Orthogonal time frequency space modulation over a plurality of narrow band subcarriers

• US 10,693,581 B2
• Filed: 07/12/2016
• Issued: 06/23/2020
• Est. Priority Date: 07/12/2015
• Status: Active Grant

• Current Assignee: Cohere Technologies Inc
• Original Assignee: Cohere Technologies Inc
• Inventors: Rakib, Shlomo Selim, Hadani, Ronny
• Primary Examiner(s): Lai, Andrew
• Assistant Examiner(s): Ganguly, Sumitra
• Application Number:
  US15/743,646
• Publication Number:
  US 20180205481A1
• Time in Patent Office: 1,442 Days
• CPC Class Codes: H04J 11/00 Orthogonal multiplex systems, e.g. using WALSH codesH04J13/00 takes precedence
• CPC Class Codes: H04J 11/0026 of multi-user interference
• CPC Class Codes: H04J 2011/0003 Combination with other multiplexing techniques
• CPC Class Codes: H04L 23/02 adapted for orthogonal signalling
• 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 27/2697 in combination with other modulation techniques
• CPC Class Codes: H04L 5/0016 Time-frequency-code

Abstract

An Orthogonal Time Frequency Space Modulation (OTFS) modulation scheme that maps data symbols, along with optional pilot symbols, using a symplectic-like transformation such as a 2D Fourier transform and optional scrambling operation, into a complex wave aggregate and be backward compatible with legacy OFDM systems, is described. This wave aggregate may be processed for transmission by selecting portions of the aggregate according to various time and frequency intervals. The output from this process can be used to modulate transmitted waveforms according to various time intervals over a plurality of narrow-band subcarriers, often by using mutually orthogonal subcarrier “tones” or carrier frequencies. The entire wave aggregate may be transmitted over various time intervals. At the receiver, an inverse of this process can be used to both characterize the data channel and to correct the received signals for channel distortions, thus receiving a clear form of the original data symbols.

Claims

1. A method of transmitting, on a per-frame basis, a plurality of data symbols over an impaired wireless channel comprising a plurality of narrow-band subcarriers, the method comprising:

for each frame, distributing the plurality of data symbols over a two-dimensional (2D) orthogonal time frequency space (OTFS) delay-Doppler frame by assigning each data symbol to its own unique 2D OTFS delay-Doppler frame location, wherein the 2D OTFS delay-Doppler frame comprises a 2D delay-Doppler grid, and wherein the 2D OTFS delay-Doppler frame location is a 2D delay-Doppler grid coordinate;

OTFS transforming, using an OTFS transform operation, the plurality of data symbols on the 2D OTFS delay-Doppler frame by using each data symbol and frame location to modulate a unique, location specific, 2D basis wave function selected from a set of mutually orthogonal 2D basis wave functions operating over a 2D OTFS time-frequency frame, wherein the OTFS transforming spreads each data symbol, in a lossless and invertible manner, throughout the 2D OTFS time-frequency frame, and wherein the OTFS transforming creates a 2D OTFS time-frequency frame based wave aggregate;

scrambling the 2D OTFS time-frequency frame based wave aggregate with a scrambling operation to generate a scrambled 2D OTFS time-frequency frame based wave aggregate; and

modulating and transmitting portions of the scrambled 2D OTFS time-frequency frame based wave aggregate, over the plurality of narrow-band subcarriers, over a plurality of time intervals,

wherein a granularity and extent of the portions, the plurality of narrow-band subcarriers, and the plurality of time intervals are chosen so that the sum of the transmitted portions characterizes the scrambled 2D OTFS time-frequency frame based wave aggregate, and

wherein the impaired wireless channel distorts the transmitted portions into channel distorted portions.

2. The method of claim 1, wherein the scrambling operation is a null operation, or wherein the scrambling operation is selected to perform at least one of managing peak transmitter power and allowing receivers to distinguish between different transmitters.

