Mobile station loop-back signal processing

• US 7,197,282 B2
• Filed: 04/30/2002
• Issued: 03/27/2007
• Est. Priority Date: 07/26/2001
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Zangi, Kambiz C., Krasny, Leonid, Dent, Paul W.
• Primary Examiner(s): Feild; Joseph
• Assistant Examiner(s): NGUYEN, KHAI MINH
• Application Number:
  US10/135,095
• Publication Number:
  US 20030036359A1
• Time in Patent Office: 1,792 Days
• Field of Search: 455/423, 455/422.1, 455/115.1, 455/456.1, 455/457, 455/226.1, 455/67.14, 455/67.11, 455/69, 455/68, 455/63.1, 455/67.13, 370/335, 370/329, 370/342, 370/336
• US Class Current: 455/67.14
• CPC Class Codes: H04B 1/7105 Joint detection techniques, e.g. linear detectors
• CPC Class Codes: H04B 7/005 Control of transmission; Equalising
• CPC Class Codes: H04B 7/022 Site diversity; Macro-diversity using two or more spaced independent antennas H04B7/04
• CPC Class Codes: H04B 7/0615 of weighted versions of same signal
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: H04B 7/0636 Feedback format
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/16 in which the return channel carries supervisory signals, e.g. repetition request signals
• CPC Class Codes: H04L 25/0202 Channel estimation
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0212 of impulse response
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 25/0244 with inversion
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 27/367 using predistortion

Abstract

Processing of loop-back information returned by one or more mobile stations that are served by a wireless communication network permits the network to compensate its transmit signals for increased transmission efficiency and reduced signal interference at the mobile stations. Generally, the network forms one or more transmit signals as a combination of different signals intended for the different mobile stations, and remembers transmit information associated with these transmit signals. The mobile stations return loop-back signals to the network, which determines transmit signal compensation information by comparing loop-back information to memorized information. The mobile stations may loop-back samples from composite received signals, from processed received signal samples, or loop-back estimates. In the first case, processing at the network involves compensating the combined transmit signals at the transmit modulation rate, while the second case involves symbol rate processing of the individual information streams intended for the different mobile stations.

Claims

1. A wireless communication network comprising:

a network transmitter transmitting a combined transmit signal that includes individual information signals intended for one or more mobile stations;

a network receiver receiving loop-back signals from the one or more mobile stations; and

a transmit processor pre-compensating the combined transmit signal by compensating the individual information signals for estimated cross-correlation interference at the one or more mobile stations, such that unwanted signal interference is reduced at each mobile station, the transmit processor comprising;

memory to retain transmit information corresponding to the combined transmit signal;

a first processing system compensating for the individual information signals by passing the individual information signals through a first interference cancellation matrix that is based on estimated transmit channel characteristics; and

a second processing system generating the estimated transmit channel characteristics based on comparing the loop-back signals with the retained transmit information.

2. The wireless communication network of claim 1, wherein the network transmitter comprises one of a plurality of network transmitters, each network transmitter transmitting a different combined transmit signal to the one or more mobile stations.

3. The wireless communication network of claim 2, wherein the transmit processor forms the different combined transmit signals based on processing the individual information signals using the estimated transmit channel characteristics, and wherein the estimated transmit channel characteristics include downlink propagation path estimates for the plurality of network transmitters relative to the one or more mobile stations.

4. The wireless communication network of claim 3, wherein processing the individual information signals comprises processing the individual information signals with time-reverse-conjugate channel impulse responses obtained from the downlink propagation path estimates.

5. The wireless communication network of claim 4, wherein processing the individual information signals with time-reverse-conjugate channel impulse responses obtained from the downlink propagation path estimates comprises forming the combined transmit symbols as weighted combinations of the individual information signals based on a pre-compensation combining matrix formed from the time-reverse-conjugate channel impulse responses.

6. The wireless communication network of claim 1, wherein the second processing system compares the loop-back signals with the retained transmit information by:

generating estimated loop-back samples representative of loop-back signal samples generated at the one or more mobile stations; and

correlating the estimated loop-back samples with actual loop-back samples received in the loop-back signals after removal of uplink channel effects.

