Distributed Rate-Splitting Multiple Access for Multilayer Satellite Communications

Future wireless networks, in particular, 5G and beyond, are anticipated to deploy dense Low Earth Orbit (LEO) satellites to provide global coverage and broadband connectivity with reliable data services. However, new challenges for interference management have to be tackled due to the large scale of dense LEO satellite networks. Rate-Splitting Multiple Access (RSMA), widely studied in terrestrial communication systems and Geostationary Orbit (GEO) satellite networks, has emerged as a novel, general, and powerful framework for interference management and multiple access strategies for future wireless networks. In this paper, we propose a multilayer interference management scheme for spectrum sharing in heterogeneous GEO and LEO satellite networks, where RSMA is implemented distributedly at GEO and LEO satellites, namely Distributed-RSMA (D-RSMA), to mitigate the interference and boost the user fairness of the system. We study the problem of jointly optimizing the GEO/LEO precoders and message splits to maximize the minimum rate among User Terminals (UTs) subject to a transmit power constraint at all satellites. A Semi-Definite Programming (SDP)-based algorithm is proposed to solve the original non-convex optimization problem. Numerical results demonstrate the effectiveness and network load robustness of our proposed D-RSMA scheme for multilayer satellite networks. Because of the data sharing and the interference management capability, D-RSMA provides significant max-min fairness performance gains when compared to several benchmark schemes.

Max-Min Fairness of Rate-Splitting Multiple Access with Finite Blocklength Communications

Rate-Splitting Multiple Access (RSMA) has emerged as a flexible and powerful framework for wireless networks. In this paper, we investigate the user fairness of downlink multi-antenna RSMA in short-packet communications with/without cooperative (user-relaying) transmission. We design optimal time allocation and linear precoders that maximize the Max-Min Fairness (MMF) rate with Finite Blocklength (FBL) constraints. The relation between the MMF rate and blocklength of RSMA, as well as the impact of cooperative transmission are investigated for a wide range of network loads. Numerical results demonstrate that RSMA can achieve the same MMF rate as Non-Orthogonal Multiple Access (NOMA) and Space Division Multiple Access (SDMA) with smaller blocklengths (and therefore lower latency), especially in cooperative transmission deployment. Hence, we conclude that RSMA is a promising multiple access for guaranteeing user fairness in low-latency communications.