# Hybrid Precoding for Multi-Group Multicasting in mmWave Systems

## TL;DR

This paper proposes a novel hybrid precoding and combining design for multi-group multicasting in mmWave systems, significantly improving power efficiency and reception success rates while approaching fully-digital performance.

## Contribution

It introduces the first joint hybrid transmit precoder and receive combiner design for mmWave multi-group multicasting using SDR and alternating optimization.

## Key findings

- 16.8% reduction in average transmit power per message
- 60% increase in successful information reception
- Performance close to fully-digital precoders in challenging scenarios

## Abstract

Multicast beamforming is known to improve spectral efficiency. However, its benefits and challenges for hybrid precoders design in millimeter-wave (mmWave) systems remain understudied. To this end, this paper investigates the first joint design of hybrid transmit precoders (with an arbitrary number of finite-resolution phase shifts) and receive combiners for mmWave multi-group multicasting. Our proposed design leverages semidefinite relaxation (SDR), alternating optimization and Cholesky matrix factorization to sequentially optimize the digital/analog precoders at the transmitter and the combiners at each receiver. By considering receivers with multiple-antenna architecture, our design remarkably improves the overall system performance. Specifically, with only two receive antennas the average transmit power per received message improves by $ 16.8\% $ while the successful information reception is boosted by $ 60\% $. We demonstrate by means of extensive simulations that our hybrid precoder design performs very close to its fully-digital counterpart even under challenging scenarios (i.e., when co-located users belong to distinct multicast groups).