HK1070759A1 - Method and apparatus for controlling transmission gated communication system - Google Patents

Description

Method and apparatus for controlling gated transmission communication system

The present application is a divisional application of the chinese patent application entitled "method and apparatus for controlling gated transmission communication system" filed on 21/1/2002 by the applicant under the application number "00810692.4".

Background

1. Field of the invention

The present invention relates to communications. More particularly, the present invention relates to a novel and improved method and apparatus for transmitting variable rate data in a wireless communication system.

2. Correlation technique

The Code Division Multiple Access (CDMA) modulation technique employed is one technique that facilitates communications in the presence of a large number of system users. Other multiple-access communication system techniques are known in the art, such as Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA). However, the spread spectrum modulation technique of CDMA has significant advantages over the modulation techniques of these multiple access communication systems. U.S. Pat. No. 4,901,307, entitled "SPECRAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM SATELLITE OR TERRESTRIAL REPEATERS," assigned to the assignee of the present invention and incorporated herein by reference, discloses the use of CDMA technology in MULTIPLE ACCESS COMMUNICATION systems. Further use of CDMA technology in multicast is disclosed in U.S. Pat. No. 5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS INA CDMA CELLULAR TELEPHONE SYSTEM", assigned to the assignee of the present invention and incorporated herein by reference.

CDMA provides a way of frequency diversity by spreading the signal energy over a large bandwidth by virtue of its inherent wideband signal characteristics. Thus, frequency selective fading affects only a small portion of the CDMA signal bandwidth. Space diversity or path diversity is obtained by providing multiple signal paths simultaneously through links established by the mobile subscriber via 2 or more cell sites. In addition, path diversity can also be obtained by making the signals reachable at different propagation delays for independent reception and processing, thereby exploiting the multipath environment through spread spectrum processing. U.S. Pat. Nos. 5,101,501 AND 5,109,390, both assigned to the assignee of the present invention AND incorporated herein by reference, describe examples of path diversity, the former patent being entitled "METHOD AND STSTSTSTSMOR PROVIDING A SOFT HANDOFF IN COMMUNICATIONS IN A CDMA CELLULARTELEPHENE SYSTEM", AND the latter patent being entitled "DIVERSITY RECEIVER IN A CDMA CELLULARTELEPHENE SYSTEM".

A method of transmitting speech in a digital communication system is provided by employing variable rate speech coding, which has the particular advantage of increased capacity while maintaining perceived speech pitch quality. Particularly useful VARIABLE RATE speech coder methods and apparatus are described in detail in U.S. patent No. 5,414,796, entitled VARIABLE RATE coder, assigned to the assignee of the present invention and incorporated herein by reference.

The use of a variable rate speech coder allows the data frame to have maximum speech data energy when the speech coder is providing high rate speech data. When a variable rate speech encoder provides speech data at a rate lower than the highest rate, there is excess capacity in the transmission frame. A METHOD of transmitting additional data in fixed, predetermined size TRANSMISSION frames in THE case where THE data source of THE data frames provides data at a variable rate is described in U.S. patent No. 5,504,773, entitled "METHOD AND APPARATUS FOR THE FORMATTING of data FOR TRANSMISSION", assigned to THE assignee of THE present invention AND incorporated herein by reference. In the above-mentioned patent application, a method and apparatus are disclosed for combining different types of data from different sources in a transmission data frame.

In a frame containing less data than a predetermined capacity, only a part of the frame containing data is transmitted by gating transmission of the transmission amplifier, and power consumption can be reduced. Furthermore, message collisions in the communication system may be reduced if the data is placed in the frame according to a predetermined pseudo-random process. 5,659,569, entitled DATR BURSTRANDOMIZER, assigned to the assignee of the present invention and incorporated herein by reference, discloses a method and apparatus for gated transmission and placement of data in frames.

