Multi-User Rate Splitting in Optical Wireless Networks

TL;DR

This paper introduces a novel multi-user rate splitting scheme for optical wireless networks, combining user grouping, blind interference alignment, and power optimization to enhance spectral efficiency and reduce CSI requirements.

Contribution

It proposes a user-grouping algorithm, an outer precoder based on blind interference alignment, and a power allocation optimization for intra-group rate splitting in OWC networks.

Findings

Improved spectral efficiency through combined user grouping and rate splitting.

Reduced CSI requirements using blind interference alignment.

Enhanced sum rate performance with optimized power allocation.

Abstract

Optical wireless communication (OWC) has recently received massive interest as a new technology that can support the enormous data traffic increasing on daily basis. Laser-based OWC networks can provide terabits per second (Tbps) aggregate data rates. However, the emerging OWC networks require clusters of optical transmitters to provide uniform coverage for multiple users. In this context, multi-user interference (MUI) is a crucial issue that must be managed efficiently to provide high spectral efficiency. Rate splitting (RS) is proposed as a transmission scheme to serve multiple users simultaneously by splitting the message of a given user into common and private messages, and then, each user decodes the desired message following a certain procedure. In radio frequency (RF) networks, RS provides higher spectral efficiency compared with orthogonal and non-orthogonal transmission schemes. Considering the high density of OWC networks, the performance of RS is limited by the cost of providing channel state information (CSI) at transmitters and by the noise resulting from interference cancellation. In this work, a user-grouping algorithm is proposed and used to form multiple groups, each group contains users spatially clustered. Then, an outer precoder is designed to manage inter-group interference following the methodology of blind interference alignment (BIA), which reduces the requirements of CSI at RF or optical transmitters. For intra-group interference, RS is applied within each group where the users belonging to a given group receive a unique common message on which their private messages are superimposed. Furthermore, an optimization problem is formulated to allocate the power among the private messages intended to all users such that the sum rate of the network is maximized.