DMA-constrained channel-estimation design

Develop an efficient channel-estimation technique for the DMA-based electromagnetic layer in the proposed OFDM-based mmWave cell-free massive MIMO system, accounting for the Lorentzian-constrained weights that restrict the set of realizable training beams.

Background

The proposed tri-hybrid cell-free massive MIMO framework assumes perfect channel state information at the central processing unit to evaluate the GEE optimization. The paper notes that practical channel acquisition would require each access point to estimate its local channels from uplink pilots and forward them to the central processor. Although existing compressive-sensing and tri-timescale approaches may be adaptable, the DMA electromagnetic layer imposes Lorentzian constraints on its weights, limiting the training beams that can be generated. A dedicated channel-estimation method for this setting is therefore not provided and remains a concrete direction for future work.