Combined turbo decoding and turbo equalization techniques

• US 9,191,246 B2
• Filed: 03/06/2014
• Issued: 11/17/2015
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: Jonathan Kanter
• Original Assignee: Jonathan Kanter
• Inventors: Kanter, Jonathan
• Primary Examiner(s): SHAH, TANMAY K
• Application Number:
  US14/199,964
• Publication Number:
  US 20140269891A1
• Time in Patent Office: 621 Days
• Field of Search: 375/233
• US Class Current: 1/1
• CPC Class Codes: H03M 13/11 using multiple parity bits
• CPC Class Codes: H03M 13/23 using convolutional codes, e.g. unit memory codes
• CPC Class Codes: H03M 13/258 with turbo codes, e.g. Turbo Trellis Coded Modulation [TTCM]
• CPC Class Codes: H03M 13/2732 Convolutional interleaver; Interleavers using shift-registers or delay lines like, e.g. Ramsey type interleaver
• CPC Class Codes: H04B 1/12 Neutralising, balancing, or compensation arrangements
• CPC Class Codes: H04J 11/00 Orthogonal multiplex systems, e.g. using WALSH codesH04J13/00 takes precedence
• CPC Class Codes: H04L 25/03159 operating in the frequency domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 27/01 Equalisers baseband equalizers at the transmitter end H04L25/03343; in analogue transmission systems H04B3/04, H04B7/005
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/0046 Determination of how many bits are transmitted on different sub-channels
• CPC Class Codes: H04L 7/005 Correction by an elastic buffer

Abstract

Techniques are disclosed for turbo decoding orthogonal frequency division multiplexing OFDM symbols. Techniques for combined turbo decoding and equalization are disclosed. The disclosed techniques can be implemented in receivers that receive wired or wireless OFDM signals and produce data and control bits by decoding the received signals.

Claims

1. A method of performing combined turbo equalization and turbo decoding of a plurality of orthogonal frequency division multiplexing (OFDM) symbols in a communication receiver, at least partially implemented in hardware, the method comprising:

operating a first iterative loop to produce decision feedback equalized (DFE) symbols by;

receiving a new symbol in a buffer;

re-encoding, when available in the buffer, data from one or more previous symbols and cancelling inter-symbol interference;

de-mapping constellations of an output of the inter-symbol interference cancellation operation;

decoding a first or an inner component code; and

performing an interleaving or de-interleaving operation; and

operating a second iterative loop on the DFE symbols to produce decoded bits by decoding, until a last iteration is reached, the first or the inner component code; and

decoding, until the last iteration is reached a second or an outer component code of the DFE symbols and an input from the decoding of the first or the inner component code; and

producing, upon reaching the last iteration, decoded bits.

2. The method of claim 1, further comprising:

buffering with reliability information a number of the plurality of OFDM symbols, wherein the number is greater than or equal to an interleaving within a concatenated code or size of an low density parity check (LDPC) code used to error code the received plurality of OFDM symbols.

3. The method of claim 2, wherein the buffering comprises time domain buffering.

4. The method of claim 2, wherein the buffering comprises frequency domain buffering.

5. The method of claim 1, further including:

operating the decision feedback equalizer to receive hard or soft data from three different classes of data.

6. The method of claim 5, wherein the three different classes of data include a first class of data comprising &

mapped data, a second class of data comprising a re-encoded synchronization symbol or re-encoded first or inner output of a turbo decoder, and a third class of data comprising re-encoded output of an outer decoder of turbo decoding.

7. The method of claim 1, further including:

turbo decoding the plurality of signal constellations, wherein a first number of least significant bits of constellations are both block coded and trellis coded, and a second number of most significant bits block coded only.

8. The method of claim 1, further comprising:

generating replicas of the received plurality of OFDM symbols for decision feedback equalization.

9. The method of claim 1, further including:

operating a peak to average ratio reducer to generate replicas of the plurality of OFDM symbols which have had their peak to average ratio reduced.

10. The method of claim 1, further including:

filtering replicas of the received plurality of OFDM symbols by a replica of a receive channel, wherein the filtering may be by a direct convolution or by a fast convolution using a fast Fourier transform (FFT) and an inverse FFT (IFFT).

11. The method of claim 1, further including:

subtracting, from the received plurality of OFDM symbols, corresponding replicas of intersymbol interference, and corresponding replicas of echo.

12. The method of claim 1, further comprising:

storing, when the new symbol is not the last symbol in the buffer, the new symbol in the buffer as a next symbol.

13. The method of claim 1, further comprising:

performing decoding of the first or inner component code when the last decoding iteration is not reached.

14. A communication receiver apparatus, comprising:

a memory storing instructions; and

a processor that reads the instructions from the memory and causes the communication receiver to perform combined turbo equalization and turbo decoding of a plurality of orthogonal frequency division multiplexing (OFDM) symbols by;

operating a first iterative loop to produce decision feedback equalized (DFE) symbols by;

receiving a new symbol in a buffer;

re-encoding, when available in the buffer, data from one or more previous symbol and cancelling inter-symbol interference;

de-mapping constellation of an output of the inter-symbol interference cancellation operation;

decoding a first or an inner component code; and

performing an interleaving or de-interleaving operation; and

operating a second iterative loop on the DFE symbols to produce decoded bits by decoding, until a last iteration is reached, the first or the inner component code; and

decoding, until the last iteration is reached a second or an outer component code of the DFE symbols and an input from the decoding of the first or the inner component code; and

producing, upon reaching the last iteration, decoded bits.

15. The communication receiver apparatus of claim 14 wherein the processor further performs:

buffering with reliability information a number of the plurality of OFDM symbols, wherein the number is greater than or equal to an interleaving within a concatenated code or size of an low density parity (LDPC) code used to error code the received plurality of OFDM symbols.

16. The communication receiver apparatus of claim 15, Wherein the buffering comprises time domain buffering.

17. The communication receiver apparatus of claim 15, wherein the buffering comprises frequency domain buffering.

18. The communication receiver apparatus of claim 14, wherein the processor further performs:

operating the decision feedback equalizer to receive hard or soft data from three different classes of data.

19. The communication receiver apparatus of claim 18, wherein the three different classes of data include a first class of data comprising demapped data, a second class of data comprising a re-encoded synchronization symbol or re-encoded first or inner output of a turbo decoder, and a third class of data comprising re-encoded output of an outer decoder of turbo decoding.

20. The communication receiver apparatus of claim 14, wherein the processor further performs:

turbo decoding the plurality of signal constellations, wherein a first number of least significant bits of constellations are both block coded and trellis coded, and a second number of most significant bits block coded only.

21. The communication receiver apparatus of claim 14, wherein the processor further performs:

generating replicas of the received plurality of OFDM symbols for decision feedback equalization.

22. The communication receiver apparatus of claim 14, wherein the processor further performs:

operating a peak to average ratio reducer to generate replicas of the plurality of OFDM symbols which have had their peak to average ratio reduced.

23. The communication receiver apparatus of claim 14, wherein the processor further performs:

filtering replicas of the received plurality of OFDM symbols by a replica of a receive channel, wherein the filtering may be by a direct convolution or by a fast convolution using a fast Fourier transform (FFT) and an inverse FFT (IFFT).

24. The communication receiver apparatus of claim 14, wherein the processor further performs:

subtracting, from the received plurality of OFDM symbols, corresponding replicas of intersymbol interference, and corresponding replicas of echo.