Transmit diversity and separating multiple loopback signals

• US 6,996,375 B2
• Filed: 02/14/2003
• Issued: 02/07/2006
• Est. Priority Date: 07/26/2001
• Status: Expired due to Term

• Current Assignee: Sony Ericsson Mobile Communications AB (Sony Group Corp.)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Zangi, Kambiz C., Dent, Paul W.
• Primary Examiner(s): Corsaro, Nick
• Assistant Examiner(s): Persino, Raymond B.
• Application Number:
  US10/367,145
• Publication Number:
  US 20040203468A1
• Time in Patent Office: 1,089 Days
• Field of Search: 455/67.11, 455/67.16, 455/63.1, 455/69, 455/70
• US Class Current: 455/67.16
• 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 7/0619 using feedback from receiving side feedback signaling for adaptive modulation/coding H04L1/0001
• CPC Class Codes: H04L 1/243 at the transmitter, using a loop-back
• 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
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

A wireless communication network processes composite loop-back signals received at one or more network antennas from a plurality of mobile stations, each transmitting an individual, mobile-specific loop-back signal. Using its knowledge of the prior network-transmitted signal(s) from which the mobile stations derive their individual loop-back signals, and its knowledge of the mobile-specific loop-back signal modifications made by each of the mobile stations, the network derives mobile-specific downlink channel information based on processing the composite loop-back signals. That is, use of the mobile-specific loop-back signals enables the network to determine downlink channel estimates as between each participating network antenna and each participating mobile station to be used for transmit signal interference and/or power pre-compensation, for example. Mobile stations incorporate loop-back signal sample processors used to impart mobile-specific modifications to signal samples obtained from network-transmitted signals. The modified signal samples, thus “imprinted,” are then transmitted back to the network.

Claims

1. A method of generating a loop-back signal at a mobile station for use in downlink channel estimation by a wireless communication network comprising:

receiving a network-transmitted signal as a received signal at a mobile station;

obtaining signal samples from the received signal;

applying a mobile-specific modification to the signal samples; and

transmitting the modified signal samples from the mobile station to the network in a loop-back signal.

2. The method of claim 1, wherein applying a mobile-specific modification to the signal samples comprises imparting characteristic phase rotations to the signal samples such that the loop-back signal received at the network from the mobile station has a characteristic frequency shift that is unique to the mobile station.

3. The method of claim 1, wherein receiving a network-transmitted signal as a received signal at a mobile station comprises receiving a CDMA signal that includes coded signals for a plurality of mobile stations.

4. The method of claim 1, wherein applying a mobile-specific modification to the signal samples comprises gating the signal samples for generation of the transmit signal according to mobile-specific timing such that transmitting the modified signal samples from the mobile station comprises transmitting gated signal samples in the loop-back signal.

5. The method of claim 1, wherein applying a mobile-specific modification to the signal samples comprises multiplying the signal samples by a mobile-specific code value.

6. The method of claim 1, wherein obtaining signal samples from the received signal comprises obtaining complex samples at a sampling rate matched to a chip rate of the received signal.

7. The method of claim 6, wherein applying a mobile-specific modification to the signal samples comprises frequency shifting the complex samples modulo the sampling rate in accordance with a mobile-specific frequency shifting sequence.

8. The method of claim 1, wherein applying a mobile-specific modification to the signal samples comprises multiplying the signal samples by a frequency shift sequence.

9. The method of claim 8, wherein multiplying the signal samples by a frequency shift sequence comprises, for each signal sample, multiplying the signal sample by a corresponding complex rotation factor.

10. The method of claim 9, wherein multiplying the signal sample by a corresponding complex rotation factor comprises multiplying the signal sample by a selected one in a sequence of complex rotation factors indexed by signal sample number.

11. The method of claim 1, further comprising determining a mobile station identifier at the network and transmitting the mobile station identifier to the mobile station for use in determining the mobile-specific modification applied to the signal samples.

12. The method of claim 11, wherein determining a mobile station identifier at the network comprises determining a mobile station index number for use in uniquely identifying the mobile station within a group of mobile stations.

13. The method of claim 12, wherein applying a mobile-specific modification to the signal samples comprises applying a characteristic frequency shift sequence to the signal samples that is based on the mobile station index, such that each mobile station in the group of mobile stations imparts a characteristic frequency shifting sequence to the signal samples in its loop-back signal.

14. The method of claim 1, wherein applying a mobile-specific modification to the signal samples comprises rotating the phase of successive signal samples by a progressively increasing phase shift corresponding to a frequency shift specific to the mobile station.

15. The method of claim 14, wherein the received signal is a CDMA signal transmitted by the network, and wherein obtaining signal samples from the received signal comprises sampling the received signal at a sample rate matched to a CDMA chip rate such that the frequency shift is a spectrum rotation modulo the sample rate, thereby leaving the loop-back signal spectrum substantially the same as the received signal spectrum.

16. The method of claim 14, further comprising combining a pilot code sequence with the modified signal samples obtained by phase rotation and transmitting the combination of modified signal samples and the pilot code sequence back to the network as the loop-back signal.

17. The method of claim 16, wherein combining a pilot code sequence with the modified signal samples comprises time-division multiplex combining.

18. The method of claim 16, wherein combining a pilot code sequence with the modified signal samples comprises additive combining.

