Method and apparatus for allocating downlink resources in a multiple-input multiple-output (MIMO) communication system

• US 20030087673A1
• Filed: 05/16/2001
• Published: 05/08/2003
• Est. Priority Date: 05/16/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Howard, Steven J., Wallace, Mark, Walton, Jay R.
• Granted Patent: US 6,662,024 B2
• Time in Patent Office: Days
• US Class Current: 455/562.1
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04B 7/061 using feedback from receiving side
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0026 Transmission of channel quality indication
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04W 16/00 Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
• CPC Class Codes: H04W 16/28 using beam steering
• CPC Class Codes: H04W 84/14 WLL [Wireless Local Loop]; RLL [Radio Local Loop]

Abstract

Techniques to schedule downlink data transmission to a number of terminals in a wireless communication system. In one method, one or more sets of terminals are formed for possible data transmission, with each set including a unique combination of one more terminals and corresponding to a hypothesis to be evaluated. One or more sub-hypotheses may further be formed for each hypothesis, with each sub-hypothesis corresponding to specific assignments of a number of transmit antennas to the one or more terminals in the hypothesis. The performance of each sub-hypothesis is then evaluated, and one of the evaluated sub-hypotheses is selected based on their performance. The terminal(s) in the selected sub-hypothesis are then scheduled for data transmission, and data is thereafter coded, modulated, and transmitted to each scheduled terminal from one or more transmit antennas assigned to the terminal.

Claims

1. A method for scheduling downlink data transmission to a plurality of terminals in a wireless communication system, comprising:

forming one or more sets of terminals for possible data transmission, wherein each set includes a combination of one or more terminals and corresponds to a hypothesis to be evaluated;

assigning a plurality of transmit antennas to the one or more terminals in each set;

evaluating performance of each hypothesis based in part on antenna assignments for the hypothesis;

selecting one of the one or more evaluated hypotheses based on the performance; and

scheduling data transmission to the one or more terminals in the selected hypothesis.

2. The method of claim 1, further comprising:

forming a plurality of sub-hypotheses for each hypothesis, wherein each sub-hypothesis corresponds to specific assignments of the transmit antennas to the one or more terminals in the hypothesis, and

wherein the performance of each sub-hypothesis is evaluated and one of the evaluated sub-hypotheses is selected based on the performance.

3. The method of claim 1, wherein the assigning includes identifying a transmit antenna and terminal pair with a best performance among all unassigned transmit antennas,

assigning the transmit antenna in the pair to the terminal in the pair, and

removing the assigned transmit antenna and terminal from consideration.

4. The method of claim 1, wherein each hypothesis is evaluated based in part on channel state information (CSI) for each terminal in the hypothesis, wherein the CSI is indicative of channel characteristics between the transmit antennas and the terminal.

5. The method of claim 4, wherein the CSI for each terminal comprise signal-to-noise-plus-interference ratio (SNR) estimates derived at the terminal based on signals transmitted from the transmit antennas.

6. The method of claim 5, wherein each set of one or more terminals to be evaluated is associated with a respective matrix of SNRs achieved by the one or more terminals in the set.

7. The method of claim 4, further comprising:

determining a coding and modulation scheme for each transmit antenna based on the CSI associated with the transmit antenna.

8. The method of claim 1, wherein the one or more terminals in each set are selected from among a pool of terminals.

9. The method of claim 8, wherein the pool of terminals includes one or more SIMO terminals each designated to receive a single data stream.

10. The method of claim 9, wherein the selected hypothesis includes a plurality of SIMO terminals.

11. The method of claim 8, wherein the pool of terminals includes one or more MIMO terminals each designated to receive multiple data streams from multiple transmit antennas.

12. The method of claim 11, wherein the selected hypothesis includes a single MIMO terminal.

13. The method of claim 11, wherein each scheduled MIMO terminal performs successive cancellation receiver processing to recover data transmitted to the MIMO terminal.

14. The method of claim 5, wherein one or more sets of antenna beams are evaluated by each terminal to be considered for scheduling to provide one or more vectors of SNRs, one vector for each set of antenna beams.

15. The method of claim 1, wherein each set includes terminals having similar link margins.

16. The method of claim 1, wherein the evaluating includes

computing a performance metric for each hypothesis.

17. The method of claim 16, wherein the performance metric is a function of throughput achievable by each terminal in the hypothesis.

18. The method of claim 16, wherein the hypothesis having the best performance metric is selected for scheduling.

19. The method of claim 1, further comprising:

prioritizing terminals to be considered for scheduling.

20. The method of claim 19, wherein the plurality of transmit antennas are assigned to the one or more terminals in each set based on the priority of the terminals in the set.

21. The method of claim 20, wherein a highest priority terminal in the set is assigned a transmit antenna associated with a highest throughput, and a lowest priority terminal in the set is assigned a transmit antenna associated with a lowest throughput.

22. The method of claim 19, further comprising:

limiting terminals to be considered for scheduling to a group of N highest priority terminals, where N is one or greater.

