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 for wireless communication, comprising:
generating, based on a feedback signal, a two-dimensional estimate of a channel, wherein the two-dimensional estimate is in a delay-Doppler domain that comprises a time delay dimension and a frequency shift dimension;
determining, based on the two-dimensional estimate, a set of precoding values and a set of perturbation values;
generating a plurality of perturbed symbols by applying the set of perturbation values to a plurality of user symbols;
generating a plurality of pre-coded symbols by applying the set of precoding values to the plurality of perturbed symbols;
generating, based on the plurality of pre-coded symbols, a pre-coded signal that is modulated using an orthogonal time frequency space (OTFS) or an orthogonal frequency division multiplexing (OFDM) modulation scheme; and
transmitting, over the channel, the pre-coded signal.
2. The method of claim 1 , further comprising:
receiving, over the channel, the feedback signal.
3. The method of claim 2 , wherein the feedback signal comprises a channel matrix with a full rank or a nearly full rank.
4. The method of claim 1 , wherein the determining the set of perturbation values comprises minimizing ∥h −1 (x+v)∥ 2 , wherein h is the two-dimensional estimate, v is the set of perturbation values, and x is the plurality of user symbols.
5. The method of claim 1 , wherein the determining the set of perturbation values is based on minimizing an expected interference and noise in the channel.
6. The method of claim 1 , wherein the determining the set of perturbation values is performed in a hybrid delay-time domain that is related to the delay-Doppler domain through a Fast Fourier Transform (FFT) taken across the frequency shift dimension.
7. The method of claim 6 , wherein the determining the set of precoding values comprises performing a decomposition of two-dimensional estimate of the channel in the hybrid delay-time domain.
8. The method of claim 7 , wherein the decomposition comprises an LDQ decomposition, wherein L is a lower triangular matrix, D is a diagonal matrix and Q is a unitary matrix.
9. The method of claim 7 , wherein the set of precoding values comprises Tomlinson-Harashima precoding values.
10. A device for wireless communication, comprising:
a processor; and
a memory that comprises instructions stored thereupon, wherein the instructions when executed by the processor configure the processor to:
generate, based on a feedback signal, a two-dimensional estimate of a channel, wherein the two-dimensional estimate is in a delay-Doppler domain that comprises a time delay dimension and a frequency shift dimension;
determine, based on the two-dimensional estimate, a set of precoding values and a set of perturbation values;
generate a plurality of perturbed symbols by applying the set of perturbation values to a plurality of user symbols;
generate a plurality of pre-coded symbols by applying the set of precoding values to the plurality of perturbed symbols;
generate, based on the plurality of pre-coded symbols, a pre-coded signal that is modulated using an orthogonal time frequency space (OTFS) or an orthogonal frequency division multiplexing (OFDM) modulation scheme; and
transmit, over the channel, the pre-coded signal.
11. The device of claim 10 , wherein the instructions when executed by the processor further configures the processor to:
receive, over the channel, the feedback signal.
12. The device of claim 11 , wherein the feedback signal comprises a channel matrix with a full rank or a nearly full rank.
13. The device of claim 10 , wherein the instructions when executed by the processor further configures the processor, as part of determining the set of perturbation values, to minimize ∥h −1 (x+v)∥ 2 , wherein h is the two-dimensional estimate, v is the set of perturbation values, and x is the plurality of user symbols.
14. The device of claim 10 , wherein determining the set of perturbation values is based on minimizing an expected interference and noise in the channel.
15. The device of claim 10 , wherein determining the set of perturbation values is performed in a hybrid delay-time domain that is related to the delay-Doppler domain through a Fast Fourier Transform (FFT) taken across the frequency shift dimension.
16. The device of claim 15 , wherein the instructions when executed by the processor further configures the processor, as part of determining the set of precoding values, to perform a LDQ decomposition of two-dimensional estimate of the channel in the hybrid delay-time domain, wherein L is a lower triangular matrix, D is a diagonal matrix and Q is a unitary matrix.
17. The device of claim 16 , wherein the set of precoding values comprises Tomlinson-Harashima precoding values.
18. A non-transitory computer readable program storage medium having code stored thereon, the code, when executed by a processor, causing the processor to implement a method for wireless communication, the method comprising:
generating, based on a feedback signal, a two-dimensional estimate of a channel, wherein the two-dimensional estimate is in a delay-Doppler domain that comprises a time delay dimension and a frequency shift dimension;
determining, based on the two-dimensional estimate, a set of precoding values and a set of perturbation values;
generating a plurality of perturbed symbols by applying the set of perturbation values to a plurality of user symbols;
generating a plurality of pre-coded symbols by applying the set of precoding values to the plurality of perturbed symbols;
generating, based on the plurality of pre-coded symbols, a pre-coded signal that is modulated using an orthogonal time frequency space (OTFS) or an orthogonal frequency division multiplexing (OFDM) modulation scheme; and
transmitting, over the channel, the pre-coded signal.
19. The non-transitory computer readable program storage medium of claim 18 , wherein the method further comprises:
receiving, over the channel, the feedback signal that comprises a channel matrix with a full rank or a nearly full rank.
20. The non-transitory computer readable program storage medium of claim 18 , wherein the determining the set of perturbation values is performed in a hybrid delay-time domain that is related to the delay-Doppler domain through a Fast Fourier Transform (FFT) taken across the frequency shift dimension.
21. The non-transitory computer readable program storage medium of claim 20 , wherein the determining the set of precoding values comprises performing a LDQ decomposition of two-dimensional estimate of the channel in the hybrid delay-time domain, wherein L is a lower triangular matrix, D is a diagonal matrix and Q is a unitary matrix, and wherein the set of precoding values comprises Tomlinson-Harashima precoding values.