Successive user data multipath interference cancellation

• US 6,580,771 B2
• Filed: 03/30/2001
• Issued: 06/17/2003
• Est. Priority Date: 03/30/2001
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Nokia Corporation
• Inventors: Kenney, Thomas J.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Kim, Kevin
• Application Number:
  US09/822,897
• Publication Number:
  US 20020172265A1
• Time in Patent Office: 809 Days
• Field of Search: 375/148, 375/144, 375/346, 375/347, 375/349, 455/296, 455/63, 455/278.1, 455/295, 455/303, 455/501
• US Class Current: 375/346
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/7113 Determination of path profile
• CPC Class Codes: H04B 1/712 Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop
• CPC Class Codes: H04B 7/0857 using maximum ratio combining techniques, e.g. signal-to- interference ratio [SIR], received signal strenght indication [RSS]
• CPC Class Codes: H04B 7/0897 using beamforming per multi-path, e.g. to cope with different directions of arrival [DOA] at different multi-paths
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 28/18 Negotiating wireless communication parameters

Abstract

A wireless receiver stores one or more frames of received data and, during an initial demodulation, resolves each individual path for the multipath channel and estimates (pilot) channel parameters in order to process the received traffic, then preferably decodes the processed traffic to produce an estimate of the transmitted data. The estimated data is re-encoded exactly as encoded by the transmitter, then scaled and time-shifted utilizing complex weights and timing estimates garnered during the initial demodulation process. For each resolvable path, all other paths are time-aligned to reproduce the interference detected in the original received signal, with the resulting information employed to cancel the interference from other paths. Once all paths have had interference from other paths canceled, the results are combined and again decoded, re-encoded and reprocessed iteratively until residual interference and/or decoding errors are eliminated.

Claims

1. For use in a wireless communications system, a portion of a receiver employed for successive user data multipath interference cancellation comprising:

a storage buffer capable of selectively storing samples from a wireless signal;

a plurality of demodulators each corresponding to one of a plurality of resolvable paths within a multipath channel in which said wireless signal is transmitted, each demodulator including a delay unit and a signal multiplier capable of being selectively employed to estimate interference from a corresponding resolvable path on a portion of said wireless signal transmitted along a selected path within said multipath channel;

a plurality of signal adders each capable of selectively subtracting said estimated interference on said wireless signal portion transmitted along said selected path from said wireless signal samples; and

a controller capable of selectively causing, for each selected path within said multipath channel, said plurality of demodulators and said plurality of signal adders to perform an interference cancellation processing cycle in which

said plurality of demodulators each estimate interference from said corresponding path on said wireless signal portion transmitted along said selected path, wherein each demodulators estimate complex gains and timing delays for interference from said corresponding path on said wireless signal transmitted along said selected path, and

said plurality of signal adders each subtract said estimated interference on said wireless signal portion transmitted along said selected path from said wireless signal samples,

each of said resolvable paths being selected in turn during said interference cancellation processing cycle until all resolvable paths have been selected,

said controller capable of selectively causing said plurality of demodulators and said plurality of signal adders to iteratively perform said interference cancellation processing cycle on all paths within the multipath channel.

2. The receiver as set forth in claim 1 wherein at least one of said demodulators resolves each individual path for said multipath channel and estimates channel parameters for said multipath channel to process said wireless signal during said initial demodulation.

4. The receiver as set forth in claim 1 wherein said controller causes said plurality of demodulators and said plurality of signal adders to perform a predetermined number of iterations of said interference cancellation processing cycle.

5. The receiver as set forth in claim 1 wherein said plurality of demodulators and said plurality of signal adders operate on unencoded symbols during said interference cancellation processing cycle.

3. For use in a wireless communications system, a portion of a receiver employed for successive user data multipath interference cancellation comprising:

a storage buffer capable of selectively storing samples from a wireless signal;

a plurality of demodulators each corresponding to one of a plurality of resolvable paths within a multipath channel in which said wireless signal is transmitted, each demodulator including a delay unit and a signal multiplier capable of being selectively employed to estimate interference from a corresponding resolvable path on a portion of said wireless signal transmitted along a selected path within said multipath channel;

a plurality of signal adders each capable of selectively subtracting said estimated interference on said wireless signal portion transmitted along said selected path from said wireless signal samples; and

a controller capable of selectively causing, for each selected path within said multipath channel, said plurality of demodulators and said plurality of signal adders to perform an interference cancellation processing cycle in which

said plurality of demodulators each estimate interference from said corresponding path on said wireless signal portion transmitted along said selected path, wherein each demodulator produces an estimate of symbols transmitted on said wireless signal based on complex gains and timing delays for interference from said corresponding path on said wireless signal transmitted along said selected path, and

said plurality of signal adders each subtract said estimated interference on said wireless signal portion transmitted along said selected path from said wireless signal samples,

each of said resolvable paths being selected in turn during said interference cancellation processing cycle until all resolvable paths have been selected,

said controller capable of selectively causing said plurality of demodulators and said plurality of signal adders to iteratively perform said interference cancellation processing cycle on all paths within the multipath channel.

