KR20020087939A - Radio communication system - Google Patents

Abstract

The wireless communication system includes a sub-station 110 having a plurality of communication channels 226a, 226b, 226c with a plurality of main-stations 100a, 100b, 100c. Separate closed loop power control is performed for each of the communication channels 226a, 226b, 226c. Accordingly, an optimal main-station for the transmission of data to the sub-station 110 may be selected. Parameters derived from the operation of each power control loop may set channel parameters optimally for each main-station 100a, 100b, 100c. This configuration is particularly well suited for high speed downlink data services where robust link and system throughput is improved by quickly selecting optimal master-station and / or channel parameters.

Description

Wireless communication system

In the field of mobile communications, there is a growing demand for systems with the ability to download large amounts of data blocks to a mobile station (MS) at an appropriate rate on demand. Such data may be web pages from the Internet, which may include, for example, video clips or the like. Since a particular MS will only require this data intermittently, fixed bandwidth dedicated links are not suitable. In order to meet this requirement in UMTS, a High-Speed Downlink Packet Access (HSDPA) scheme is being developed that enables the transmission of packet data to mobile stations up to 4 Mpbs.

In known wireless communication systems, the MS generally communicates with a single base station (BS) at any one time. During a call, the MS wants to investigate, for example, when the communication link quality deteriorates as the MS moves away from its BS, or when the relative traffic loading of other cells requires coordination to move to another BS. You may. The process of moving from one BS to another is known as handover.

In a system operating in accordance with current UMTS specifications, the MS maintains a list of BSs known as an "active set" that allows radio links to be maintained at an appropriate quality. When the MS is in a dedicated channel mode and there are multiple BSs in the active set, the MS is in "soft handover" with the BSs in the active set. In this mode, uplink transmissions are received by all BSs in the active set, and all BSs in the active set transmit the same downlink information to the MS (usually the data and most of the control information will be the same, but the power control command May be different). The drawback of this "soft handover" method is that when only one set of power control commands are transmitted on the uplink, the power control commands transmitted from the BSs to the downlink may not match the requirements for the uplink transmit power. That is, it is impossible to optimize the uplink and downlink transmission powers for each radio link.

A typical soft handover procedure is particularly suitable for real time services such as voice links where a continuous connection should be maintained. However, for packet data links, it may be advantageous to select the optimal BS for transmission of each data packet to the MS, taking into account dynamically changing radio link and traffic conditions. Improved throughput of the system can be achieved if the optimal BS is selected just before transmitting each packet by minimizing the number of packets received in the error state and minimizing the total transmit power per packet.

In addition to selecting the optimal BS, or instead of selecting the optimal BS, it is necessary to set other characteristics of the link for data packet transmission. These characteristics in a UMTS system may include a suitable Modulation and Coding Scheme (MCS) and a suitable transmit power level. It is also desirable to minimize the signaling required to provide such facilities.

FIELD OF THE INVENTION The present invention relates to wireless communication systems and primary and secondary stations for use in such systems, and methods of operating such systems. In this specification, in particular with respect to the Universal Mobile Telecommunication System (UMTS), these techniques are equally applicable to use in other mobile wireless systems.

1 is a schematic block diagram of a wireless communication system.

2 is a schematic block diagram of a wireless communication system with an MS in a soft handover process.

3 is a known UMTS uplink slot structure diagram;

4 is a schematic diagram of a UMTS uplink slot in accordance with the present invention;

5 is a flow chart illustrating a method for transmitting data in accordance with the present invention.

Summary of the Invention

It is therefore an object of the present invention to enable improved data throughput in such a system.

According to a first aspect of the invention, physical control channels arranged for bidirectional transmission of control information sets between a sub-station and a plurality of main-stations, and one or more main-stations selected from a plurality of main-stations A wireless communication system having at least one data channel for transmission of data from said or each selected main-station to a sub-station between a and a sub-station, wherein some or all of the physical to which a set of control information is mapped. A wireless communication system is provided, in which each closed loop power control means is provided for individually adjusting the power of control channels, or portions thereof.

Many advantages are provided by being able to quickly select the best BS at any time. In particular, the delay before transmission of each packet is reduced, and accurate power control is surely performed at the start of each packet even if the transmitting BS is changed.

