BEAMFORMING SPATIAL DE-MULTIPLEXING FOR COLLABORATIVE SPATIALLY MULTIPLEXED WIRELESS COMMUNICATION

• US 20100157861A1
• Filed: 12/18/2008
• Published: 06/24/2010
• Est. Priority Date: 12/18/2008
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Na, Yanxin, Jin, Hang
• Granted Patent: US 8,625,542 B2
• Time in Patent Office: Days
• US Class Current: 370/310
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems

Abstract

Techniques are provided herein to enable collaborative spatial multiplexing in a wireless communication system. At M plurality of antennas of a first wireless communication device, N plurality of spatially multiplexed transmissions are received from corresponding ones of N plurality of second wireless communication devices. The first wireless communication device produces M receive signals from the transmissions received at the M plurality of antennas. The first wireless communication device applies beamforming weight vectors to the M receive signals and in so doing produces N signals or signal streams, where N is less than or equal to M. The first wireless communication device then recovers the modulated data for each of the transmissions from the N signals.

Claims

1. A method comprising:

at M plurality of antennas of a first wireless communication device, receiving N plurality of spatially multiplexed transmissions from corresponding ones of N plurality of second wireless communication devices, and producing M receive signals from the transmissions received at the M plurality of antennas;

applying beamforming weight vectors to the M receive signals and producing N signals, where N is less than or equal to M; and

recovering modulated data for each of the transmissions from the N signals.

2. The method of claim 1, and further comprising computing the beamforming weight vectors based on information derived from the M receive signals.

3. The method of claim 2, and further comprising computing a spatial signature for each of the N plurality of second wireless communication devices, and wherein computing the beamforming weight vectors comprises computing N beamforming weight vectors from the spatial signatures.

4. The method of claim 3, wherein computing the spatial signature for each of the N plurality of second wireless communication devices is based on received pilot signals at predetermined subcarriers of each transmission.

5. The method of claim 4, wherein computing the spatial signature for each of the N plurality of second wireless communication devices comprises computing an average spatial signature from the received pilot signals at the predetermined subcarriers for each of the transmissions.

6. The method of claim 4, and further comprising computing a covariance matrix for each of the N plurality of second wireless communication devices from received pilot signals at the predetermined subcarriers for each of the transmissions, and computing the spatial signature for each of the N plurality of second wireless communication devices from the corresponding covariance matrix.

7. The method of claim 3, wherein computing the N beamforming weight vectors comprises computing beamforming weight vectors W₁ to W_N as:

$\begin{array}{c}{W}_1=<br><br>{\left[\begin{array}{cccc}{w}_{1,1}& w_{2,1}& \mathrm{\Lambda <br><br>}& w_{M,1}\end{array}\right]}^T\\ =<br><br>{\hat{V}}_1-\underset{i=2}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\alpha <br><br>}}_{1<br><br>i}<br><br>{\hat{V}}_i^H<br><br>{\hat{V}}_1<br><br>{\hat{V}}_i/\left({\hat{V}}_i^H<br><br>{\hat{V}}_i\right),\end{array}$ $\begin{array}{c}{W}_2=<br><br>{\left[\begin{array}{cccc}{w}_{1,2}& w_{2,2}& \mathrm{\Lambda <br><br>}& w_{M,2}\end{array}\right]}^T\\ =<br><br>{\hat{V}}_2-\underset{i=1,i\ne <br><br>2}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\alpha <br><br>}}_{2<br><br>i}<br><br>{\hat{V}}_i^H<br><br>{\hat{V}}_2<br><br>{\hat{V}}_i/\left({\hat{V}}_i^H<br><br>{\hat{V}}_i\right),\end{array}$ $\begin{array}{c}{W}_n=<br><br>{\left[\begin{array}{cccc}{w}_{1,n}& w_{2,n}& \mathrm{\Lambda <br><br>}& w_{M,n}\end{array}\right]}^T\\ =<br><br>{\hat{V}}_n-\underset{i=1,i\ne <br><br>n}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\alpha <br><br>}}_{\mathrm{ni}}<br><br>{\hat{V}}_i^H<br><br>{\hat{V}}_n<br><br>{\hat{V}}_i/\left({\hat{V}}_i^H<br><br>{\hat{V}}_i\right),\end{array}$ $\begin{array}{c}{W}_N=<br><br>{\left[\begin{array}{cccc}{w}_{1,N}& w_{2,N}& \mathrm{\Lambda <br><br>}& w_{M,N}\end{array}\right]}^T\\ =<br><br>{\hat{V}}_N-\underset{i=1,i\ne <br><br>N}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\alpha <br><br>}}_{\mathrm{Ni}}<br><br>{\hat{V}}_i^H<br><br>{\hat{V}}_N<br><br>{\hat{V}}_i/\left({\hat{V}}_i^H<br><br>{\hat{V}}_i\right)\end{array}$

where 0≦

α

_ni≦

1 is a nulling factor for 1≦

i≦

N, 1≦

n≦

N and V_i is the spatial signature for the i-th second wireless communication device.