19. A mobile station to generate a loop-back signal for use in downlink channel estimation by a wireless communication network comprising:

a receiver to receive a network-transmitted signal as a received signal and obtain signal samples therefrom;

a sample processor to apply a mobile-specific modification to the signal samples obtained from the received signal; and

a transmitter to transmit a loop-back signal based on the modified signal samples back to the network.

20. The mobile station of claim 19, wherein the sample processor comprises a digital circuit included in a baseband processor of the mobile station.

21. The mobile station of claim 19, wherein the sample processor applies a mobile-specific modification to the signal samples by imparting characteristic phase rotations to the signal samples such that the loop-back signal received at the network from the mobile station has a characteristic frequency shift that is unique to the mobile station.

22. The mobile station of claim 19, wherein the mobile station receives the network-transmitted signal as a CDMA signal that includes coded signals for a plurality of mobile stations.

23. The mobile station of claim 19, wherein the mobile station applies a mobile-specific modification to the signal samples by gating the signal samples for generation of the transmit signal according to mobile-specific timing such that transmitting the modified signal samples from the mobile station comprises transmitting gated signal samples in the loop-back signal.

24. The mobile station of claim 19, wherein the mobile station applies a mobile-specific modification to the signal samples by multiplying the signal samples by a mobile-specific code value.

25. The mobile station of claim 19, wherein the receiver obtains signal samples from the received signal by obtaining complex samples of the received signal at a sampling rate matched to a chip rate of the received signal.

26. The mobile station of claim 25, wherein the sample processor applies a mobile-specific modification to the signal samples by frequency shifting the complex samples modulo the sampling rate in accordance with a mobile-specific frequency shifting sequence.

27. The mobile station of claim 19, wherein the sample processor applies a mobile-specific modification to the signal samples by multiplying the signal samples by a mobile-specific frequency shift sequence.

28. The mobile station of claim 27, wherein the sample processor multiplies each signal sample by a corresponding complex rotation factor.

29. The mobile station of claim 28, wherein the sample processor multiplies each signal sample by a selected one in a sequence of complex rotation factors indexed by signal sample number.

30. The mobile station of claim 19, wherein the mobile station determines the mobile-specific modification applied to the signal samples based on receiving a mobile station identifier from the network.

31. The mobile station of claim 30, wherein the mobile station identifier comprises a mobile station index number for use in uniquely identifying the mobile station within a group of mobile stations.

32. The mobile station of claim 31, wherein the sample processor applies a mobile-specific modification to the signal samples by applying a characteristic frequency shift sequence to the signal samples that is based on the mobile station index, such that each mobile station in the group of mobile stations imparts a characteristic frequency shifting sequence to the signal samples in its loop-back signal.

33. The mobile station of claim 19, wherein applying a mobile-specific modification to the signal samples comprises rotating the phase of successive signal samples by a progressively increasing phase shift corresponding to a frequency shift specific to the mobile station.

34. The mobile station of claim 33, wherein the received signal is a CDMA signal transmitted by the network, and wherein the mobile station obtains signal samples from the received signal by sampling the received signal at a sample rate matched to a CDMA chip rate such that the frequency shift is a spectrum rotation modulo the sample rate, thereby leaving the loop-back signal spectrum substantially the same as the received signal spectrum.

35. The mobile station of claim 33, wherein the mobile station combines a pilot code sequence with the modified signal samples obtained by phase rotation and transmits the combination of modified signal samples and the pilot code sequence back to the network as the loop-back signal.

36. The mobile station of claim 35, wherein the mobile station combines a pilot code sequence with the modified signal samples by time-division multiplex combining.

37. The mobile station of claim 35, wherein the mobile station combines a pilot code sequence with the modified signal samples by additive combining.

41. The method of claim 30, wherein assigning an index value to each mobile station comprises:

identifying the plurality of mobile stations as a particular group of mobile stations;

indexing the group of mobile stations; and

transitting an index value to each mobile station that uiquely identifies that mobile station within the particular group of mobile stations.

38. A method of enabling the generation of individual loop-back signals by a plurality of mobile stations to be used in downlink channel estimation by a wireless communication network comprising:

determining one or more index values for each mobile station to be used by the mobile station in generating a mobile-specific loop-back signal for return transmission to the network; and

transmitting the one or more index values for each mobile station from the network to each mobile station;

transmitting a count value for receipt by the mobile stations; and

each mobile station forming its mobile-specific loop-back signal by imparting a mobile-specific frequency shift derived from the index and count values to signal samples obtained from a signal transmitted by the network to the mobile station.

39. The method of claim 38, wherein determining one or more index values for each mobile station comprises assigning an index value to each mobile station that uniquely identifies the mobile station within the plurality of mobile stations.

40. The method of claim 39, wherein assigning an index value to each mobile station comprises assigning index values to mobile stations as each mobile station is admitted to the network for service.

42. The method of claim 38, futher comprising receiving the individual loop-back sigals from the moble stations as one or more composite loop-ack signals received at one or more netwrok antennas.

43. The method of claim 42, further comprising identifying individual loop-back signals within the composite loop-back signals based on knowledge of the mobile-specific frequency shift applied by each mobile station.

44. The method of claim 42, further comprising processing the one or more composite loop-back signals to obtain downlink channel estimates relating the one or more network antennas to each mobile station based on applying mobile-specific frequency de-shifting to the one or more composite loop-back signals based on knowledge of the mobile-specific frequency shift applied by each mobile station.