3. The method of claim 1, wherein the set of mutually orthogonal 2D basis wave functions are 2D Fourier or Fourier-like basis functions.

4. The method of claim 1, wherein the OTFS transform is a symplectic Fourier transform, a symplectic discrete Fourier transform, a symplectic finite Fourier transform, a fast Fourier transform, a wavelet transform, or a discrete wavelet transform.

5. The method of claim 1, wherein the 2D OTFS time-frequency frame comprises a rectangular time-frequency grid and parameters, wherein the rectangular time-frequency grid comprises the plurality of time intervals that include N time intervals and the plurality of narrow band subcarriers that include M subcarriers, wherein N and M are integers greater than one, wherein each time interval has a duration T, and wherein each narrow band subcarrier has a frequency bandwidth Δ

f.

6. The method of claim 5, wherein the 2D OTFS delay-Doppler frame comprises N*M locations, and wherein the OTFS transform distributes N*M data symbols over the 2D OTFS time-frequency frame.

7. The method of claim 5, further comprising:

configuring parameters of the 2D OTFS delay-Doppler frame using anticipated wireless time delay characteristics or anticipated wireless Doppler shift characteristics of the impaired wireless channel.

8. A method of receiving, on a per-frame basis, a plurality of data symbols over an impaired wireless channel comprising a plurality of narrow-band subcarriers, wherein the plurality of data symbols corresponds to transmitted portions of a waveform, wherein the impaired wireless channel distorts the transmitted portions into channel distorted portions, the method comprising:

receiving and demodulating the channel distorted portions over the plurality of narrow-band subcarriers, over a plurality of time intervals, to recover a channel distorted replica of a scrambled two-dimensional (2D) orthogonal time frequency space (OTFS) time-frequency frame based wave aggregate;

using an inverse of a scrambling operation to descramble the channel distorted replica of the scrambled 2D OTFS time-frequency frame based wave aggregate, wherein the inverse of the scrambling operation creates a descrambled channel distorted replica of the 2D OTFS time-frequency based wave aggregate;

inverse OTFS transforming, using an inverse of an OTFS transform operation, the channel distorted replica of the 2D OTFS time-frequency frame based wave aggregate, to produce, once the channel distorted portions have been received, a channel distorted replica of a 2D OTFS delay-Doppler frame;

correcting, using a delay-Doppler 2D equalizer, the channel distorted replica of the 2D OTFS delay-Doppler frame, to produce a channel deconvoluted 2D OTFS delay-Doppler frame; and

extracting a plurality of replica data symbols from the channel deconvoluted 2D OTFS delay-Doppler frame.

9. The method of claim 8, wherein the scrambling operation is a null operation, or wherein the scrambling operation is selected to perform at least one of managing peak transmitter power and allowing the channel distorted portions of the plurality of data symbols received to be distinguished as being received from different transmitters.

10. The method of claim 8, wherein the inverse of the OTFS transform is an inverse symplectic Fourier transform, an inverse symplectic discrete Fourier transform, an inverse symplectic finite Fourier transform, an inverse fast Fourier transform, an inverse wavelet transform, or an inverse discrete wavelet transform.

11. The method of claim 8, wherein at least some of the plurality of data symbols comprise delay-Doppler pilot symbols, the method further comprising:

distributing at least one delay-Doppler pilot symbol on at least one defined delay-Doppler pilot symbol location, along with the plurality of data symbols, over the 2D OTFS delay-Doppler frame;

recovering a 2D impulse response of the impaired wireless channel using knowledge pertaining to the at least one delay-Doppler pilot symbol and the at least one defined delay-Doppler pilot symbol location, and channel distortions; and

configuring the delay-Doppler 2D equalizer using the recovered 2D impulse response.

12. The method of claim 11, wherein the delay-Doppler 2D equalizer is operating without use of OFDM cyclic prefixes or use of OFDM subcarrier or symbol time localized pilot symbols.

