Feedback scheduling to reduce feedback rates in MIMO systems

• US 20090034636A1
• Filed: 08/03/2007
• Published: 02/05/2009
• Est. Priority Date: 08/03/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Kotecha, Jayesh H., Huang, Kaibin
• Granted Patent: US 8,675,743 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04B 7/0478 Special codebook structures directed to feedback optimisation
• CPC Class Codes: H04B 7/0643 Feedback on request
• CPC Class Codes: H04L 2025/03808 Transmission of equaliser coefficients
• CPC Class Codes: H04L 43/0864 Round trip delays
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0075 Allocation using proportional fairness
• CPC Class Codes: H04L 5/0078 Timing of allocation
• CPC Class Codes: H04L 5/0094 Indication of how sub-channels of the path are allocated
• CPC Class Codes: H04W 72/0446 Resources in time domain, e.g. slots or frames

Abstract

In a closed-loop wireless communication system, a codebook-based feedback control mechanism is provided where feedback from each of a plurality of receivers is scheduled to control the feedback so that the receiving devices do not needlessly feed back precoding information to the transmitting device. The feedback may be controlled by establishing and distributing a schedule to control when each receiver feeds back preceding information, or by establishing and distributing a metric-based feedback threshold that must be satisfied before feedback is permitted.

Claims

1. A method for controlling feedback of preceding information in a MIMO communication system comprising a transmitting device and a plurality of receiving devices, wherein the transmitting device communicates with each receiving device over a respective transmission channel, the method comprising:

generating feedback control information at the transmitting device for each receiving device to control feedback of preceding information from the plurality of receiving devices so that the plurality of receiving devices do not needlessly feed back preceding information to the transmitting device;

transmitting feedback control information to the plurality of receiving devices; and

receiving precoding information at the transmitting device from one or more of the plurality of receiving devices, where each receiving device evaluates the feedback control information to determine a feedback constraint.

2. The method of claim 1, where the feedback control information comprises a schedule specifying a time slot for each receiving device to feed back precoding information to the transmitting device.

3. The method of claim 2, where generating feedback control information comprises:

estimating a round-trip delay for each of the plurality of receiving devices, and

using the round-trip delay for each receiving device to compute a feedback instant and duration for each receiving device, where the feedback instant and duration specify a time slot during which each receiving device is to feed back preceding information to the transmitting device.

4. The method of claim 2, where transmitting feedback control information comprises sending a synchronization signal to each receiving device over a downlink control channel, where the synchronization signal specifies the time slot for the said receiving device.

5. The method of claim 1, where the preceding information fed back from each receiving device comprises information representing a profile specifying a preceding parameter, a power allocation parameter or an adaptive modulation and coding parameter.

6. The method of claim 1, where the feedback control information comprises a feedback threshold specifying a metric value at each receiving device that must be met before preceding information can be fed back to the transmitting device.

7. The method of claim 6, where generating feedback control information comprises:

estimating a metric distribution for the plurality of receiving devices, and computing the feedback threshold from the metric distribution, where the feedback threshold specifies a metric value that will be met by at least one receiving device to a predetermined probability so that any receiving device having a metric value that meets or exceeds the feedback threshold can feed back preceding information to the transmitting device.

8. The method of claim 6, where the metric value comprises a scheduling fairness index, a channel capacity, a channel Frobenius norm, a channel quality indicator, a CINR value or an SINR value.

9. The method of claim 1, where receiving preceding information comprises receiving either preceding information or channel quality indicator information at the transmitting device, where each receiving device feeds back preceding information and channel quality indicator information together in accordance with the feedback control information for said receiving device.

10. The method of claim 1, where each receiving device evaluates the feedback control information to determine if preceding information is fed back by said receiving device.

11. The method of claim 1, where each receiving device evaluates the feedback control information to determine how much feedback to send. and to determine how much feedback to send

12. A method for controlling feedback of preceding information in a MIMO communication system comprising a base station and a plurality of user equipment devices, wherein the base station communicates with each user equipment device over a respective transmission channel, the method comprising:

receiving feedback control information at a first user equipment device from a base station, where the feedback control information is generated at the base station to control feedback of precoding information from the plurality of user equipment devices so that the user equipment devices do not needlessly feed back preceding information to the base station; and

feeding back preceding information from the first user equipment device to the base station by evaluating the feedback control information at said first user equipment device to determine if preceding information is to be fed back and to determine how much feedback to send.

13. The method of claim 12, where the feedback control information comprises a schedule specifying a time slot for the first user equipment device to feed back precoding information to the base station.

14. The method of claim 13, where the feedback control information comprises a feedback instant and duration for the first user equipment device, where the feedback instant and duration specify a time slot during which the first user equipment device is to feed back precoding information to the base station.

15. The method of claim 13, where receiving feedback control information comprises receiving a synchronization signal at the first user equipment device over a downlink control channel, where the synchronization signal specifies the time slot for the first user equipment device.

16. The method of claim 12, where the preceding information fed back from the first user equipment device comprises information representing a profile specifying a precoding parameter, a power allocation parameter or an adaptive modulation and coding parameter.

17. The method of claim 12, where the feedback control information comprises a feedback threshold specifying a metric value that must be met before the first user equipment device can feed back precoding information to the base station.

18. The method of claim 17, where the feedback control information comprises a feedback threshold that is computed from a metric distribution for the plurality of user equipment devices, where the feedback threshold specifies a metric value that will be met by at least one user equipment device to a predetermined probability so that the first user equipment device can feed back precoding information to the base station if the first user equipment device has a metric value that meets or exceeds the feedback threshold.

19. The method of claim 18, where the metric value comprises a scheduling fairness index, a channel capacity, a channel Frobenius norm, a channel quality indicator, a CINR value or an SINR value.

20. The method of claim 12, where feeding back preceding information comprises feeding back preceding information and channel quality indicator information to the base station from the first user equipment device, where the first user equipment device feeds back precoding information and channel quality indicator information together in accordance with the feedback control information for the first user equipment device.

21. The method of claim 12, where feedback control information act as a trigger at the first user equipment device to control and coordinate the feedback from the first user equipment device.

22. The method of claim 12, where evaluating the feedback control information comprises tracking a scheduling history for the first user equipment device to determine if the first user equipment device has been frequently scheduled so that preceding information need not be fed back in a subsequent scheduling cycle.

23. The method of claim 12, where evaluating the feedback control information comprises tracking a scheduling history for the first user equipment device to determine if the first user equipment device has not been frequently scheduled so that precoding information should be fed back in a subsequent scheduling cycle.

24. A base station for use in a wireless LTE communication system, comprising:

scheduling logic operable to define one or more scheduling criteria for scheduling feedback of preceding information at each of a plurality of user devices so that each user device evaluates the one or more scheduling criteria to determine if precoding information is to be fed back by said user device and to determine how much feedback to send; and

transmission logic operable to transmit the one or more scheduling criteria to the plurality of user devices using a downlink channel.

25. The base station of claim 24, where the scheduling logic is operable to sequentially allocate a transmission time slot to each of the plurality of user devices to thereby define a predetermined schedule for feedback of precoding information by each user device.

26. The base station of claim 24, where the scheduling logic is operable to estimate a metric distribution for the plurality of user devices and to determine a feedback threshold from the metric distribution so that at least one user device has a predetermined probability of meeting the feedback threshold.

27. The base station of claim 24, where the scheduling logic is operable to estimate a metric distribution for the plurality of user devices and to determine a plurality of feedback thresholds from the metric distribution, where each threshold is assigned to one or more user devices.