Fast Antenna Selection for Near-Field Delay Alignment Modulation

Delay alignment modulation (DAM) is a promising technology for achieving inter-symbol interference (ISI)-free communications via the spatial-delay processing, which bypasses the conventional channel equalization or multi-carrier transmissions. Nevertheless, existing works on DAM mainly concentrate on the far-field communications relying on the uniform plane wave (UPW) model. This letter considers the near-field extremely large-scale array (XL-array) DAM communications, by considering the non-uniform spherical wave (NUSW) and spatial non-stationarity channel characteristics. Antenna selection (AS) for maximizing the received signal-to-interference-plus-noise ratio (SINR) of DAM is considered, and two fast AS schemes tailored for DAM are proposed, i.e., the low-complexity scheme based on the maximum channel power and the greedy scheme based on the maximum SINR. For the latter, an incremental form of the SINR expression is derived to reuse the result of the previous step, so as to reduce the computational complexity. Numerical results verify the superior performance of the greedy AS scheme, and the effectiveness of the low-complexity AS scheme for a large selected antenna number, thanks to the exploitation of near-field spatial non-stationarity.