16	15	Bit
						Code tail bit	5	5	5	5	Bit
Total bit/packet	256	512	512	1024	Bit
						Coded packet length	1024	2048	2048	4096	Code element
Walsh symbol length	32	16	8	4	Raising yuan
						Request for	Is not limited to	Is that	Is that	Is that

As shown in table 5, the reverse link supports multiple data rates. In the exemplary embodiment, a minimum rate of 9.6Kbps is allocated for each mobile station 6 registered with base station 4. In the exemplary embodiment, mobile station 6 may transmit data on the lowest rate channel on any time slot without requesting permission from base station 4. In the exemplary embodiment, the selected base station 4 grants data transmission at a higher data rate based on a set of system parameters (such as system load, fairness, and total throughput). An example scheduling mechanism for high speed data transmission is described in detail in the above-mentioned U.S. patent application No. 08/798,951.

XV. reverse link pilot/DRC channel

An example block diagram of a pilot/DRC channel is shown in fig. 6. The DRC message is provided to a DRC encoder 626, which encodes the message according to a predetermined encoding format. Since the error probability of the DRC message must be sufficiently low, encoding of the DRC message is important because incorrect forward link data rate determination can impact the throughput performance of the system. In the exemplary embodiment, DRC encoder 626 is a rate (8, 4) CRC block encoder that encodes a 3-bit DRC message into an 8-bit codeword. The encoded DRC message is provided to a multiplier 628 that covers the message with a walsh code that uniquely identifies the target base station 4 to which the DRC message is directed. The covered DRC message is provided to a Multiplexer (MUX)630 that multiplexes the message with pilot data. The DRC message and pilot data are provided to multipliers 650a and 650c, which spread the data with PN _ I and PN _ Q signals, respectively. Thus, the pilot and DRC messages are sent on the two in-phase and quadrature phases of the sinusoid.

In an exemplary embodiment, the DRC message is sent to the selected base station 4. This is achieved by covering the DRC message with a walsh code that identifies the selected base station 4. In an exemplary embodiment, the length of the walsh code is 128 chips. The origin of 128-chip walsh codes is well known in the art. Each base station 4 communicating with mobile station 6 is assigned a unique walsh code. Each base station 4 decovers the signal on the DRC channel with the walsh code assigned to it. The selected base station 4 can decover the DRC message and send data to the requesting mobile station 6 on the forward link in response. Other base stations can determine that the requested data rate is not directed to them because these base stations 4 are assigned different walsh codes.

In the exemplary embodiment, the reverse link short PN code is the same for all base stations 4 in the data communication system and there is no offset in the short PN sequence that distinguishes the different base stations 4. The data communication system of the present invention supports soft handoff on the reverse link. Using the same short PN code without an offset allows multiple base stations 4 to receive the same reverse link transmission from mobile station 6 during soft handoff. The short PN codes provide spectral spreading but do not allow for identification of the base station 4.

In the exemplary embodiment, the DRC message carries the data rate requested by mobile station 6. In another embodiment, the DRC message carries an indication of the forward link quality (e.g., C/I information measured by mobile station 6). Mobile station 6 may simultaneously receive forward link pilot signals from one or more base stations 4 and perform C/I measurements on each received pilot signal. The mobile station 6 then selects the best base station 4 based on a set of parameters that may include current and previous C/I measurements. In one of several embodiments, the rate control information is formatted into a DRC message that may be transmitted to the base station 4.

In a first embodiment, mobile station 6 transmits DRC messages according to the requested data rate. The requested data rate is the highest rate that supports the data rate, which yields satisfactory performance on the C/I measured at the mobile station 6. Mobile station 6 first calculates the maximum data rate that yields satisfactory performance from the C/I measurements. The maximum data rate is then quantized to one of the supported data rates and designated as the requested data rate. An index corresponding to the requested data rate is sent to the selected base station 4. An example set of supported data rates and corresponding data rate indices are shown in table 1.

In a second embodiment, the mobile station 6 sends an indication of the forward link quality to the selected base station 4 and the mobile station 6 sends a C/I index representing a quantized value of the C/I measurement. The C/I measurements can be mapped into a table and correlated with the C/I index. Using more bits to represent the C/I index allows finer quantization of the C/I measurements. Also, the map may be linear or pre-compensated. For a linear map, each increment in the C/I index represents a corresponding increase in the C/I measurement. For the pre-compensation map, each increment in the C/I index represents a different increase in the C/I measurement. As an example, the pre-compensation map can be used to quantify the C/I measurements to match the Cumulative Distribution Function (CDF) curve of the C/I distribution as shown in FIG. 10.

