In visible light communications, hybrid asymmetrically clipped optical orthogonal frequency division multiplexing (HACO-OFDM) is an attractive scheme with high power efficiency and high spectral efficiency. This paper compares the implementation complexity and receiving performance of three HACO-OFDM systems. The comparison results show that the implementation complexity of the HACO-OFDM system that eliminate noise through time domain signal processing(TD-HACO-OFDM) and the interference-free hybrid OOFDM(IF-HOOFDM) system is lower. In terms of receiving performance, IF-HOOFDM system has the best bit error rate (BER) performance on the asymmetrically clipped optical OFDM(ACO-OFDM) branch; When the clipping noise estimation is inaccurate, the BER performance of the TD-HACO-OFDM system on the pulse-amplitude-modulated discrete multitone (PAM-DMT) branch is significantly better than the other two systems, the BER performance of the IF-HOOFDM system on the PAM-DMT branch is better than the conventional HACO-OFDM system based on frequency domain processing(FD-HACO-OFDM).
KEYWORDS: Telecommunications, Orthogonal frequency division multiplexing, Signal to noise ratio, Transmitters, Error analysis, Communication engineering, Light emitting diodes, Distortion
For the first time, a channel estimation method for hybrid ACO-OFDM (HACO-OFDM) based visible light communications systems is proposed. The channel characteristics carried on the ACO-OFDM subcarriers are estimated by the least square (LS) method, and the channel response on the PAM-DMT subcarriers can be obtained by linear interpolation of which on the ACO-OFDM subcarriers. While considering the multipath channel in the paper, the simulation results show that the proposed scheme is able to estimate the channel effectively for HACOOFDM system. After equalization based on the results of the channel estimation, the average BER on the ACOOFDM branch will be lower than10-3 when SNR>18.2dB, the average BER on the pulse-amplitude-modulated discrete multitone (PAM-DMT) branch will be lower than 10-3 when SNR>19.4dB.
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