11 research outputs found
Sum Rate and Fairness Analysis for the MU-MIMO Downlink under PSK Signalling: Interference Suppression vs Exploitation
In this paper, we analyze the sum rate performance of multi-user
multiple-input multiple-output (MU-MIMO) systems, with a finite constellation
phase-shift keying (PSK) input alphabet. We analytically calculate and compare
the achievable sum rate in three downlink transmission scenarios: 1) without
precoding, 2) with zero forcing (ZF) precoding 3) with closed form constructive
interference (CI) precoding technique. In light of this, new analytical
expressions for the average sum rate are derived in the three cases, and Monte
Carlo simulations are provided throughout to validate the analysis.
Furthermore, based on the derived expressions, a power allocation scheme that
can ensure fairness among the users is also proposed. The results in this work
demonstrate that, the CI strictly outperforms the other two schemes, and the
performance gap between the considered schemes increases with increase in the
MIMO size. In addition, the CI provides higher fairness and the power
allocation algorithm proposed in this paper can achieve maximum fairness index
Rate Splitting with Finite Constellations: The Benefits of Interference Exploitation vs Suppression
Rate-Splitting (RS) has been proposed recently to enhance the performance of
multi-user multiple-input multiple-output (MU-MIMO) systems. In RS, a user
message is split into a common and a private part, where the common part is
decoded by all users, while the private part is decoded only by the intended
user. In this paper, we study RS under a phase-shift keying (PSK) input
alphabet for multi-user multi-antenna system and propose a constructive
interference (CI) exploitation approach to further enhance the sum-rate
achieved by RS under PSK signaling. To that end, new analytical expressions for
the ergodic sum-rate are derived for two precoding techniques of the private
messages, namely, 1) a traditional interference suppression zero-forcing (ZF)
precoding approach, 2) a closed-form CI precoding approach. Our analysis is
presented for perfect channel state information at the transmitter (CSIT), and
is extended to imperfect CSIT knowledge. A novel power allocation strategy,
specifically suited for the finite alphabet setup, is derived and shown to lead
to superior performance for RS over conventional linear precoding not relying
on RS (NoRS). The results in this work validate the significant sum-rate gain
of RS with CI over the conventional RS with ZF and NoRS
Rate-Splitting Multiple Access: Finite Constellations, Receiver Design, and SIC-free Implementation
Rate-Splitting Multiple Access (RSMA) has emerged as a novel multiple access
technique that enlarges the achievable rate region of Multiple-Input
Multiple-Output (MIMO) broadcast channels with linear precoding. In this work,
we jointly address three practical but fundamental questions: (1) How to
exploit the benefit of RSMA under finite constellations? (2) What are the
potential and promising ways to implement RSMA receivers? (3) Can RSMA still
retain its superiority in the absence of successive interference cancellers
(SIC)? To address these concerns, we first propose low-complexity precoder
designs taking finite constellations into account and show that the potential
of RSMA is better achieved with such designs than those assuming Gaussian
signalling. We then consider some practical receiver designs that can be
applied to RSMA. We notice that these receiver designs follow one of two
principles: (1) SIC: cancelling upper layer signals before decoding the lower
layer and (2) non-SIC: treating upper layer signals as noise when decoding the
lower layer. In light of this, we propose to alter the precoder design
according to the receiver category. Through link-level simulations, the
effectiveness of the proposed precoder and receiver designs are verified. More
importantly, we show that it is possible to preserve the superiority of RSMA
over Spatial Domain Multiple Access (SDMA), including SDMA with advanced
receivers, even without SIC at the receivers. Those results therefore open the
door to competitive implementable RSMA strategies for 6G and beyond
communications.Comment: Submitted to IEEE for publicatio