Analysis and Comparison of the LDPC and Reed Solomon Encodings in Mitigating the Impact of Clipping Noise in OFDM-Based VLC

Abstract

The linear error-correcting codes are known to be well suited for battling and correcting the burst errors caused by noise in the wireless data transmission system. However, different types of codes offer different decoding and burst-error-correcting capabilities. This paper compares the Low-Density-Parity Check (LDPC) and Reed Solomon (RS) encoding schemes in battling and correcting the burst error caused by the clipping distortion occurred due to the dynamic range constraints in an Orthogonal Frequency Division Multiplexing (OFDM) based Visible Light Communication (VLC). The unipolar conversion applied to the output of the multiplexer in this system results in a clipping noise which distorts the data symbols on the subcarriers in OFDM block. Considering that such distortion impacts the data symbol on each subcarrier differently, RS and LDP are used to encode the data block before being modulated for mapping the OFDM block. In order to control the extreme value of the output of the multiplexer, the transmitter applies puncturing to the generated codeword before mapping OFDM subcarriers, leaving the corresponding subcarriers of the punctured symbols empty. This will lead to the reduction of clipping events in the optical front-end and will mitigate the impact of nonlinear distortion on the modulated symbols for the occupied subcarriers. The redundancy in the codeword generated by the encoder is used not only to control the clipping probability by shortening the number of active subcarriers but also for the reconstruction of the original codeword and correction of the errors caused by channel noise. This work investigates the ability of LDCP and RS encoders in battling the effects of clipping noise in the frequency domain and compares their performances in improving the bit error ratio (BER) performance of an OFDM-based VLC.