Mobile station loop-back signal processing

• US 20030036359A1
• Filed: 04/30/2002
• Published: 02/20/2003
• Est. Priority Date: 07/26/2001
• Status: Active Grant

• 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.
• Granted Patent: US 7,197,282 B2
• Time in Patent Office: Days
• US Class Current: 455/63.1
• 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 based on estimated transmit channel characteristics, the transmit processor comprising;

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

a first processing system performing pre-compensation processing for the combined transmit signal based on the 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 streams 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 streams comprises processing the individual information streams 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 streams 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 streams 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 transmit processor pre-compensates 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.

12. The wireless communication network of claim 11, wherein the transmit processor compensates the individual information signals by passing the individual information signals through a first interference cancellation matrix that is based on the estimated transmit channel characteristics.

13. The wireless communication network of claim 12, wherein the first interference cancellation matrix comprises an inverse cross-correlation matrix determined from the estimated transmit channel characteristics.

14. 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.

15. 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.

16. The wireless communication network of claim 15, 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.

17. The wireless communication network of claim 16, 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.

18. The wireless communication network of claim 15, wherein the network further retains information symbols from the individual information signals as part of the retained transmit information.

19. The wireless communication network of claim 18, 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.

20. The wireless communication network of claim 19, 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.

21. 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;

receiving loop-back signals from the mobile stations;

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; and

performing pre-compensation processing for the combined transmit signal based on the estimated transmit channel characteristics.

22. The method of claim 21, wherein the loop-back signals comprise looped-back samples of composite received signals received at individual ones of the mobile stations.

23. The method of claim 22, 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.

24. The method of claim 23, 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.

25. The method of claim 22, 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.

26. The method of claim 25, further comprising retaining the individual information signals as part of the retained transmit information.

27. The method of claim 26, 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.

28. The method of claim 21, wherein the loop-back signals comprise mobile station receiver output values, and wherein retaining transmit information associated with a combined transmit signal transmitted from the network to one or more mobile stations comprises retaining the individual information signals used to form the combined transmit signal.

29. The method of claim 28, further comprising:

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 streams; and

compensating the individual information streams used to form the combined transmit signal with the cross correlation compensation values.

30. The method of claim 29, wherein compensating the individual information streams used to form the combined transmit signal with the cross correlation compensation values comprises passing the individual information streams through an interference cancellation matrix having matrix coefficients based on the cross-correlation compensation values.

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

receiving a composite signal transmitted by the network at a mobile station;

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

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

32. The method of claim 31, 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.

33. The method of claim 31, wherein receiving a composite signal transmitted by the network at a mobile station comprises receiving a composite spread spectrum signal including a plurality of differently spread individual information signals intended for different ones of a plurality of mobile stations.

34. The method of claim 33, wherein processing the composite signal to recover mobile-specific signal samples comprises:

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

demodulating symbol values from the individual information signal; and

transmitting at least some of the symbol values back to the network as at least a portion of the loop-back signal.

35. The method of claim 34, wherein demodulating symbol values from the individual information signal comprises demodulating soft symbol values from the individual information signal.

36. The method of claim 35, wherein transmitting at least some of the symbol values back to the network as at least a portion of the loop-back signal comprises transmitting at least some of the soft symbol values back to the network.

37. The method of claim 31, 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.

38. The method of claim 37, 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.

39. The method of claim 37, 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.

40. The method of claim 37, 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.

41. The method of claim 37, wherein the locally generated samples comprise pilot signal samples known to the network.

42. The method of claim 37, wherein the locally generated samples comprise uplink traffic samples.

43. The method of claim 37, wherein the locally generated samples comprise a combination of pilot signal samples and uplink traffic samples.

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

receiving a composite signal transmitted by the network at a mobile station, wherein the composite signal comprises a combination of individual information signals intended for different ones of a plurality of mobile stations;

generating composite signal samples at a receiver in the mobile station;

transmitting a combination of composite signal samples and locally-generated signal samples back to the network from a transmitter in the mobile station.

45. The method of claim 44, wherein generating the composite signal samples at a receiver in the mobile station comprises generating composite signal samples at a first sampling rate equal to a transmit modulation rate of the composite signal.

