The generalized WAX decomposition validity conjecture

Let A{\boldsymbol{A}} be given by the Kronecker construction in the source, with A~T=ITP\widetilde{{\boldsymbol{A}}}_\mathrm{T}=\mathbf{I}_{T_{\mathrm{P}}}, and let A~B\widetilde{{\boldsymbol{A}}}_\mathrm{B} be constructed through the stated generalized algorithm. For each iteration i=1,,NQi=1,\dots,N_\text{Q}, let QiQ_i be the quotient defined by that algorithm, and let NQN_\text{Q} be the iteration at which the dimensions are exhausted. Define

Qtot=Q1+1Q2+1+1QNQ.Q_\mathrm{tot}=Q_1+\frac{1}{Q_2+\frac{1}{\ddots+\frac{1}{Q_{N_\text{Q}}}}}.

Generalized WAX decomposition validity conjecture. A randomly chosen matrix H{\boldsymbol{H}} admits WAX decomposition with probability 11 for the given A{\boldsymbol{A}} if

LK1+Qtot.L\geq \frac{K}{1+Q_\mathrm{tot}}.

Moreover, in the regime TP<MP/2+1T_{\mathrm{P}}<M_{\mathrm{P}}/2+1, the first column of A~B\widetilde{{\boldsymbol{A}}}_\mathrm{B}, written as [α1,,αΦ]T[\alpha_1,\dots,\alpha_\Phi]^\mathrm{T}, should satisfy the same restrictions as in Proposition 2 of the source. The conjecture is motivated by the proposed generalization of earlier valid constructions. A formal proof for general NQN_\text{Q} was not found, although extensive simulations reportedly found no exceptions and produced valid matrices exactly when the stated condition was satisfied.

Sources & referencesView supporting material

Primary source

Juan Vidal Alegría and Fredrik Rusek, “Trade-Offs in Decentralized Multi-Antenna Architectures: Sparse Combining Modules for WAX Decomposition”, arXiv:2309.04297 (2023).

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