Rate-Splitting for Multi-Antenna Non-Orthogonal Unicast and Multicast Transmission

Abstract

In a superimposed unicast and multicast transmission system, one layer of Successive Interference Cancellation (SIC) is required at each receiver to remove the multicast stream before decoding the unicast stream. In this paper, we show that a linearly-precoded Rate-Splitting (RS) strategy at the transmitter can efficiently exploit this existing SIC receiver architecture. By splitting the unicast message into common and private parts and encoding the common parts along with the multicast message into a super-common stream decoded by all users, the SIC is used for the dual purpose of separating the unicast and multicast streams as well as better managing the multi-user interference between the unicast streams. The precoders are designed with the objective of maximizing the Weighted Sum Rate (WSR) of the unicast messages subject to a Quality of Service (QoS) requirement of the multicast message and a sum power constraint. Numerical results show that RS outperforms existing Multi-User Linear-Precoding (MU-LP) and power-domain Non-Orthogonal Multiple Access (NOMA) in a wide range of user deployments (with a diversity of channel directions and channel strengths). Moreover, since one layer of SIC is required to separate the unicast and multicast streams, the performance gain of RS comes without any increase in the receiver complexity compared with MU-LP. Hence, in such non-orthogonal unicast and multicast transmissions, RS provides rate and QoS enhancements at no extra cost for the receivers.Index Terms-non-orthogonal multicast and unicast transmission, rate-splitting, rate region, WMMSE algorithm

Rate-Splitting Unifying SDMA, OMA, NOMA, and Multicasting in MISO Broadcast Channel: A Simple Two-User Rate Analysis

“…Linearly precoded Rate-Splitting (RS) with Successive Interference Cancellation (SIC) receivers has recently appeared as a powerful non-orthogonal transmission and robust interference management strategy for multi-antenna wireless networks [1]. Though originally introduced for the two-user Single-Input Single-Output Interference Channel (IC) in [2], RS has become an underpinning communication-theoretic strategy to tackle modern interference-related problems and has recently been successfully investigated in several Multiple-Input Single-Output (MISO) Broadcast Channel (BC) settings, namely, unicast-only transmission with perfect Channel State Information at the Transmitter (CSIT) [3], [4] and imperfect CSIT [5]- [13], (multigroup) multicast-only transmission [14], as well as superimposed unicast and multicast transmission [15]. Results highlight that RS provides significant benefits in terms of spectral efficiency [3], [6], [7], [9], [13]- [15], energy efficiency [4], robustness [8], and CSI feedback overhead reduction [6], [12] over conventional strategies used in LTE-A/5G that rely on fully treating interference as noise (e.g.…”

An Efficient Rate-Splitting Multiple Access Scheme for the Downlink of C-RAN Systems

“…The channel bandwidth and the noise power spectral density are set to 10 MHz and -169 dBm/Hz, respectively. For comparison, we present the performance of the conventional SDMA [2] and NOMA schemes [4] as well as of the RSMA-SC scheme [5] with L = 1 and S 1 = N U . To validate the effectiveness of the proposed design of sets S 1 , S 2 , .…”

“…Instead, the work [5] proposed to use a single common signal which is decoded by all UEs, i.e., L = 1 with S 1 = N U . We refer to the RSMA scheme optimized with this choice as RSMA with a single common signal (RSMA-SC).…”

“…Each UE decodes and cancels a predetermined set of common messages and then decodes its private message. The advantages of RSMA in terms of rate region or sum-rate were discussed in [3] and [5] for a multi-user downlink system. The discussion was extended in [6] to a coordinated multi-cell system in which BSs can perfectly cooperate, and in [7] to a C-RAN system under the assumption that, as in [8], each UE has a single common message, and different common messages are independently encoded.…”

Interference Mitigation Via Rate-Splitting in Cloud Radio Access Networks

“…Since then, RS has gained a lot of attention. Recently, the authors of [4] studied RS in non-orthogonal unicast and multicast transmission based on Layered Division Multiplexing (LDM), showing the gain of RS in these scenarios. The authors in [5] proposed a novel RS based multiple access scheme which generalizes and outperforms conventional interference mitigation techniques in multiple access systems such as Space-Division Multiple Access (SDMA) and Non-Orthogonal Multiple Access (NOMA).…”