Interference cancellation for wireless communications

• US 8,611,305 B2
• Filed: 09/22/2009
• Issued: 12/17/2013
• Est. Priority Date: 08/22/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Black, Peter J., Lott, Christopher G., Attar, Rashid A., Jou, Yu-Cheun, Ma, Jun
• Primary Examiner(s): DOAN, PHUOC HUU
• Application Number:
  US12/564,607
• Publication Number:
  US 20100142479A1
• Time in Patent Office: 1,547 Days
• Field of Search: 455/442, 370/331, 370/335, 370/342, 375/346, 375/260, 375/267
• US Class Current: 370/331
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/71072 Successive interference cancellation
• CPC Class Codes: H04L 1/0048 in conjunction with detection of multiuser or interfering signals, e.g. iteration between CDMA or MIMO detector and FEC decoder for spatial equalizer H04L25/03286
• CPC Class Codes: H04L 1/0052 Realisations of complexity reduction techniques, e.g. pipelining or use of look-up tables
• CPC Class Codes: H04L 25/03006 Arrangements for removing intersymbol interference
• CPC Class Codes: H04W 36/00692 using simultaneous multiple data streams, e.g. cooperative multipoint [CoMP], carrier aggregation [CA] or multiple input multiple output [MIMO] allocation of physical resources in CoMP or in CA H04L5/0035
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 52/08 Closed loop power control
• CPC Class Codes: H04W 52/12 Outer and inner loops
• CPC Class Codes: H04W 52/362 Aspects of the step size
• CPC Class Codes: H04W 52/40 during macro-diversity or soft handoff
• CPC Class Codes: H04W 52/54 Signalisation aspects of the TPC commands, e.g. frame structure

Abstract

Techniques for improving the capacity of a wireless communications system using interference cancellation (IC). In an early decoding and IC aspect, a frame transmitted from a user to a base station may be decoded prior to the entire frame being received by the base station. The remaining portion of the frame may then be re-constructed at the base station prior to its reception, and cancelled from the receive signal to reduce the interference to frames received from other users. In a power control aspect for early decoding and IC, the power control target level at a local base station may be adjusted in response to successfully early decoding a frame, without affecting the overall outer loop power control operation. Further aspects include late decoding techniques for utilizing the IC of other users'"'"' signals to improve the probability of decoding a given user'"'"'s frames, as well as techniques for traffic channel demodulation using channel re-estimation.

Claims

1. A method for processing a composite signal, the composite signal comprising at least a first channel and a second channel overlapping in time with the first channel, the method comprising:

demodulating a first portion of the first channel;

decoding the first channel based on the demodulated first portion to generate decoded symbols;

if the decoding is successful, generating an expected receive signal for a second portion of the first channel transmitted after the first portion, the generating comprising re-encoding the decoded symbols;

cancelling the expected receive signal from the composite signal to generate a processed composite signal; and

decoding the second channel based on the processed composite signal.

2. The method of claim 1, the first and second users comprising access terminals, the composite signal being received at a base station according to the cdma2000 standard.

3. The method of claim 2, each frame comprising sixteen power control groups (PCG'"'"'s) transmitted in succession, the first portion of the first channel comprising less than sixteen PCG'"'"'s, the second portion of the first channel comprising the PCG'"'"'s of the first user'"'"'s frame not included in the first portion.

4. The method of claim 3, the decoding comprising:

attempting to decode the first user'"'"'s frame once every time a predetermined number of PCG'"'"'s is demodulated.

5. The method of claim 1, the first channel comprising a frame transmitted by a first user, the second channel comprising a frame transmitted by a second user, the first portion of the first channel comprising an initial portion of the first user'"'"'s frame, the second portion of the first channel comprising a second portion of the first user'"'"'s frame following the initial portion, the decoding the second channel comprising decoding the second user'"'"'s frame.

6. The method of claim 1, the decoding comprising:

periodically attempting to decode the first channel based on the portion of the first channel demodulated; and

checking a frame quality indicator after each attempt to determine a successful decode.

7. The method of claim 1, further comprising:

storing samples of the composite signal in a sample memory;

demodulating symbols corresponding to the first channel from the samples stored in the sample memory;

storing the demodulated symbols in a demodulated symbol buffer;

the decoding the first channel comprising attempting to decode the stored demodulated symbols corresponding to the first channel.

8. The method of claim 7, the cancelling the expected receive signal from the composite signal comprising subtracting the expected receive signal from the samples of the composite signal stored in the sample memory to generate the processed composite signal, the method further comprising storing the processed composite signal back in the sample memory.

9. The method of claim 8, further comprising demodulating symbols corresponding to the second channel from the samples stored in the sample memory, the decoding the second channel comprising attempting to decode the stored demodulated symbols corresponding to the second channel.