7. The wireless communication network of claim 6, wherein the second processing system generates the estimated loop-back samples by passing transmit signal samples obtained from the retained transmit information through an estimated uplink channel.

8. The wireless communication network of claim 1, wherein the second processing system:

generates reference signals by processing the loop-back signals with estimated loop-back channel characteristics; and

correlates the reference signals with the loop-back signals to determine the estimated transmit channel characteristics.

9. The wireless communication network of claim 8, wherein the transmit processor determines the estimated loop-back channel characteristics based on correlating selected samples in the loop-back signals with corresponding sample values known a priori to the network.

10. The wireless communication network of claim 9, wherein the selected samples in the loop-back signals comprise pilot information samples, and wherein the corresponding sample values comprise pilot information stored at the network.

11. The wireless communication network of claim 1, wherein the first interference cancellation matrix comprises an inverse cross-correlation matrix determined from the estimated transmit channel characteristics.

12. The wireless communication network of claim 1, wherein the transmit processor pre-compensates the combined transmit signal by passing combinations of the individual information signals through one or more transmit pre-filters having filter coefficients determined from the estimated transmit channel characteristics.

13. The wireless communication network of claim 1, wherein the loop-back signals comprise loop-back samples of composite received signals as received by individual ones of the mobile stations, and wherein the retained transmit information comprises retained samples of the combined transmit signal.

14. The wireless communication network of claim 13, wherein comparing the loop-back signals with the retained transmit information comprises:

generating reference signal samples based on passing the retained samples of the combined transmit signal through an estimated uplink channel; and

correlating the reference signal samples with corresponding samples in the loop-back signals.

15. The wireless communication network of claim 14, wherein the transmit processor obtains transmit rate compensation information from the correlations between the reference signal samples and the corresponding samples in the loop-back signals for pre-compensating the combined transmit signal.

16. The wireless communication network of claim 13, wherein the network further retains information symbols from the individual information signals as part of the retained transmit information.

17. The wireless communication network of claim 16, further comprising deriving receiver output samples from the loop-back signals representative of receiver-processed samples that would be obtained from the combined transmit signal at the one or more mobile stations based on modeling mobile station receiver processing.

18. The wireless communication network of claim 17, wherein the transmit processor obtains information symbol rate compensation information by correlating the derived receiver output samples and corresponding ones of the information symbols in the retained transmit information.

19. A method of transmit signal pre-compensation at a wireless communication network, the method comprising:

retaining transmit information associated with a combined transmit signal transmitted from the network to one or more mobile stations, wherein the combined transmit signal is formed from one or more individual information signals intended for different ones of the mobile stations, and wherein the transmit information associated with the combined transmit signal comprises the individual information signals used to form the combined transmit signal;

receiving loop-back signals from the mobile stations, wherein the loop-back signals comprise mobile station receiver output values;

determining one or more estimated transmit channel characteristics based on comparing the retained transmit information with loop-back information obtained from the loop-back signals;

generating cross-correlation compensation values based on correlating the mobile station receiver output values obtained from the loop-back signals with corresponding information symbols in the retained individual information signals; and

performing pre-compensation processing for the combined transmit signal based on the estimated transmit channel characteristics and compensating the individual information signals used to form the combined transmit signal with the cross correlation compensation values.

20. The method of claim 19, wherein the loop-back signals comprise looped-back samples of composite received signals received at individual ones of the mobile stations.

21. The method of claim 20, wherein retaining transmit information associated with a combined transmit signal transmitted from the network to one or more mobile stations comprises retaining samples of the combined transmit signal.

22. The method of claim 21, wherein determining one or more estimated transmit channel characteristics based on comparing the retained transmit information with loop-back information obtained from the loop-back signals comprises:

generating reference samples based on passing the retained samples of the combined transmit signal through an estimated uplink channel; and

correlating the reference samples with corresponding loop-back samples from the loop-back signals.

23. The method of claim 20, further comprising deriving receiver output samples from the loop-back signals representative of receiver-processed samples that would be obtained from the composite received signals at the one or more mobile stations based on modeling mobile station receiver processing.

