Multiuser time-reversal division multiple access uplink system with parallel interference cancellation

• US 9,559,874 B2
• Filed: 08/16/2013
• Issued: 01/31/2017
• Est. Priority Date: 08/16/2013
• Status: Active Grant

• Current Assignee: Origin Wireless, Inc.
• Original Assignee: Origin Wireless, Inc.
• Inventors: Han, Feng, Liu, K. J. Ray
• Primary Examiner(s): Burd, Kevin M
• Application Number:
  US13/969,320
• Publication Number:
  US 20150049792A1
• Time in Patent Office: 1,264 Days
• Field of Search: 375/316, 375/346, 375/349, 375/219
• US Class Current: 1/1
• CPC Class Codes: H04B 17/309 Measuring or estimating channel quality parameters
• CPC Class Codes: H04L 2025/03802 Signalling on the reverse channel
• CPC Class Codes: H04L 25/03012 operating in the time domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 25/0328 with interference cancellation circuitry adaptations for interference cancellation within a sequence estimator H04L25/03305; interference related aspects of direct sequence spread spectrum H04B1/7097; interference related aspects of frequency hopping spread spectrum H04B1/715; see also H04B1/10
• CPC Class Codes: H04L 25/03318 Provision of soft decisions
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 43/12 Network monitoring probes
• CPC Class Codes: H04W 24/08 Testing, supervising or monitoring using real traffic

Abstract

In a time-reversal wireless system, a transceiver receives a combined signal that includes signals from a plurality of devices, each device sending a signal to the transceiver through multiple wireless propagation paths. Signals sent from each of the devices are estimated based on the combined signal and a signature waveform associated with the device. Interference associated with the estimated signal from each of the devices is determined based on the estimated signals from the devices. The signal sent from each of the devices is determined by subtracting the interference associated with the estimated signal associated with the device from the estimated signal associated with the device.

Claims

1. A method comprising:

at a transceiver of a base station,

receiving a first probe signal from a first terminal device,

determining a first location-specific signature waveform associated with a location of the first terminal device based on the first probe signal,

receiving a second probe signal from a second terminal device,

determining a second location-specific signature waveform associated with a location of the second terminal device based on the second probe signal, and

receiving a combined uplink signal that includes a first uplink signal from the first terminal device and a second uplink signal from the second terminal device, the first uplink signal sent from the first terminal device to the transceiver of the base station through first multiple wireless propagation paths, the second uplink signal sent from the second terminal device to the transceiver of the base station through second multiple wireless propagation paths, the first uplink signal including a plurality of symbols sent from the first terminal device, the second uplink signal including a plurality of symbols sent from the second terminal device;

generating a first set of estimated symbols based on the received combined uplink signal and the first location-specific signature waveform associated with the first terminal device, in which the first location-specific signature waveform is determined based on the first probe signal sent from the first device, the first set of estimated symbols representing a rough estimate of the symbols sent from the first device;

generating a second set of estimated symbols based on the received combined uplink signal and the second location-specific signature waveform associated with the second device, in which the second location-specific signature waveform is determined based on the second probe signal sent from the second device, the second set of estimated symbols representing a rough estimate of the symbols sent from the second device;

determining interference based on at least one of the first set of estimated symbols or the second set of estimated symbols; and

generating a refined first set of estimated symbols by canceling the interference from the first set of estimated symbols, the refined first set of estimated symbols representing a refined estimate of the symbols sent from the first device.

2. The method of claim 1 in which the interference comprises inter-user interference, and determining interference comprises determining inter-user interference based on the second set of estimated symbols.

3. The method of claim 2 in which generating a refined first set of estimated symbols comprises canceling the inter-user interference due to the second device from the first set of estimated symbols.

4. The method of claim 2 in which the interference also comprises inter-symbol interference, and determining interference comprises determining inter-symbol interference based on the first set of estimated symbols.

5. The method of claim 4 in which generating a refined first set of estimated symbols comprises canceling the inter-user interference and the inter-symbol interference from the first set of estimated symbols.

