# D2D-Aided Multi-Antenna Multicasting

## TL;DR

This paper enhances D2D-aided multicasting by integrating base station precoding, selecting optimal relaying UEs, and optimizing transmission strategies to improve multicast rate and reliability in large networks.

## Contribution

It introduces a novel scheme combining D2D relaying with BS precoding, along with an algorithm for joint relay selection and precoding optimization.

## Key findings

- Improved multicast rate with D2D relaying and precoding.
- Algorithm converges to optimal relay and precoding configuration.
- Enhanced reliability under outage constraints.

## Abstract

Multicast services, whereby a common valuable message needs to reach a whole population of user equipments (UEs), are gaining attention on account of new applications such as vehicular networks. As it proves challenging to guarantee decodability by every UE in a large population, service reliability is indeed the Achilles' heel of multicast transmissions. To circumvent this problem, a two-phase protocol capitalizing on device-to-device (D2D) links between UEs has been proposed, which overcomes the vanishing behavior of the multicast rate. In this paper, we revisit such D2D-aided protocol in the new light of precoding capabilities at the base station (BS). We obtain an enhanced scheme that aims at selecting a subset of UEs who cooperate to spread the common message across the rest of the network via D2D retransmissions. With the objective of maximizing the multicast rate under some outage constraint, we propose an algorithm with provable convergence that jointly identifies the most pertinent relaying UEs and optimizes the precoding strategy at the BS.