24. The method of claim 23, further comprising retaining the individual information signals as part of the retained transmit information.

25. The method of claim 24, further comprising:

determining cross-correlations between the individual information signals based on correlating the derived receiver output signals with corresponding ones of the retained individual information signals; and

generating cross-correlation compensation values from the determined cross-correlations for pre-compensating the individual information signals used to form the combined transmit signal.

26. The method of claim 19, wherein compensating the individual information signals used to form the combined transmit signal with the cross correlation compensation values comprises passing the individual information signals through an interference cancellation matrix having matrix coefficients based on the cross-correlation compensation values.

27. A method of providing loop-back information to a wireless communication network, the method comprising:

receiving a composite spread spectrum signal transmitted by the network at a mobile station, the composite spread spectrum signal including a plurality of differently spread individual information signals intended for different ones of a plurality of mobile stations;

processing the composite signal to recover mobile-specific signal samples by;

despreading the composite spread spectrum signal to recover the individual information signal intended for the mobile station; and

demodulating soft symbol values from the individual information signal as the mobile specific signal samples; and

transmitting at least some of the mobile-specific signal samples back to the network as a loop-back signal.

28. The method of claim 27, wherein receiving a composite signal transmitted by the network at a mobile station comprises receiving one or more combined transmit signals comprising a combination of individual information signals intended for different ones of a plurality of mobile stations.

29. The method of claim 27, wherein transmitting at least some of the mobile-specific signal samples back to the network as a loop-back signal comprises transmitting selected mobile-specific samples together with locally-generated signal samples, such that the loop-back signal includes both mobile-specific sample and locally-generated signal information.

30. The method of claim 29, wherein transmitting selected mobile-specific samples together with locally-generated signal samples comprises alternating between transmitting the locally-generated signal samples and the mobile-specific samples.

31. The method of claim 29, wherein transmitting selected mobile-specific samples together with locally-generated signal samples comprises linearly combining the mobile-specific samples and the locally-generated signal samples.

32. The method of claim 29, wherein transmitting selected mobile-specific samples together with locally-generated signal samples comprises linearly combining the mobile-specific samples and the locally-generated signal samples using a desired time offset between the mobile-specific samples and the locally-generated samples.

33. The method of claim 29, wherein the locally generated samples comprise pilot signal samples known to the network.

34. The method of claim 29, wherein the locally generated samples comprise uplink traffic samples.

35. The method of claim 29, wherein the locally generated samples comprise a combination of pilot signal samples and uplink traffic samples.

36. A method of pre-compensating a transmit signal transmitted to one or more mobile stations by a wireless communication network, the method comprising:

receiving a plurality of loop-back signals from the plurality of mobile stations comprising loop-back samples of the transmit signal as received by the mobile stations;

retaining samples of individual information signals intended for different ones of the plurality of mobile stations, including a mobile station from which a loop-back signal is received, wherein one or more of the individual information signals are included in the transmit signal;

removing uplink channel effects from the plurality of loop-back signals;

generating estimated output samples that would be obtained at the receivers of the plurality of mobile stations based on processing the loop-back signals at the network using one or more mobile station receiver models;

determining interference between the plurality of individual information signals based on cross-correlating the retained samples for the individual information signals with the estimated output samples; and

compensating the individual information signals to reduce the determined interference.

37. The method of claim 36, wherein the network includes receiver models for each of the plurality of mobile stations.

38. The method of claim 36, wherein the network includes a database of receiver models, and further comprising:

receiving receiver model information from the mobile stations; and

selecting one of the receiver models to use for each mobile station based on receiver model information received from that mobile station.

39. The method of claim 38, further comprising interrogating mobile stations for the receiver model information.

40. The method of claim 36 further comprising retaining transmit signal samples at the network.

41. The method of claim 40, further comprising processing the loop-back signal after removal of the uplink channel effects to determine downlink channel characteristics.

42. The method of claim 41, further comprising compensating the transmit signal for the downlink channel characteristics based the determined downlink channel characteristics.