Multi-user MIMO-SDMA for finite rate feedback systems

• US 20080165875A1
• Filed: 01/05/2007
• Published: 07/10/2008
• Est. Priority Date: 01/05/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Mundarath, Jayakrishnan C., Kotecha, Jayesh H.
• Granted Patent: US 8,073,069 B2
• Time in Patent Office: Days
• US Class Current: 375/262
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0632 Channel quality parameters, e.g. channel quality indicator [CQI]
• CPC Class Codes: H04B 7/0634 Antenna weights or vector/matrix coefficients
• CPC Class Codes: H04B 7/0857 using maximum ratio combining techniques, e.g. signal-to- interference ratio [SIR], received signal strenght indication [RSS]
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: H04L 5/14 Two-way operation using the same type of signal, i.e. duplex
• CPC Class Codes: H04W 88/02 Terminal devices
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

A multi-user MIMO downlink beamforming system with limited feedback (200) is provided to enable preceding for multi-stream transmission, where a channel codeword (u_i) and one or more channel quality indicator values (CQI_A, CQI_B) are computed at the user equipment (201.i) on the basis of maximizing a predetermined SINR performance metric (ρ_i) which estimates the receive signal-to-noise-ratio (SINR) at the user equipment (201.i). The computed codeword (u_i) and CQI values (or differential values related thereto) are quantized and fed back to help the base station (210) which applies a correction to the appropriate CQI value in the course of designing the transmit beamforming vectors w and determining the appropriate modulation and coding level to be used for downlink data transmission.

Claims

1. A channel information feedback method for a multiple input, multiple output (MIMO) space division multiple access (SDMA) system, comprising:

estimating channel state information for a transmission channel from a transmitting device to a first receiving device by receiving one or more signals;

generating a receive beamforming vector v for the transmission channel and a codeword u which represents a product of the receive beamforming vector v and a channel matrix H for the transmission channel;

generating a first estimated channel quality indicator for the transmission channel based on the codeword u and receive beamforming vector v, where the first estimated channel quality indicator is computed for a minimum interference case where there is a minimum number of receiving devices sharing a time-frequency resource block with the first receiving device;

generating a second estimated channel quality indicator for the transmission channel based on the codeword u and receive beamforming vector v, where the second estimated channel quality indicator is computed for an additional interference case where there is more than the minimum number of receiving devices sharing a time-frequency resource block with the first receiving device; and

transmitting feedback information to the transmitting device that is representative of the codeword u and at least one of the first or second estimated channel quality indicators.

2. The method of claim 1, where the first estimated channel quality indicator is generated by calculating

3. The method of claim 1, where transmitting feedback information comprises transmitting feedback information to the transmitting device that is representative of the codeword u, and at least one of the first estimated channel quality indicator or the second estimated channel quality indicator.

4. The method of claim 1, where transmitting feedback information comprises:

generating a differential value between the first estimated channel quality indicator and the second estimated channel quality indicator; and

transmitting feedback information to the transmitting device that is representative of the codeword u, the first estimated channel quality indicator and the differential value.

5. The method of claim 1, further comprising:

generating a third estimated channel quality indicator for the transmission channel based on the codeword u and receive beamforming vector v, where the third estimated channel quality indicator is computed for a multi-interference case where there are two or more other receiving devices sharing a time-frequency resource block with the first receiving device, and

generating a weighted average differential value by computing an average of a first difference (between the second estimated channel quality indicator and the first estimated channel quality indicator), and a second difference (between the third estimated channel quality indicator and the first estimated channel quality indicator);

where transmitting feedback information comprises transmitting feedback information to the transmitting device that is representative of the codeword u, the first estimated channel quality indicator and the weighted average differential value.

6. The method of claim 1, where transmitting feedback information comprises:

selecting one of the first or second estimated channel quality indicators as a reference CQI;

generating a differential value between the reference CQI and whichever of the first or second estimated channel quality indicators was not selected; and

transmitting feedback information to the transmitting device that is representative of the codeword u, the reference CQI and the differential value so that the transmitting device can extract the first and second estimated channel quality indicators from the feedback information.

7. The method of claim 1, further comprising:

generating one or more additional estimated channel quality indicators for the transmission channel based on the codeword u and receive beamforming vector v, where each additional estimated channel quality indicator is computed for a different interference case;

selecting one of the first, second or additional estimated channel quality indicators as a reference CQI;

generating a weighted average differential value between the reference CQI and any of the first, second or additional estimated channel quality indicators that were not selected; and

transmitting feedback information to the transmitting device that is representative of the codeword u, the reference CQI and the weighted average differential value so that the transmitting device can extract the first, second or additional estimated channel quality indicators from the feedback information.

8. The method of claim 1, further comprising:

decoding the feedback information at the transmitting device to obtain the codeword u and to compute an actual channel quality indicator for the first receiving device as a function of how many receiving devices will share a time-frequency resource block with the first receiving device; and

using the codeword u at the transmitting device to design a transmit beamforming vector w for the first receiving device; and

updating the actual channel quality indicator for the first receiving device at the transmitting device based upon the transmit beamforming vector w and the codeword u.

9. The method of claim 8, where the transmitting device computes an adjusted channel quality indicator ρ

_eff=ρ

(v)|w^Hu|² after designing a transmit beamforming vector w for the first receiving device, where ρ

(v) is the actual estimated channel quality indicator and u is codeword for the first receiving device.