One useful method of mobile unit power control in a communication system is to monitor the signal power received from the wireless communication device at the base station. The base station transmits power control bits to the radio communication apparatus at predetermined intervals based on the monitored power level. 5,056,019 entitled "METHOD AND APPARATUS FOR CONTROLLING RANSMSION POWER IN A CDMA MOBILE TELEPHONE SYSTEM", assigned to the assignee of the present invention AND incorporated herein by reference, discloses a METHOD AND APPARATUS FOR controlling transmit POWER IN this manner.

In a communication system that provides data using a QPSK modulation format, useful information can be obtained by taking the cross product of the I component and Q component of a QPSK signal. Knowing the relative phases of these 2 components, the velocity of the wireless communication device relative to the base station can be determined approximately. U.S. patent No. 5,506,865, entitled PILOT CARRIER dot tprdoduct CIRCUIT, assigned to the assignee of the present invention and incorporated herein by reference, discloses circuitry for determining I, Q component cross products in QPSK modulated communication systems.

There is an increasing demand for wireless communication systems that can transmit digital information at high rates. One method of transmitting high rate digital data from a wireless communication device to a central base station is for the wireless communication device to transmit the data using CDMA spread spectrum techniques. One proposed method is for a wireless communication device to transmit its information using a small set of orthogonal channels. 08/866,604 entitled "HIGH DATA RATE CDMA WIRELESS COMMUNICATION STSTSTSTTEM," assigned to the assignee of the present invention and incorporated herein by reference.

In the above application, a system is disclosed that transmits a pilot signal on the reverse link (the link from the wireless communication device to the base station) to enable coherent demodulation of the reverse link signal at the base station. Using the pilot signal data, coherent processing can be performed at the base station by determining and canceling the phase shift of the reverse link signal. The pilot data may also be used to optimally weight multipath signals received at different delays before combining in the rake receiver. Once the phase shifts are removed and the multipath signals are appropriately weighted, the multipath signals can be combined to reduce the power at which the reverse link signal must be received for appropriate processing. This reduces the required received power to enable successful processing of higher transmission rates or, conversely, reduces interference between sets of reverse link signals.

Although some additional transmit power is required for transmitting the pilot signal, the ratio of pilot signal power to the total power of the reverse link signal at higher transmission rates is substantially lower than that associated with lower data rate digital voice data transmission cellular systems. Therefore, high dataE obtained using coherent reverse link in rate CDMA system_b/N₀The gain exceeds the additional power required to transmit pilot data from each wireless communication device.

However, at lower data rates, the pilot signal transmitted continuously on the reverse link contains more energy related to the data signal. At these low rates, reductions in talk time and system capacity may exceed the benefits of coherent demodulation and interference reduction provided by continuously transmitting the reverse link pilot signal in some applications.

Disclosure of Invention

The present invention is a novel and improved method and system for transmitting frames of information in a discontinuous transmission format. In particular, the present invention describes a method of transmitting eighth rate voice or data frames that utilizes transmit gating and energy scaling to reduce battery usage of a variable rate wireless communication device while increasing reverse link capacity and providing reliable communication of 1/8 rate frames. In the present invention, four methods of transmitting 1/8 rate data frames are provided, half of the frames being gated off and the remaining data being transmitted at nominal transmit energy, thereby achieving the above objectives.

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 functional block diagram of an exemplary embodiment of a transmission system of the present invention implemented in a wireless communication device 50;

FIG. 2 is a functional block diagram of an exemplary embodiment of modulator 26 of FIG. 1;

FIGS. 3A-3G illustrate 4 alternative embodiments of the energy t used to transmit a variable rate frame for four different data rates and including transmitting 1/8 rate frames;

fig. 4 is a functional block diagram of selected portions of a base station 400 of the present invention;

FIG. 5 is an expanded functional block diagram of an exemplary single demodulation chain of demodulator 404 of FIG. 4;

fig. 6 is a block diagram illustrating the forward link power control mechanism of the present invention.