13. The method of claim 8, wherein the 2D OTFS time-frequency based wave aggregate is based on an OTFS time-frequency frame, wherein at least the 2D OTFS time-frequency frame has a non-rectangular grid structure, and wherein the non-rectangular grid structure in turn controls one or more of start times, time durations, frequencies, frequencies over time, bandwidths, bandwidths over time of any of the portions, the plurality of time intervals, and the plurality of narrow-band subcarriers.

14. An apparatus for receiving, on a per-frame basis, a plurality of data symbols over an impaired wireless channel comprising a plurality of narrow-band subcarriers, the plurality of data symbols corresponding to transmitted portions of a waveform, the impaired wireless channel distorting the transmitted portions into channel distorted portions, the apparatus comprising:

a processor; and

a memory comprising processor executable code, the processor executable code when executed by the processor causes the processor to implement;

receiving and demodulating the channel distorted portions over the plurality of narrow-band subcarriers, over a plurality of time intervals, to recover a channel distorted replica of a scrambled two-dimensional (2D) orthogonal time frequency space (OTFS) time-frequency frame based wave aggregate;

using an inverse of a scrambling operation to descramble the channel distorted replica of the scrambled 2D OTFS time-frequency frame based wave aggregate, wherein the inverse of the scrambling operation creates a descrambled channel distorted replica of the 2D OTFS time-frequency based wave aggregate;

inverse OTFS transforming, using an inverse of an OTFS transform operation, the channel distorted replica of the 2D OTFS time-frequency frame based wave aggregate, to produce, once the channel distorted portions have been received, a channel distorted replica of a 2D OTFS delay-Doppler frame;

correcting, using a delay-Doppler 2D equalizer, the channel distorted replica of the 2D OTFS delay-Doppler frame to produce a channel deconvoluted 2D OTFS delay-Doppler frame; and

extracting a plurality of replica data symbols from the channel deconvoluted 2D OTFS delay-Doppler frame.

15. The apparatus of claim 14, further comprising:

an OFDM backward compatible receiver.

16. The apparatus of claim 15, wherein 4G/LTE symbols are transmitted along with a plurality of OFDM subcarriers and symbol time localized legacy 4G/LTE pilot symbols, and wherein the processor executable code causes the OFDM backward compatible receiver to implement:

receiving the legacy 4G/LTE pilot symbols as channel distorted legacy 4G/LTE pilot symbols, and using the channel distorted 4G/LTE pilot symbols to at least partially configure either a delay-Doppler 2D equalizer or a time-frequency 2D equalizer.

17. The apparatus of claim 14, further comprising:

a time-frequency 2D equalizer configured to operate on the contents of the 2D OTFS time-frequency frame; and

a delay-Doppler 2D equalizer configured to operate on the contents of the 2D OTFS delay-Doppler frame.

18. The apparatus of claim 14, further comprising:

a plurality of receiver subsections,

wherein each receiver subsection is configured with fractionally different time offsets and fractionally different frequency offsets, and

wherein the processor executable code further causes the plurality of receiver subsections to implement;

sampling the channel distorted replica of the scrambled 2D OTFS time-frequency frame based wave aggregate according to the fractionally different time and frequency offsets; and

combining the channel distorted replica samples in a manner that produces a high resolution channel distorted replica of the scrambled 2D OTFS time-frequency frame based wave aggregate over a high resolution version of the 2D OTFS time-frequency frame.

19. The apparatus of claim 18, wherein the processor executable code further causes the processor to further implement:

using the high resolution version of the 2D OTFS time-frequency frame to distinguish between multiple users;

or

using the high resolution version of the 2D OTFS time-frequency frame with at least one 2D equalizer to further correct for channel distortions.

20. The apparatus of claim 14, wherein the inverse of the OTFS transform is an inverse symplectic Fourier transform, an inverse symplectic discrete Fourier transform, an inverse symplectic finite Fourier transform, an inverse fast Fourier transform, an inverse wavelet transform, or an inverse discrete wavelet transforms.