Mao Yijie, Clerckx Bruno, Li Victor O K
1Department of Electrical and Electronic Engineering, The University of Hong Kong, Pok Fu Lam Road, Hong Kong, China.
2Department of Electrical and Electronic Engineering, Imperial College London, Exhibition Road, London, SW7 2AZ UK.
EURASIP J Wirel Commun Netw. 2018;2018(1):133. doi: 10.1186/s13638-018-1104-7. Epub 2018 May 29.
Space-division multiple access (SDMA) utilizes linear precoding to separate users in the spatial domain and relies on treating any residual multi-user interference as noise. Non-orthogonal multiple access (NOMA) uses linearly precoded superposition coding with successive interference cancellation (SIC) to superpose users in the power domain and relies on user grouping and ordering to enforce some users to fully decode and cancel interference created by other users. In this paper, we argue that to efficiently cope with the high throughput, heterogeneity of quality of service (QoS), and massive connectivity requirements of future multi-antenna wireless networks, multiple access design needs to depart from those two extreme interference management strategies, namely fully treat interference as noise (as in SDMA) and fully decode interference (as in NOMA). Considering a multiple-input single-output broadcast channel, we develop a novel multiple access framework, called rate-splitting multiple access (RSMA). RSMA is a more general and more powerful multiple access for downlink multi-antenna systems that contains SDMA and NOMA as special cases. RSMA relies on linearly precoded rate-splitting with SIC to decode part of the interference and treat the remaining part of the interference as noise. This capability of RSMA to decode interference and partially treat interference as noise enables to softly bridge the two extremes of fully decoding interference and treating interference as noise and provides room for rate and QoS enhancements and complexity reduction. The three multiple access schemes are compared, and extensive numerical results show that RSMA provides a smooth transition between SDMA and NOMA and outperforms them both in a wide range of network loads (underloaded and overloaded regimes) and user deployments (with a diversity of channel directions, channel strengths, and qualities of channel state information at the transmitter). Moreover, RSMA provides rate and QoS enhancements over NOMA at a lower computational complexity for the transmit scheduler and the receivers (number of SIC layers).
空分多址（SDMA）利用线性预编码在空间域中分离用户，并将任何残留的多用户干扰视为噪声。非正交多址（NOMA）使用具有连续干扰消除（SIC）的线性预编码叠加编码在功率域中叠加用户，并依靠用户分组和排序来强制一些用户完全解码并消除其他用户产生的干扰。在本文中，我们认为，为了有效应对未来多天线无线网络的高吞吐量、服务质量（QoS）异构性以及大规模连接需求，多址设计需要背离这两种极端的干扰管理策略，即完全将干扰视为噪声（如SDMA中那样）和完全解码干扰（如NOMA中那样）。考虑到多输入单输出广播信道，我们开发了一种新颖的多址框架，称为速率分割多址（RSMA）。RSMA是一种更通用、更强大的下行多天线系统多址方式，SDMA和NOMA是其特殊情况。RSMA依靠具有SIC的线性预编码速率分割来解码部分干扰，并将其余干扰部分视为噪声。RSMA这种解码干扰并部分将干扰视为噪声的能力能够在完全解码干扰和将干扰视为噪声这两个极端之间实现软过渡，并为速率和QoS提升以及复杂度降低提供空间。对这三种多址方案进行了比较，大量数值结果表明，RSMA在SDMA和NOMA之间提供了平滑过渡，并且在广泛的网络负载（欠载和过载状态）和用户部署（具有多种信道方向、信道强度以及发射机处信道状态信息质量）下均优于它们两者。此外，对于发射调度器和接收机（SIC层数），RSMA以较低的计算复杂度提供了比NOMA更高的速率和QoS提升。
