Channel Customization for Joint Tx-RISs-Rx Design in Hybrid mmWave Systems

In strong line-of-sight millimeter-wave (mmWave) wireless systems, the rank-deficient channel severely hampers spatial multiplexing. To address this inherent deficiency, multiple reconfigurable-intelligent-surfaces (RISs) are introduced in study to customize channel. Utilizing RIS reshape electromagnetic waves, we theoretically show that a favorable with an arbitrary tunable rank and minimized truncated condition number can be established by elaborately designing placement reflection matrix of RISs. Different from existing works on multi-RISs, elements needed for each combat path loss limited phase control is also considered. On basis proposed customization, joint transmitter-RISs-receiver (Tx-RISs-Rx) design under hybrid mmWave system investigated maximize spectral efficiency. Using scheme, optimal singular value decomposition-based beamforming at Tx Rx obtained without decomposition digital analog beamforming. The bottoms sub-channel mode water-filling algorithm, which conventionally uncontrollable, proven independently adjustable Moreover, transmit power required realizing multi-stream transmission derived. Numerical results presented verify our theoretical analysis exhibit substantial gains over systems