Tomlinson-harashima precoding in an OTFS communication system
A method for signal transmission using precoded symbol information involves estimating a two-dimensional model of a communication channel in a delay-Doppler domain. A perturbation vector is determined in a delay-time domain wherein the delay-time domain is related to the delay-Doppler domain by an FFT operation. User symbols are modified based upon the perturbation vector so as to produce perturbed user symbols. A set of Tomlinson-Harashima precoders corresponding to a set of fixed times in the delay-time domain may then be determined using a delay-time model of the communication channel. Precoded user symbols are generated by applying the Tomlinson-Harashima precoders to the perturbed user symbols. A modulated signal is then generated based upon the precoded user symbols and provided for transmission over the communication channel.
1. A method of signal transmission, comprising:
determining, by a transmitter, a two-dimensional model of a communication channel between the transmitter and a receiver that is a function of time delay defined by a delay dimension and frequency shift defined by a Doppler dimension;
selecting, based on the two-dimensional model of the communication channel, a set of subcarriers within a plurality of subcarriers available for transmissions, wherein the transmissions are precoded using a set of transmit precoding values;
generating a precoded input data by applying the set of transmit precoding values to input data mapped to the set of subcarriers; and
providing a modulated signal using the precoded input data for transmission over the communication channel.
2. The method of claim 1 , wherein the set of subcarriers are selected based on matching an error pattern for transmission over the communication channel by minimizing a geometric mean of a channel transfer function corresponding to the set of subcarriers.
3. The method of claim 1 , wherein the set of subcarriers are selected further based on a sparse and evenly distributed grid to follow a diversity of the communication channel.
4. The method of claim 1 , wherein the set of transmit precoding values are determined from the two-dimensional model using Tomlinson Harashima precoding.
5. The method of claim 4 , wherein the generating the precoded input data comprises:
adding perturbations to input data prior to the applying the set of transmit precoding values, wherein the perturbations are defined in a hybrid domain obtained by applying a transform across the Doppler dimension.
6. The method of claim 4 , wherein the set of transmit precoding values are determined by performing a decomposition of the two-dimensional model of the communication channel.
7. The method of claim 6 , wherein the decomposition comprises an LQD decomposition, and wherein L is a lower triangular matrix, D is a diagonal matrix, and Q is a unitary matrix.
8. The method of claim 1 , wherein the selecting the set of subcarriers comprises pseudo randomly selecting the set of subcarriers.
9. The method of claim 1 , wherein the modulated signal is generated by applying forward error correction coding to the precoded input data.
10. The method of claim 1 , wherein the precoded input symbols are equalized for expected inter-symbol interference over the communication channel to allow for reception at a receiver without using a decision feedback equalizer (DFE).
11. The method of claim 1 , wherein the modulated signal comprises quadrature amplitude modulation (QAM) modulated symbols.
12. An apparatus for signal transmission, comprising a processor configured to:
determine a two-dimensional model of a communication channel between the transmitter and a receiver that is a function of time delay defined by a delay dimension and frequency shift defined by a Doppler dimension;
select, based on the two-dimensional model of a communication channel, a set of subcarriers within a plurality of subcarriers available for transmissions, wherein the transmissions are precoded using a set of transmit precoding values;
generate a precoded input data by applying the set of transmit precoding values to input data mapped to the set of subcarriers; and
provide a modulated signal using the precoded input data for transmission over the communication channel.
13. The apparatus of claim 12 , wherein the set of subcarriers are selected based on matching an error pattern for transmission over the communication channel by minimizing a geometric mean of a channel transfer function corresponding to the set of subcarriers.
14. The apparatus of claim 12 , wherein the set of transmit precoding values are determined from the two-dimensional model using Tomlinson Harashima precoding.
15. The apparatus of claim 14 , wherein the processor is further configured, as part of generating the precoded input data, to: add perturbations to input data prior to the applying the set of transmit precoding values, wherein the perturbations are defined in a hybrid domain obtained by applying a transform across the Doppler dimension.
16. The apparatus of claim 14 , wherein the set of transmit precoding values are determined by performing a decomposition of the two-dimensional model of the communication channel.
17. The apparatus of claim 16 , wherein the decomposition comprises an LQD decomposition, and wherein L is a lower triangular matrix, D is a diagonal matrix, and Q is a unitary matrix.
18. The apparatus of claim 12 , wherein the selecting the set of subcarriers comprises pseudo randomly selecting the set of subcarriers.
19. The apparatus of claim 12 , wherein the modulated signal is generated by applying forward error correction coding to the precoded input data.
20. The apparatus of claim 12 , wherein the precoded input symbols are equalized for expected inter-symbol interference over the communication channel to allow for reception at a receiver without using a decision feedback equalizer (DFE).