In addition, separate information obtained by operating a plurality of parallel power control loops helps with MCS selection. Rapid selection of the optimal BS and / or improved selection of the MCS improves overall system throughput while requiring minimal additional signaling.

According to a second aspect of the present invention, physical control channels arranged for bidirectional transmission of control information sets between a sub-station and a plurality of main-stations, and one or more main-stations selected from the plurality of main-stations A main-station for use in a wireless communication system having at least one data channel for transmission of data from said or each selected main-station to a sub-station between and a sub-station, said set of control information A main-station is provided, in which closed loop power control means for regulating the power of some or all physical control channels, or parts thereof, between the main-station and the sub-station are provided.

According to a third aspect of the invention, physical control channels arranged for bidirectional transmission of control information sets between a sub-station and a plurality of main-stations, and one or more main-stations selected from the plurality of main-stations A sub-station for use in a wireless communication system having at least one data channel for transmission of data from said or each selected main-station to a sub-station between a sub-station and a sub-station. A sub-station is provided, in which closed loop power control means for individually adjusting the power of some or all of the physical control channels, or parts thereof, are mapped.

According to a fourth aspect of the present invention, physical control channels arranged for bidirectional transmission of control information sets between a sub-station and a plurality of main-stations, and one or more main-stations selected from the plurality of main-stations A method of operating a wireless communication system having at least one data channel for transmission of data from said or each selected main-station to a sub-station between and a sub-station, said method comprising: a set of control information A method of operating a wireless communication system is provided, comprising operating each closed loop power control means for individually adjusting the power of some or all of the physical control channels, or portions thereof, to which is mapped.

The present invention facilitates the high speed selection of suitable sites and / or the selection of MCS for data transmission by operating a plurality of parallel closed power control loops and enables improved operation of the data transmission system. Based on perceptions that are not in technology

Embodiments of the present invention are described below by way of example with reference to the accompanying drawings.

In the drawings like reference numerals have been used to indicate corresponding features.

Modes for Carrying Out the Invention

Referring to FIG. 1, a wireless communication system includes a main station (BS) and a plurality of sub-stations (MS) 110. BS 100 is a microcontroller (μC) 102, transceiver means (Tx / Rx) 104 connected to antenna means 106, and power control means (PC) 107 for changing the transmitted power level. And connection means 108 for connecting to the PSTN or other suitable network. Each MS 110 is a microcontroller (μC) 122, a transceiver means (Tx / Rx) 114 connected to an antenna means 116, and a power control means (PC) for changing the transmitted power level. 118; Communication from BS 100 to MS 110 occurs on the downlink channel, and communication from MS 110 to BS 100 occurs on uplink channel 124.

In many wireless communication systems, power control typically operates in the form of a closed loop. For uplink power control in the UMTS system, the BS 100 determines the changes required for transmit power from the MS 110 and transmits these changes to the MS 110 by Transmit Power Control (TPC) instructions. To signal. To minimize overheads, the TPC command typically instructs the MS 110 to increase or decrease its power, which is changed in steps of a predetermined magnitude. However, in some systems the TPC command may determine the step size to use. Similarly, for downlink power control, MS 110 determines the necessary changes and signals them to BS 100 using TCP commands.

In the system according to the invention, closed loop power control is used to select the most suitable parameters such as MSC since the power level requested by the MS 110 for the downlink physical channel indicates the current prevailing radio link state. It may be. Therefore, there is no need to send a separate uplink message by MS 110 to BS 100 to indicate radio link conditions.

The MS 110 involved in the soft handover process is shown in FIG. MS 110 has three respective BSs 100a, 100b, 100c and three bidirectional communication channels 226a, 226b, 226c, each of which includes an uplink and a downlink channel. In a given time slot, the MS 110 receives TPC commands from each of the BSs 100a, 100b, 100c on the downlink channels and transmits TPC commands to each of the BSs on the uplink channels. In a conventional UMTS system, each MS 110 only transmits one set of uplink TPC commands to all BSs 100a, 100b, 100c in the active set. Therefore, even in the form of a power control loop, the powers of the downlink channels are not individually controlled.

