Iterative two dimensional equalization of orthogonal time frequency space modulated signals

• US 10,355,887 B2
• Filed: 10/01/2018
• Issued: 07/16/2019
• 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:
  US16/148,922
• Publication Number:
  US 20190036741A1
• Time in Patent Office: 288 Days
• Field of Search: 375235, 375346, 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 two dimensional 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, a symbol estimate from a previous iteration, and an input autocorrelation matrix estimate from the previous iteration, and

computing, from the iteration inputs, a Wiener estimate of the stream of received symbols;

transforming the Wiener estimate to symbol estimates in a two dimensional delay-Doppler grid using a two-dimensional symplectic Fourier transform;

estimating likelihoods of the symbol estimates in the two dimensional delay-Doppler grid; and

generating estimates of information bits from the likelihoods.

2. The method of claim 1, wherein the generating the estimates includes:

deinterleaving the likelihoods of the symbols; and

performing error correction on an output of the deinterleaving.

3. The method of claim 1, further including, processing in a feedback direction, by generating a symbol estimate and an input autocorrelation matrix estimate for a next iteration.

4. The method of claim 3, wherein the processing in the feedback direction includes:

performing soft symbol mapping using the likelihoods resulting in intermediate symbol estimates and an intermediate autocorrelation estimate; and

generating the symbol estimate and the input autocorrelation matrix estimate by transforming, using an inverse of the two-dimensional symplectic Fourier transform, the intermediate symbol estimates and the intermediate autocorrelation estimate.

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

6. The method of claim 1, wherein the computing the Wiener estimate comprises:

receiving information about erased time-frequency resource elements from the received signal; and

using prior symbol estimates from a feedback direction as outputs of the computing the Wiener estimates.

7. A wireless communication method for recovering information bits from a received signal, by performing iterative two dimensional 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, a symbol estimate from a previous iteration, an input autocorrelation matrix estimate from the previous iteration, and

computing, from the iteration inputs, a Wiener estimate of the stream of received symbols;

transforming the Wiener estimate to symbol estimates a two dimensional delay-Doppler grid using a two-dimensional symplectic Fourier transform; and

processing in a feedback direction, by generating a symbol estimate and an input autocorrelation matrix estimate for a next iteration.

8. The method of claim 7, further including:

estimating likelihoods of the symbol estimates in the two dimensional delay-Doppler grid and

generating estimates of data from the likelihoods.

9. The method of claim 7, wherein the generating the estimates includes

deinterleaving the likelihoods of the symbols;

and

performing error correction on an output of the deinterleaving.

10. The method of claim 9, wherein the processing in the feedback direction includes:

performing soft symbol mapping using the likelihoods resulting in intermediate symbol estimates and an intermediate autocorrelation estimate; and

generating the symbol estimate and the input autocorrelation matrix estimate by transforming, using an inverse of the two-dimensional symplectic Fourier transform, the intermediate symbol estimates and the intermediate autocorrelation estimate.

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

12. The method of claim 7, wherein the computing the Wiener estimates comprises:

receiving information about erased time-frequency resource elements from the received signal; and

using prior symbol estimates from a feedback direction as outputs of the computing the Wiener estimates.

13. 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, a symbol estimate from a previous iteration, and an input autocorrelation matrix estimate from the previous iteration, and

computing, from the iteration inputs, a Wiener estimate of the stream of received symbols;

transforming the Wiener estimate to symbol estimates in a two dimensional delay-Doppler grid using a two-dimensional symplectic Fourier transform;

estimating likelihoods of the symbol estimates in the two dimensional delay-Doppler grid; and

generating estimates of information bits from the likelihoods.

14. The apparatus of claim 13, further configured to:

deinterleave the likelihoods of the symbols; and

perform error correction on an output of the deinterleaving.

15. The apparatus of claim 13, further configured to process in a feedback direction, by generating a symbol estimate and an input autocorrelation matrix estimate for a next iteration.

16. The apparatus of claim 15, wherein the processing in the feedback direction includes:

performing soft symbol mapping using the likelihoods resulting in intermediate symbol estimates and an intermediate autocorrelation estimate; and

generating the symbol estimate and the input autocorrelation matrix estimate by transforming, using an inverse of the two-dimensional symplectic Fourier transform, the intermediate symbol estimates and the intermediate autocorrelation estimate.

17. The apparatus of claim 13, wherein the processing in the feedback direction includes:

performing soft symbol mapping using the likelihoods resulting in intermediate symbol estimates and an intermediate autocorrelation estimate; and

generating the symbol estimate and the input autocorrelation matrix estimate by transforming, using an inverse of the two-dimensional symplectic Fourier transform, the intermediate symbol estimates and the intermediate autocorrelation estimate.

19. The non-transitory computer readable storage medium of claim 17, wherein the method further includes:

estimating likelihoods of the symbol estimates in the two dimensional delay-Doppler grid and

generating estimates of data from the likelihoods.

20. The non-transitory computer readable storage medium of claim 19, wherein the generating the estimates includes

deinterleaving the likelihoods of the symbols;

and

performing error correction on an output of the deinterleaving.

18. A non-transitory computer readable storage medium having code stored thereupon, the code, when executed, causing a processor to implement a method recovering information bits from a received signal by performing iterative two dimensional 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, a symbol estimate from a previous iteration, an input autocorrelation matrix estimate from the previous iteration, and

computing, from the iteration inputs, a Wiener estimate of the stream of received symbols;

transforming the Wiener estimate to symbol estimates a two dimensional delay-Doppler grid using a two-dimensional symplectic Fourier transform; and

processing in a feedback direction, by generating a symbol estimate and an input autocorrelation matrix estimate for a next iteration.

21. The non-transitory computer readable storage medium of claim 18, wherein the processing in the feedback direction includes:

performing soft symbol mapping using the likelihoods resulting in intermediate symbol estimates and an intermediate autocorrelation estimate; and

generating the symbol estimate and the input autocorrelation matrix estimate by transforming, using an inverse of the two-dimensional symplectic Fourier transform, the intermediate symbol estimates and the intermediate autocorrelation estimate.

22. The non-transitory computer readable storage medium of claim 18, wherein the two-dimensional symplectic Fourier transform is a symplectic fast Fourier transform (SFFT).

23. The non-transitory computer readable storage medium of claim 18, wherein the computing the Wiener estimates comprises:

receiving information about erased time-frequency resource elements from the received signal; and

using prior symbol estimates from a feedback direction as outputs of the computing the Wiener estimates.