Detailed description of the preferred embodiments

Fig. 1 illustrates a functional block diagram of an exemplary embodiment of the transmission system of the present invention in a wireless communication device 50. Those skilled in the art will appreciate that the methods described herein may also be used for transmissions from a central base station (not shown). The reader will also appreciate that other embodiments of the invention may not have the various functional blocks shown in fig. 1. The functional block diagram of fig. 1 corresponds to an embodiment that may be used to operate in accordance with the IS-95C standard of the TIA/EIA (also known as IS-2000). Other embodiments of the present invention may be used with other standards, including wideband cdma (wcdma) standards as proposed by the standardization bodies ETSI and ARIB. Those skilled in the art will appreciate that the present invention can be readily extended to the WCDMA standard due to the wide similarity between the reverse link modulation of the WCDMA standard and the reverse link modulation of the IS-95C standard.

In the exemplary embodiment of fig. 1, the wireless communication device transmits multiple different messages that are distinguished from each other by short orthogonal spreading sequences as described in the aforementioned U.S. patent application No. 08/886,604. The wireless communication device transmits 5 separate code channels: (1) a first supplemental data channel 38, (2) a time division multiplexed channel of pilot and power control symbols 40, (3) a dedicated control channel 42, (4) a second supplemental data channel 44, and (5) a fundamental channel 46. The first supplemental data channel 38 and the second supplemental data channel 44 carry digital data, such as facsimile, multimedia applications, images, email, or other types of digital data, that exceeds the capacity of the base channel 46. The multiplexed channel of pilot and power control symbols 40 carries pilot symbols to allow for coherent demodulation of the data channel by the base station and also carries power control bits to control the transmit energy in the base station's communication with the wireless communication device 50. The control channel 42 conveys control information to the base station, such as the operating mode and capabilities of the wireless communication device 50, as well as other required signaling information. The fundamental channel 46 is used to carry basic information from the wireless communication device to the base station. In the case of voice transmission, the fundamental channel 46 carries voice data.

The supplemental data channels 38 and 44 are encoded and processed for transmission by a method not shown and then provided to the modulator 26. The power control bits are provided to a repetition generator 22 which repeats the power control bits before providing the data bits to a Multiplexer (MUX) 24. The redundant power control bits are time division multiplexed with pilot symbols in multiplexer 24 and provided on line 40 to modulator 26.

The message generator 12 generates a message of the required control information and provides the control message to the CRC and tail bit generator 14. The generator 14 appends a set of cyclic redundancy check bits, which are parity bits, for checking the accuracy of the base station decoding. The generator 14 also adds predetermined tail bits groups to the control message to clear the decoder memory at the base station receiver subsystem. This message is then provided to decoder 16 which provides forward error correction coding to the control message. The encoded symbols are provided to a repetition generator 20 which repeats the encoded symbols to provide additional time diversity in the transmission. After the repetition generator, a Puncturing Unit (PUNC)19 punctures certain symbols according to some predetermined puncturing pattern to provide a predetermined number of symbols within the frame. The symbols are then provided to an interleaver 18, which reorders the symbols according to a predetermined interleaving format. The interleaved symbols are provided on line 42 to modulator 26.

The variable rate data source 1 generates a variable data rate. In a typical embodiment, the variable rate data source 1 is a variable rate speech coder such as that described in U.S. patent No. 5,414,796, discussed above. The use of variable rate speech encoders has been generalized in wireless communications as the use of such encoders increases the battery life of wireless communication devices and increases system capacity with minimal impact on perceived speech quality. The american telecommunications industry association has incorporated the most popular variable rate speech coders in the interim standards IS-96 and IS-733. These variable rate speech coders encode speech signals at 4 rates, referred to as full rate, half rate, 1/4 rate, and 1/8 rate, respectively, depending on the level of speech activity. This rate represents the number of bits used in encoding 1 frame of speech and varies from frame to frame. Full rate encodes frames with a predetermined maximum number of bits, half rate encodes frames with a predetermined maximum number of half bits, 1/4 rate encodes frames with a predetermined maximum number of 1/4 bits, and 1/8 rate encodes frames with a predetermined maximum number of 1/8 bits.

