Systems and Methods for Forward Link Closed Loop Beamforming

• US 20080008264A1
• Filed: 01/18/2007
• Published: 01/10/2008
• Est. Priority Date: 01/20/2006
• Status: Active Grant

• Current Assignee: ATC Technology Corporation (FedEx Corporation)
• Original Assignee: ATC Technology Corporation (FedEx Corporation)
• Inventors: Zheng, Dunmin
• Granted Patent: US 8,090,041 B2
• Time in Patent Office: Days
• US Class Current: 375/299
• CPC Class Codes: H04B 7/06 at the transmitting station
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: H04B 7/18534 for enhancing link reliablility, e.g. satellites diversity
• CPC Class Codes: H04B 7/18545 Arrangements for managing station mobility, i.e. for station registration or localisation
• CPC Class Codes: H04L 1/0606 Space-frequency coding
• CPC Class Codes: H04L 1/0625 Transmitter arrangements
• CPC Class Codes: H04L 1/0643 block codes
• CPC Class Codes: H04L 1/0668 Orthogonal systems, e.g. using Alamouti codes

Abstract

Methods of forming a beam to a wireless terminal from a transmitter including an antenna having a plurality of antenna feed elements include generating channel estimates at the wireless terminal, obtaining channel phase information from the channel estimates, quantizing the channel phase information to obtain quantized channel phase values, and transmitting the quantized channel phase values to the transmitter. The methods may further include receiving the quantized channel phase values at the transmitter, obtaining channel gain estimates, constructing channel estimates using the quantized channel phase values and the channel gain estimates, and determining transmit beamforming weights in response to the channel estimates. Related transmitters, wireless terminals, and communications systems are also disclosed.

Claims

1. A method of forming a beam to a wireless terminal from a transmitter including an antenna having a plurality of antenna feed elements, comprising:

generating channel estimates at the wireless terminal;

obtaining channel phase information from the channel estimates;

quantizing the channel phase information using a 2-bit quantization for each channel to obtain quantized channel phase values; and

transmitting the quantized channel phase values to the transmitter.

2. The method of claim 1, wherein the quantized channel phase values comprise in-phase (I) and quadrature (Q) quantized phase values for channels from each of the plurality of antenna feed elements to the receiver, the method further comprising:

constructing a frame structure including in-phase (I) and quadrature (Q) quantized phase values for each of the channels;

wherein transmitting the quantized channel phase values comprises transmitting the frame structure on a return link control channel.

3. The method of claim 2, wherein the frame structure comprises M in-phase (I) quantized phase values and M quadrature (Q) quantized phase values corresponding to M of the plurality of antenna feed elements.

4. The method of claim 3, wherein the frame structure comprises the M in-phase (I) quantized phase values followed by the M quadrature (Q) quantized phase values.

5. The method of claim 1, wherein the channel phase information comprises in-phase (I) and quadrature (Q) phase information for channels from each of the plurality of antenna feed elements to the wireless terminal, and wherein quantizing the channel phase information comprises quantizing the in-phase (I) phase information with a first bit and quantizing the quadrature (Q) phase information with a second bit.

6. The method of claim 5, wherein quantizing the channel phase information comprises quantizing the in-phase (I) phase information as π

or 0 and quantizing the quadrature (Q) phase information as π

/2 or −

π

/2.

7. The method of claim 1, further comprising:

determining a geographic location of the wireless terminal; and

transmitting the determined geographic location to the transmitter.

8. The method of claim 1, further comprising:

receiving the quantized channel phase values at the transmitter;

obtaining channel gain estimates;

constructing channel estimates using the quantized channel phase values and the channel gain estimates; and

determining transmit beamforming weights in response to the channel estimates.

9. The method of claim 8, wherein receiving the quantized channel phase values comprises receiving a frame structure including quantized channel phase values for M of the plurality of channels, wherein the frame structure includes M in-phase (I) quantized phase values followed by M quadrature (Q) quantized phase values.

10. The method of claim 9, further comprising:

generating a channel phase estimate for an mth channel of the M channels in response to an in-phase (I) quantized phase value and a quadrature (Q) quantized phase value for the mth channel, wherein constructing a channel estimate for the channel comprises constructing a channel estimate using the channel phase estimate and the channel gain estimate for the mth channel.

11. The method of claim 10, further comprising:

updating the channel phase estimate for the mth channel upon receipt of a most recently received one of an in-phase (I) quantized phase value for the mth channel or a quadrature (Q) quantized phase value for the mth channel.

12. The method of claim 11, wherein updating the channel phase estimate for the mth channel comprises updating the channel phase estimate for the mth channel according to the following equation:

13. The method of claim 8, wherein obtaining channel gain estimates comprises obtaining an average feed gain value from a feed gain database in response to a location of the wireless terminal.

14. The method of claim 13, further comprising receiving an indication of the location of the wireless terminal from the wireless terminal.

15. The method of claim 8, wherein determining transmit beamforming weights in response to the channel estimates comprises determining transmit beamforming weights that generate an increased response in a direction of the wireless terminal.

16. The method of claim 15, wherein determining transmit beamforming weights further comprises determining transmit beamforming weights that generate a null response in a direction of another wireless terminal.