10. The method of claim 1, the generating the expected receive signal comprising:

encoding the decoded symbols;

interleaving the encoded symbols;

modulating the interleaved symbols; and

filtering the modulated symbols, the filtering comprising applying a gain corresponding to an estimate of the channel response of the first channel.

11. The method of claim 1, further comprising:

reducing a power control setpoint for the first channel from an initial setpoint after successfully decoding the first channel; and

returning the power control setpoint for the first channel to the initial setpoint after the second portion of the first channel.

12. The method of claim 11, the first channel transmitted by a first device, the returning the power control setpoint comprising increasing the power control setpoint at a rate no greater than a maximum slew rate of the first device.

13. The method of claim 12, the first device being an access terminal.

14. The method of claim 11, further comprising receiving an outer loop power control (OLPC) target level for the first channel from a controller, the initial setpoint determined as the OLPC target level, the reducing the power control setpoint comprising applying a negative power control offset to the OLPC target level.

15. The method of claim 1, further comprising demodulating a frame of the second channel, the decoding the second channel comprising decoding the frame of the second channel, the decoding the first channel comprising decoding the first channel after demodulating the entire frame of the second channel.

16. A method for processing a composite signal, the composite signal comprising at least a first channel and a second channel overlapping in time with the first channel, the method comprising:

demodulating a frame of the second channel;

decoding the first channel after the demodulating the frame of the second channel to generate decoded symbols;

if the decoding is successful, generating an expected receive signal for the first channel based on the decoded symbols;

cancelling the expected receive signal from the composite signal to generate a processed composite signal; and

decoding the frame of the second channel based on the processed composite signal.

17. The method of claim 16, the frame of the second channel having a nominal frame span, the demodulating the frame of the second channel comprising demodulating up to the termination of the nominal frame span, the second channel further having a virtual frame span longer than the nominal frame span, the termination of the virtual frame span being after the termination of the nominal frame span, the decoding the frame of the second channel comprising:

attempting to decode the frame of the second channel throughout the virtual frame span.

18. The method of claim 17, each frame comprising sixteen power control group'"'"'s (PCG'"'"'s), the attempting to decode the frame of the second channel throughout the virtual frame span comprising attempting to decode the frame once every predetermined number of PCG'"'"'s up to the end of the termination of the virtual frame span.

19. An apparatus for processing a composite signal, the composite signal comprising at least a first channel and a second channel overlapping at least in part with the first channel, the apparatus comprising:

a demodulator for demodulating a first portion of the first channel;

a decoder for decoding the first channel based on the demodulated first portion to generate decoded symbols;

an interference reconstruction block for, if first channel is successfully decoded, generating an expected receive signal for a second portion of the first channel transmitted after the first portion by re-encoding the decoded symbols; and

a cancellation block for cancelling the expected receive signal from the composite signal to generate a processed composite signal;

the decoder further configured to decode the second channel based on the processed composite signal.

20. The apparatus of claim 19, the first and second users comprising access terminals, the apparatus comprising a base station for receiving signals according to the cdma2000 standard.

21. The apparatus of claim 20, each frame comprising sixteen power control groups (PCG'"'"'s) transmitted in succession, the first portion of the first channel comprising less than sixteen PCG'"'"'s, the second portion of the first channel comprising the PCG'"'"'s of the first user'"'"'s frame not included in the first portion.

22. The apparatus of claim 20, the first channel comprising a frame transmitted by a first user, the second channel comprising a frame transmitted by a second user, the first portion of the first channel comprising an initial portion of the first user'"'"'s frame, the second portion of the first channel comprising a second portion of the first user'"'"'s frame following the initial portion, the decoder configured to decode the second channel by decoding the second user'"'"'s frame.

23. The apparatus of claim 22, the decoder configured to attempt to decode the first user'"'"'s frame at periodic intervals.

24. The apparatus of claim 19, the decoder configured to periodically attempt to decode the first channel based on the portion of the first channel demodulated;

and to check a frame quality indicator after each attempt to determine a successful decode.

25. The apparatus of claim 19, further comprising:

a sample memory storing samples of the composite signal;

a demodulator for demodulating symbols corresponding to the first channel from the samples stored in the sample memory; and

a demodulated symbol buffer storing the demodulated symbols, the decoder configured to attempt to decode the stored demodulated symbols corresponding to the first channel.

26. The apparatus of claim 25, the cancellation block configured to subtract the expected receive signal from the samples of the composite signal stored in the sample memory to generate the processed composite signal, the apparatus further configured to store the processed composite signal back in the sample memory.

27. The apparatus of claim 26, the demodulator further configured to demodulate symbols corresponding to the second channel from the samples stored in the sample memory, the decoder further configured to attempt to decode the stored demodulated symbols corresponding to the second channel.

