Abstract
Space-division multiple access (SDMA) utilizes linear precoding to separate users in the spatial domain and relies on fully 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 partially 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).
Highlights
With the dramatic upsurge in the number of devices expected in 5G and beyond, wireless networks will be operated in a variety of regimes ranging from underloaded to overloaded (where the number of scheduled devices is smaller and larger than the number of transmit antennasMao et al EURASIP Journal on Wireless Communications and Networking (2018) 2018:133 interests in re-thinking multiple access for the downlink of communication systems.In this paper, we propose a new multiple access called rate-splitting multiple access (RSMA)
In order to fully assess the novelty of the proposed multiple access paradigm and the design philosophy, we first review the state of the art of two major multiple accesses, namely non-orthogonal multiple access (NOMA) [1], called Multi-User Superposition Transmission (MUST) in 3GPP LTE Rel-13 [2] and space-division multiple access (SDMA)
Though superposition coding (SC)–successive interference cancellation (SIC) is optimal to achieve the capacity region of single-input single-output (SISO) broadcast channel (BC), we show that a single-layer rate splitting (RS) is a lowcomplexity alternative that only requires a single layer of SIC at each receiver and achieves close to Superposition coding with successive interference cancellation (SC–SIC) performance in a SISO BC deployment
Summary
With the dramatic upsurge in the number of devices expected in 5G and beyond, wireless networks will be operated in a variety of regimes ranging from underloaded to overloaded (where the number of scheduled devices is smaller and larger than the number of transmit antennasMao et al EURASIP Journal on Wireless Communications and Networking (2018) 2018:133 interests in re-thinking multiple access for the downlink of communication systems.In this paper, we propose a new multiple access called rate-splitting multiple access (RSMA). In order to fully assess the novelty of the proposed multiple access paradigm and the design philosophy, we first review the state of the art of two major multiple accesses, namely non-orthogonal multiple access (NOMA) [1], called Multi-User Superposition Transmission (MUST) in 3GPP LTE Rel-13 [2] and space-division multiple access (SDMA). We identify their benefits and limitations and make critical observations, before motivating the introduction of the novel and more powerful RSMA. On the other hand, when users exhibit the same channel strengths, OMA based on TDMA is sufficient to achieve the capacity region [8]
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