6. The method of claim 1 in which the interference comprises inter-symbol interference, and determining interference comprises determining inter-symbol interference based on the first set of estimated symbols.

7. The method of claim 6 in which generating a refined first set of estimated symbols comprises canceling the inter-symbol interference from the first set of estimated symbols.

8. The method of claim 1 in which determining interference and generating a refined first set of estimated symbols are part of a first stage interference cancelation operation, and the method further comprises performing a second stage interference cancelation operation that includes:

determining refined interference values based on the first set of estimated symbols, the second set of estimated symbols, and the symbols sent by the first device as determined by the first stage interference cancelation operation, and

generating a further refined first set of estimated symbols by canceling the refined interference values from the first set of estimated symbols, the further refined first set of estimated symbols representing a further refined estimate of the symbols sent from the first device.

9. The method of claim 1, comprising performing a hand-shaking process between the transceiver and the first device to identify multipath channel characteristics associated with the first device, and calculating the first location-specific signature waveform for the first device based on the multipath channel characteristics associated with the first device.

10. The method of claim 1 in which generating a first set of estimated symbols comprises performing a convolution operation, or an operation equivalent to the convolution operation, between the combined signal and the first location-specific signature waveform.

11. The method of claim 1, comprising transmitting, from the transceiver to the first device and the second device, a combined downlink signal derived from a combination of a first downlink waveform and a second downlink waveform, the first downlink waveform including data intended for the first device, the second downlink waveform including data intended for the second device.

12. The method of claim 11, comprising generating the first downlink waveform based on the data intended for the first device and the location-specific signature waveform for the first device.

13. The method of claim 12 in which generating the first downlink waveform comprises performing a convolution of the data intended for the first device and the location-specific signature waveform for the first device.

14. The method of claim 11 in which the combined downlink signal is configured to enable each of the first device and the second device to receive multipath signals that can be used determine a data signal intended for the device, the first and second devices receiving the downlink signal through different propagation paths and determining different data signals.

15. The method of claim 1 in which the transceiver is part of a base station.

16. The method of claim 1 in which receiving the combined signal comprises receiving a combined signal that include signals from three or more devices communicating with the transceiver, each of the devices being associated with a corresponding location-specific signature waveform.

17. The method of claim 16 in which determining interference comprises, for each of the devices, determining inter-user interference due to each of the other devices, and the method comprises canceling the inter-user interferences due to the other devices from the estimated symbols for the each of the device.

18. The method of claim 1, comprising:

at the transceiver, receiving a second combined signal that includes a third signal from the first device and a fourth signal from the second device, and

generating a third set of estimated symbols based on the second combined signal and the first location-specific signature waveform.

19. The method of claim 1, comprising:

receiving a plurality of combined signals over time, each combined signal including signals from the first and second devices,

reusing the same first location-specific signature waveform to extract signals sent by the first device from the plurality of combined signals.

20. The method of claim 1, comprising generating the first location-specific signature waveform by time-reversing a channel response signal derived from a first probe signal sent from the first device.

21. A method comprising:

at a transceiver of a base station,

receiving a first probe signal from a first terminal device,

determining a first location-specific signature waveform associated with a location of the first terminal device based on the first probe signal,

receiving a second probe signal from a second terminal device,

determining a second location-specific signature waveform associated with a location of the second terminal device based on the second probe signal, and

receiving a combined uplink signal that includes a first uplink signal from the first terminal device and a second uplink signal from the second terminal device, the first uplink signal sent from the first terminal device to the transceiver of the base station through first multiple wireless propagation paths, the second uplink signal sent from the second terminal device to the transceiver of the base station through second multiple wireless propagation paths;

estimating the first uplink signal sent from the first terminal device to generate a first estimated uplink signal based on the received combined uplink signal and the first location- specific signature waveform associated with the first terminal device, in which the first location- specific signature waveform is determined based on the first probe signal sent from the first device;

estimating the second uplink signal sent from the second terminal device to generate a second estimated uplink signal based on the received combined uplink signal and the second location-specific signature waveform associated with the second terminal device, in which the second location-specific signature waveform is determined based on the second probe signal sent from the second device;

determining interference based on at least one of the first estimated uplink signal or the second estimated uplink signal; and

determining the signal sent from the first device by subtracting the interference from the first estimated signals.