In the system according to the present invention, parallel closed power control loops are installed between the MS 110 and the plurality of BSs 100a, 100b, 100c to enable a fast BS selection process. Such power control loops may be maintained between the MS 110 and some or all of the BSs 100a, 100b, 100c of the active set. These power control loops are used to control the power of at least some or all of the downlink transmissions to the MS 110, and these power control loops may also be used to control the power of the respective uplink transmissions. Perhaps these BSs are chosen to be BSs in an active set with the best quality radio links. In order to determine which BSs 100a, 100b, 100c will send packets to the MS 110, closed power control loops with these BSs allow a very fast selection to be made between them.

As an example, the BS to use for packet transmission may be selected to be the BS with the lowest transmit power for the power controlled physical control channel. The selection may be made by the MS 110 (by sending a BS selection message to the network) or by the network. Closed loop power control ensures that the transmit power on the downlink channel is already at a level suitable for the radio link conditions and can be used to help predict the most suitable MCS and / or other parameters.

Operation of the plurality of parallel closed power control loops requires the transmission of each of a plurality of sets of control information on the uplink and the downlink. At a minimum, if these parallel closed control loops are only used to control the power of the downlink transmissions, each uplink control information set will include one or more TPC commands derived from the corresponding downlink control information set, and downlink information Each set includes one or more sets of pilot information from which the TPC commands in the corresponding uplink control information set are derived by techniques such as signal to interference ratio (SIR) estimation. Could be. Also, if these parallel closed power control loops are used to control the power of uplink transmissions, each uplink control information set will also include one or more pilot information sets from which TPC commands in the corresponding downlink control information set can be derived. Each downlink control information set also includes one or more TPC commands derived from the corresponding uplink control information set.

First consider the uplink. The MS 110 must transmit a plurality of sets of uplink control information including TPC instructions. In the embodiments described below this is accomplished by mapping each set of control information to a separate uplink physical control channel, time multiplexing all sets of control information into one physical control channel, or by some combination of these two techniques. . For example, other techniques may be used that code a combination of TPC commands or use a high order modulation scheme.

The first technique includes transmitting separate uplink physical control channels to each of the BSs 100a, 100b, 100c selected to participate in the fast site selection process. In a UMTS implementation, these separate uplink physical control channels will all use the same scrambling code (to identify MS 110). The uplink physical control channel for each BS 100a, 100b, 100c may be distinguished by one or the following methods.

Code multiplexing where each physical control channel uses a different orthoginal channelisation code. In the current UMTS specifications, only one uplink physical control channel is allowed from each MS 110, which channel has a spreading factor of 256 from an Orthogonal Variable Spreading Factor (OVSF) code tree. Always use channelization codes. Additional physical control channels may use any of 63 of other channelization codes from the same set while being orthogonal to all possible channelization codes used for uplink data channels.

I / Q multiplexing. In the current UMTS specifications, uplink control information is coded for a physical channel using the carrier's Q (quadragcher-phase) component, up to three data channels, and I (in-phase) up to three data channels. )) Component (before complex scrambling). If only two sets of uplink control information were needed and no uplink data was being transmitted at the same time, the control information sets could be I / Q multiplexed (before complex scrambling) using the same channelization code, thus controlling The need for multicode transmission of channels is avoided. It would also be possible to transmit two sets of control information, one for each of the I and Q components, while transmitting a reduced amount of data using multicode transmission.

Advantageously, the timing of uplink transmissions may be arranged so that there is no need to reliably make a multicode transmission. For example, one of the uplink physical control channels may be arranged to temporarily switch off each time some uplink data is transmitted.

Control channel gating, ie intermittent transmission of a physical control channel, may be used in conjunction with the above methods as a means of reducing MS power consumption and uplink interference levels.

A second technique is to time multiplex the control information sets for different BSs using a modified type of uplink physical control channel. In this case only one uplink physical control channel using only one channelization codes will be needed. 3 illustrates the structure of a frame 300 of a UMTS uplink physical control channel. Frame 300 has a length of 10 ms and includes 15 slots S ₀ to S ₁₄ . Each slot has a length of 2560 chips and contains 10 bits of control data. Looking at the i th slot (S _i ), the pilot (P) field 304, the Transprot Format Combination Indication (TFCI) field 306, and the Feedback Information (FBI) field ( 308 and a TPC field 310, each field having a predetermined number of bits.

