Beamforming signaling in a wireless network

1. A method comprising:

a) receiving, by a first base station from a second base station, at least one application protocol message, said first base station and said second base station configured to communicate with wireless devices employing a downlink carrier, said downlink carrier comprising a plurality of resource blocks, said at least one application protocol message comprising a downlink beamforming information element for at least one resource block in said downlink carrier, said downlink beamforming information element indicating a second beamforming codeword employed by said second base station for said at least one resource block, said second beamforming codeword included in a second beamforming codebook;

b) computing, by said first base station, a channel state input information element for a wireless device based on, at least in part, processing said downlink beamforming information element; and

c) transmitting, by said first base station, said channel state input information element to said wireless device for computing a precoding matrix indicator; and

d) receiving, by said first base station, a channel state feedback from said wireless device, said channel state feedback comprising said precoding matrix indicator.

2. The method of claim 1 , further comprising receiving, by said first base station from said second base station, a plurality of downlink beamforming information elements; and wherein said computing, by said first base station, said channel state input information element further comprises selecting a subset of said plurality of downlink beamforming information elements.

3. The method of claim 1 , further comprising transmitting a plurality of packets to said wireless device, said plurality of packets transmitted employing said precoding matrix indicator.

4. The method of claim 1 , further comprising said first base station demodulating, despreading, and decoding the received channel state feedback.

5. The method of claim 1 , further comprising receiving from said second base station, beamforming information identifying a cause of substantial inter-cell interference for inclusion in said subset of downlink beamforming information.

6. The method of claim 1 , further including defining said second beamforming codebook for a number of layers, said second beamforming codebook comprising a set of codewords having a number of columns or rows equal to or less than said number of layers.

7. The method of claim 6 , further comprising constructing codewords for a smaller number of layers employing a subset of columns or rows of said original codewords.

8. The method of claim 7 , further comprising indicating a rank of said smaller number of layers equal to a rank indicator field in said channel state feedback received from said wireless device.

9. A method comprising:

a) receiving, by a wireless device, a control message from a first base station, said control message comprising:

i) an identifier of a second base station in said plurality of base stations; and

ii) a channel state input information element based, at least in part, on a downlink beamforming information element received by said first base station from a second base station, said downlink beamforming information element indicating a beamforming codeword employed by said second base station for at least one downlink resource block;

b) measuring, by said wireless device, reference signals received from said second base station;

c) processing, by said wireless device, said measured reference signals based, at least in part, on said channel state input information element to compute a precoding matrix indicator; and

d) transmitting, by said wireless device, channel state information comprising said precoding matrix indicator to said first base station.

10. The method of claim 9 , wherein said processing of said measured reference signals comprises multiplying measured reference signal by at least one codeword in said channel state input information.

11. The method of claim 9 , wherein said channel state input information element comprises a codebook subset restriction bitmap parameter.

12. The method of claim 11 , further comprising said wireless device selecting a precoding matrix indicator from a subset of precoding codebook indicated by said codebook subset restriction bitmap parameter.

13. The method of claim 9 , wherein said processing of said measured reference signals further comprises multiplying a measured reference signal by at least one codeword in said downlink beamforming information element.

14. The method of claim 9 , further comprising calculating said precoding matrix indicator to reduce downlink inter-cell interference.

15. The method of claim 9 , further comprising selecting said precoding matrix indicator from a plurality of predetermined precoding matrix indicators.

16. The method of claim 9 , further comprising computing said precoding matrix indicator for a sub-band of said downlink carrier.

17. The method of claim 9 , wherein said said precoding matrix indicator is computed employing a minimum mean squared error criterion.

18. A wireless device comprising:

a) one or more communication interfaces;

b) one or more processors; and

c) memory storing instructions that, when executed, cause said wireless device to:

i) receive from a first base station, a channel state input information element based, at least in part, on a downlink beamforming information element received by said first base station from a second base station, said downlink beamforming information element indicating a beamforming codeword employed by said second base station for at least one downlink resource block;

ii) compute a precoding matrix indicator employing said channel state input information element; and

iii) transmit channel state information comprising said precoding matrix indicator to said first base station.

19. The wireless device of claim 18 , wherein said precoding matrix indicator is computed employing a zero-forcing criterion.

20. The wireless device of claim 18 , wherein said precoding matrix indicator is computed employing a minimum mean squared error criterion.