Other embodiments for transmitting rate control information from mobile station 6 to base station 4 are contemplated and are within the scope of the present invention. In addition, it is within the scope of the present invention to use different numbers of bits to represent the rate control information. For simplicity, DRC messages are used to convey the requested data rate, and throughout much of the description the invention is described in the context of the first embodiment.

In an exemplary embodiment, the C/I measurements may be made on the forward link pilot signal in a similar manner as used by CDMA systems. A method and apparatus for making C/I measurements is disclosed in U.S. patent application No. 08/722,763 entitled "method and apparatus for measuring link quality in a spread spectrum system", filed 1996 on 27.9.9.78, which is assigned to the assignee of the present invention and incorporated herein by reference. In general, a short PN code may be used to despread a received signal to obtain a C/I measurement on a pilot signal. The C/I measurement on the pilot signal may contain inaccuracies if the channel conditions change between the time of the C/I measurement and the time of the actual data transmission. In the present invention, the use of the FAC bit allows the mobile station 6 to take into account the forward link activity when determining the requested data rate.

In another embodiment, the C/I measurements may be made on the forward link traffic channel. The traffic channel signal is first despread with the long PN code and the short PN code and decovered with the walsh code. The C/I measurement on the data channel signal may be more accurate because a larger percentage of the transmit power is allocated for data transmission. Other methods of C/I measurement of the forward link signal received by the mobile station 6 are also contemplated and are within the scope of the present invention.

In an exemplary embodiment, the DRC message is sent in the first half of the slot (see fig. 7A). For an example slot of 1.667 milliseconds, the DRC message includes the first 1024 chips or 0.83 millisecond slot. The base station 4 uses the remaining 1024 chips of time to demodulate and decode the message. Transmission of the DRC message in an earlier part of the slot allows the base station 4 to decode the DRC message in the same slot and possibly transmit data at the requested data rate in the next slot. The short processing delay allows the communication system of the present invention to quickly adapt to changes in the operating environment.

In another embodiment, the requested data rate is communicated to the base station 4 through the use of an absolute reference and a relative reference. In this embodiment, the absolute reference comprises periodically transmitting the requested data rate. The absolute reference allows the base station 4 to determine the correct data rate requested by the mobile station 6. For each time slot between absolute reference transmissions, the mobile station 6 sends a relative reference to the base station 4 that indicates whether the requested data rate for the upcoming time slot is higher, lower, or the same as the requested data rate for the previous time slot. The mobile station 6 periodically transmits the absolute reference. The periodic transmission of the data rate index allows the requested data rate to be set in a known state and ensures that no false receptions relative to a baseline are accumulated. The use of the absolute reference and the relative reference can reduce the transmission rate of the DRC message to the base station 6. Other protocols for transmitting the requested data rate are contemplated and are within the scope of the invention.

XVI. reverse link access channel

During the registration phase, mobile station 6 sends a message to base station 4 using the access channel. In an exemplary embodiment, the access channel is implemented using a slotted structure, with mobile station 6 randomly accessing each slot. In an example embodiment, the DRC channel is used to time multiplex the access channels.

In an example embodiment, the access channel sends the message in an access channel container. In the exemplary embodiment, the access channel frame format IS the same as that specified by the IS-95 standard, except that the 20-millisecond frame specified by the IS-95 standard IS replaced with a 26.67 millisecond timing. An example access channel container is shown in fig. 7B. In the exemplary embodiment, each access channel container 712 includes a preamble 722, one or more message containers 724, and padding 726. Each message container 724 includes a message length (MSG LEN) field 732, a message body 734, and CRC parity bits 736.

Forward link NACK (not acknowledged) channel

In the present invention, mobile station 6 transmits a NACK message on the data channel. Mobile station 6 generates NACK information for each packet received in error. In an exemplary embodiment, the NACK message may be transmitted using the blank and burst signaling data format disclosed in the above-mentioned U.S. patent No. 5,504,773.

