Capacity-Optimized Pre-Equalizer Design for Visible Light Communication Systems

TL;DR

This paper introduces a capacity-optimized pre-equalizer design for VLC systems that balances bandwidth extension and SNR to maximize channel capacity, addressing the limitations of LED bandwidth and traditional equalizer approaches.

Contribution

It provides a fundamental capacity model as a function of pre-equalizer parameters and proposes a systematic design methodology to optimize VLC channel capacity.

Findings

The capacity model explicitly relates pre-equalizer parameters to channel capacity.

The proposed design improves capacity compared to conventional bandwidth-focused equalizers.

Numerical results validate the effectiveness of the capacity-optimized pre-equalizer.

Abstract

Since commercial LEDs are primarily designed for illumination rather than data transmission, their modulation bandwidth is inherently limited to a few MHz. This becomes a major bottleneck in the implementation of visible light communication (VLC) systems necessiating the design of pre-equalizers. While state-of-the-art equalizer designs primarily focus on the data rate increasing through bandwidth expansion, they often overlook the accompanying degradation in signal-to-noise ratio (SNR). Achieving effective bandwidth extension without introducing excessive SNR penalties remains a significant challenge, since the channel capacity is a non-linear function of both parameters. In this paper, we present a fundamental analysis of how the parameters of the LED and pre-equalization circuits influence the channel capacity in intensity modulation and direct detection (IMDD)-based VLC systems. We derive a closed-form expression for channel capacity model that is an explicitly function of analog pre-equalizer circuit parameters. Building upon the derived capacity expression, we propose a systematic design methodology for analog pre-equalizers that effectively balances bandwidth and SNR, thereby maximizing the overall channel capacity across a wide range of channel attenuations. We present extensive numerical results to validate the effectiveness of the proposed design and demonstrate the improvements over conventional bandwidth-optimized pre-equalizer designs.