Reciprocal geometric precoding
A wireless communication method includes determining, by a network device, uplink power allocations assigned to each user device of multiple user devices; estimating a channel response for each user device of multiple user devices based on a corresponding uplink reference signal transmission received from the each user device; computing, for the each user device, a covariance matrix based on a corresponding channel response, determining a maximum eigenvector of an uplink signal to interference and noise ratio (SINR) matrix for the each user device; computing, from the uplink SINR matrix, a downlink cross-interference matrix for the each user device; selecting, from the downlink cross-interference matrix for the each user device, a selected vector that maximizes a selected criterion for the each user device; and determining, from the selected vectors of the multiple user devices, a downlink power allocation for the each user device of multiple user devices.
1. A wireless communication method, comprising:
determining, by a network device, uplink power allocations assigned to each user device of multiple user devices;
estimating, by the network device, a channel response for each user device of multiple user devices based on a corresponding uplink reference signal transmission received from the each user device,
computing, for the each user device, a covariance matrix based on a corresponding channel response,
determining a maximum eigenvector of an uplink signal to interference and noise ratio (SINR) matrix for the each user device;
computing, from the uplink SINR matrix, a downlink cross-interference matrix for the each user device;
selecting, from the downlink cross-interference matrix for the each user device, a selected vector that maximizes a selected criterion for the each user device,
determining, from the selected vectors of the multiple user devices, a downlink power allocation for the each user device of multiple user devices.
2. The method of claim 1 , wherein the reference signal transmission comprises a cell specific reference signal, a sounding reference signals (SRS) or demodulation reference signals (DMRS).
3. The method of claim 1 , further comprising:
using the selected vectors and downlink power allocations for determining a precoding scheme that is used for generating a precoded transmission waveform from the network device.
4. The method of claim 3 , wherein the uplink reference signal transmission and the precoded transmission waveform are multiplexed using time division duplexing (TDD) or frequency division duplexing (FDD).
5. The method of claim 1 wherein the covariance matrix has a dimension LxL, wherein L represents a number of transmission antennas of the network device.
6. The method of claim 1 , wherein the computing the covariance matrix includes computing the covariance matrix using a maximum likelihood technique.
7. The method of claim 1 , wherein the computing the covariance matrix includes computing the covariance matrix using a direct multiplication between a channel response matrix and a Hermitian of the channel response matrix.
8. The method of claim 1 , wherein the selected criterion for the each user device includes (a) using a maximum eigenvector of the cross-interference matrix, and/or (b) downlink traffic requirements.
9. The method of claim 1 , wherein the multiple user devices form a subset of all user devices served by the network device, and wherein the subset is chosen based on covariance matrices of all user devices served by the network device.
10. The method of claim 1 , wherein the downlink power allocation for each user device (p i ) is based on a normalized absolute value of elements (V A (DL) (i)) of the corresponding maximum eigenvector (A (DL) ) that is given by:
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wherein the cross-interference matrix (A K×K (DL) ) in a downlink direction comprises entries given by:
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wherein i and j are indexes for the multiple user devices, SINR i * (UL) is a signal to interference and noise ratio for i-th user device for the uplink channel, V i * is a vector space for the i-th user device, R i is the covariance matrix, and No is a noise variance.
11. An apparatus for wireless communication, comprising:
a processor of a network device; and
a wireless transceiver,
wherein the processor is configured for:
determining, uplink power allocations assigned to each user device of multiple user devices;
estimating, a channel response for each user device of multiple user devices based on a corresponding uplink reference signal transmission received from the each user device,
computing, for the each user device, a covariance matrix based on a corresponding channel response,
determining a maximum eigenvector of an uplink signal to interference and noise ratio (SINR) matrix for the each user device;
computing, from the uplink SINR matrix, a downlink cross-interference matrix for the each user device;
selecting, from the downlink cross-interference matrix for the each user device, a selected vector that maximizes a selected criterion for the each user device,
determining, from the selected vectors of the multiple user devices, a downlink power allocation for the each user device of multiple user devices; and
the wireless transceiver is configured to receive the uplink reference signal transmission.
12. The apparatus of claim 11 , wherein the reference signal transmission comprises a cell specific reference signal, a sounding reference signals (SRS) or demodulation reference signals (DMRS).
13. The apparatus of claim 11 , wherein the processor is further configured to perform:
using the selected vectors and downlink power allocations for determining a precoding scheme that is used for generating a precoded transmission waveform from the network device.
14. The apparatus of claim 13 , wherein the uplink reference signal transmission and the precoded transmission waveform are multiplexed using time division duplexing (TDD) or frequency division duplexing (FDD).
15. The apparatus of claim 11 , wherein the covariance matrix has a dimension L×L, wherein L represents a number of transmission antennas of the network device.
16. The apparatus of claim 11 , wherein the computing the covariance matrix includes computing the covariance matrix using a maximum likelihood technique.
17. The apparatus of claim 11 , wherein the computing the covariance matrix includes computing the covariance matrix using a direct multiplication between a channel response matrix and a Hermitian of the channel response matrix.
18. The apparatus of claim 11 , wherein the selected criterion for the each user device includes (a) using a maximum eigenvector of the cross-interference matrix, and/or (b) 1 downlink traffic requirements.
19. The apparatus of claim 11 , wherein the multiple user devices form a subset of all user devices served by the network device, and wherein the subset is chosen based on covariance matrices of all user devices served by the network device.
20. The apparatus of claim 13 , wherein the precoding scheme operates in:
a. a spatial dimension only, or
b. spatial-delay dimensions, or
c. spatial-Doppler dimensions, or
d. spatial-delay-Doppler dimensions, or
e. spatial-frequency dimensions, or
f. spatial-time dimensions, or
g. spatial-frequency-time dimensions, and
wherein the network device is operating using a long-term evolution (LTE) protocol or a 5G new radio (NR) protocol.