The variable rate data source 1 provides encoded voice frames to the CRC and tail bit generator 2. The generator 2 adds a set of cyclic redundancy check bits, which are parity bits, for checking the accuracy of the base station encoding. The generator 2 also adds predetermined tail bits groups to the control message to clear the decoder memory at the base station. The frames are then provided to an encoder 4 which provides forward error correction coding to the voice frames. The encoded symbols are provided to a repetition generator 8 which repeats the encoded symbols. The puncturing unit 9 punctures the repetition generator 8 with a certain symbol rate (throughput) according to a predetermined puncturing pattern so that a predetermined number of symbols are within the frame. The symbols are then provided to an interleaver 6, which reorders the symbols according to a predetermined interleaving format. The interleaved symbols are provided on line 46 to modulator 26.

In the exemplary embodiment, modulator 26 modulates the data channels in accordance with a code division multiple access modulation format and provides the modulated information to a transmitter (TMTR)28, which amplifies and filters the signal and provides the information through a duplexer 30 for transmission via an antenna 32.

In a typical embodiment, the variable rate data source 1 sends a signal to the control processor 36 indicative of the encoding frame rate. Control processor 36, in response to the rate indication, provides a control signal to transmitter 28 indicating the transmit energy.

In IS-95 and cdma 2000 systems, a 20ms frame IS divided into 16 groups of identical symbols, referred to as Power Control Groups (PCGs). The reference to controlling power is based on the fact that, for each PCG, the base station receiving the frame issues a power control command based on the sufficiency or non-sufficiency of the reverse link signal as determined at the base station.

Fig. 3A to 3C depict the relationship between time and transmission energy for 3 transmission rates (full rate, half rate and 1/4 rate) (in the PCG). 3D-3G depict 4 alternative embodiments for 1/8 rate frame transmission, in which half of the time is not transmitting energy. Because a large amount of redundancy is introduced in frames that are less than full rate, the energy of the transmitted symbols can be reduced to approximately proportional to the amount of additional redundancy in the frame.

In fig. 3A, each power control group PCG 0-PCG 15 is transmitted at energy E for a full-rate frame 300. For simplicity, the frames therein are described as being transmitted with the same energy for the duration of the frame. Those skilled in the art will appreciate that this energy will vary from frame to frame, and that the representation in fig. 3A-3G may be considered as the baseline energy for transmitting a frame when not affected by the outside world. In the exemplary embodiment, remote station 50 is responsive to closed loop power control commands and internally generated open loop power control commands from the base station based on the received forward link signal. The response to the power control algorithm will cause the transmit energy to vary with the duration of the frame.

In fig. 3B, the energy of the half-rate frame 302 is equal to half the predetermined maximum level, i.e., equal to E/2. As shown in fig. 3B. The interleaver is structured to distribute the repeated symbols across the frame in a manner that achieves maximum time diversity.

In fig. 3C, for the 1/4 rate transmission 304, the frame is transmitted at a level of 1/4 (i.e., E/4) which is approximately the predetermined maximum level.

In typical embodiments, the pilot signal is continuously transmitted during full rate, half rate and 1/4 rate frame transmissions. However, in fig. 3B-3G, transmitter 28 gates-the transmission of a field. In the preferred embodiment, the pilot channel is disconnected during times when the traffic channel is not being gated on for reduced battery consumption and increased reverse link capacity. In each embodiment, the frame is transmitted during a 50% duty cycle, wherein half of the time the transmit energy is off. During frame transmission, the energy is scaled to transmit 1/4 rate frames with energy of approximately E/4. However, the inventors have determined through extensive simulations that sending 1/8 rate frames should have a better average energy or better baseline energy for sending 1/8 rate frames for each of the other embodiments. These energies are calculated to maximize both battery savings and reverse link capacity while maintaining transmission reliability.