28. The apparatus of claim 19, the interference reconstruction block comprising:

an encoder for encoding the decoded symbols;

an interleaver for interleaving the encoded symbols;

a modulator for modulating the interleaved symbols; and

a filter for filtering the modulated symbols and applying a gain corresponding to an estimate of the channel response of the first channel.

29. The apparatus of claim 19, further comprising:

a power control set-point calculation module configured to reduce a power control setpoint for the first channel from an initial setpoint after successfully decoding the first channel, and to return the power control setpoint for the first channel to the initial setpoint after the second portion of the first channel; and

a power control command generator for generating a power control command for the first user based on the power control setpoint.

30. The apparatus of claim 29, the first channel being transmitted by a first device, the power control set-point calculation module configured to return the power control setpoint by increasing the power control setpoint at a rate no greater than a maximum slew rate of the first device.

31. The apparatus of claim 30, the first device being an access terminal.

32. The apparatus of claim 29, the power control set-point calculation module further configured to receive an outer loop power control (OLPC) target level for the first channel from a controller, the initial setpoint determined as the OLPC target level, the power control set-point calculation module configured to the reduce the power control setpoint by applying a negative power control offset to the OLPC target level.

33. The apparatus of claim 19, the decoder further configured to decode the first channel after the demodulator further demodulates an entire frame of the second channel.

34. An apparatus for processing a composite signal, the composite signal comprising at least a first channel and a second channel overlapping in time with the first channel, the apparatus comprising:

a demodulator for demodulating an entire frame of the second channel;

a decoder for decoding the first channel to generate decoded symbols after the entire frame of the second channel is demodulated;

an interference reconstruction block for, if the first channel is successfully decoded, generating an expected receive signal for the first channel based on the decoded symbols;

a cancellation block for cancelling the expected receive signal from the composite signal to generate a processed composite signal, the decoder further configured to decode the frame of the second channel based on the processed composite signal.

35. The apparatus of claim 34, the frame of the second channel having a nominal frame span, the demodulator further configured to demodulate the frame of the second channel up to the termination of the nominal frame span, the second channel further having a virtual frame span longer than the nominal frame span, the termination of the virtual frame span being after the termination of the nominal frame span, the decoder further configured to decode the frame of the second channel by attempting to decode the frame of the second channel throughout the virtual frame span.

36. The apparatus of claim 35, each frame comprising sixteen power control group'"'"'s (PCG'"'"'s), the decoder further configured to attempt to decode the frame of the second channel once every predetermined number of PCG'"'"'s up to the end of the termination of the virtual frame span.

37. An apparatus for processing a composite signal, the composite signal comprising at least a first channel and a second channel overlapping in time with the first channel, the apparatus comprising:

means for demodulating a first portion of the first channel;

means for decoding the first channel based on a first portion of the first channel to generate decoded symbols;

means for generating an expected receive signal for a second portion of the first channel transmitted after the first portion;

means for cancelling the expected receive signal from the composite signal to generate a processed composite signal; and

means for decoding the second channel based on the processed composite signal.

38. An apparatus for processing a composite signal, the composite signal comprising at least a first channel and a second channel overlapping in time with the first channel, the apparatus comprising:

means for demodulating a frame of the second channel;

means for decoding the first channel after the receiving the frame of the second channel to generate decoded symbols;

means for, if the decoding is successful, generating an expected receive signal for the first channel based on the decoded symbols;

means for cancelling the expected receive signal from the composite signal to generate a processed composite signal; and

means for decoding the frame of the second channel based on the processed composite signal.

39. A computer program product for processing a composite signal, the composite signal comprising at least a first channel and a second channel overlapping in time with the first channel, the product comprising:

computer-readable medium comprising;

code for causing a computer to demodulate a first portion of the first channel;

code for causing a computer to decode the first channel based on the demodulated first portion to generate decoded symbols;

code for causing a computer to, if the decoding is successful, generate an expected receive signal for a second portion of the first channel transmitted after the first portion, the generating comprising re-encoding the decoded symbols;

code for causing a computer to cancel the expected receive signal from the composite signal to generate a processed composite signal; and

code for causing a computer to decode the second channel based on the processed composite signal.

40. A computer program product for processing a composite signal, the composite signal comprising at least a first channel and a second channel overlapping in time with the first channel, the product comprising:

computer-readable medium comprising;

code for causing a computer to demodulate a frame of the second channel;

code for causing a computer to decode the first channel after the demodulating the frame of the second channel to generate decoded symbols;

code for causing a computer to, if the decoding is successful, generate an expected receive signal for the first channel based on the decoded symbols;

code for causing a computer to cancel the expected receive signal from the composite signal to generate a processed composite signal; and

code for causing a computer to decode the frame of the second channel based on the processed composite signal.