Rate-Splitting for Multi-Antenna Non-Orthogonal Unicast and Multicast Transmission: Spectral and Energy Efficiency Analysis

Abstract

In a Non-Orthogonal Unicast and Multicast (NOUM) transmission system, a multicast stream intended to all the receivers is superimposed in the power domain on the unicast streams. One layer of Successive Interference Cancellation (SIC) is required at each receiver to remove the multicast stream before decoding its intended unicast stream. In this paper, we first show that a linearly-precoded 1layer Rate-Splitting (RS) strategy at the transmitter can efficiently exploit this existing SIC receiver architecture. By splitting the unicast messages into common and private parts and encoding the common parts along with the multicast message into a super-common stream decoded by all the users, the SIC is better reused for the dual purpose of separating the unicast and multicast streams as well as better managing the multi-user interference among the unicast streams. We further propose multi-layer transmission strategies based on the generalized RS and power-domain Non-Orthogonal Multiple Access (NOMA). Two different objectives are studied for the design of the precoders, namely, maximizing the Weighted Sum Rate (WSR) of the unicast messages and maximizing the system Energy Efficiency (EE), both subject to Quality of Service (QoS) rate requirements of all the messages and a sum power constraint. A Weighted Minimum Mean Square Error (WMMSE)-based algorithm and a Successive Convex Approximation (SCA)-based algorithm are proposed to solve the WSR and EE problems, respectively. Numerical results show that the proposed RS-assisted NOUM transmission strategies are more spectrally and energy efficient than the conventional Multi-User Linear-Precoding (MU-LP), Orthogonal Multiple Access (OMA) and power-domain NOMA in a wide range of user deployments (with a diversity of channel directions, channel strengths and qualities of channel state information at the transmitter) and network loads (underloaded and overloaded regimes). It is superior for the downlink multi-antenna NOUM transmission.

Precoder Design For Multi-Group Multicasting With a Common Message

“…In this letter, we build upon the benefits demonstrated in [8]- [10] and look at RS in multigroup multicasting with a common message. Compared to [8], this letter considers the presence of a common message.…”

“…Compared to [9], this letter considers an RS strategy. Finally, when compared to [10], this letter considers multi-group multicasting. Moreover, in this letter, precoders are designed based on RS and superposition ideas and three different schemes are compared:…”

Cooperative Rate Splitting for MISO Broadcast Channel With User Relaying, and Performance Benefits Over Cooperative NOMA

“…In this analysis, the rate region serves as the key performance indicator as it conveys information about the achievable rate by each user under different service requirement priorities. Following a similar setup as in [13], [20], we consider the specific channel realizations to investigate the effect of several channel parameters. When N T = 4, the channels are given by h 1 = [1, 1, 1, 1] H , h 2 = λ 1 × [1, e jα , e j2α , e j3α ] H , and h 3 = λ 2 , respectively, where λ 1 and λ 2 control the relative channel strength, α controls the channel angle between U 1 and U 2 .…”

“…In contrast to NOMA that relies on some users to fully decode the messages of other users (i.e. fully decode interference), Rate-Splitting (RS) also exploits SIC but exploits a more flexible framework of non-orthogonal transmission, which enables to partially decode interference and partially treat remaining interference as noise, and hence provide significant benefits in terms of spectral efficiency [13], [15]- [20], energy efficiency [21], robustness [22], and CSI feedback overhead reduction [15], [23]. In addition, on the standpoint of encoding structure, the combination of a common stream decoded by all users and private streams dedicated to each user also provides a fundamental compatibility with other advanced techniques [24].…”

Energy-Spectrum Efficient Content Distribution in Fog-RAN Using Rate-Splitting, Common Message Decoding, and 3D-Resource Matching

“…The problem of SE optimization for RS-CMD system was extensively studied for various wireless networking scenarios, such as, multi-user broadcast system [24], cloud-radio access network [25], cooperative network with user relaying [26], and aerial network [27]. Meanwhile, both EE maximization and EE-SE trade-off optimization for RS-CMD systems were studied in [28]- [30]. Because of the well demonstrated success of RS-CMD in mitigating multi-user interference, in this work, RS-CMD is employed to distribute contents in multi-level EC enabled F-RAN.…”