46. The method of claim 44, wherein the composite signal comprises a spread spectrum signal having a transmit spreading rate, and wherein the first sampling rate equals the transmit spreading rate.

47. The method of claim 44, wherein the transmit spreading rate is a CDMA chip rate.

48. The method of claim 47, wherein transmitting a combination of composite signal samples and locally-generated signal samples back to the network from a transmitter in the mobile station comprises performing chip-rate combining of pilot signal chips and composite signal chips.

49. 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 loop-back signal from a mobile station comprising loop-back samples of the transmit signal as received by the mobile station;

removing uplink channel effects from the loop-back signal; and

generating estimated output samples that would be obtained at a receiver in the mobile station based on processing the loop-back signal at the network using a mobile station receiver model.

50. The method of claim 49, further comprising retaining samples of individual information signals intended for different ones in a plurality of mobile stations, including the mobile station from which the loop-back signal is received, wherein one or more of the individual information streams are included in the transmit signal.

51. The method of claim 50, further comprising:

determining interference between the individual information signal intended for the mobile station from which the loop-back signal is received and one or more others of the individual information streams based on cross-correlating the retained samples with the estimated output samples; and

compensating the individual information signal of the mobile station from which the loop-back signal to reduce the determined interference.

52. The method of claim 51, further comprising:

receiving a plurality of loop-back signals from the plurality of mobile stations;

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;

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

compensating the individual information signals to reduce the determined interference.

53. The method of claim 52, wherein the network includes receiver models for each of the plurality of mobile stations.

54. The method of claim 52, 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.

55. The method of claim 54, further comprising interrogating mobile stations for the receiver model information.

56. The method of claim 51, further comprising retaining transmit signal samples at the network.

57. The method of claim 56, further comprising processing the loop-back signal after removal of the uplink channel effects to determine downlink channel characteristics.

58. The method of claim 57, further comprising compensating the transmit signal for the downlink channel characteristics based the determined downlink channel characteristics.

59. A method of providing downlink channel information from a mobile station to a wireless communication network, the method comprising:

receiving a signal from the network at the mobile station through a downlink channel;

generating a channel estimate comprising path coefficients and corresponding delays for the downlink channel based on the signal received by the mobile station;

forming a discrete-time filter representation of the channel estimate;

generating a channel estimate sequence by convolving the discrete-time filter representation with a defined pseudo-random sequence;

quantizing samples in the channel estimate sequence to form a quantized sequence; and

transmitting the quantized sequence from the mobile station to the network to provide the network with the downlink channel information.

60. The method of claim 59, wherein receiving a signal from the network at the mobile station through a downlink channel comprises receiving a plurality of network transmit signals through a plurality of downlink channels.

61. The method of claim 60, wherein generating a channel estimate comprising path coefficients and corresponding delays for the downlink channel based on the signal received by the mobile station comprises generating channel estimates for each one of the plurality of downlink channels.

62. The method of claim 61, wherein forming a discrete-time filter representation of the channel estimate comprises forming a discrete-time filter representations for each channel estimate.

63. The method of claim 62, wherein generating a channel estimate sequence by convolving the discrete-time filter representation with a defined pseudo-random sequence comprises:

generating a plurality of channel estimate sequences by convolving each discrete-time filter representation corresponding to each channel estimate; and

combining the channel estimate sequences to form a combined channel estimate sequence including information for the plurality of downlink channels estimated by the mobile station.

64. The method of claim 63, wherein quantizing samples in the channel estimate sequence to form a quantized sequence comprises quantizing samples in the combined channel estimate sequence to form the quantized sequence.

65. The method of claim 61, wherein generating a channel estimate sequence by convolving the discrete-time filter representation with a defined pseudo-random sequence comprises convolving the discrete-time filter representation for each channel estimate with a different defined pseudo-random sequence.

66. The method of claim 60, further comprising assuming a common set of delays for each of the downlink channels.

67. The method of claim 66, further comprising forming the quantized sequence to include the common set of delays.

68. The method of claim 59, wherein forming a discrete-time filter representation of the channel estimate comprises quantizing the delays corresponding to the path coefficients such that the delay values are based on a pre-defined sampling interval.

