Interference erasure using soft decision weighting of the Viterbi decoder input in OFDM systems

• US 8,019,029 B1
• Filed: 04/03/2008
• Issued: 09/13/2011
• Est. Priority Date: 06/26/2007
• Status: Expired due to Fees

• Current Assignee: Microsemi Storage Solutions, Inc (Microchip Technology Incorporated)
• Original Assignee: PMC-Sierra Incorporated (Microchip Technology Incorporated)
• Inventors: Katic, Ognjen
• Primary Examiner(s): Corrielus; Jean B
• Application Number:
  US12/062,392
• Time in Patent Office: 1,258 Days
• Field of Search: 375/229, 375259-260, 375/267, 375/285, 375/316, 375/340, 375346-347, 375349-350, 370/203, 370/206, 370/210
• US Class Current: 375/346
• CPC Class Codes: H04L 1/0047 Decoding adapted to other signal detection operation in conjunction with sequence estimation or equalization H04L25/03286
• CPC Class Codes: H04L 1/0054 Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 25/03821 Inter-carrier interference cancellation [ICI]
• CPC Class Codes: H04L 25/03891 Spatial equalizers MIMO diversity systems H04B7/0413
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

Disclosed is a technique for mitigating the effect of an in-band interferer in Orthogonal Frequency Division Multiplexing (OFDM) wireless or wired networks that employ soft decision Viterbi decoder in the physical layer. The technique uses an independent estimation of the signal quality, which is passed to the Viterbi algorithm decoder so that it is able to discard the corrupted subcarriers. This improves the error correction capability of the Viterbi algorithm decoder in a receiver, which leads to fewer retransmissions and into higher information throughput.

Claims

1. An apparatus for receiving an orthogonal frequency division multiplexing (OFDM) signal, the apparatus comprising:

a Fourier transform processor configured to receive the OFDM signal and to generate a transformed output;

a monitor and control circuit configured to detect when one or more subcarriers of the OFDM signal is obstructed by interference, and to generate a control signal based on such identification;

an interferer removal circuit configured to receive the transformed output and to attenuate one or more subcarriers of the transformed output when activated by the control signal from the monitor and control circuit to generate a modified transformed output; and

an equalizer configured to generate weights for decoding of a forward error correction code, wherein the equalizer is configured to receive the modified transformed output from the interferer removal circuit;

wherein the interferer removal circuit is disposed in a signal path between the Fourier transform processor and the equalizer;

wherein the interferer removal circuit is configured to cause the weights corresponding to the one or more obstructed subcarriers to be modified such that the weights are decreased when interference is detected.

2. The apparatus of claim 1, wherein the monitor and control circuit is operatively coupled to the equalizer to identify the one or more subcarriers for which interference is detected, and wherein the equalizer is configured to modify the generated weights for the identified one or more subcarriers.

3. The apparatus of claim 1, wherein the apparatus is embodied in a wireless receiver for a multiple-input-multiple-output (MIMO) system, further comprising:

a plurality of processing paths configured to process respective spatial streams of subcarriers, wherein a first processing path of the plurality of processing paths comprises the Fourier transform processor, the monitor and control circuit, and the interferer removal circuit, wherein each processing path of one or more remaining ones of the plurality of processing paths comprises the same configuration as the first processing path, wherein the equalizer is operatively coupled to outputs of each of the interferer removal circuits of each of the plurality of processing paths;

wherein respective ones of the monitor and control circuits and interferer removal circuits are configured to cause the weights for the one or more obstructed subcarriers to be reduced for respective ones of the plurality of processing paths.

4. The apparatus of claim 1, wherein the monitor and control circuit is configured to detect when one or more subcarriers is obstructed by interference by detecting a presence of a signal during a time slot when no OFDM subcarrier signal should be present.

5. The apparatus of claim 4, wherein the monitor and control circuit is configured to monitor the transformed output of the Fourier transform processor.

6. The apparatus of claim 4, wherein the monitor and control circuit is configured to monitor an output of a receiver front-end.

7. The apparatus of claim 4, wherein the monitor and control circuit is coupled to a dedicated receiver front-end that is configured to detect interference.

8. The apparatus of claim 1, wherein the monitor and control circuit further comprises a baseband receiver configured to detect interferers.

9. The apparatus of claim 1, further comprising a Viterbi algorithm decoder configured to decode the forward error correction code, wherein the Viterbi algorithm decoder is further configured to feedback measures of subcarrier quality and reliability to the monitor and control circuit.

10. A method of receiving an orthogonal frequency division multiplexing (OFDM) signal, the method comprising:

generating, using a Fourier transform processor, a transformed output from the OFDM signal;

determining, using a monitor and control circuit, when one or more subcarriers of the OFDM signal is obstructed by interference, and generating a control signal based on such identification;

attenuating, using an interferer removal circuit, one or more subcarriers of the transformed output in response to the control signal from the monitor and control circuit to generate a modified transformed output;

receiving the modified transformed output in an equalizer;

generating, using the equalizer, weights for decoding of a forward error correction code such that weights associated with data of the one or more obstructed subcarriers are reduced based on the determination of interference;

wherein the interferer removal circuit is disposed in a signal path between the Fourier transform processor and the equalizer.

