Rate-Splitting Multiple Access for Downlink Communication Systems:
Bridging, Generalizing and Outperforming SDMA and NOMA
release_4rddcej5nbcrhgc6pg4ikw4ayi
by
Yijie Mao, Bruno Clerckx, Victor O.K. Li
2018
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) 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 SDMA and NOMA. We develop a novel multiple access
framework, called Rate-Splitting Multiple Access (RSMA). RSMA is a more general
and 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
provide 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).
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