10. The method of claim 1, further comprising:

generating one or more additional estimated channel quality indicators for the transmission channel based on the codeword u and receive beamforming vector v, where each additional estimated channel quality indicator is computed for a different interference case;

selecting one of the estimated channel quality indicators as a reference CQI; and

generating, for each estimated channel quality indicator not selected to be the reference CQI, a differential value by computing a difference between each said estimated channel quality indicator and the reference CQI;

where transmitting feedback information comprises transmitting feedback information to the transmitting device that is representative of the codeword u, the reference CQI and each computed differential value.

11. The method of claim 1, further comprising:

generating one or more additional estimated channel quality indicators for the transmission channel based on the codeword u and receive beamforming vector v, where each additional estimated channel quality indicator is computed for a different interference case;

selecting one of the estimated channel quality indicators as a reference CQI; and

generating, for each estimated channel quality indicator not selected to be the reference CQI, a differential value by computing a difference between each said estimated channel quality indicator and the reference CQI; and

generating a weighted average differential value by computing a weighted average of the generated differential values;

where transmitting feedback information comprises transmitting feedback information to the transmitting device that is representative of the codeword u, the reference CQI and the weighted average differential value.

12. The method of claim 1, further comprising:

generating a third estimated channel quality indicator for the transmission channel based on the codeword u and receive beamforming vector v, where the third estimated channel quality indicator is computed for a third interference case where there are two other receiving devices sharing a time-frequency resource block with the first receiving device;

generating a fourth estimated channel quality indicator for the transmission channel based on the codeword u and receive beamforming vector v, where the fourth estimated channel quality indicator is computed for a fourth interference case where there are three or more other receiving devices sharing a time-frequency resource block with the first receiving device; and

generating a weighted average differential value by computing a weighted average of a first difference (between the second estimated channel quality indicator and the first estimated channel quality indicator), a second difference (between the third estimated channel quality indicator and the first estimated channel quality indicator), and a third difference (between the fourth estimated channel quality indicator and the first estimated channel quality indicator);

where transmitting feedback information comprises transmitting feedback information to the transmitting device that is representative of the codeword u, the first estimated channel quality indicator and the average differential value.

13. A wireless communication method using beamforming for a multiple input, multiple output (MIMO) space division multiple access (SDMA) system, the method comprising:

estimating a channel matrix H for a transmission channel from a transmitting device to a first receiving device by receiving one or more signals;

generating at the first receiving device a receive beamforming vector v for the transmission channel and a codeword u which represents a product of the receive beamforming vector v and the channel matrix H for the transmission channel by using a predetermined channel quality indicator (CQI) metric; and

transmitting feedback information to the transmitting device that is representative of the codeword u for use in designing a transmit beamforming vector w for the first receiving device.

14. The method of claim 13, where the receive beamforming vector v and codeword u are jointly designed by maximizing a predetermined CQI metric comprising a receive SINR performance metric that is defined as

15. The method of claim 13, where the receive beamforming vector v and codeword u are jointly designed at the first receiving device by maximizing a predetermined CQI metric.

16. The method of claim 13, where the codeword u is designed given a fixed receive beamforming vector v by maximizing a predetermined CQI metric.

17. The method of claim 13, where the receive beamforming vector v is designed given a fixed codeword u by maximizing a predetermined CQI metric.

18. The method of claim 13, where transmitting feedback information to the transmitting device comprises:

quantizing the codeword u into a feedback index value by selecting a codeword u from a pre-specified set of codewords in a codebook and retrieving a feedback index value corresponding to the selected codeword u; and

transmitting the feedback index value to the transmitting device for use in designing a transmit beamforming vector w for the first receiving device.

19. The method of claim 13, where the codeword u is generated by optimizing a predetermined CQI metric as a function of an assumed number of K interfering receiving devices.

20. The method of claim 13, further comprising generating at the first receiving device an adjusted receive beamforming vector v* by recomputing the predetermined CQI metric based on how many additional receiving devices are scheduled to share a time-frequency resource block with the first receiving device.

21. The method of claim 13, further comprising:

receiving at the first receiving device information representative of the transmit beamforming vector w for the first receiving device; and

generating at the first receiving device an adjusted receive beamforming vector v_adj by selecting a candidate receive beamforming vector v_adj that maximizes a predetermined receive SINR performance metric that is defined as

22. The method of claim 13, further comprising:

receiving at the first receiving device information representative of K* which identifies how many receiving devices are scheduled to share a time-frequency resource block with the first receiving device; and

generating at the first receiving device an adjusted receive beamforming vector v_adj by selecting a candidate receive beamforming vector v_adj that maximizes a predetermined receive SINR performance metric that is defined as

23. A communication device for feeding back channel information and designing a receive beamformer in a MIMO-SDMA communication system, comprising:

a vector design module for jointly designing a receive beamforming vector v and selecting a corresponding equivalent channel codeword u=Hv which are optimized using a predetermined performance metric for estimating an SINR value for a MIMO channel between a transmitter and the communication device; and

a CQI estimation module for computing a first estimated CQI and a second estimated CQI, where the first estimated CQI is computed for a minimum interference case, and where the second estimated CQI is computed for an additional interference case where there is additional interference from one or more other communication devices.