Time multiplexing of TPC commands and pilot fields may be achieved by one or both of the following methods.

Modify the fields of the uplink physical control channel so that multiple sets of TPC commands and pilot information can be transmitted at a typical 1500 Hz slot rate. The TFCI may be transmitted once, with the greatest power needed to communicate with all relevant BSs 100a, 100b, 100c. This may include reducing the amount of pilot information sent to each BS. 4 illustrates a frame 300 with a field structure modified according to the present invention for use with two BSs. Two pilot fields P ₁ 404 and P ₂ 405 are provided along with two power control fields TPC ₁ 409 and TPC ₂ 410. TFCI field 306 in the field structure of FIG. Does not change, while the TBI field 308 is dropped (since there is no need for accurate transmitter diversity information if only control information is being transmitted). The field structure is adapted to accommodate the needs of the present invention. It will be apparent that there are other ways to modify.

. Reduce the power control rate to each cell. For example, having a power control rate in a scenario where two BSs are involved in a fast selection process eliminates the need to make any modifications to the frame field structure. Each BS only responds to different TPC commands and similarly uses only all other pilot fields for SIR estimation. The TPC rate may be further reduced by “gating off” the physical control channel (eg in slowly changing radio links with low Doppler frequency).

The downlink will now be discussed. Each BS 100a, 100b, 100c involved in the fast selection process must send pilot information to the MS 10 to maintain a closed power control loop for the downlink. If the uplinks are controlled by closed loop power control, the BSs must also send TPC commands to the MS 110. This is similar to a conventional soft handover process except that each BS 100a, 100b, 100c calculates its downlink TPC commands based on the SIR of each portion of each uplink physical control channel. Possible methods for the downlink include using other scrambling codes or time multiplexing the transmissions.

Other scrambling codes may be used to distinguish the control information sets from the BSs 100a, 100b, 100c. This allows the MS 110 to process TPC commands from BSs separately, generating other uplink TPC commands needed for other BSs according to their respective downlink SIRs. This also allows the MS 110 to distinguish TPC commands from other BSs.

For example, instead of combining TPC commands received from other BSs as in a conventional soft handover process as disclosed in our pending U.S. Patent Application Publication No. 0022633.2 (Applicant reference number PHGB000121), MS 110 ) Is the value of each uplink physical channel (or each portion of the uplink physical control channel in the case of time multiplexing uplink control information sets) according to TPC commands received from the associated BSs 100a, 100b, 100c). Adjust the power

Alternatively, downlink control information sets from other BSs 100a, 100b, 100c may be time multiplexed in a manner similar to the uplink described above. In this case, to avoid synchronization problems between BSs, it may be desirable to combine multiplexing and gating, in which case the downlink pilot information rate and / or TPC command rate may likewise be reduced.

In embodiments of the system according to the present invention, certain restrictions may apply to uplink transmission powers from the MS 110 to other BSs 100a, 100b, 100c. For example, the transmission power ratio between transmissions to other BSs may be limited to, for example, 6 dB, whereby the BS in the other cell has a dynamic range sufficient to maintain the proper uplink error rate for TPC commands. dynamic range, while requiring greater power, the occurrence of interference in one cell is avoided. This constraint improves EMC operation by avoiding sudden regular changes in power, and simplifies implementation of MS 110 because there is no need to accurately power large changes.

Alternatively, if the MS 110 reaches its maximum transmit power (according to the MS's power rating or by the network), the primary purpose is for the BS 100a, 100b, 100c while maintaining the best downlink SIR. Maintain accurate uplink transmit power. To achieve this, the uplink transmit power to other BSs may be reduced. Thus, if the power ratio between transmissions to each BS is greater than some predetermined limit, e.g. the 6 dB limit given above, transmissions to one or more BSs other than the BS with the best downlink SIR are terminated, or alternatively With this, it is possible to reduce the transmission power of transmissions to all BSs.

In practical implementations, the number of parallel closed power control loops is probably limited to two or three in order to avoid implementation complexity that obviates the benefits of fast selection techniques.