11. The method of claim 10, wherein the method is embodied in a wireless receiver for a multiple-input-multiple-output (MIMO) system, further comprising:

processing a plurality of spatial streams of subcarriers; and

reducing weights for the one or more obstructed subcarriers for each of the plurality of processing paths.

12. The method of claim 10, wherein determining when one or more subcarriers is obstructed by interference further comprises detecting a presence of a signal during a time slot when no OFDM subcarrier signal should be present.

13. The method of claim 10, further comprising a weighting circuit configured to apply the weights, wherein the weighting circuit is disposed in a signal path between an output of a soft decision demodulator and an input to a Viterbi algorithm decoder.

14. The method of claim 10, wherein determining further comprises using a baseband receiver of the monitor and control circuit to determine when one or more subcarriers of the OFDM signal is obstructed by interference.

15. The method of claim 10, further comprising decoding, using a Viterbi algorithm decoder, a forward error correction code, and feeding back measures of subcarrier quality and reliability from the Viterbi algorithm decoder to the monitor and control circuit.

16. The method of claim 10, further comprising applying the weights to a soft decision demodulator output prior to passing the output to a Viterbi algorithm decoder.

17. A method of receiving an orthogonal frequency division multiplexing (OFDM) signal, the method comprising:

generating, using a Fourier transform processor, a transformed output from the OFDM signal;

determining, using a monitor and control circuit, when one or more subcarriers of the OFDM signal is obstructed by interference, and generating a control signal based on such identification; and

attenuating, using an interferer removal circuit, one or more subcarriers of the transformed output in response to the control signal from the monitor and control circuit to generate a modified transformed output such that weights associated with data of the one or more obstructed subcarriers are reduced based on the determination of interference, wherein the interferer removal circuit is disposed in a signal path between the Fourier transform processor and an equalizer;

wherein the weights are reduced by modifying weights generated by the equalizer for the identified one or more subcarriers.

18. A method of receiving an orthogonal frequency division multiplexing (OFDM) signal, the method comprising:

generating, using a Fourier transform processor, a frequency domain output from the OFDM signal;

determining when one or more subcarriers of the OFDM signal is obstructed by interference by monitoring, using a monitor and control circuit, the frequency domain output of the Fourier transform processor and detecting a presence of a signal during a time slot when no OFDM subcarrier signal should be present, and generating a control signal based on such identification;

attenuating, using an interferer removal circuit, one or more subcarriers of the frequency domain output in response to the control signal from the monitor and control circuit to generate a modified frequency domain output; and

providing the modified frequency domain output as an input to an equalizer, which generates weights for decoding of a forward error correction code, such that weights associated with data of the one or more obstructed subcarriers are reduced based on the determination of interference;

wherein the interferer removal circuit is disposed in a signal path between the Fourier transform processor and the equalizer.

19. A method of receiving an orthogonal frequency division multiplexing (OFDM) signal, the method comprising:

generating, using a Fourier transform processor, a transformed output from the OFDM signal;

determining when one or more subcarriers of the OFDM signal is obstructed by interference by monitoring, using a monitor and control circuit, an output of a receiver front-end and detecting a presence of a signal during a time slot when no OFDM subcarrier signal should be present, and generating a control signal based on such identification;

attenuating, using an interferer removal circuit, one or more subcarriers of the transformed output in response to the control signal from the monitor and control circuit to generate a modified transformed output, wherein the interferer removal circuit is disposed in a signal path between the Fourier transform processor and an equalizer; and

providing the modified transformed output as an input to the equalizer, which generates weights for decoding of a forward error correction code, such that weights associated with data of the one or more obstructed subcarriers are reduced based on the determination of interference.

20. A method of receiving an orthogonal frequency division multiplexing (OFDM) signal, the method comprising:

generating, using a Fourier transform processor, a transformed output from the OFDM signal;

determining when one or more subcarriers of the OFDM signal is obstructed by interference by monitoring, using a monitor and control circuit, an output of a dedicated receiver front-end that is configured to detect interference and detecting a presence of a signal during a time slot when no OFDM subcarrier signal should be present;

attenuating, using an interferer removal circuit, one or more subcarriers of the transformed output in response to a control signal from the monitor and control circuit to generate a modified transformed output; and

providing the modified transformed output as an input to an equalizer, which generates weights for decoding of a forward error correction code, such that weights associated with data of the one or more obstructed subcarriers are reduced based on the determination of interference;

wherein the interferer removal circuit is disposed in a signal path between the Fourier transform processor and the equalizer.