8. The method of claim 1, and further comprising computing estimated channel information from received pilot signals in each of the transmissions received at the M plurality of antennas, and wherein recovering comprises computing estimates of modulated data for each transmission from the N signals using the estimated channel information.

9. The method of claim 8, wherein computing the estimated channel information comprises computing elements of a channel matrix representing a channel between the M plurality of antennas of the first wireless communication device and an antenna of each of the respective N plurality of second wireless communication devices.

10. An apparatus comprising:

M plurality of antennas;

a receiver configured to connect to the M plurality of antennas and to produce M plurality of receive signals associated with N plurality of spatially multiplexed transmissions received at the M plurality of antennas from corresponding ones of N plurality of source wireless communication devices;

a processor configured to connect to the receiver, wherein the processor is configured to;

apply beamforming weight vectors to the M receive signals to produce N signals,

where N is less than or equal to M; and

recover modulated data for each transmission from the N signals.

11. The apparatus of claim 10, wherein the processor is configured to compute the beamforming weight vectors based on information derived from the M receive signals.

12. The apparatus of claim 11, wherein the processor is configured to compute a spatial signature for each of the N plurality of source wireless communication devices, and to compute N beamforming weight vectors from the spatial signatures.

13. The apparatus of claim 12, wherein the processor is configured to compute the spatial signature for each of the N plurality of source wireless communication devices from received pilot signals contained at predetermined subcarriers of each transmission.

14. The apparatus of claim 12, wherein the processor is configured to compute a covariance matrix for each of the N plurality of source wireless communication devices from received pilot signals at predetermined subcarriers for each of the transmissions, and to compute the spatial signature for each of the N plurality of source wireless communication devices from the corresponding covariance matrix.

15. The apparatus of claim 12, wherein the processor is configured to compute the N beamforming weight vectors W₁ to W_N by computing:

$\begin{array}{c}{W}_1=<br><br>{\left[\begin{array}{cccc}{w}_{1,1}& w_{2,1}& \mathrm{\Lambda <br><br>}& w_{M,1}\end{array}\right]}^T\\ =<br><br>{\hat{V}}_1-\underset{i=2}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\alpha <br><br>}}_{1<br><br>i}<br><br>{\hat{V}}_i^H<br><br>{\hat{V}}_1<br><br>{\hat{V}}_i/\left({\hat{V}}_i^H<br><br>{\hat{V}}_i\right),\end{array}$ $\begin{array}{c}{W}_2=<br><br>{\left[\begin{array}{cccc}{w}_{1,2}& w_{2,2}& \mathrm{\Lambda <br><br>}& w_{M,2}\end{array}\right]}^T\\ =<br><br>{\hat{V}}_2-\underset{i=1,i\ne <br><br>2}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\alpha <br><br>}}_{2<br><br>i}<br><br>{\hat{V}}_i^H<br><br>{\hat{V}}_2<br><br>{\hat{V}}_i/\left({\hat{V}}_i^H<br><br>{\hat{V}}_i\right),\end{array}$ $\begin{array}{c}{W}_n=<br><br>{\left[\begin{array}{cccc}{w}_{1,n}& w_{2,n}& \mathrm{\Lambda <br><br>}& w_{M,n}\end{array}\right]}^T\\ =<br><br>{\hat{V}}_n-\underset{i=1,i\ne <br><br>n}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\alpha <br><br>}}_{\mathrm{ni}}<br><br>{\hat{V}}_i^H<br><br>{\hat{V}}_n<br><br>{\hat{V}}_i/\left({\hat{V}}_i^H<br><br>{\hat{V}}_i\right),\end{array}$ $\begin{array}{c}{W}_N=<br><br>{\left[\begin{array}{cccc}{w}_{1,N}& w_{2,N}& \mathrm{\Lambda <br><br>}& w_{M,N}\end{array}\right]}^T\\ =<br><br>{\hat{V}}_N-\underset{i=1,i\ne <br><br>N}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\alpha <br><br>}}_{\mathrm{Ni}}<br><br>{\hat{V}}_i^H<br><br>{\hat{V}}_N<br><br>{\hat{V}}_i/\left({\hat{V}}_i^H<br><br>{\hat{V}}_i\right)\end{array}$

where 0≦

α

_ni≦

1 is a nulling factor for 1≦

i≦

N, 1≦

n≦

N and V_i is the spatial signature for the i-th source wireless communication device.