Fig. 3D depicts a first embodiment in which the transmission of frames is alternately turned off at 1.25ms intervals. Thus, the transmitter 28 is first turned off within the first 1.25 ms. Then, a second power control group (PCG1) is transmitted with energy E1 during the second 1.25 ms. The third power control group is turned off (PCG 2). In this embodiment, all odd PCGs (1, 3, 5, 7, 9, 11, 13, 15) are transmitted, while all even PCGs (0, 2, 4, 6,8, 10, 12, 14) are off. The puncturing structure discards half of the repeated symbols and makes about 4 patterns per transmitted symbol. In a first preferred embodiment, the symbols are transmitted at an average or baseline energy of 0.385E. In the preferred embodiment, the last portion of the frame is turned off for gated transmitter 28. This is preferable because it allows for the receiving base station to transmit meaningful closed loop power control commands, facilitating reliable transmission of subsequent frames.

In a second embodiment, depicted in fig. 3E, which is a preferred embodiment of the present invention, the frames are transmitted such that they are alternately turned off at 2.5ms intervals. The transmission method depicted in fig. 3E is representative of the preferred embodiment because it optimizes battery savings and reverse link capacity. During the first 2.5ms (PCG0 and PCG1), transmitter 28 is turned off. The transmitter 28 is then gated on during the next 2.5ms (PCG2 and PCG3), and so on. In this embodiment, the PCGs 2, 3, 6, 7, 10, 11, 14, 15 are gated on, while the PCGs 0, 1, 4, 5, 8, 9, 12, 13 are disconnected. In this embodiment, the puncturing structure is such that exactly half of the repeated symbols are discarded during the off period. In a second preferred embodiment, the symbols are transmitted at an average or baseline energy of 0.32E.

Fig. 3F depicts a third embodiment in which the frames are transmitted such that they are alternately turned off at 5.0ms intervals. During the first 5.0ms (PCG 0-PCG 3), transmitter 28 is turned off. Then, during the next 5.0ms, the PCGs 4, 5,6, 7 are transmitted, and so on. In this embodiment, the PCGs 4, 5,6, 7, 12, 13, 14, 15 are launched, while the PCGs 0, 1, 2, 3, 8, 9, 10, 11 are disconnected. In this embodiment, the puncturing structure is such that exactly half of the repeated symbols are discarded during puncturing. In a third preferred embodiment, the symbols are transmitted at an average or baseline energy of 0.32E.

Fig. 3G depicts a fourth embodiment in which the frame is transmitted such that it is turned off during the first 10ms and during the next 10ms PCGs 8 to 15 are transmitted. In this embodiment, the PCGs 8, 9, 10, 11, 12, 13, 14, 15 are launched while the PCGs 0, 1, 2, 3,4, 5,6, 7 are disconnected. In this embodiment, the interleaver structure is such that exactly half of the repeated symbols are discarded during the off period. In a second preferred embodiment, the symbols are transmitted at an average or baseline energy of 0.335E.

Fig. 2 depicts a functional block diagram of an exemplary embodiment of modulator 26 of fig. 1. The first supplemental data channel data is provided on line 38 to the spreading unit 52 which is covered in accordance with a predetermined spreading sequence. In the preferred embodiment, spreading unit 52 spreads the supplemental channel data with a short walsh sequence (+ + - -). The spread data is provided to relative gain unit 54 which adjusts the gain of the spread supplemental channel data relative to the energy of the pilot and power control symbols. The gain adjusted supplemental channel data is provided to a first summing input of summing element 56. The pilot and power control multiplexed symbols are provided on line 40 to a second summing input of summing unit 56.

