Max-min Fairness of K-user Cooperative Rate-Splitting in MISO Broadcast Channel with User Relaying

TL;DR

This paper extends cooperative rate-splitting to K-user MISO broadcast channels, proposing an optimization framework that significantly improves the minimum user rate while reducing computational complexity.

Contribution

It generalizes two-user CRS to K-users, introduces a self-organizing relaying protocol, and develops an SCA-based algorithm for joint optimization.

Findings

CRS outperforms NRS and SDMA in various network scenarios.

The SCA-based algorithm reduces complexity without rate loss.

Proposed K-user CRS scheme achieves higher minimum rates.

Abstract

Cooperative Rate-Splitting (CRS) strategy, relying on linearly precoded rate-splitting at the transmitter and opportunistic transmission of the common message by the relaying user, has recently been shown to outperform typical Non-cooperative Rate-Splitting (NRS), Cooperative Non-Orthogonal Multiple Access (C-NOMA) and Space Division Multiple Access (SDMA) in a two-user Multiple Input Single Output (MISO) Broadcast Channel (BC) with user relaying. In this work, the existing two-user CRS transmission strategy is generalized to the K-user case. We study the problem of jointly optimizing the precoders, message split, time slot allocation, and relaying user scheduling with the objective of maximizing the minimum rate among users. An efficient self-organizing relaying protocol is first proposed followed by a Successive Convex Approximation (SCA)-based algorithm to jointly optimize time slot, precoders and message split. Numerical results show that the worst-case achievable rate achieved by CRS is significantly increased over that of NRS and SDMA in a wide range of network loads and user deployments. Importantly, the proposed SCA-based algorithm dramatically reduces the computational complexity without any rate loss compared with the conventional algorithm in the literature of CRS. Therefore, we conclude that the proposed K-user CRS is more powerful than the existing transmission schemes.