Although the invention has been described in the context of a NACK protocol, the application of an ACK protocol is envisaged and is within the scope of the invention.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Variations of those embodiments may become apparent to those of ordinary skill in the art and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (53)

1. A method for controlling a data rate of a signal transmitted from a first entity to a second entity over a wireless channel during a time frame, the time frame comprising a plurality of time slots, the method comprising the steps of:

in each time slot, the first entity receives information representative of a quality measure of said channel; and

during the time frame, the first entity transmits the signal at a data rate corresponding to the received information.

2. The method of claim 1, wherein the step of receiving information comprises receiving a carrier-to-interference ratio.

3. The method of claim 2, wherein the channel comprises a forward link for transmission from the first entity to the second entity and a reverse link for transmission from the second entity to the first entity, and the carrier-to-interference ratio is a carrier-to-interference ratio for the forward link.

4. The method of claim 1, wherein the step of receiving information comprises receiving information based on a quality measurement of a channel during a previous time frame.

5. The method of claim 2, wherein the step of receiving a carrier-to-interference ratio comprises receiving a measurement from a second entity.

6. The method of claim 5, wherein the first entity is a base station and the second entity is a mobile station.

7. The method of claim 1, further comprising the step of selecting a data rate based on the received information.

8. The method of claim 7, wherein said selecting step comprises selecting said data rate from a set of predetermined data rates.

9. The method of claim 7, wherein the selecting step comprises selecting a channel coding structure corresponding to the data rate.

10. The method of claim 7, wherein the selecting step comprises selecting a packet format corresponding to the data rate.

11. The method of claim 7, further comprising determining an amount of user data to be transmitted during the time frame, the amount of user data corresponding to the data rate.

12. An infrastructure equipment for transmitting a signal to a mobile station during a time frame over a wireless channel, the time frame comprising a plurality of time slots, comprising:

means for receiving information indicative of a quality measure of the wireless channel from the mobile station in each time slot; and

means for transmitting a signal at a data rate corresponding to the received information.

13. The infrastructure equipment of claim 12, wherein the means for receiving comprises means for receiving a carrier-to-interference ratio of a wireless channel.

14. The infrastructure device of claim 13, wherein the wireless channel includes a forward link for transmission from the infrastructure device to the mobile station and a reverse link for transmission from the mobile station to the infrastructure device, and the carrier-to-interference ratio is a carrier-to-interference ratio for the forward link.

15. The infrastructure equipment of claim 12, wherein the means for receiving comprises means for receiving information based on a quality measurement of a wireless channel during a previous time frame.

16. The infrastructure equipment of claim 12, further comprising a selection means for selecting a data rate.

17. The infrastructure equipment of claim 16, wherein the selecting means comprises data rate selecting means for selecting the data rate from a set of predetermined data rates.

18. The infrastructure equipment of claim 16, wherein the data rate selection means comprises means for selecting a channel coding structure corresponding to the data rate.

19. The infrastructure equipment of claim 16, wherein the data rate selection means comprises means for selecting a packet format corresponding to the data rate.

20. The base device of claim 16, further comprising means for determining an amount of user data to be transmitted within the time frame, the amount of user data corresponding to the data rate.

21. An infrastructure equipment for transmitting a signal to a mobile station during a time frame over a wireless channel, the time frame comprising a plurality of time slots, comprising:

a receiver for receiving information indicative of a quality measure of the wireless channel from the mobile station in each time slot; and

a transmitter coupled to the receiver for transmitting the signal at a data rate corresponding to the received information.

22. The infrastructure equipment of claim 21, wherein the quality measurement is a carrier-to-interference ratio of a wireless channel.

23. The infrastructure equipment of claim 22, wherein the wireless channel comprises a forward link for transmission from the infrastructure equipment to the mobile station and a reverse link for transmission from the mobile station to the infrastructure equipment, and the carrier-to-interference ratio is a carrier-to-interference ratio for the forward link.

24. The infrastructure device of claim 21, wherein the information is based on a quality measurement of a wireless channel during a previous time frame.

25. The infrastructure equipment of claim 21, further comprising a selection unit coupled to the receiver and the transmitter for selecting the data rate based on the received information.

26. The infrastructure equipment of claim 25, wherein the selection unit is configured to select the data rate from a set of predetermined data rates.

27. The infrastructure equipment of claim 25, wherein the selection unit is configured to select a channel coding structure for transmitting the signal during the time frame, the selected channel coding structure corresponding to the data rate.

28. The infrastructure equipment of claim 25, wherein the selection unit is configured to select a packet format for transmitting signals during the time frame, the selected packet format corresponding to the data rate.