5 is a flowchart illustrating a method according to the present invention for transmitting data over one of a plurality of BSs 100a, 100b, 100c. The method begins at step 502 when there is data to send to the MS 100. Step 504 is a test to determine whether there is any data left to transmit. If there is data remaining, then at step 506, BS 100a, 100b, 100c having the best overall characteristics is selected from the BSs available to MS 110 for fast selection, and at step 508, the data packet is sent to MS 110; Is sent). The process of testing for data, selecting a BS and sending a data packet continues until there is no more data to send, and the process ends at step 510 when the test for more data fails.

In practice, the amount of data transmitted before BS selection is performed can be more than one packet, depending on the system overheads of changing the transmitting BS.

In another embodiment, the operation of a plurality of power control loops may be used to facilitate the selection of the most suitable MCS for packet transmission from BS 100 to MS 110 when the control channels are in soft handover. . This may be done independently of the method used to determine which BS 100a, 100b, 100c will send downlink packets. It is already known that the MCS selection can be based on an estimate of the appropriate SIR to be obtained at the MS 110. It is also understood that the value for this estimated SIR may be transmitted from the MS to the BS in the form of a measurement report (or derived from other measurements, such as the signal strength of the pilot channel).

However, if these measurement reports are sent using higher layersignalling, there may be a significant gap between them. This can cause significant errors in MSC selection in time varying channels. In addition, some changes in the transmitted power may correlate with changes in downlink path loss, i.e., changes in SIR that may be obtained at MS 110, thus preventing the operation of closed loop power control for downlink transmission. It can be seen that it can be used to correct previous SIR estimates. However, in soft handover, changes in the downlink transmission power from each BS 100a, 100b, 100c will not be much correlated with changes in the respective downlink path losses. Therefore, in soft handover, the power level of the downlink channel from each BS in the active set (or subset of the active set) can be changed by using a plurality of power control loops for the downlink control channels. Independently track. This means that given appropriate measurement reports, the SIR that can be obtained at the MS 110 can be estimated for any BS in the active set (or subset of the active set). Then an MCS suitable for packet transmission can be selected.

In the above embodiments, the data channel is transmitted to MS 110 at one BS at a time. However, in some situations it may be advantageous for data channels to be transmitted simultaneously from more than one BS. For example, in a situation where three BSs 100a, 100b, 100c are under closed loop power control, if two of the BSs provide an equally good link, a data packet or packets may be transmitted simultaneously from these two base stations. (Similar to transmissions during soft handover).

In a variation of the above embodiments, there may be one or more data links between the main-station and the sub-station. For example, the present invention can be applied to wireless links transmitted at different frequencies or from different antennas, which would require separate power control even if these links are between the same pair of stations.

In a system in which the BS 100 has a plurality of antennas 106, or antenna beams, the above references for the selection of the preferred BS 100 for packet transmission are among those provided by one or more main stations. It is taken to include the selection of the preferred subset of antennas or antenna beams. In a system employing Multi-Input Multi-Output (MIMO) techniques, the selection of the preferred BS 100 is also an optimal radio path or one between the main-station 100 and the sub-station 110. It is understood to include the selection of a set of paths in a set.

By reading this disclosure, other modifications will be apparent to those skilled in the art. Such modifications may include other features that are already known in the design, manufacture, and use of wireless communication systems and components thereof, and that may be used in place of or in addition to the features already described herein. It will be appreciated that certain features of the invention, which are, for clarity, described in the context of individual embodiments, may be provided in combination with a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may be provided individually or in any suitable partial combination. While the claims are set forth herein as specific combinations of features, the scope of the disclosure herein is expressly or implicitly, or by any generalization thereof, any novel feature or combination of features disclosed herein is claimed in the present claims. Regardless of whether the problem is related to the same invention as described above, or any problem or all of the same technical problems as the present invention are solved, these are included. The applicant intends to inform that new features may be made with these features and / or combinations of features during the ensuing application herein and any other application therefrom.

Singular expressions before components in the specification and claims do not exclude the presence of a plurality of such components. Also, the word "comprising" does not exclude the presence of elements or steps other than the listed elements.

