Systems and methods for calculating frequency-localized adaptive beamformer weights using weighted overlapping beamform and add techniques applied to adjacent subbands
Examples described herein include Weighted Overlap Beamform and Add techniques for calculating frequency-localized weights for adaptive beamformers. Intermediate weights are calculated for overlapping subbands (e.g., using a least-squares solution or a windowed least-squares solution). Each set of intermediate weights may be multiplied by an overlap factor, and combined to provide final weights for a subcarrier.
1. A receiver comprising:
a plurality of antennas, the plurality of antennas configured to receive RF signals in a frequency band spanning multiple subcarrier frequencies; and
a beamformer coupled to the plurality of antennas and configured to receive data streams corresponding to the RF signals, the beamformer comprising a weight processor configured to calculate, for each subcarrier of the frequency band, a respective plurality of weights used to generate signals for transmission by or combine the signals received at respective ones of the plurality of antennas; and
wherein the weight processor is configured to calculate the respective plurality of weights at least in part by:
calculating multiple sets of intermediate weights for a particular subcarrier using multiple overlapping subbands of subcarriers including the particular subcarrier;
weighting the multiple sets of intermediate weights in accordance with an overlap factor for each subband of the multiple overlapping subbands, wherein the overlap factor is based partly on a distance between a center of a respective overlapping subband and the particular subcarrier, to provide weighted sets of intermediate weights; and
combining the weighted sets of intermediate weights to provide final frequency-localized weights for the particular subcarrier.
2. The receiver of claim 1 , wherein the overlap factor is based on the distance between the center of the respective overlapping subband and the particular subcarrier and a number of subcarriers in the respective overlapping subband.
3. The receiver of claim 2 , wherein calculating the multiple sets of intermediate weights for the subcarrier using multiple overlapping subbands of subcarriers including the particular subcarrier comprises calculating a least-squares solution of the respective overlapping subband based on a respective plurality of subcarriers in the respective overlapping subband, the respective plurality of subcarriers including the particular subcarrier.
4. The receiver of claim 3 , wherein calculating the multiple sets of intermediate weights for the subcarrier using multiple overlapping subbands of subcarriers including the particular subcarrier comprises calculating a minimum mean-squared error (MMSE) solution of the respective overlapping subband based on the respective plurality of subcarriers in the respective overlapping subband, the respective plurality of subcarriers including the particular subcarrier.
5. The receiver of claim 3 , wherein the least-squares solution is based on a recursive least squares algorithm.
6. The receiver of claim 5 , wherein the recursive least-squares algorithm comprises an inverse covariance calculation for each respective plurality of subcarriers including the particular subcarrier.
7. The receiver of claim 6 , wherein an additional least-squares solution of another plurality of subcarriers in an adjacent overlapping subband to the respective overlapping subband utilizes the inverse covariance calculation for each respective plurality of subcarriers including the particular subcarrier and an additional subcarrier of the another plurality of subcarriers in the adjacent overlapping subband.
8. The receiver of claim 2 , wherein calculating the multiple sets of intermediate weights for the subcarrier using multiple overlapping sub-bands of subcarriers including the particular subcarrier comprise performing a direct matrix inversion (DMI) algorithm of the respective overlapping subband based on a respective plurality of subcarriers in the respective overlapping subband, the respective plurality of subcarriers including the particular subcarrier.
9. The receiver of claim 8 , wherein the performing the DMI algorithm comprises performing a QR-decomposition of the respective overlapping subband or a Modified Gram-Schmidt Orthogonalization (MGSO) of the respective overlapping subband.
10. The receiver of claim 1 , wherein calculating multiple sets of intermediate weights comprises weighting individual subcarriers in each of the overlapping subbands in accordance with a window.
11. The receiver of claim 10 , wherein calculating the multiple sets of intermediate weights comprises calculating a windowed least-squares solution of the respective overlapping subband based on a respective plurality of subcarriers in the respective overlapping subband.
12. The receiver of claim 1 , wherein one of the multiple overlapping subbands is centered at the particular subcarrier.
13. The receiver of claim 12 , wherein each of the multiple overlapping subbands correspond to a range of subcarriers for which a frequency response of a channel is flat.
14. The receiver of claim 1 , wherein the beamformer is further configured to receive additional data streams and to apply weights for each respective subcarrier including the particular subcarrier to each of the additional data streams.
15. The receiver of claim 1 , wherein the receiver is implemented in a processor of a remote node of a wireless network, the processor configured to execute instructions, stored in a non-transitory computer-readable medium, for implementation of the beamformer.
16. The receiver of claim 1 , wherein each data stream of the data streams corresponds to a corresponding discretized version of a respective RF signal of a plurality of RF signals.
17. A method comprising:
receiving data streams at a plurality of antennas in a range of subcarrier frequencies; and
at a beamformer, for each subcarrier frequency in the range of subcarrier frequencies:
calculating multiple sets of intermediate weights for a particular subcarrier frequency using multiple overlapping subbands of subcarriers, each overlapping subband including the particular subcarrier frequency;
weighting the multiple sets of intermediate weights in accordance with an overlap factor for each subband of the multiple overlapping subbands to provide weighted sets of intermediate weights; and
combining the weighted sets of intermediate weights to provide the weights for the particular subcarrier frequency.
18. The method of claim 17 , wherein the overlap factor is based on a distance between a center of a respective overlapping subband and the particular subcarrier frequency and a number of subcarriers in the respective overlapping subband.
19. The method of claim 17 , further comprising:
calculating a Fast Fourier Transform (FFT) for each data stream to generate a corresponding representation of the data stream in a frequency domain; and
providing the corresponding representation of the data stream in the frequency domain to a respective input of the beamformer.
20. The method of claim 17 , wherein calculating the multiple sets of intermediate weights for the subcarrier frequency using the multiple overlapping subbands including the particular subcarrier frequency comprises performing a least-squares algorithm.
21. The method of claim 17 , wherein combining the weighted sets of intermediate weights to provide the weights for the particular subcarrier frequency comprises adding each weighted set of intermediate weights with each other to provide the weights for the particular subcarrier frequency.
22. The method of claim 17 , further comprising:
receiving additional data streams; and
applying weights for each respective subcarrier including the particular subcarrier frequency to each additional data stream.
23. The method of claim 17 , further comprising:
selecting, from the weights for each particular subcarrier frequency in the range of subcarrier frequencies, a plurality of beamformed weights for each respective input of the beamformer.
24. The method of claim 23 , wherein the data streams include training data to generate the plurality of beamformed weights for each respective input of the beamformer.