System and Method for Coordinated Spatial Multiplexing Using Second Order Statistical Information

• US 20110115675A1
• Filed: 11/18/2009
• Published: 05/19/2011
• Est. Priority Date: 11/18/2009
• Status: Active Grant

• Current Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Inventors: Sanayei, Shahab
• Granted Patent: US 8,260,209 B2
• Time in Patent Office: Days
• US Class Current: 342/373
• CPC Class Codes: H01Q 1/246 specially adapted for base stations
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/0634 Antenna weights or vector/matrix coefficients

Abstract

A system and method for coordinated spatial multiplexing using second order statistical information is provided. A method for controller operations includes receiving second order statistics from a plurality of communications devices, computing a beamforming vector for each communications device in the plurality of communications devices, selecting a subset of communications devices from the plurality of communications devices to receive transmissions, and transmitting transmissions to the subset of selected communications devices. The beamforming vector for a communications device is based on the second order statistics provided by the communications device, and the transmitting uses the computed beamforming vector for each selected communications device to transmit the transmissions to the selected communications device.

Claims

1. A method for controller operations, the method comprising:

receiving second order statistics from a plurality of communications devices;

computing a beamforming vector for each communications device in the plurality of communications devices, wherein the beamforming vector for a communications device is based on the second order statistics provided by the communications device;

selecting a subset of communications devices from the plurality of communications devices to receive transmissions; and

transmitting transmissions to the selected subset of communications devices, wherein the transmitting uses the computed beamforming vector for each selected communications device to transmit the transmissions to the selected communications device.

2. The method of claim 1, wherein receiving second order statistics comprises receiving a spatial covariance matrix.

3. The method of claim 1, wherein computing a beamforming vector comprises maximizing a sum-rate capacity for each communications device in the plurality of communications devices.

4. The method of claim 3, wherein the plurality of communications devices comprises two communications devices, and the sum-rate capacity for the two communications devices is expressible as:

C=log₂(1+SNR₁)+log₂(1+SNR₂),

where SNR_i is a signal-to-noise ratio for an i-th communications device.

5. The method of claim 4, wherein the two communications devices are operating in a high SNR environment, and wherein maximizing the sum-rate capacity comprises maximizing a cost function expressible as:

6. The method of claim 5, wherein w₁ is an eigen vector corresponding to a maximum eigen value of matrix R₂⁻

1R₁, expressible as

R₂<sup>−

1</sup>R₁·

w₁=λ

_max·

w₁,

and wherein w₂ is an eigen vector corresponding to a minimum eigen value of matrix R₂<sup>−

1</sup>R₁, expressible as

R₂<sup>−

1</sup>R₁·

w₂=λ

_max·

w₂,

where λ

_max is the maximum eigen value, λ

_min is the minimum eigen value, and R_i<sup>−

1</sup> is an inverse of R_i.

7. The method of claim 4, wherein two controllers communicate with the two communications devices using multi-terminal coordinated spatial multiplexing, wherein w_ij are beamforming weights used by a j-th controller to transmit to an i-th communications device, and wherein w_i1 is given by eigen vectors of R₁₂⁻

1R₁₁ corresponding to maximum and minimum eigen values and w_i2 is given by eigen vectors of R₂₁<sup>−

1</sup>R₂₂ corresponding to maximum and minimum eigen values, where R_ij is the second order statistics for a i-th communications device from an j-th controller, and R_ij<sup>−

1</sup> is the inverse of R_ij.

8. A method for communications device operations, the method comprising:

estimating a communications channel between the communications device and a controller;

estimating second order statistics for the communications channel based on the estimated communications channel;

transmitting the second order statistics to the controller, wherein the second order statistics are used by the controller to compute a beamforming vector to be used in communications to the communications device; and

receiving a transmission that uses the computed beamforming vector.

9. The method of claim 8, further comprising, prior to transmitting the second order statistics, smoothing the second order statistics.

10. The method of claim 9, wherein smoothing the second order statistics comprises filtering the second order statistics.

11. The method of claim 10, wherein filtering the second order statistics comprises applying an exponential averaging filter.

12. The method of claim 9, further comprising, prior to transmitting the second order statistics, quantizing the second order statistics.

13. The method of claim 8, wherein estimating a communications channel comprises sampling the communications channel at different times and frequencies, thereby producing time-frequency samples.

14. The method of claim 13, wherein sampling the communications channel comprises sampling a pilot sequence or a reference sequence transmitted by the controller over the communications channel.

15. The method of claim 14, wherein sampling the communications channel comprises sampling transmissions made over the communications channel for a period of time.

16. The method of claim 8, wherein the second order statistics comprise a spatial covariance matrix.

17. The method of claim 16, wherein estimating the second order statistics comprises evaluating

18. The method of claim 8, wherein the communications device is communicating with two controllers using multi-terminal coordinated spatial multiplexing, and wherein estimating the second order statistics comprises, evaluating

R₁₁=E[h₁₁h₂₁^H] and R₂₁=E[h₂₁h₂₁^H],

where R_ij is the second order statistics for a i-th communications device from an j-th controller, h_ij is a communications channel between the j-th controller and the i-th communications device, h_ij^H is the Hermitian of h_ij, and E[.] is an expected value function.

19. A controller comprising:

a scheduler configured to select one or more communications devices for transmission in a transmission opportunity;

a beamforming unit coupled to the scheduler, the beamforming unit configured to map information for the selected communications devices onto a beamforming vector for transmission;

a beamforming vector compute unit configured to construct a beamforming vector from channel feedback information provided by the selected communications devices, wherein the beamforming vector compute unit computes the beamforming vector from second order statistics provided by the selected communications devices, and wherein the second order statistics are conveyed in the channel feedback information;

a single user unit coupled to the scheduler, to the beamforming unit, and to the beamforming vector compute unit, the single user unit configured to provide single user beamforming vectors to the beamforming unit, wherein the single user beamforming vectors are generated by the single user unit based on the selected communications devices and the second order statistics; and

a multi-user unit coupled to the scheduler and to the beamforming unit, the multi-user unit configured to provide multi-user beamforming vectors to the beamforming unit, wherein the multi-user beamforming vectors are generated by the multi-user unit based on the selected communications devices and the second order statistics.

20. The controller of claim 19, further comprising a modulation and coding unit coupled between the scheduler and the beamforming unit, the modulation and coding unit configured to convert the information from the selected communications devices into transmission symbols.

21. The controller of claim 19, further comprising a switching unit coupled to the scheduler, to the beamforming vector compute unit, to the single user unit, and to the multi-user unit, the switching unit configured to selectively couple an output of the beamforming vector compute unit to either the single user unit or the multi-user unit.