22. The method of claim 21, comprising:

at the transceiver, receiving a second combined signal that includes a third signal from the first device and a fourth signal from the second device, and

estimating the third signal to generate a third set of estimated symbols based on the second combined signal and the first location-specific signature waveform.

23. The method of claim 21, comprising:

receiving a plurality of combined signals over time, each combined signal including signals from the first and second devices,

reusing the same first location-specific signature waveform to extract signals sent by the first device from the plurality of combined signals.

24. The method of claim 21, comprising generating the first location-specific signature waveform by time-reversing a channel response signal derived from a first probe signal sent from the first device.

25. A method comprising:

at a transceiver of a base station,

receiving a probe signal from each of a plurality of terminal devices,

for each terminal device, determining a location-specific signature waveform associated with a location of the terminal device based on the probe signal sent from the terminal device, and

receiving a combined uplink signal that includes signals from the plurality of terminal devices, each terminal device sending an uplink signal to the transceiver of the base station through multiple wireless propagation paths;

estimating uplink signals sent from each of the terminal devices based on the received combined uplink signal and a location-specific signature waveform associated with the terminal device, in which the location-specific signature waveform is determined based on the probe signal sent from the terminal device;

determining an interference associated with the estimated signal from each of the terminal devices based on the estimated uplink signals from the terminal devices; and

determining the uplink signal sent from each of the terminal devices by subtracting the interference associated with the estimated uplink signal associated with the terminal device from the estimated uplink signal associated with the terminal device.

26. The method of claim 25 in which the interference comprises inter-user interference, and determining interference associated with each of the devices comprises determining inter-user interference associated with each of the devices based on the signals sent from the other devices.

27. The method of claim 26 in which determining the signal sent from each of the devices comprises subtracting the inter-user interferences due to the other devices from the estimated signal associated with the device.

28. The method of claim 26 in which the interference also comprises inter-signal interference, and determining interference comprises determining inter-signal interference associated with each of the devices based on the estimated signal associated with the device.

29. The method of claim 28 in which determining signal sent from each of the devices comprises subtracting the inter-user interference and the inter-signal interference associated with the device from the estimated signal associated with the device.

30. The method of claim 25 in which the interference comprises inter-signal interference, and determining interference comprises determining inter-signal interference for each of the devices based on the estimated signal associated with the device.

31. The method of claim 30 in which determining the signal sent from each of the devices comprises subtracting the inter-signal interference for the device from the estimated signal for the device.

32. The method of claim 25, comprising:

at the transceiver, receiving a second combined signal that includes a plurality of signals from the plurality of devices, and

estimating the signals sent from each of the devices based on the second combined signal and the location-specific signature waveform associated with the device.

33. The method of claim 25, comprising:

receiving a plurality of combined signals over time, each combined signal including signals from the plurality of devices,

reusing the same location-specific signature waveforms to extract signals sent by the respective devices from the plurality of combined signals.

34. The method of claim 25, comprising generating each of the location-specific signature waveforms by time-reversing a corresponding channel response signal derived from a corresponding probe signal sent from a corresponding device.

35. An apparatus, comprising:

a base station having an input circuit configured to

receive a probe signal from each of a plurality of terminal devices,

for each terminal device, determine a location-specific signature waveform associated with a location of the terminal device based on the probe signal sent from the terminal device, and

receive a combined uplink signal that includes uplink signals from the plurality of terminal devices, each uplink signal being sent from a corresponding terminal device to the base station through multiple wireless propagation paths;

a time-reversal mirror module configured to estimate uplink signals sent from each of the terminal devices based on the received combined uplink signal and a location-specific signature waveform associated with the terminal device, in which the location-specific signature waveform is determined based on the probe signal sent from the terminal device; and

an interference cancellation and decision module configured to;

determine an interference associated with the estimated uplink signal from each of the terminal devices based on the estimated uplink signals from the terminal devices; and

determine the uplink signal sent from each of the terminal devices by subtracting the interference associated with the estimated uplink signal associated with the terminal device from the estimated uplink signal associated with the terminal device.

