Receiver for differentially modulated multicarrier signals

• US 8,275,055 B2
• Filed: 11/19/2008
• Issued: 09/25/2012
• Est. Priority Date: 11/20/2007
• Status: Expired due to Fees

• Current Assignee: Her Majesty The Queen In Right Of Canada, As Represented By The Minister Of Industry, Through The Communications Research Centre Canada
• Original Assignee: Her Majesty The Queen In Right Of Canada, As Represented By The Minister Of Industry, Through The Communications Research Centre Canada
• Inventors: Zhang, Liang, Thibault, Louis
• Primary Examiner(s): Burd, Kevin M
• Application Number:
  US12/274,037
• Publication Number:
  US 20090129493A1
• Time in Patent Office: 1,406 Days
• Field of Search: 375/259, 375/260, 375/229, 375/232, 375/233, 375/316, 375/346
• US Class Current: 375/260
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 25/0236 using estimation of the other symbols
• CPC Class Codes: H04L 25/03159 operating in the frequency domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

The invention relates to receivers and methods for receiving multi-carrier differentially modulated signals utilizing iterative decision-directed differential detection. The receiver includes a decision feedback loop including a channel estimator for estimating inter-symbol channel variations, and a differential equalizer for correcting channel-induced errors in a differentially detected signal based on the estimated inter-symbol channel variations.

Claims

1. A receiver for receiving a differentially modulated multicarrier (DMM) signal from a communication channel, the DMM signal comprising a plurality of modulated subcarriers, the receiver comprising:

a channel estimator for estimating an inter-symbol channel variation characteristic (ISCVC) based on the received DMM signal and a differentially decoded signal obtained from the received DMM signal;

a first smoothing filter for smoothing the inter-symbol channel variation characteristic in frequency or time and for producing a filtered ISCVC; and

,

an equalizing differential detector (EDD) for generating the differentially decoded signal from the received DMM signal based on the filtered ISCVC so as to correct for channel-induced distortions of the received DMM signal.

2. A receiver of claim 1, wherein the channel estimator comprises:

a channel gain estimator (CGE) for generating a channel gain estimate of the communication channel based on the received DMM signal and the differentially decoded signal; and

,

an inter-symbol channel variation estimator (ISCVE) for estimating the ISCVC from the subcarrier gain estimates.

3. A receiver of claim 1, wherein the DMM signal comprises an OFDM signal.

4. A receiver of claim 1, wherein the channel estimator includes the first smoothing filter.

5. A receiver for receiving a differentially modulated multicarrier (DMM) signal from a communication channel, the DMM signal comprising a plurality of modulated subcarriers, the receiver comprising:

a channel estimator for estimating an inter-symbol channel variation characteristic (ISCVC) based on the received DMM signal and a differentially decoded signal obtained from the received DMM signal, wherein the channel estimator comprises;

a channel gain estimator (CGE) for generating a channel gain estimate of the communication channel based on the received DMM signal and the differentially decoded signal; and

,

an inter-symbol channel variation estimator (ISCVE) for estimating the ISCVC from the subcarrier gain estimates;

a first smoothing filter for smoothing the inter-symbol channel variation characteristic in frequency or time and for producing a filtered ISCVC; and

,

an equalizing differential detector (EDD) for generating the differentially decoded signal from the received DMM signal based on the filtered ISCVC so as to correct for channel-induced distortions of the received DMM signal;

wherein the channel estimator further includes a second smoothing filter operatively connected between the CGE and the ISCVE for;

smoothing the channel gain estimate in time if the first smoothing filter is for smoothing the differential channel characteristic in frequency, or

smoothing the channel gain estimate in frequency if the first smoothing filter is for smoothing the differential channel characteristic in time.

6. A receiver of claim 5 further comprising a differential encoder operatively connected to an output of the EDD for producing a re-generated DMM signal based on the differentially decoded signal, wherein the channel estimator is operatively connected to the differential encoder so as to form a decision feedback loop for iteratively correcting channel-induced distortions in the differentially decoded signal.

7. A receiver of claim 6 wherein the decision feedback loop further comprises:

an error correction decoder (ECD) operatively connected in series with the EDD for performing error correction in the differentially decoded signal; and

,

an error correction encoder (ECE) complimentary to the ECD and operatively connected between the ECD and the differential encoder for encoding the differentially decoded signal with an error correction code.