23. The method of claim 19, further comprising:

maintaining one or more metrics for each terminal to be considered for scheduling, and

wherein the priority of each terminal is determined based in part on the one or more metrics maintained for the terminal.

24. The method of claim 23, wherein one metric maintained for each terminal relates to an average throughput rate achieved by the terminal.

25. The method of claim 19, wherein the priority of each terminal is further determined based on one or more factors maintained for the terminal and associated with quality of service (QoS).

26. The method of claim 1, wherein the one or more terminals in the selected hypothesis are scheduled for data transmission over a channel that includes plurality of spatial subchannels.

27. The method of claim 1, wherein the one or more terminals in the selected hypothesis are scheduled for data transmission over a channel that includes plurality of frequency subchannels.

28. A method for scheduling data transmission to a plurality of terminals in a wireless communication system, comprising:

forming one or more sets of terminals for possible data transmission, wherein each set includes a unique combination of one or more terminals and corresponds to a hypothesis to be evaluated;

forming one or more sub-hypotheses for each hypothesis, wherein each sub-hypothesis corresponds to specific assignments of a plurality of transmit antennas to the one or more terminals in the hypothesis;

evaluating performance of each sub-hypothesis;

selecting one of a plurality of evaluated sub-hypotheses based on their performance;

scheduling data transmission to the one or more terminals in the selected sub-hypothesis; and

transmitting data to each scheduled terminal in the selected sub-hypothesis from one or more transmit antennas assigned to the terminal.

29. The method of claim 28, wherein the evaluating includes

determining a throughput for the one or more terminals in the sub-hypothesis based on the specific antenna assignments, and

wherein the sub-hypothesis with highest throughput is selected.

30. The method of claim 28, wherein one set of terminals is formed, and wherein the terminals in the set is selected based on priority of terminals desiring data transmission.

31. A multiple-input multiple-output (MIMO) communication system, comprising:

a base station comprising

a plurality of transmit antennas,

a scheduler configured to receive channel state information (CSI) indicative of channel estimates for a plurality of terminals in the communication system, select a set of one or more terminals for data transmission on a downlink, and assign the plurality of transmit antennas to the one or more selected terminals,

a transmit data processor configured receive and process data for the one or more selected terminals based on the CSI to provide a plurality of data streams, and

a plurality of modulators configured to process the plurality of data streams to provide a plurality of modulated signals suitable for transmission from the plurality of transmit antennas; and

one or more terminals, each terminal comprising

a plurality of receive antennas, each receive antenna configured to receive the plurality of modulated signals transmitted from the base station,

a plurality of front-end units, each front-end unit configured to process a signal from an associated received antenna to provide a respective received signal,

a receive processor configured to process a plurality of received signals from the plurality of front-end units to provide one or more decoded data streams, and to further derive CSI for the plurality of modulated signals, and

a transmit data processor configured to process the CSI for transmission back to the base station.

32. A base station in a multiple-input multiple-output (MIMO) communication system, comprising:

a transmit data processor configured to receive and process data to provide a plurality of data streams for transmission to one or more terminals scheduled for data transmission, wherein the data is processed based on channel state information (CSI) indicative of channel estimates for the one or more scheduled terminals;

a plurality of modulators configured to process the plurality of data streams to provide a plurality of modulated signals;

a plurality of transmit antennas configured to receive and transmit the plurality of modulated signals to the one or more scheduled terminals; and

a scheduler configured to receive CSI for a plurality of terminals in the communication system, select a set of one or more terminals for data transmission, and assign the plurality of transmit antennas to the one or more selected terminals.

33. The base station of claim 32, wherein the data stream for each transmit antenna is processed based on a coding and modulation scheme selected for the transmit antenna based on the CSI associated with the transmit antenna.

34. The base station of claim 32, further comprising:

a plurality of demodulators configured to process a plurality of signals received via the plurality of transmit antennas to provide a plurality of received signals, and

a receive data processor configured to further process the plurality of received signals to derive CSI for the plurality of terminals in the communication system.

35. A terminal in a multiple-input multiple-output (MIMO) communication system, comprising:

a plurality of receive antennas, each receive antenna configured to receive a plurality of modulated signals transmitted from a base station;

a plurality of front-end units, each front-end unit configured to process a signal from an associated received antenna to provide a respective received signal;

a receive processor configured to process a plurality of received signals from the plurality of front-end units to provide one or more decoded data streams, and to further derive channel state information (CSI) for each decoded data stream; and

a transmit data processor configured to process the CSI for transmission back to the base station, and

wherein the terminal is one of one or more terminals included in a set scheduled to receive data transmission from the base station in a particular time interval, and wherein the set of one or more terminals scheduled to receive data transmission is selected from among one or more sets of terminals based on performance evaluated for each set.

36. The terminal of claim 35, wherein the terminal is scheduled to receive data transmission from one or more transmit antennas at the base station assigned to the terminal.