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Open Access Research

EVM and achievable data rate analysis of clipped OFDM signals in visible light communication

Zhenhua Yu1*, Robert J Baxley2 and Guo Tong Zhou1

Author Affiliations

1 School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0250, USA

2 Georgia Tech Research Institute, Atlanta, GA 30332-0821, USA

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EURASIP Journal on Wireless Communications and Networking 2012, 2012:321  doi:10.1186/1687-1499-2012-321

Published: 26 October 2012

Abstract

Orthogonal frequency division multiplexing (OFDM) has been considered for visible light communication (VLC); thanks to its ability to boost data rates as well as its robustness against frequency-selective fading channels. A major disadvantage of OFDM is the large dynamic range of its time-domain waveforms, making OFDM vulnerable to nonlinearity of light emitting diodes. DC-biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM) are two popular OFDM techniques developed for the VLC. In this article, we will analyze the performance of the DCO-OFDM and ACO-OFDM signals in terms of error vector magnitude (EVM), signal-to-distortion ratio (SDR), and achievable data rates under both average optical power and dynamic optical power constraints. EVM is a commonly used metric to characterize distortions. We will describe an approach to numerically calculate the EVM for DCO-OFDM and ACO-OFDM. We will derive the optimum biasing ratio in the sense of minimizing EVM for DCO-OFDM. In addition, we will formulate the EVM minimization problem as a convex linear optimization problem and obtain an EVM lower bound against which to compare the DCO-OFDM and ACO-OFDM techniques. We will prove that the ACO-OFDM can achieve the lower bound. Average optical power and dynamic optical power are two main constraints in VLC. We will derive the achievable data rates under these two constraints for both additive white Gaussian noise channel and frequency-selective channel. We will compare the performance of DCO-OFDM and ACO-OFDM under different power constraint scenarios.

Keywords:
Orthogonal frequency division multiplexing (OFDM); Visible light communications (VLC); DC-biased optical OFDM (DCO-OFDM); Asymmetrically clipped optical OFDM (ACO-OFDM); Error vector magnitude (EVM); Achievable data rate; Clipping