Subcarrier and Power Allocations for Dimmable Enhanced ADO-OFDM With Iterative Interference Cancellation

Abstract

In this paper, a novel modulation scheme called enhanced asymmetrically clipped DC-biased optical OFDM (eADO-OFDM) is proposed to accommodate different demands of multi-users in downlink multiple access for visible light communication systems. Meanwhile, to satisfy various dimming levels, enhanced negative ADO-OFDM (eNADO-OFDM) is investigated and combined with eADO-OFDM for multiplexing transmission. By adjusting the proportion of these two signals, the dimming control scheme can be achieved, while the entire dynamic range of light-emitting diodes is exploited. In order to achieve superior transmission performance, the optimal power allocation under the desired dimming level is studied to minimize the overall bit error rate (BER). Moreover, to obtain more accurate estimation, an iterative receiver with interference cancellation, in which the pairwise averaging and pairwise clipping are exploited, is proposed. The simulation results show that the proposed scheme can effectively carry out the dimming control with wide dimming range for illumination and achieve superior BER performance at the same signalto-noise ratio compared to the conventional counterparts, while only a few iterations are required. INDEX TERMS Visible light communications (VLC), enhanced asymmetrically clipped DC biased optical OFDM (eADO-OFDM), interference cancellation, power allocation, dimming control.

Performance enhancement for visible light communication based ADO-OFDM

“…Where βdc is DC bias could be added and selected concerning the standard deviation of the DCO-OFDM signal [6]. The performance of DCO-OFDM is strongly affected by the DC bias, as the optical power efficiency of the system decreases [8], [12], [14].…”

BER Comparison and Enhancement of Different Optical OFDM for VLC

“…The O-OFDM produces real positive values that differ from OFDM used in RF systems that deal with complex bipolar signals [10]. Many O-OFDM types are proposed depending on generating non-negative values, and Hermitian symmetry is used to convert complex values to real [10][11][12]. In DC Biased Optical OFDM (DCO-OFDM), the DC bias values are added to the generating OFDM signals to produce positive symbols [13].…”

“…Asymmetrically Clipped Optical OFDM (ACO-OFDM) uses only odd subcarriers for transmission and clipping the OFDM signals to zero for creating non-negative OFDM without affecting the information [8,10]. The optical power of DCO-OFDM is ineffective due to DC bias, while ACO-OFDM is better, but it has low spectral efficiency [11] 13]. ADO-OFDM has the same spectral efficiency as DCO-OFDM, but it has better optical power efficiency [14].…”

Comparative Analysis of Optical Multicarrier Modulations: An Insight into Machine Learning-based Multicarrier Modulation

“…For RF application, the signal is complex (with real and imaginary signal components) and bipolar (positive and negative signal cycle) and must be transmitted via electrical fields while being coherently detected. Conversely, for visible light application, the signal is real and unipolar (positive) and can only be transmitted via optical intensity and received through direct detection [5]. This has left the adoption of multicarrier modulation with orthogonal frequency division multiplexing (OFDM) to ingenious investigations and implementation in the visible light communication plane.…”