16. The apparatus of claim 10, wherein the processor is configured to compute estimated channel information from received pilot signals in each of the transmissions received at the M plurality of antennas, and to recover the modulated data by computing estimates of the modulated data for each transmission contained in the N signals using the estimated channel information.

17. The apparatus of claim 16, wherein the processor is configured to compute the estimated channel information by computing elements of a channel matrix that represents a channel between the M plurality of antennas and an antenna of each of the respective N plurality of source wireless communication devices.

18. Logic encoded in one or more tangible media for execution and when executed operable to:

apply beamforming weight vectors to M plurality of receive signals to produce N signals, wherein the M plurality of receive signals are derived from reception at M plurality of antennas of a first communication device of N plurality of spatially multiplexed transmissions from corresponding ones of N plurality of second wireless communication devices; and

recover modulated data for each transmission from the N signals.

19. The logic of claim 18, and further comprising logic that is configured to compute the beamforming weight vectors based on information derived from the M plurality of receive signals.

20. The logic of claim 19, and further comprising logic that is configured to compute a spatial signature for each of the N plurality of second wireless communication devices, and wherein the logic that computes the beamforming weight vectors comprises logic that computes N beamforming weight vectors from the spatial signatures.

21. The logic of claim 20, wherein the logic that computes the N beamforming weight vectors comprises logic that computes beamforming weight vectors W₁ to W_N by computing:

$\begin{array}{c}{W}_1=<br><br>{\left[\begin{array}{cccc}{w}_{1,1}& w_{2,1}& \mathrm{\Lambda <br><br>}& w_{M,1}\end{array}\right]}^T\\ =<br><br>{\hat{V}}_1-\underset{i=2}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\alpha <br><br>}}_{1<br><br>i}<br><br>{\hat{V}}_i^H<br><br>{\hat{V}}_1<br><br>{\hat{V}}_i/\left({\hat{V}}_i^H<br><br>{\hat{V}}_i\right),\end{array}$ $\begin{array}{c}{W}_2=<br><br>{\left[\begin{array}{cccc}{w}_{1,2}& w_{2,2}& \mathrm{\Lambda <br><br>}& w_{M,2}\end{array}\right]}^T\\ =<br><br>{\hat{V}}_2-\underset{i=1,i\ne <br><br>2}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\alpha <br><br>}}_{2<br><br>i}<br><br>{\hat{V}}_i^H<br><br>{\hat{V}}_2<br><br>{\hat{V}}_i/\left({\hat{V}}_i^H<br><br>{\hat{V}}_i\right),\end{array}$ $\begin{array}{c}{W}_n=<br><br>{\left[\begin{array}{cccc}{w}_{1,n}& w_{2,n}& \mathrm{\Lambda <br><br>}& w_{M,n}\end{array}\right]}^T\\ =<br><br>{\hat{V}}_n-\underset{i=1,i\ne <br><br>n}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\alpha <br><br>}}_{\mathrm{ni}}<br><br>{\hat{V}}_i^H<br><br>{\hat{V}}_n<br><br>{\hat{V}}_i/\left({\hat{V}}_i^H<br><br>{\hat{V}}_i\right),\end{array}$ $\begin{array}{c}{W}_N=<br><br>{\left[\begin{array}{cccc}{w}_{1,N}& w_{2,N}& \mathrm{\Lambda <br><br>}& w_{M,N}\end{array}\right]}^T\\ =<br><br>{\hat{V}}_N-\underset{i=1,i\ne <br><br>N}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\alpha <br><br>}}_{\mathrm{Ni}}<br><br>{\hat{V}}_i^H<br><br>{\hat{V}}_N<br><br>{\hat{V}}_i/\left({\hat{V}}_i^H<br><br>{\hat{V}}_i\right)\end{array}$

where 0≦

α

_ni≦

1 is a nulling factor for 1≦

i≦

N, 1≦

n≦

N and V_i is the spatial signature for the i-th second wireless communication device.

22. The logic of claim 18, and further comprising logic that computes estimated channel information from received pilot signals in each of the transmissions received at the M plurality of antennas, and wherein the logic that recovers comprises logic that computes estimates of modulated data for each transmission from the N signals using the estimated channel information.

23. The logic of claim 22, wherein the logic that computes the estimated channel information comprises logic that computes elements of a channel matrix representing a channel between the M plurality of antennas of the first wireless communication device and an antenna of each of the respective N plurality of second wireless communication devices.