The control channel data is provided on line 42 to spreading unit 58 to cover the supplemental channel data in accordance with a predetermined spreading sequence. In the preferred embodiment, spreading unit 58 spreads the supplemental channel data with a short walsh sequence (+++++++ - - - - - - -). The spread data is provided to relative gain unit 60 which adjusts the gain of the spread control channel data relative to the energy of the pilot and functional control symbols. The gain adjusted control data is provided to a third summing input of the summing element 56.

Summing unit 56 sums the gain adjusted control data symbols, the gain adjusted supplemental channel symbols, and the time division multiplexed pilot and power control symbols and provides the sum to a first input of multiplexer 72 and a first input of multiplexer 78.

The second supplemental channel is provided on line 44 to spreading unit 62 to cover the supplemental channel data in accordance with a predetermined spreading sequence. In the present exemplary embodiment, the spreading unit 62 spreads the supplemental channel data with a short walsh sequence (+ -). The spread data is provided to relative gain unit 64 to adjust the gain of the spread supplemental channel data. The gain adjusted supplemental channel data is provided to a first summing input of summer 66.

The base channel data is provided on line 46 to spreading unit 68 which overlays the base channel data in accordance with a predetermined spreading sequence. In the exemplary embodiment, spreading unit 68 spreads the base channel data with a short walsh sequence (+ ++++ - - - + +++ - - - - -). The spread data is provided to relative gain unit 70 which adjusts the gain of the spread base channel data. The gain adjusted base channel data is provided to a second summing input of summer 66.

The addition unit 66 sums the gain-adjusted second supplemental channel data symbol and the base channel data symbol and supplies the sum to a first input terminal of a multiplier 74 and a first input terminal of a multiplier 76.

In the exemplary embodiment, two different short PN sequences (PN) will be used_IAnd PN_Q) The pseudo-noise spreading of (2) is used to spread the data. In the present exemplary embodiment, the short PN sequence PN_IAnd PN_QMultiplied by the long PN code to provide additional security. The generation of pseudo-noise sequences is well known in the artSee, for example, U.S. Pat. No. 5,103,459, supra. The long PN sequence is provided to first inputs of multipliers 80 and 82. Short PN sequence PN_ISupplied to a second input of the multiplier 80, a short PN sequence PN_QThen to a second input of multiplier 82.

The PN sequence generated from multiplier 80 is provided to second inputs of multipliers 72 and 74, respectively. The PN sequence generated from multiplier 82 is provided to second inputs of multipliers 76 and 78, respectively. The product sequence from multiplier 72 is provided to the addition input of subtractor 84. The product sequence from multiplier 74 is provided to a first summing input of adder 86. The product sequence from multiplier 76 is provided to a minus input of subtractor 84. The product sequence from multiplier 78 is provided to a second summing input of adder 86.

The difference sequence from subtractor 84 is provided to baseband filter (BBF) 88. Baseband filter 88 performs the necessary filtering on the difference sequence and provides the filtered sequence to gain element 92. Gain unit 92 adjusts the gain of the signal and provides the gain adjusted signal to upconverter 96. An upconverter 96 upconverts the gain adjusted signal in accordance with a QPSK modulation format and provides the upconverted signal to a first input of an adder 100.

The summed sequence of summer 86 is provided to baseband filter 90. Baseband filter 90 performs the necessary filtering on the difference sequence and provides the filtered sequence to gain element 94. Gain unit 94 adjusts the gain of the signal and provides the gain adjusted signal to upconverter 98. An up-converter 98 up-converts the gain-adjusted signal in accordance with the QPSK modulation format and provides the up-converted signal to a second input of the adder 100. A summer 100 sums the two QPSK modulated signals and provides the result to transmitter 28.

Turning now to fig. 4, a functional block diagram of selected portions of a base station 400 of the present invention is shown. Receiver (RCVR)402 receives a reverse link Radio Frequency (RF) signal from wireless communication device 50 (fig. 1) and downconverts the received reverse link RF signal to baseband frequency. In the present exemplary embodiment, receiver 402 down-converts the received signal in accordance with a QPSK demodulation format. The baseband signal is then demodulated by a demodulator 404. Demodulator 404 is further described below with reference to fig. 5.

