Hybrid analog-digital transceiver designs for mmwave amplify-and-forward relaying systems

Hybrid Analog/Digital (A/D) pre-/post-coding solutions aim at the reduction of the hardware complexity and power consumption of a system employed with a large-scale antenna array functioning in the millimeter (mmWave) band. This is achieved by enabling the transceiver design with fewer Radio Frequency (RF) chains than antennas. In this work, hybrid A/D transceiver designs are developed for a relay assisted mmWave system that aims at data transmission from a source to a destination node via the well-known amplify-and-forward cooperative protocol. To that end, hybrid solutions are proposed for the joint design of the source and relay nodes precoders and for the destination ones, as well. Contrariwise to existing literature approaches that develop codebook-based solutions and exhibit limitations on the performance, the proposed approaches are codebook-free and present significantly improved spectral efficiency, as it is verified via the presented simulations.