Claims (20)

Physical control channels arranged for bidirectional transmission of control information sets between a secondary station and a plurality of primary stations, and one or more main-stations selected from the plurality of primary stations 17. A wireless communication system having at least one data channel for transmission of data from the or each selected main-station to the sub-station between and a sub-station, wherein a set of control information is mapped or Each closed loop power control means is provided for individually adjusting the power of all physical control channels, or portions thereof. The method of claim 1, wherein each downlink physical control channel to which a set of control information is mapped to each scrambling code, or a portion thereof, so that the associated master station can be identified. Means provided, wireless communication system. 2. The apparatus of claim 1, wherein means are provided for transmitting power control commands pertaining to each downlink physical control channel to which a set of control information is mapped, or a portion thereof, over a single time multiplexed uplink physical channel. Wireless communication system. 4. A wireless device as claimed in any preceding claim, characterized in that means are provided for selecting the main-station connected to the or each data channel in response to requests from the sub-stations. Communication system. 5. The main-station and the sub-station according to any one of claims 1 to 4, in order to determine which main-stations comprise selected main-stations and which of the communication links is selected. And means for establishing a plurality of communication links between the wireless communication system. Physical control channels arranged for bidirectional transmission of control information sets between a sub-station and a plurality of main-stations, and between the sub-station and one or more main-stations selected from the plurality of main-stations. Or a main-station for use in a wireless communication system having at least one data channel for transmission of data from each selected main-station to the sub-station, wherein the set of control information is mapped. A closed-loop power control means for regulating the power of some or all of the physical control channels, or portions thereof, between the station and the sub-station. 7. The main-station according to claim 6, wherein a means is provided for becoming or leaving the selected main-station by acquiring or releasing a data channel in response to changing radio link conditions. 8. A main-station as claimed in claim 6 or 7, wherein means are provided for determining operating parameters of the data channel according to the physical control channel to which a set of control information is mapped, or a power level of a portion thereof. . 9. The master station of claim 8, wherein the operating parameters are modulation and / or coding methods. Physical control channels arranged for bidirectional transmission of control information sets between a sub-station and a plurality of main-stations, and between the sub-station and one or more main-stations selected from the plurality of main-stations. Or a sub-station for use in a wireless communication system having at least one data channel for transmission of data from each selected main-station to the sub-station, in which a set of control information is mapped, some or Sub-station, provided with closed loop power control means for individually adjusting the power of all physical control channels, or portions thereof. 11. The sub-station according to claim 10, characterized in that means are provided for determining which of said main-stations comprises said selected main-station or stations in response to changing radio link conditions. 12. The sub-station according to claim 10 or 11, characterized in that means are provided for transmitting each set of uplink control information on separate physical channels. 13. The sub-station according to claim 12, wherein means are provided for distinguishing said physical channels using different channelisation codes. 14. The method of claim 12 or 13, wherein the physical is transmitted by transmitting a first physical channel using in-phase components of the carrier and a second physical channel using quadrature-phase components of the carrier. A sub-station, characterized in that means are provided for distinguishing two of the channels. 15. The sub-station according to claim 14, wherein means are provided for stopping the uplink physical control channel when uplink data transmission is required. 12. The sub-station according to claim 10 or 11, characterized in that means are provided for transmitting each set of uplink control information in a time-multiplexed manner over a single physical channel. 17. The sub-station according to claim 16, wherein means are provided for achieving time multiplexing by reducing the transmission speed of power control commands. 18. The sub-station according to claim 17, wherein the speed reduction is proportional to the number greater than or equal to the number of main-stations in which control information sets are exchanged. 17. The sub-station according to claim 16, wherein means are provided for achieving time multiplexing by including separate power control associated with each main-station in which control information sets are exchanged in a single physical control channel. Physical control channels arranged for bidirectional transmission of control information sets between a sub-station and a plurality of main-stations, and between the sub-station and one or more main-stations selected from the plurality of main-stations. Or a method of operating a wireless communication system having at least one data channel for transmission of data from each selected main-station to the sub-station, wherein the method comprises some or all of which a set of control information is mapped. Operating each closed loop power control means for individually adjusting the power of the physical control channels, or portions thereof.