17. A transmitter for use in a wireless communications system, comprising:

a plurality of antenna feed elements;

a phase bits detector configured to receive quantized channel phase values;

a phase vector constructor configured to generate a vector of channel phase estimates for a plurality of channels from the plurality of antenna feed elements to a wireless terminal in response to the quantized channel phase values;

a gain vector constructor configured to generate a vector of channel gain estimates for the plurality of channels;

a vector channel constructor configured to generate a vector of channel estimates for the plurality of channels in response to the vector of channel phase estimates and the vector of channel gain estimates; and

an adaptive beamformer configured to generate a vector of transmit beamforming weights in response to the vector of channel estimates.

18. The transmitter of claim 17, wherein the phase bits detector is further configured to receive a frame structure over a return link control channel, the frame structure including quantized channel phase values for M of the plurality of channels, wherein the frame structure includes M in-phase (I) quantized phase values followed by M quadrature (Q) quantized phase values.

19. The transmitter of claim 18, wherein the phase vector constructor is further configured to generate a channel phase estimate for an mth channel of the plurality of channels in response to an in-phase (I) quantized phase value and a quadrature (Q) quantized phase value for the mth channel;

and

wherein the vector channel constructor is further configured to construct a channel estimate for the mth channel using the channel phase estimate for the mth channel and a channel gain estimate for the mth channel.

20. The transmitter of claim 19, wherein the phase vector constructor is further configured to update the channel phase estimate for the mth channel upon receipt of a most recently received one of an in-phase (I) quantized phase value for the channel or a quadrature (Q) quantized phase value for the mth channel.

21. The transmitter of claim 20, wherein the phase vector constructor is further configured to update the channel phase estimate for the mth channel according to the following equation:

22. The transmitter of claim 17, further comprising a feed gain database containing average feed gain information, wherein the gain vector constructor is further configured to obtain channel gain estimates by obtaining an average feed gain value from the feed gain database in response to a location of the wireless terminal.

23. The transmitter of claim 22, wherein the gain vector constructor is further configured to receive an indication of the location of the wireless terminal from the wireless terminal.

24. The transmitter of claim 17, wherein the adaptive beamformer is further configured to determine transmit beamforming weights that generate an increased response in a direction of the wireless terminal.

25. The transmitter of claim 24, wherein the adaptive beamformer is further configured to determine transmit beamforming weights that generate a null response in a direction of another wireless terminal.

26. A wireless terminal for use in a communications system, comprising:

a vector channel estimator configured to generate channel estimates for a plurality of channels to the wireless terminal from a plurality of antenna feed elements at a remote transmitter;

a phase vector calculator configured to obtain channel phase information from the channel estimates; and

a phase quantizer configured to quantize the channel phase information using a 2-bit quantization for each channel to obtain quantized channel phase values.

27. The wireless terminal of claim 26, wherein the quantized channel phase values comprise in-phase (I) and quadrature (Q) quantized phase values for channels from each of the plurality of antenna feed elements to the wireless terminal;

and

wherein the wireless terminal further comprises a frame packer configured to construct a frame structure including in-phase (I) and quadrature (Q) quantized phase values for each of the plurality of channels.

28. The wireless terminal of claim 27, wherein the frame structure comprises M in-phase (I) quantized phase values and M quadrature (Q) quantized phase values corresponding to M of the antenna feed elements.

29. The wireless terminal of claim 28, wherein the frame structure comprises the M in-phase (I) quantized phase values followed by the M quadrature (Q) quantized phase values.

30. The wireless terminal of claim 26, wherein the channel phase information comprises in-phase (I) and quadrature (Q) phase information for channels from each of the plurality of antenna feed elements to the wireless terminal, and wherein the phase quantizer is further configured to quantize the in-phase (I) phase information with a first bit and the quadrature (Q) phase information with a second bit.

31. The wireless terminal of claim 30, wherein the phase quantizer is further configured to quantize the in-phase (I) phase information as π

or 0 and quantizing the quadrature (Q) phase information as π

/2 or −

π

/2.

32. The wireless terminal of claim 26, further comprising:

a location determination unit configured to determine a geographic location of the wireless terminal.

33. A communications system, comprising:

(a) a wireless terminal comprising;

a vector channel estimator configured to generate channel estimates for a plurality of channels to the wireless terminal;

a phase vector calculator configured to obtain channel phase information from the channel estimates;

a phase quantizer configured to quantize the channel phase information to obtain quantized channel phase values; and

a transceiver configured to transmit the quantized channel phase values; and

(b) a transmitter, comprising;

a plurality of antenna feed elements;

a phase bits detector configured to receive the quantized channel phase values from the wireless terminal;

a phase vector constructor configured to generate a vector of channel phase estimates for the plurality of channels in response to the quantized channel phase values, wherein the plurality of channels comprise channels from the plurality of antenna feed elements to the wireless terminal;

a gain vector constructor configured to generate a vector of channel gain estimates for the plurality of channels;

a vector channel constructor configured to generate a vector of channel estimates for the plurality of channels in response to the vector of channel phase estimates and the vector of channel gain estimates; and

an adaptive beamformer configured to generate a vector of transmit beamforming weights in response to the vector of channel estimates.

