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

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.

Using delta-sigma modulators in visible light OFDM systems

“…Since NTF is actually a high-pass filter, very few distortions fall on the in-band subcarriers. We use error vector magnitude (EVM) [13], [21] to quantify the in-band distortions…”

“…Since the primary function of the VLC is providing illumination [2], [10], modification of driving circuits of LED will be not beneficial to the application and commercialization of VLC. Moreover, the high peak to average power ratio (PAPR) makes OFDM signals sensitive to LED nonlinearities [12], [13], [14], [15], [16]. In this work, we propose using a delta-sigma modulator [17], [18], [19] to convert the OFDM signal into a two level representation and directly drive the LED.…”

PAPR Reduction of OFDM Signal for Visible Light Communication by Using Hartley Transform and Companding Techniques

“…To reduce the PAPR, various techniques have been proposed for OFDM-based VLC systems, such as clipping [4], nonlinear companding transforms [5,6], precoding transforms [7] and other techniques etc [8]. These schemes can mainly be categorized into signal scrambling techniques, such as PTS, and signal distortion techniques such as clipping, companding techniques.…”

Transceiver Design for MIMO DCO-OFDM in Visible Light Communication

“…In Ref. [9], the authors only analysed the performance of the double-sided clipped DCO-OFDM in terms of the achievable data rate and error vector magnitude. In Ref.…”

“…In Refs. [3][4][5][6][7][8][9], only the conventional receiver is utilized in DCO-OFDM. The conventional receiver for DCO-OFDM usually does not care for the clipping noise and only simply subtracts the DC bias from the received signal in the process of demodulation.…”