System and Method for Spatial Multiplexing for Coordinated Multi-Point Transmission

• US 20110286341A1
• Filed: 05/20/2010
• Published: 11/24/2011
• Est. Priority Date: 05/20/2010
• Status: Active Grant

• Current Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Inventors: Al-Shalash, Mazin, Sanayei, Shahab
• Granted Patent: US 8,681,644 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• CPC Class Codes: H04B 7/024 Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
• CPC Class Codes: H04B 7/0634 Antenna weights or vector/matrix coefficients
• CPC Class Codes: H04B 7/0697 using spatial multiplexing
• CPC Class Codes: H04L 43/0876 Network utilisation, e.g. volume of load or congestion level

Abstract

A system and method for spatial multiplexing for coordinated multi-point transmission are provided. A method for communications device operations includes receiving transmissions from at least two access points, measuring channels between the communications device and each of the at least two access points based on the received transmissions, computing beamforming weights based on the measured channels, and transmitting the beamforming weights to the at least two access points. The computing is based on attempting to maximize a capacity of a communications system containing the communications device and the at least two access points with the beamforming weights, and the beamforming weights are used at the at least two access points to beamform transmissions to the communications device using coordinated multi-point transmission.

Claims

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

receiving transmissions from at least two access points;

measuring channels between the communications device and each of the at least two access points based on the received transmissions;

computing beamforming weights based on the measured channels, wherein the computing is based on attempting to maximize a capacity of a communications system containing the communications device and the at least two access points with the beamforming weights; and

transmitting the beamforming weights to the at least two access points, wherein the beamforming weights are used at the at least two access points to beamform transmissions to the communications device using coordinated multi-point transmission.

2. The method of claim 1, wherein the transmissions comprise pilot signals, or reference sequences.

3. The method of claim 1, wherein the transmissions comprise information transmissions, and wherein measuring a channel comprises measuring the information transmissions for an extended amount of time.

4. The method of claim 1, wherein the at least two access points comprises first and second access points, each having two transmit antennas, wherein the communications device includes two antennas, and wherein computing beamforming weights comprises determining w₁ and w₂ such that a capacity expressible as

5. The method of claim 4, wherein computing beamforming weights comprises maximizing a cost function J in terms of w₁^H and w₂^H, the cost function J is expressible as

6. The method of claim 5, wherein maximizing a cost function J comprises utilizing a numeric method to calculate the beamforming weights.

7. The method of claim 6, wherein utilizing a numeric method comprises calculating

8. The method of claim 7, wherein the numeric method comprises a gradient method.

9. The method of claim 7, wherein utilizing a numeric method comprises:

selecting initial values for computed beamforming weights, w₁(n) and w₂(n), where n=0;

calculating an initial value for the cost function J, J(n);

calculating updated values for the computed beamforming weights, w₁(n+1) and w₂(n+1);

calculating an updated value for the cost function J, J(n+1);

repeating the calculating updated values, the calculating an updated value, and incrementing n until the updated value of the cost function, J(n+1), converges; and

selecting the computed beamforming weights, w₁(n) and w₂(n), as the beamforming weights.

10. The method of claim 9, wherein the initial values of the computed beamforming weights are non-zero vectors.

11. The method of claim 9, wherein the updated value of the cost function converges when an absolute value of J(n)−

J(n+1) is less than a threshold.

12. The method of claim 1, further comprising quantizing the beamforming weights prior to the transmitting the beamforming weights.

13. The method of claim 12, wherein quantizing the beamforming weights comprises quantizing each of the beamforming weights using codebook quantization.

14. The method of claim 12, wherein the beamforming weights are individually quantized.

15. The method of claim 1, further comprising receiving at least two transmissions from the at least two access points, wherein each of the at least two transmissions is beamformed using one of the beamforming weights.

16. A method for operations at an access point, the method comprising:

transmitting a pilot signal;

receiving beamforming weights from a communications device served by the access point, wherein the access point and at least one additional access point is transmitting to the communications device using coordinated multi-point transmission, wherein the beamforming weights are used to beamform transmissions to the communications device, and wherein the beamforming weights are computed at the communications device based on attempting to maximize a capacity of a communications system containing the communications device, the access point, and the at least one additional access point;

beamforming a transmission with the beamforming weights; and

transmitting the beamformed transmission to the communications device.

17. The method of claim 16, wherein the receiving beamforming weights comprises receiving a quantized version of the beamforming weights.

18. The method of claim 17, wherein the quantized version of the beamforming weights comprises indices to codewords in a codebook used to quantize the beamforming weights.

19. The method of claim 16, wherein the receiving beamforming weights comprises:

receiving the beamforming weights; and

selecting a beamforming weight from the beamforming weights.

20. A communications device comprising:

a receiver to be coupled to a receive antenna in order to receive signals detected by the receive antenna;

a transmitter to be coupled to a transmit antenna in order to transmit signals with the transmit antenna; and

a controller coupled to the receiver and to the transmitter, the controller configured to measure a channel between the communications device and an access point of a plurality of access points transmitting to the communications device, and to compute beamforming weights for use by the plurality of access points transmitting to the communications device in coordinated multi-point transmissions, wherein the controller computes the beamforming weights based on attempting to maximize a capacity of a communications system containing the communications device and the access points.

21. The communications device of claim 20, wherein the controller comprises a

a measure channel unit configured to measure a channel between the communications device and each access point in the plurality of access points based on transmissions made by the access point;

and

a beamforming weights compute unit coupled to the measure channel unit, the beamforming weights compute unit configured to iteratively compute values of the beamforming weights based on the channel measurements, to compute a value of a cost function based on the channel measurements and the beamforming weights, and to determine a convergence of the value of the cost function.

22. The communications device of claim 20, wherein the controller further comprises a quantization unit coupled the beamforming weights compute unit and to the terminating condition unit, the quantization unit configured to quantize the beamforming weights.

23. The communications device of claim 22, wherein the quantization unit is further configured to individually quantize each of the beamforming weights using codebook quantization.