8. A receiver of claim 6 wherein the channel gain estimator is coupled to the differential encoder for generating subcarrier channel gain estimates based on the received DMM signal and the re-generated DMM signal.

9. A receiver of claim 5, wherein the channel estimator is for estimating a plurality of subcarrier ISCVC values representing an inter-symbol channel phase variation, an inter-symbol channel amplitude variation, or an inter-symbol channel gain variation for each of the modulated subcarriers.

10. A receiver of claim 9, wherein the DMM signal is modulated differentially in time, and wherein the first smoothing filter is a frequency-domain filter for smoothing the ISCVC in frequency by reducing noise-induced variations between subcarrier ISCVC values of adjacent subcarriers.

11. A receiver of claim 10, wherein the second smoothing filter comprises one of:

a time-domain Wiener filter, a time domain DFT/IDFT based smoothing filter, a time-domain MMSE estimator, or a time-domain weighted-averaging windowing filter.

12. A receiver of claim 10, wherein the first smoothing filter is a frequency-domain filter for smoothing variations between the ISCVC values of adjacent subcarriers based on at least one of:

a channel delay spread estimation,

a frequency-domain correlation between subcarrier channel gain variation values, and

a known guard interval length.

13. A receiver of claim 10, wherein the first smoothing filter utilizes one of:

DFT/IDFT-based filter, a Wiener filter, a weighted-averaging windowing function, an MMSE estimator, or a SVD-based estimator.

14. A receiver of claim 13, wherein the DFT/IDFT-based filter utilizes one of:

a DFT processor followed by a windowing module followed by an IDFT processor or an IDFT processor followed by a windowing module followed by a DFT processor.

15. A receiver of claim 5, wherein the DMM signal is modulated differentially in frequency, the second smoothing filter is for smoothing the channel gain estimate in frequency, and the first smoothing filter is for smoothing the differential channel characteristic in time.

16. In a wireless receiver, a method of decoding a differentially modulated multicarrier (DMM) signal comprising a plurality of modulated subcarriers, the method comprising:

a) receiving the differentially modulated multicarrier (DMM) signal from a communication channel;

b) storing the DMM signal in a computer-usable buffer memory;

c) obtaining a decoded signal corresponding to the received DMM signal using a differential decoder;

d) estimating channel gain values for the plurality of subcarriers based on the stored DMM signal and the decoded signal;

e) estimating an inter-symbol channel variation characteristic (ISCVC) from the channel gain values;

f) applying a smoothing filter for smoothing the ISCVC in frequency or time to obtain a filtered ISCVC; and

,

g) updating the decoded signal using the filtered ISCVC so as to at least partially correct for channel-induced distortions thereof.

17. A method of claim 16, wherein steps (d)-(g) are performed iteratively.

18. A method of claim 16, wherein step (f) includes performing DFT/IDFT processing or FFT/IFFT processing of the ISCVC.

19. A method of claim 16, further comprising estimating a time delay spread of the channel for determining a size of a DFT window utilized in step (f).

20. A method of claim 16, wherein the DMM signal is modulated differentially in time domain with respect to consecutive data symbols in each subcarrier, and wherein:

step (e) comprises estimating at least one of;

channel phase variations and channel amplitude variations in the time domain for consecutive symbols in each of the subcarriers; and

,

the smoothing filter in step (f) is applied in the frequency domain with respect to coincidental symbols in adjacent subcarriers.

21. A method of claim 16, wherein the DMM signal is differentially modulated in frequency domain with respect to adjacent subcarriers, and wherein:

step (e) comprises estimating at least one of;

channel phase variations and channel amplitude variations in the frequency domain between coincidental symbols of adjacent subcarriers; and

,

the smoothing filter in step (f) is applied in the time domain with respect to consecutive symbols in each of the subcarriers.

22. A method of claim 16 wherein step (g) comprises performing multiple-symbol differential detection.

23. A method of claim 16, wherein the DMM signal comprises audio or video data, further comprising:

extracting the audio or video data from the decoded signal, and

using the extracted data to produce an image displayed on a screen or a sound played by an audio device.