Joint Design of Probabilistic Constellation Shaping and Precoding for Multi-user VLC Systems

TL;DR

This paper introduces a joint design of probabilistic constellation shaping and precoding for multi-user VLC systems, significantly improving sum-rate performance by optimizing symbol probabilities and transmit precoding.

Contribution

It presents a novel joint optimization framework for PCS and precoding in VLC, employing heuristic and low-complexity methods to enhance system throughput.

Findings

Joint design outperforms conventional uniform signaling.

The FA-based approach achieves better sum-rate with higher complexity.

The ZF-based approach offers a low-complexity alternative with competitive performance.

Abstract

This paper proposes a joint design of probabilistic constellation shaping (PCS) and precoding to enhance the sum-rate performance of multi-user visible light communications (VLC) broadcast channels subject to signal amplitude constraint. In the proposed design, the transmission probabilities of bipolar $M$-pulse amplitude modulation ($M$-PAM) symbols for each user and the transmit precoding matrix are jointly optimized to improve the sum-rate performance. The joint design problem is shown to be a complex non-convex problem due to the non-convexity of the objective function. To tackle the problem, the firefly algorithm (FA), a nature-inspired heuristic optimization approach, is employed to solve a local optima to the original non-convex optimization problem. The FA-based approach, however, suffers from high computational complexity. Therefore, we propose a low-complexity design based on zero-forcing (ZF) precoding, which is solved using an alternating optimization (AO) approach. Simulation results reveal that the proposed joint design with PCS significantly improves the sum-rate performance compared to the conventional design with uniform signaling. Some insights into the optimal symbol distributions of the two joint design approaches are also provided.