29. The infrastructure equipment of claim 25, wherein the selection unit is configured to determine an amount of user data to be transmitted within the signal during the time frame, the selected amount of user data corresponding to the data rate.

30. A method for controlling a data rate of a signal transmitted by a second entity to a first entity over a wireless channel and received by the first entity during a time frame, the time frame comprising a plurality of time slots, comprising the steps of:

the first entity transmitting information representative of a quality measure of the wireless channel in each time slot; and

the first entity receives signals at a data rate, which is based on the quality measure.

31. The method of claim 30, further comprising measuring a carrier-to-interference ratio of the wireless channel, wherein the information indicative of the quality measurement is based on the measured carrier-to-interference ratio.

32. The method of claim 30, wherein the first entity is a mobile station and the receiving step comprises receiving from an infrastructure device.

33. The method of claim 30, wherein said transmitting step comprises transmitting information indicative of a desired data rate.

34. The method of claim 30, wherein said transmitting step comprises transmitting information indicative of a carrier-to-interference ratio of the wireless channel.

35. The method of claim 34, wherein the wireless channel comprises a reverse link transmitting from the first entity to the second entity and a forward link transmitting from the second entity to the first entity, and wherein the carrier-to-interference ratio is a carrier-to-interference ratio of the forward link.

36. The method of claim 34, wherein said receiving step comprises receiving a packet having a packet format, said packet format corresponding to said data rate.

37. The method of claim 34, wherein the receiving step comprises receiving a packet having a packet format corresponding to the data rate and including a predetermined amount of coded bits.

38. The method of claim 34, wherein said receiving step comprises receiving a packet having a packet format corresponding to said data rate and comprising a predetermined amount of user data bits.

39. A mobile station for receiving a signal from an infrastructure device over a wireless channel during a time frame, the time frame comprising a plurality of time slots, comprising:

means for transmitting information representative of a quality measure of the wireless channel to the base unit in each time slot; and

means for receiving the signal from the base unit at a data rate, the data rate based on a quality measurement.

40. The mobile station of claim 39, further comprising means for measuring a carrier-to-interference ratio of the wireless channel to obtain information indicative of the quality measurement.

41. The mobile station of claim 39, wherein said means for transmitting comprises means for transmitting information indicative of a desired data rate.

42. The mobile station of claim 39, wherein said means for transmitting comprises means for transmitting information indicative of a carrier-to-interference ratio of the wireless channel.

43. The mobile station of claim 42, wherein the wireless channel comprises a forward link for transmission from the infrastructure device to the mobile station and a reverse link for transmission from the mobile station to the infrastructure device, and wherein the carrier-to-interference ratio is a carrier-to-interference ratio for the forward link.

44. The mobile station of claim 42, wherein said receiving means includes means for determining a packet format of a received signal, said packet format corresponding to said data rate.

45. The mobile station of claim 42, wherein said receiving means comprises means for determining a channel coding structure for decoding a signal, said channel coding structure corresponding to said data rate.

46. A mobile station for receiving a signal from an infrastructure device over a wireless channel during a time frame, the time frame comprising a plurality of time slots, comprising:

a transmitter for transmitting information representative of a quality measure of the wireless channel to the base unit in each time slot; and

a receiver for receiving the signal from the base device at a data rate, the data rate based on a quality measurement.

47. The mobile station of claim 46, wherein said information indicative of a quality measure comprises information indicative of a desired data rate.

48. The mobile station of claim 46, wherein said information indicative of a quality measurement comprises information indicative of a carrier-to-interference ratio of a wireless channel.

49. The mobile station of claim 48, wherein the wireless channel comprises a forward link for transmission from the infrastructure device to the mobile station and a reverse link for transmission from the mobile station to the infrastructure device, and wherein the carrier-to-interference ratio is a carrier-to-interference ratio for the forward link.

50. The mobile station of claim 48, wherein a packet format of a packet within said signal corresponds to said data rate.

51. The mobile station of claim 50, wherein an amount of user data present in said packet is predetermined based on a data rate of a received signal.

52. The mobile station of claim 48, wherein the receiver is configured to decode a signal from the signal using a channel coding structure, the channel coding structure corresponding to the data rate.

53. The mobile station of claim 48, wherein the receiver is configured to decode information from the signal using a channel coding structure, the channel coding structure being predetermined based on the data rate.