The demodulated signal is provided to accumulator 405. The accumulator 405 accumulates the symbol energy of the redundantly transmitted symbol PCG. The accumulated symbol energy is provided to a deinterleaver 406 that reorders the symbols according to a predetermined deinterleaving format. The reordered symbols are provided to a decoder 408, which decodes the symbols to provide an estimate of the transmitted frame. The estimate is then provided to a CRC check 410 to determine the accuracy of the frame estimate based on the CRC bits contained in the transmitted frame.

In the exemplary embodiment, base station 400 blindly decodes the reverse link signal. Blind decoding is a variable rate data decoding method in which the receiver does not know the transmission rate a priori. In the exemplary embodiment, base station 400 accumulates, deinterleaves, and decodes the data based on each possible rate hypothesis. The frame is selected as the best estimate based on quality metrics such as symbol error rate, CRC check, and Yamamoto metrics.

The frame estimates for each rate hypothesis are provided to control processor 414, along with a set of quality metrics for each decoded estimate. The quality metrics may include symbol error rate, codebook metrics, and CRC check. The control processor selectively provides a decoded frame to the remote station user or declares an erasure.

Turning now to fig. 5, an extended functional block diagram of a typical single demodulation chain of the demodulator 404 depicted in fig. 4 is shown. In the preferred embodiment, decoder 404 has one demodulation chain for each information channel. The exemplary decoder 404 of fig. 5 complex demodulates the signal modulated by the exemplary modulator of fig. 1. As described above, receiver (RCVR)402 downconverts the received reverse link RF signal to a baseband frequency, producing an I baseband signal and a Q baseband signal. Despreaders 502 and 504 despread the I and Q baseband signals, respectively, with the long code from fig. 1. Baseband Filters (BBF)506 and 508 filter the I and Q baseband signals, respectively.

Despreaders 510 and 512 using PN in FIG. 2_IThe sequences despread the I and Q signals, respectively. Similarly, despreaders 514 and 516 use PN from FIG. 2_QThe sequences despread the Q and I signals, respectively. The outputs of the despreaders 510 and 512 are combined in a combiner 518. The output of despreader 516 is subtracted from the output of despreader 512 in combiner 520.

The outputs of combiners 518 and 520 are then decovered in walsh decoverers 522 and 524 using the walsh codes used in covering the particular channel of interest in fig. 2. Accumulators 530 and 532 then accumulate the outputs of walsh decovers 522 and 524 for one walsh symbol, respectively.

Walsh chip add elements 526 and 528 also add the outputs of combiners 518 and 520 to one walsh chip. The respective outputs of walsh chip add elements 526 and 528 are then applied to pilot filters 534 and 536. Pilot filters 534 and 536 generate channel condition estimates by determining the estimated gain and phase of pilot signal data 40 (see fig. 1). The output of pilot filter 534 is then complex multiplied by the respective outputs of accumulators 530 and 532 in complex multipliers 538 and 540. Similarly, the outputs of the accumulators 530 and 532 are complex multiplied by the pilot filter output in complex multipliers 542 and 544. Then, in the combiner 540, the output of the complex multiplier 542 is added to the output of the complex multiplier 538. In combiner 548, the output of complex multiplier 544 is subtracted from the output of complex multiplier 540. Finally, the outputs of combiners 546 and 548 are combined in combiner 550 to produce the demodulated signal that is input to accumulator 405 shown in FIG. 4.

