ORTHOGONAL TIME FREQUENCY SPACE COMMUNICATION SYSTEM COMPATIBLE WITH OFDM

• US 20170012749A1
• Filed: 07/12/2016
• Published: 01/12/2017
• Est. Priority Date: 06/25/2012
• Status: Active Grant

• Current Assignee: Cohere Technologies Inc
• Original Assignee: Cohere Technologies Inc
• Inventors: Rakib, Shlomo Selim, Hadani, Ronny
• Granted Patent: US 10,411,843 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• 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 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT

Abstract

A system and method for orthogonal time frequency space communication and waveform generation compatible with OFDM. The method includes receiving a plurality of information symbols and encoding an N×M array containing the plurality of information symbols into a two-dimensional array of modulation symbols by spreading each of the plurality of information symbols with respect to both time and frequency. The two-dimensional array of modulation symbols is then transmitted along with one or more OFDM symbols using a plurality of narrowband subcarriers.

Claims

1. A method of transmitting data over a communication channel, the method comprising:

receiving a plurality of information symbols;

encoding an N×

M array containing the plurality of information symbols into a two-dimensional array of OTFS modulation symbols by spreading each of the plurality of information symbols with respect to both time and frequency wherein the array of OTFS modulation symbols is arranged in a time frequency frame along with one or more OFDM symbols;

transmitting, the two-dimensional array of OTFS modulation symbols using M narrowband subcarriers; and

transmitting the one or more OF symbols using at least one OFDM subcarrier.

2. The method of claim 1 wherein the at least one OFDM subcarrier is included within the M narrowband subcarriers.

3. The method of claim 1 wherein the encoding includes:

transforming the N×

M array into an array of filtered OFDM symbols using at least one Fourier transform and a filtering process;

transforming the array of filtered OFDM symbols into an array of OTFS symbols using at least one two-dimensional Fourier transform wherein the array of OTFS symbols corresponds to the two-dimensional array of modulation symbols.

4. The method of claim 1 wherein the encoding includes combining an inverse symplectic transform with a windowing operation.

5. The method of claim 1 wherein the encoding is performed in accordance with the following relationship:

41. The method of claim 1 further including selecting N and M based upon at least one of a latency and a rate associated with transmission of the data over the communication channel.

42. The method of claim 1 further including selecting N and M based upon at least one of an anticipated Doppler shift and anticipated multi-path delay associated with transmission of the data over the communication channel.

6. A communication device, comprising:

a wireless transmitter;

a processor; and

a memory including program code executable by the processor, the program code including code for causing the processor to;

receive a plurality of information symbols;

encode an N×

M array containing the plurality of information symbols into a two-dimensional array of OTFS modulation symbols by spreading each of the plurality of information symbols with respect to both time and frequency wherein the array of OTFS modulation symbols is arranged in a time frequency frame along with one or more OFDM symbols;

transmit the two-dimensional array of OTFS modulation symbols using M narrowband subcarriers. and

transmit the one or more OFDM symbols using at least one OFDM subcarrier.

7. The communication device of claim 6 wherein the at least one OFDM subcarrier is included within the M narrowband subcarriers.

8. The communication device of claim 6 wherein the code for causing the processor to encode includes code for causing the processor to:

transform the N×

M array into an array of filtered OFDM symbols using at least one Fourier transform and a filtering process;

transform the array of filtered OFDM symbols into an array of OTFS symbols using at least one two-dimensional Fourier transform.

9. The communication device of claim 6 wherein the code for causing the processor to encode includes code for causing the processor to combine an inverse symplectic transform with a windowing operation.

10. A method of receiving data transmitted over a communication channel, the method comprising:

receiving M mutually orthogonal waveforms included within M frequency sub-bands;

receiving at least one OFDM pilot symbol included within a frequency sub-band;

demodulating the M mutually orthogonal waveforms to recover an estimate of a two-dimensional array of OTFS symbols;

configuring a two-dimensional equalizer based at least in part upon the at least one OFDM pilot symbol;

decoding the two-dimensional array of OTFS symbols in order to generate an estimate of an N×

M array containing a plurality of information symbols, the N×

M array having been encoded prior to transmission of the data by spreading each of the plurality of information symbols with respect to both time and frequency; and

processing the estimate of the N×

M array using the two-dimensional equalizer in order to obtain an equalized estimate of the N×

M array.

11. The method of claim 10 wherein the decoding includes transforming the two-dimensional array of OTFS symbols into an array of OFDM symbols using at least one two-dimensional Fourier transform and transforming the array of OFDM symbols into the estimate of the N×

M array using at least one inverse Fourier transform.

12. The method of claim 10 wherein the at least one frequency sub-band is included within the M frequency sub-bands.

13. A method of providing a modulated signal useable in a signal transmission system, the method comprising:

performing a two dimensional time-frequency transformation of a data frame including a plurality of information symbols to generate a frame of OTFS modulation symbols arranged within a time-frequency plane wherein a plurality of OFDM symbols are also arranged within the time-frequency plane; and

generating, using an OFDM modulator, the modulated signal based upon the frame of OTFS modulation symbols and the plurality of OFDM symbols.

14. The method of claim 13 wherein the performing the two dimensional transformation includes performing an inverse time-frequency symplectic transformation and a windowing operation.

15. A transmitter apparatus, the apparatus comprising:

an OTFS pre-processing unit configured to perform a two dimensional time-frequency transformation of a data frame including a plurality of information symbols to generate a frame of OTFS modulation symbols arranged within a time-frequency plane wherein a plurality of OFDM symbols are also arranged within the time-frequency plane; and

an OFDM modulator configured to generate the modulated signal based upon the frame of OTFS modulation symbols and the plurality of OFDM symbols.

16. The transmitter apparatus of claim 15 wherein the two dimensional transformation comprises an inverse time-frequency symplectic transformation and a windowing operation.

17. A method of receiving a modulated signal, the method comprising:

receiving a plurality of signal components of the modulated signal;

generating, by performing an OFDM demodulation operation using the plurality of signal components, a plane of estimated time-frequency modulation symbols; and

providing an estimated OTFS data frame by performing an inverse of a two dimensional time-frequency transformation with respect to ones of the estimated time-frequency modulation symbols wherein other of the estimated time-frequency modulation symbols comprise OFDM symbols.

18. The method of claim 17 further including:

configuring a two-dimensional equalizer based upon one or more OFDM pilot symbols included within the OFDM symbols; and

processing, using the two-dimensional equalizer, the estimated OTFS data frame in order to generate equalized OTFS symbols.

19. The method of claim 17 wherein the performing the inverse of the two dimensional time-frequency transformation includes performing a windowing operation and a symplectic Fourier transform.

40. A receiver apparatus, the apparatus comprising:

a receiver front end, the receiver front end being configured to receive a plurality of signal components of a modulated signal;

an OFDM demodulator configured to generate a plane of estimated time-frequency modulation symbols based upon the plurality of signal components; and

an OTFS post-processing unit operative to provide an estimated OTFS data frame, the OTFS post-processing unit performing an inverse of a two dimensional time-frequency transformation with respect to ones of the estimated time-frequency modulation symbols wherein other of the estimated time-frequency modulation symbols comprise OFDM symbols.