69. The method of claim 59, wherein generating a channel estimate sequence by convolving the discrete-time filter representation with a defined pseudo-random sequence comprises convolving digital filter values in the discrete-time filter representation with sample values in the defined pseudo-random sequence.

70. The method of claim 59, further comprising selecting a number P of samples in the defined pseudo-random sequence, wherein the convolution of the discrete-time filter representation with the defined pseudo-random sequence results in P samples in the channel estimate sequence.

71. The method of claim 70, further comprising selecting P based on a desired transmit time for transmitting the quantized sequence from the mobile station.

72. The method of claim 70, further comprising selecting P such that the quantized sequence received by the network includes sufficient samples for determining the downlink channel information as estimated by the mobile station.

73. The method of claim 59, wherein each sample in the channel estimate sequence comprises a complex value, and wherein quantizing samples in the channel estimate sequence comprises quantizing each sample to a desired number, B, of bits.

74. The method of claim 73, wherein quantizing samples in the channel estimate sequence comprises quantizing each sample to a desired number, B, of bits comprises separately quantizing real and imaginary parts of the complex samples.

75. The method of claim 73, wherein transmitting the quantized sequence to the network to provide the network with the downlink channel information comprises transmitting the digital bits of the quantized sequence on a defined digital reverse link channel to the network.

76. The method of claim 73, further comprising selecting B equal to one (1) such that the channel estimate sequence is quantized as a sequence of sign values.

77. The method of claim 76, further comprising generating a first sequence of sign values for a real part of the channel estimate sequence, and a second sequence of sign values for an imaginary part of the channel estimate sequence.

78. The method of claim 77, wherein transmitting the quantized sequence to the network to provide the network with the downlink channel information comprises transmitting the first and second sequences of sign values to the network.

79. The method of claim 59, wherein transmitting the quantized sequence to the network to provide the network with the downlink channel information comprises transmitting at one or more defined time intervals on a common feedback channel used by other mobile stations to provide downlink channel information to the network.

80. The method of claim 79, wherein transmitting the quantized sequence to the network to provide the network with the downlink channel information comprises transmitting the quantized sequence responsive to a request from the network.

81. The method of claim 79, wherein transmitting the quantized sequence to the network to provide the network with the downlink channel information comprises transmitting the quantized sequence starting at a time commanded by the network.

82. A method of obtaining downlink channel information from a mobile station at a wireless communication network, the method comprising:

receiving a channel estimate sequence from the mobile station, said channel estimate sequence comprising a convolution of a discrete-time filter representation of a downlink channel estimate with a defined pseudo-random sequence known to the network;

generating a channel estimate sequence at the network based on hypothesizing a discrete-time filter representation of a downlink channel estimate corresponding to hypothesized path delays and coefficients;

selecting as estimated downlink channel information the discrete-time filter representation that minimizes a difference between the generated channel estimate sequence and the received channel estimate sequence.

83. A method of obtaining downlink channel information from a plurality of mobile stations at a wireless communication network, the method comprising:

identifying one or more mobile stations from which downlink channel information is desired based on downlink service scheduling of the plurality of mobile stations by the network;

transmitting requests for downlink channel information from the network to the identified mobile stations; and

receiving downlink channel information at the network from each of the identified mobile stations on a shared uplink channel used by the plurality of mobile stations to report downlink channel information.

84. The method of claim 83, wherein the shared uplink channel is a CDMA channel that is shared in TDMA fashion between the plurality of mobile stations.

85. The method of claim 84, further comprising including scheduling information for use of the shared uplink channel in the requests for downlink channel information transmitted by the network.

86. The method of claim 83, wherein the network is a WCDMA network.

87. The method of claim 83, wherein the network is an HDR network.

88. The method of claim 83, wherein the network comprises a shared downlink channel on which individual mobile stations are individually served according to a network scheduling algorithm.

89. The method of claim 88, wherein identifying one or more mobile stations from which downlink channel information is desired based on downlink service scheduling of the plurality of mobile stations by the network comprises identifying the one or more mobile stations that will be next served by the network on the shared downlink channel.