Optimization of Signal-to-Noise-and-Distortion Ratio for Dynamic Range Limited Nonlinearities

TL;DR

This paper develops an optimal predistortion strategy to maximize the signal-to-noise-and-distortion ratio in nonlinear optical wireless communication systems, improving system performance by tailoring the response based on input signal statistics.

Contribution

It introduces a method to design an optimal double-sided limiter for nonlinear devices, maximizing SNDR considering input distribution and noise, with applications to LED linearization.

Findings

Optimal predistortion response is a double-sided limiter with specific gain and bias.

Derived bounds on system capacity based on SNDR and DSNR.

Provided design guidelines for nonlinear device linearization in optical communications.

Abstract

Many components used in signal processing and communication applications, such as power amplifiers and analog-to-digital converters, are nonlinear and have a finite dynamic range. The nonlinearity associated with these devices distorts the input, which can degrade the overall system performance. Signal-to-noise-and-distortion ratio (SNDR) is a common metric to quantify the performance degradation. One way to mitigate nonlinear distortions is by maximizing the SNDR. In this paper, we analyze how to maximize the SNDR of the nonlinearities in optical wireless communication (OWC) systems. Specifically, we answer the question of how to optimally predistort a double-sided memory-less nonlinearity that has both a "turn-on" value and a maximum "saturation" value. We show that the SNDR-maximizing response given the constraints is a double-sided limiter with a certain linear gain and a certain bias value. Both the gain and the bias are functions of the probability density function (PDF) of the input signal and the noise power. We also find a lower bound of the nonlinear system capacity, which is given by the SDNR and an upper bound determined by dynamic signal-to-noise ratio (DSNR). An application of the results herein is to design predistortion linearization of nonlinear devices like light emitting diodes (LEDs).