# Precoded Chebyshev-NLMS based pre-distorter for nonlinear LED compensation in NOMA-VLC

## TL;DR

This paper introduces a novel precoding and power allocation scheme for NOMA-based VLC systems that compensates for LED nonlinearities, enhancing capacity and performance in high-speed green communication scenarios.

## Contribution

It proposes a Chebyshev-NLMS based pre-distorter and a generalized power allocation strategy for nonlinear NOMA-VLC, addressing LED nonlinearity issues and improving system capacity.

## Key findings

- Improved bit error rate bounds for the proposed detector.
- Enhanced system capacity with the new precoding and power allocation.
- Effective nonlinear LED compensation in NOMA-VLC systems.

## Abstract

Visible light communication (VLC) is one of the main technologies driving the future 5G communication systems due to its ability to support high data rates with low power consumption, thereby facilitating high speed green communications. To further increase the capacity of VLC systems, a technique called non-orthogonal multiple access (NOMA) has been suggested to cater to increasing demand for bandwidth, whereby users' signals are superimposed prior to transmission and detected at each user equipment using successive interference cancellation (SIC). Some recent results on NOMA exist which greatly enhance the achievable capacity as compared to orthogonal multiple access techniques. However, one of the performance-limiting factors affecting VLC systems is the nonlinear characteristics of a light emitting diode (LED). This paper considers the nonlinear LED characteristics in the design of pre-distorter for cognitive radio inspired NOMA in VLC, and proposes singular value decomposition based Chebyshev precoding to improve performance of nonlinear multiple-input multiple output NOMA-VLC. A novel and generalized power allocation strategy is also derived in this work, which is valid even in scenarios when users experience similar channels. Additionally, in this work, analytical upper bounds for the bit error rate of the proposed detector are derived for square $M$-quadrature amplitude modulation.