ABER Performance of LDPC-Coded OFDM Free-Space Optical Communication System Over Exponentiated Weibull Fading Channels With Pointing Errors

A low-density parity-check (LDPC)-coded free space optical (FSO) orthogonal frequency-division multiplexing (OFDM) communication system over aggregated exponentiated Weibull (EW) fading channels with pointing errors considered is investigated. On the basis of the probability density function and cumulative distribution function of the composite channel gain, the analytical expressions of average bit error rate (ABER) of this FSO-OFDM system with on-off keying, K-ary quadrature amplitude modulation (QAM) and phase shift keying (PSK) modulation schemes are derived by using generalized Gauss-Lagurre quadrature rule, respectively. Monte Carlo simulations are provided to verify the validity of these three expressions. Furthermore, LDPC codes are applied in the simulation to improve the ABER performance. The results show that the ABER performance of 16-QAM-OFDM is better than that of the 16-PSK-OFDM system over composite EW fading channels, regardless of the turbulence strengths. For the modulation schemes involved, the degradation due to the increase of atmospheric turbulence strength for turbulence only scenario is more severe when compared with pointing errors included case. The study also demonstrates that significant coding gain improvement can be achieved by LDPC codes over EW fading channels, especially under strong turbulence condition. With pointing errors, more coding gain can be obtained when the jitter increases or beamwidth decreases.