34. The communications system of claim 33, wherein the phase bits detector is further configured to receive a frame structure from the wireless terminal over a return link control channel, the frame structure including the quantized channel phase values for M of the plurality of channels, wherein the frame structure includes M in-phase (I) quantized phase values followed by M quadrature (Q) quantized phase values.

35. The communications system of claim 34, wherein the phase vector constructor is further configured to generate a channel phase estimate for an mth channel of the plurality of channels in response to an in-phase (I) quantized phase value and a quadrature (Q) quantized phase value for the mth channel;

and

wherein the vector channel constructor is further configured to construct a channel estimate for the mth channel using the channel phase estimate for the mth channel and a channel gain estimate for the mth channel.

36. The communications system of claim 35, wherein the phase vector constructor is further configured to update the channel phase estimate for the mth channel upon receipt of a most recently received one of an in-phase (I) quantized phase value for the channel or a quadrature (Q) quantized phase value for the mth channel.

37. The communications system of claim 36, wherein the phase vector constructor is further configured to update the channel phase estimate for the mth channel according to the following equation:

38. The communications system of claim 33, further comprising a feed gain database containing average feed gain information, wherein the gain vector constructor is further configured to obtain channel gain estimates by obtaining an average feed gain value from the feed gain database in response to a location of the wireless terminal.

39. The communications system of claim 38, wherein the gain vector constructor is further configured to receive an indication of the location of the wireless terminal from the wireless terminal.

40. The communications system of claim 39, wherein the adaptive beamformer is further configured to determine transmit beamforming weights that generate an increased response in a direction of the wireless terminal.

41. The communications system of claim 40, wherein the adaptive beamformer is further configured to determine transmit beamforming weights that generate a null response in a direction of another wireless terminal.

42. The communications system of claim 33, wherein the quantized channel phase values comprise in-phase (I) and quadrature (Q) quantized phase values for channels from each of the plurality of antenna feed elements to the wireless terminal;

and

wherein the wireless terminal further comprises a frame packer configured to construct a frame structure including in-phase (I) and quadrature (Q) quantized phase values for each of the plurality of channels.

43. The communications system of claim 42, wherein the frame structure comprises M in-phase (I) quantized phase values and M quadrature (Q) quantized phase values corresponding to M of the antenna feed elements, and wherein the frame structure comprises the M in-phase (I) quantized phase values followed by the M quadrature (Q) quantized phase values.

44. The communications system of claim 33, wherein the phase quantizer is further configured to quantize the channel phase information using a 2-bit quantization for each channel.

45. The communications system of claim 44, wherein the channel phase information comprises in-phase (I) and quadrature (Q) phase information for channels from each of the plurality of antenna feed elements to the wireless terminal, and wherein the phase quantizer is further configured to quantize the in-phase (I) phase information with a first bit and the quadrature (Q) phase information with a second bit.

46. The communications system of claim 45, wherein the phase quantizer is further configured to quantize the in-phase (I) phase information as π

or 0 and quantizing the quadrature (Q) phase information as π

/2 or −

π

/2.

47. The communications system of claim 33, wherein the wireless terminal further comprises a location determination unit configured to determine a geographic location of the wireless terminal.

56. The method of claim 45, wherein determining transmit beamforming weights further comprises determining transmit beamforming weights that generate a null response in a direction of another wireless terminal.

48. A method of forming a beam to a wireless terminal from a transmitter including an antenna having a plurality of antenna feed elements, comprising:

receiving quantized channel phase values from the wireless terminal;

obtaining channel gain estimates;

constructing channel estimates using the quantized channel phase values and the channel gain estimates; and

determining transmit beamforming weights in response to the channel estimates.

49. The method of claim 48, wherein receiving the quantized channel phase values comprises receiving a frame structure including quantized channel phase values for M of the plurality of channels, wherein the frame structure includes M in-phase (I) quantized phase values followed by M quadrature (Q) quantized phase values.

50. The method of claim 49, further comprising:

generating a channel phase estimate for an mth channel of the M channels in response to an in-phase (I) quantized phase value and a quadrature (Q) quantized phase value for the mth channel, wherein constructing a channel estimate for the channel comprises constructing a channel estimate using the channel phase estimate and the channel gain estimate for the mth channel.

51. The method of claim 50, further comprising:

updating the channel phase estimate for the mth channel upon receipt of a most recently received one of an in-phase (I) quantized phase value for the mth channel or a quadrature (Q) quantized phase value for the mth channel.

52. The method of claim 51, wherein updating the channel phase estimate for the mth channel comprises updating the channel phase estimate for the mth channel according to the following equation:

53. The method of claim 48, wherein obtaining channel gain estimates comprises obtaining an average feed gain value from a feed gain database in response to a location of the wireless terminal.

54. The method of claim 53, further comprising receiving an indication of the location of the wireless terminal from the wireless terminal.

55. The method of claim 48, wherein determining transmit beamforming weights in response to the channel estimates comprises determining transmit beamforming weights that generate an increased response in a direction of the wireless terminal.