36. The apparatus of claim 35 in which the apparatus comprises a base station that comprises the input circuit, the time-reversal mirror module, and the interference cancellation module.

37. The apparatus of claim 35 in which the interference comprises inter-user interference, and the interference cancellation and decision module is configured to determine inter-user interference associated with the estimated signal from each of the devices based on the estimated signals of the other devices.

38. The apparatus of claim 37 in which the interference cancellation and decision module is configured to determine the signal sent from each of the devices by subtracting the inter-user interferences due to the other devices from the estimated signal for the device.

39. The apparatus of claim 37 in which the interference also comprises inter-symbol interference, and the interference cancellation and decision module is configured to determine inter-symbol interference for each of the devices based on the estimated signal for the device.

40. The apparatus of claim 39 in which the interference cancellation and decision module is configured to determine the signal sent from each of the devices by subtracting the inter-user interference and the inter-symbol interference from the estimated signal associated with the device.

41. The apparatus of claim 35 in which the interference comprises inter-symbol interference, and the interference cancellation and decision module is configured to determine inter-symbol interference associated with the estimated signal for each of the devices based on the estimated signal associated with the device.

42. The apparatus of claim 41 in which the interference cancellation and decision module is configured to determine the signal sent from each of the devices by subtracting the inter-symbol interference associated with the estimated signal for the device from the estimated signal for the device.

43. The apparatus of claim 35, comprising a second interference cancellation and decision module configured to determine refined interference for each of the devices based on the signal sent from each of the devices as determined by the first interference cancellation and decision module and the estimated signal associated with each of the devices as determined by the time-reversal mirror module.

44. The apparatus of claim 43 in which the second interference cancellation and decision module is configured to determine refined signals for each of the devices by subtracting the refined interference for each of the devices from the estimated signal associated with the device as determined by the time-reversal mirror module.

45. The apparatus of claim 35 in which the time-reversal mirror module is configured to calculate the location-specific signature waveform for each of the devices based on characteristics of the multiple propagation paths associated with the device.

46. The apparatus of claim 35 in which the time-reversal mirror module is configured to estimate the signal sent from each of the devices by performing a convolution operation, or an operation equivalent to the convolution operation, between the combined signal and the location-specific signature waveform for the device.

47. The apparatus of claim 35, comprising a downlink module configured to determine a combined downlink signal derived from a combination of downlink waveforms each including data intended for one of the devices.

48. The apparatus of claim 47 in which the downlink module is configured to determine each of the downlink waveforms based on the data intended for the corresponding device and the location-specific signature waveform for the corresponding device.

49. The apparatus of claim 48 in which the downlink module is configured to determine the downlink waveform for each of the devices by performing a convolution, or an operation equivalent to the convolution, of the data intended for the device and the location-specific signature waveform for the device.

50. The apparatus of claim 47 in which the combined downlink signal is configured to enable each of the devices to receive multipath signals that can be used determine a data signal intended for the device, different devices receiving the downlink signal through different propagation paths and determining different data signals.

51. The apparatus of claim 35 in which the input circuit is configured to receive a second combined signal that includes signals from the plurality of devices, and

the time-reversal mirror module is configured to estimate signals sent from each of the devices based on the second combined signal and the location-specific signature waveform associated with the device.

52. The apparatus of claim 35 in which the input circuit is configured to receive a plurality of combined signals over time, each combined signal including signals from the plurality of devices, and

the time-reversal mirror module is configured to reuse the same location-specific signature waveforms to extract signals sent by the respective devices from the plurality of combined signals.

53. The apparatus of claim 35 in which the time-reversal mirror module is configured to generate each of the location-specific signature waveforms by time- reversing a corresponding channel response signal derived from a corresponding probe signal sent from a corresponding device.