Error performance analysis of optically-preamplified QPSK M-ary PPM systems over atmospheric turbulent channels

Fading experienced in free-space optical channels is known to impede the performance of pulse position modulation (PPM) communication systems. In this paper, we study the effects of log-normal and gamma-gamma fading on the error performance of optically-preamplified coherent hybrid polarization division-multiplexed (PDM) and quadrature phase-shift keying (QPSK) M-ary PPM systems, referred to as PQ-mPPM. We also provide a comparison with of the performance of direct-detection optically-preamplified PPM systems, referred to as DD-mPPM, under similar channel conditions.