Analysis of multi-pulse position modulation free space optical communication system employing wavelength and time diversity over Malaga turbulence channel

Abstract

Free space optics (FSO) communication has proved to be a useful technology both in the scientific and commercial domains in response to exponential growth in demand for ultrahigh bandwidth for applications such as urban broadband services, cellular backhaul and earth to satellite links among others. However, atmospheric turbulence, prevailing adverse weather conditions and pointing errors between the transmitter and receiver affect significantly this technology. To mitigate these challenges, different approaches have been considered in literature such as error control coding, spatial diversity, the use of relays and so on alongside different modulation techniques. Therefore in this paper, we have considered the use of multipulse position modulation (MPPM) modulation technique first with wavelength diversity and then with time diversity techniques over the Malaga (M) distribution as a way of mitigating against turbulence fading and pointing error effects. Closed form expressions for the average bit error rate (BER) and outage probability have been derived and later on used to analyze the system performance. The effect of diversity order, normalized jitter and beam width has been scrutinized, all as functions of the transmitted power. Beside the fact that the increase in diversity order improves both the BER and outage probability, it has been noted that the system performance is highly degraded when the normalized jitter is increased beyond 4 for any given diversity order. The BER decreases while the receiver beam width, Wz increases for all diversity orders, reaching to an optimum value of 0.5 m and 1.2 m for normalized jitter of 2 and 5 respectively. Ultimately, the conclusion drawn from the analytical results of this paper support the application of wavelength as well as time diversity as means of enhancing the FSO communication system performance