Iterative two dimensional equalization of orthogonal time frequency space modulated signals

• US 10,673,659 B2
• Filed: 07/15/2019
• Issued: 06/02/2020
• Est. Priority Date: 04/01/2016
• Status: Active Grant

• Current Assignee: Cohere Technologies Inc
• Original Assignee: Cohere Technologies Inc
• Inventors: Hadani, Ronny, Kons, Shachar
• Primary Examiner(s): Puente, Eva Y
• Application Number:
  US16/512,055
• Publication Number:
  US 20190342126A1
• Time in Patent Office: 323 Days
• Field of Search: 375346, 375235, 370329
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0054 Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
• CPC Class Codes: H04L 25/00 Baseband systems
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0212 of impulse response
• CPC Class Codes: H04L 25/03012 operating in the time domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 25/03159 operating in the frequency domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 25/03178 Arrangements involving sequence estimation techniques
• CPC Class Codes: H04L 25/03286 with channel-decoding circuitry
• CPC Class Codes: H04L 25/03318 Provision of soft decisions
• CPC Class Codes: H04L 25/08 Modifications for reducing interference; Modifications for reducing effects due to line faults ; Receiver end arrangements for detecting or overcoming line faults
• CPC Class Codes: H04L 27/2639 Modulators using other transforms, e.g. discrete cosine transforms, Orthogonal Time Frequency and Space [OTFS] or hermetic transforms
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04W 72/30 Resource management for broadcast services

Abstract

An iterative two dimension equalizer usable in a receiver of orthogonal time frequency space (OTFS) modulated signals is described. In one configuration of the equalizer, a forward path generates, from received time-frequency domain samples and a channel estimate, estimates of data bits and likelihood numbers associated with the estimates of data bits, generated by delay-Doppler domain processing. In the feedback direction, the estimates of data bits are used to generate symbol estimates and autocorrelation matrix estimate in the time domain. In another configuration, a soft symbol mapper is used in the feedback direction for directly generating the feedback input symbol estimate without having to generate estimates of data bits.

Claims

1. A wireless communication method for recovering information bits from a received signal, by performing iterative equalization, comprising:

receiving, at an iterative equalizer, iteration inputs including a two-dimensional estimate of a wireless channel over which the received signal is received, a stream of received symbols, and at least one symbol estimate from a previous iteration;

performing, based on the iteration inputs, an affine minimum mean-squared error (MMSE) equalization operation on the stream of received symbols to generate a first stream of estimated symbols;

transforming, using a two-dimensional symplectic Fourier transform, the first stream of estimated symbols from a two-dimensional time-frequency grid to a second stream of estimated symbols in a two-dimensional delay-Doppler grid; and

generating, based on the second stream of estimated symbols in the two-dimensional delay-Doppler grid, estimates of the information bits.

2. The method of claim 1, wherein the iteration inputs further include an input autocorrelation matrix estimate from the previous iteration.

3. The method of claim 1, further comprising:

generating a plurality of likelihoods for the second stream of estimated symbols.

4. The method of claim 3, wherein the plurality of likelihoods is based on a variance of an estimation error for the second stream of estimated symbols.

5. The method of claim 3, wherein generating the estimates of the information bits comprises:

deinterleaving the plurality of likelihoods; and

performing a forward error correction (FEC) operation on an output of the deinterleaving.

6. The method of claim 5, wherein the FEC operation is based on a convolutional code, a turbo code or a low-density parity-check (LDPC) code.

7. The method of claim 1, wherein the two-dimensional symplectic Fourier transform is a symplectic fast Fourier transform (SFFT).

8. A wireless transceiver apparatus comprising a processor, transmission and reception circuitry and a memory, the apparatus configured to perform a method for recovering information bits from a received signal, the method comprising:

receiving, at an iterative equalizer, iteration inputs including a two-dimensional estimate of a wireless channel over which the received signal is received, a stream of received symbols, and at least one symbol estimate from a previous iteration;

performing, based on the iteration inputs, an affine minimum mean-squared error (MMSE) equalization operation on the stream of received symbols to generate a first stream of estimated symbols;

transforming, using a two-dimensional symplectic Fourier transform, the first stream of estimated symbols from a two-dimensional time-frequency grid to a second stream of estimated symbols in a two-dimensional delay-Doppler grid; and

generating, based on the second stream of estimated symbols in the two-dimensional delay-Doppler grid, estimates of the information bits.

9. The apparatus of claim 8, wherein the iteration inputs further include an input autocorrelation matrix estimate from the previous iteration.

10. The apparatus of claim 8, further comprising:

generating a plurality of likelihoods for the second stream of estimated symbols.

11. The apparatus of claim 10, wherein the plurality of likelihoods is based on a variance of an estimation error for the second stream of estimated symbols.

12. The apparatus of claim 10, wherein generating the estimates of the information bits comprises:

deinterleaving the plurality of likelihoods; and

performing a forward error correction (FEC) operation on an output of the deinterleaving, wherein the FEC operation is based on a convolutional code, a turbo code or a low-density parity-check (LDPC) code.

13. The apparatus of claim 8, wherein the two-dimensional symplectic Fourier transform is a symplectic fast Fourier transform (SFFT).

14. The apparatus of claim 8, wherein a number of iterations performed by the iterative equalizer is based on a total number of iterations, a time budget for recovering the information bits from the received signal, or a comparison of an improvement in successive iterations to a threshold.

15. A non-transitory computer readable storage medium having instructions stored thereupon, the instructions, when executed by a processor, causing the processor to implement a method for recovering information bits from a received signal by performing iterative equalization, comprising:

instructions for receiving, at an iterative equalizer, iteration inputs including a two-dimensional estimate of a wireless channel over which the received signal is received, a stream of received symbols, and at least one symbol estimate from a previous iteration;

instructions for performing, based on the iteration inputs, an affine minimum mean-squared error (MMSE) equalization operation on the stream of received symbols to generate a first stream of estimated symbols;

instructions for transforming, using a two-dimensional symplectic Fourier transform, the first stream of estimated symbols from a two-dimensional time-frequency grid to a second stream of estimated symbols in a two-dimensional delay-Doppler grid; and

instructions for generating, based on the second stream of estimated symbols in the two-dimensional delay-Doppler grid, estimates of the information bits.

16. The non-transitory computer readable storage medium of claim 15, wherein the iteration inputs further include an input autocorrelation matrix estimate from the previous iteration.

17. The non-transitory computer readable storage medium of claim 15, further comprising:

generating a plurality of likelihoods for the second stream of estimated symbols.

18. The non-transitory computer readable storage medium of claim 17, wherein the plurality of likelihoods is based on a variance of an estimation error for the second stream of estimated symbols.

19. The non-transitory computer readable storage medium of claim 17, wherein generating the estimates of the information bits comprises:

deinterleaving the plurality of likelihoods; and

performing an forward error correction (FEC) operation on an output of the deinterleaving, wherein the FEC operation is based on a convolutional code, a turbo code or a low-density parity-check (LDPC) code.

20. The non-transitory computer readable storage medium of claim 15, wherein the two-dimensional symplectic Fourier transform is a symplectic fast Fourier transform (SFFT).