On the performance evaluation of LQAM-MPPM techniques over exponentiated Weibull fading free-space optical channels

Abstract We investigate the performance of hybrid L -ary quadrature-amplitude modulation-multi-pulse pulse-position modulation ( L QAM-MPPM) techniques over exponentiated Weibull (EW) fading free-space optical (FSO) channel, considering both weather and pointing-error effects. Upper bound and approximate-tight upper bound expressions for the bit-error rate (BER) of L QAM-MPPM techniques over EW FSO channels are obtained, taking into account the effects of fog, beam divergence, and pointing-error. Setup block diagram for both the transmitter and receiver of the L QAM-MPPM/FSO system are introduced and illustrated. The BER expressions are evaluated numerically and the results reveal that L QAM-MPPM technique outperforms ordinary L QAM and MPPM schemes under different fading levels and weather conditions. Furthermore, the effect of modulation-index is investigated and it turned out that a modulation-index greater than 0.4 is required in order to optimize the system performance. Finally, the effect of pointing-error introduces a great power penalty on the L QAM-MPPM system performance. Specifically, at a BER of 1 0 − 9 , pointing-error introduces power penalties of about 45 and 28 dB for receiver aperture sizes of D R = 50 and 200 mm, respectively.