6. For use in a wireless communications system, a method of successive user data multipath interference cancellation comprising the steps of:

(a) storing samples from a wireless signal in a storage buffer;

(b) estimating, within each of a plurality of demodulators each corresponding to one of a plurality of resolvable paths within a multipath channel in which the wireless signal is transmitted, interference from a corresponding resolvable path on a portion of the wireless signal transmitted along a selected path within the multipath channel and operating on encoded symbol;

(c) subtracting the estimated interference on the wireless signal portion transmitted along the selected path from the wireless signal samples;

(d) repeating steps (b) and (c) for all resolvable paths within the multipath channel to perform an interference cancellation processing cycle;

(e) iteratively performing interference cancellation processing cycles on the wireless signal samples to reduce multipath interference within the wireless signal samples asymptotically to zero; and

(f) estimating complex gains and timing delays for interference from each path on the wireless signal portion transmitted along a selected path.

7. The method as set forth in claim 6 further comprising:

resolving each individual path for the multipath channel; and

estimating channel parameters for the multipath channel to process the wireless signal during the initial demodulation.

9. The method as set forth in claim 6 further comprising:

performing a predetermined number of interference cancellation processing cycle.

10. The method as set forth in claim 6 wherein steps (b) and (c) further comprise:

operating on unencoded symbols.

8. For use in a wireless communications system, a method of successive user data multipath interference cancellation comprising the steps of:

(a) storing samples from a wireless signal in a storage buffer;

(b) estimating, within each of a plurality of demodulators each corresponding to one of a plurality of resolvable paths within a multipath channel in which the wireless signal is transmitted, interference from a corresponding resolvable path on a portion of the wireless signal transmitted along a selected path within the multipath channel;

(c) subtracting the estimated interference on the wireless signal portion transmitted along the selected path from the wireless signal samples;

(d) repeating steps (b) and (c) for all resolvable paths within the multipath channel to perform an interference cancellation processing cycle;

(e) iteratively performing interference cancellation processing cycles on the wireless signal samples to reduce multipath interference within the wireless signal samples asymptotically to zero; and

(f) producing an estimate of symbols transmitted on the wireless signal based on complex gains and timing delays for interference train each path on the wireless signal portion transmitted along the selected path.

11. For use in a wireless communications system, a portion of a receiver employed for successive user data multipath interference cancellation comprising:

a storage buffer capable of selectively storing samples from a wireless signal;

a plurality of demodulators each corresponding to one of a plurality of resolvable paths within a multipath channel in which said wireless signal is transmitted, each demodulator including a delay unit and a signal multiplier capable of being selectively employed to estimate interference from a corresponding resolvable path on a portion of said wireless signal transmitted along a selected path within said multipath channel;

a plurality of signal adders each capable of selectively subtracting said estimated interference on said wireless signal portion transmitted along said selected path from said wireless signal samples;

a controller capable of selectively causing, for each selected path within said multipath channel, said plurality of demodulators and said plurality of signal adders to perform an interference cancellation processing cycle in which

said plurality of demodulators each estimate interference from said corresponding path on said wireless signal portion transmitted along said selected path, and

said plurality of signal adders each subtract said estimated interference on said wireless signal portion transmitted along said selected path from said wireless signal samples,

each of said resolvable paths being selected in turn during said interference cancellation processing cycle until all resolvable paths have been selected,

said controller capable of selectively causing said plurality of demodulators and said plurality of signal adders to iteratively perform said interference cancellation processing cycle on all paths within the multipath channel;

a unit combining outputs from all of said signal adders to produce a result for each interference cancellation processing cycle;

a decoder operating on said interference cancellation processing cycle result to generate an estimate of data transmitted by said wireless signal; and

a encoder operating on said estimate of data transmitted by said wireless signal to produce a re-encoded estimated signal in a same manner as an encoder employed by a transmitter transmitting said wireless signal, wherein said re-encoded estimated signal is employed by said plurality of demodulators in estimating interference from said corresponding path on said wireless signal transmitted along said selected path.

12. For use in a wireless communications system, a method of successive user data multipath interference cancellation comprising the steps of;

(a) storing samples from a wireless signal in a storage buffer;

(b) estimating, within each of a plurality of demodulators each corresponding to one of a plurality of resolvable paths within a multipath channel in which the wireless signal is transmitted, interference from a corresponding resolvable path on a portion of the wireless signal transmitted along a selected path within the multipath channel;

(c) subtracting the estimated interference on the wireless signal portion transmitted along the selected path from the wireless signal samples;

(d) repeating steps (b) and (c) for all resolvable paths within the multipath channel to perform an interference cancellation processing cycle;

(e) iteratively performing interference cancellation processing cycles on the wireless signal samples to reduce multipath interference within the wireless signal samples asymptotically to zero;

(f) combining outputs from all of the plurality of signal adders to produce a result for an interference cancellation processing cycle;

(g) decoding the interference cancellation processing cycle result to generate an estimate of data transmitted by said wireless signal; and

(h) encoding the estimate of data transmitted by the wireless signal in a same manner as an encoder employed by a transmitter transmitting the wireless signal to produce a re-encoded estimated signal, wherein the re-encoded estimated signal is employed in estimating interference from each path on a wireless signal portion transmitted along the selected path.