A rank-constrained coordinate ascent approach to hybrid precoding for the downlink of wideband massive MIMO systems
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Date
2023-02-01
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Abstract
An innovative approach to hybrid analog-digital
precoding for the downlink of wideband massive MIMO systems
is developed. The proposed solution, termed Rank-Constrained
Coordinate Ascent (RCCA), starts seeking the full-digital pre coder that maximizes the achievable sum-rate over all the
frequency subcarriers while constraining the rank of the overall
transmit covariance matrix. The frequency-flat constraint on the
analog part of the hybrid precoder and the non-convex nature
of the rank constraint are circumvented by transforming the
original problem into a more suitable one, where a convenient
structure for the transmit covariance matrix is imposed. Such
structure makes the resulting full-digital precoder particularly
adequate for its posterior analog-digital factorization. An addi tional problem formulation to determine an appropriate power
allocation policy according to the rank constraint is also pro vided. The numerical results show that the proposed method
outperforms baseline solutions even for practical scenarios with
high spatial diversity.