Orthogonal time frequency space communication system compatible with OFDM
View Patent ↗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.
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 orthogonal time frequency space (OTFS) modulation symbols by spreading the plurality of information symbols across both time and frequency by a corresponding plurality of two-dimensional basis functions wherein the corresponding plurality of two-dimensional basis functions are mutually orthogonal with respect to both time and frequency and wherein the array of OTFS modulation symbols is arranged in a time frequency frame along with one or more orthogonal frequency-division multiple access (OFDM) symbols and wherein N and M are integers;
transmitting the two-dimensional array of OTFS modulation symbols using M narrowband subcarriers; and
transmitting the one or more OFDM 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 narrrowband 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 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.
6. 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.
7. 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 orthogonal time frequency space (OTFS) modulation symbols by using each of the plurality of information symbols frequency to modulate one of by a corresponding plurality of two-dimensional basis functions wherein the array of OTFS modulation symbols is arranged in a time frequency frame along with one or more orthogonal frequency-division multiple access (OFDM) symbols, wherein N and M are integers, and wherein the encoding is performed in accordance with the following relationship:
X
[
m
,
n
]
=
1
MN
W
tr
[
n
,
m
]
∑
k
=
0
N
-
1
∑
l
=
0
M
-
1
x
[
l
,
k
]
b
k
,
l
[
n
,
m
]
b
k
,
l
[
n
,
m
]
=
e
j
2
π
(
m
l
M
-
nk
N
)
where x[l,k], k=0, . . . , N−1, l=0, . . . , M−1 represents the N×M array containing the plurality of information symbols, X[n,m], n=0, . . . , N−1, m=0, . . . , M−1 represents the two-dimensional array of modulation symbols, W tr [n,m] is a windowing function, and b k,l [n,m] represents the plurality of two-dimensional basis functions;
transmitting the two-dimensional array of OTFS modulation symbols using M narrowband subcarriers; and
transmitting the one or more OFDM symbols using at least one OFDM subcarrier.
8. A communication device, comprising:
a wireless transmitter;
a processor; and
a non-transitory 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 orthogonal time frequency space (OTFS) modulation symbols by spreading the plurality of information symbols across both time and frequency by a corresponding plurality of two-dimensional basis functions wherein the corresponding plurality of two-dimensional basis functions are mutually orthogonal with respect to both time and frequency and wherein the array of OTFS modulation symbols is arranged in a time frequency frame along with one or more orthogonal frequency-division multiple access (OFDM) symbols and wherein N and M are integers;
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.
9. The communication device of claim 8 wherein the at least one OFDM subcarrier is included within the M narrrowband subcarriers.
10. The communication device of claim 8 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.
11. The communication device of claim 8 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.