A second aspect of the present invention is directed to controlling forward link transmit energy in the current face of potentially gated reverse link transmissions. The performance of the forward link may be affected when the reverse link is in the gated mode of operation. The forward link power control bits are punctured into the reverse link pilot signal based on a base station transmit power increase or decrease. Thus, when the reverse link is disconnected 50% of the time, the actual forward link power control commands are sent at 400Hz instead of 800 Hz. However, the base station does not know in advance whether the mobile station is disconnected. Thus, in normal operation, the base station may increase power during periods when the mobile station is off. Simulations show that the performance degrades by approximately 1dB when the base station ignores the mobile station transmission mode, rather than when the base station already knows that the mobile station is in gated mode and reacts to forward link power control commands (400Hz) sent on the reverse link pilot. Therefore, there is a need for a method by which a base station can detect the transmission mode (gated/ungated) of a mobile station.

One way to achieve this is to specify a forward link power control bit erasure decision region. That is, when the magnitude of the dot product (the sum of all the combined fingers) is smaller than the threshold, it is determined as erasure and the forward power is kept unchanged. In this way, the base station will effectively react to 400Hz forward link control commands sent on the reverse link pilot in the gated mode.

As described above, in the preferred embodiment, forward power control symbols are multiplexed into the pilot symbol stream. The demodulated pilot and power control symbols are provided to a demultiplexer 412 which separates out the power control bit energy and provides it to a control processor 414 (shown in fig. 4).

Control processor 414 also receives the power control bit energy of other fingers of the reverse link signal provided by remote station 50. Based on the sum of the energies of the different demodulation fingers, control processor 414 generates commands that control the transmit energy of the forward link signal and provides these commands to transmitter (TMTR) 420. In the present invention, control processor 414 detects the power control bits by comparing the sum of the energy of the power control bits to a threshold when the reverse link frame is disconnected, and disables the closed loop power control response when the sum of the energy is less than the threshold.

The forward link traffic data transmitted to remote station 50 shown in fig. 1 is provided to forward traffic processing unit 416, which formats and encodes the data, and interleaves the resulting data frame. The processed data frames are provided to a modulator 418. A modulator 418 modulates the data for transmission on the forward link. In the exemplary embodiment, the forward link signal IS modulated according to a CDMA modulation format, and in particular, according to a CDMA 2000 or IS-2000 modulation format.

The modulated signal is provided to a transmitter 420, which upconverts, amplifies, and filters the signal for transmission. The energy at which the signal is transmitted is determined in accordance with a control signal that controls the processor 414.

Fig. 6 illustrates operations performed by the control processor 414. The decovered pilot and power control symbols from walsh chip add elements 526 and 528 shown in fig. 5 are provided to demultiplexers 600 and 602 to resolve the multiplexed power control symbol energy. In finger combiner 604, the energy of the functional control bit symbols from all demodulation fingers is summed. The resulting summed energy is provided to a threshold comparator 606, which compares the summed energy to a predetermined threshold and outputs a signal indicative of the comparison.

If the energy of the function control bit is less than the threshold value, then function control processor 608 determines that the forward link power control bit has been disengaged and refrains from adjusting the forward link transmit energy. If the energy of the power control bit is greater than the threshold, power control processor 608 determines that the forward link power control bit is not gated and adjusts the forward link transmit energy according to the estimate of the received power control bit.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled 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 (3)

1. A method for controlling the transmit energy of a forward link signal in a base station, comprising the steps of:

receiving a potentially gated reverse link signal including forward link power control bits;

determining whether the power control bit is gated;

adjusting forward link transmit energy in accordance with the forward link power control bit only if the decision as to whether the forward link power control bit is gated indicates that the power control bit is not gated.

2. The method of claim 1, wherein the step of determining whether the power control bit has been gated comprises:

measuring an energy of the received power control bits;

the energy of the function control bit is compared to a predetermined threshold.

3. A base station for controlling the transmit energy of forward link signals, comprising a control processor, said control processor comprising:

means for receiving a potentially gated reverse link signal including forward link power control bits;

means for determining whether said power control bit is gated;

means for adjusting forward link transmit energy in accordance with the forward link power control bit only if the determination of whether the forward link power control bit is gated indicates that the power control bit is not gated.