Mohamed Abaza

Diversity techniques for a free-space optical communication system in correlated log-normal channels

Abstract. Performance analysis of free-space optical (FSO) communication systems in different channel conditions has gained significant attention in literature. Nevertheless, most existing studies consider uncorrelated channel conditions. An uncorrelated channel requires sufficient spacing between transmitters and limits the receiver field of view and link distance. However, this might not be feasible in all applications. Thereby, this paper studies repetition code (RC) and orthogonal space time block code (OSTBC) performance in correlated log-normal FSO channels using intensity modulation and direct detection. An approximate analytical expressions using moment generating function for the average bit error probability are derived. Our simulation results show that RCs are superior to OSTBCs in correlated channel conditions.

Spatial diversity for FSO communication systems over atmospheric turbulence channels

This paper investigates the bit error rate (BER) performance of spatial diversity free-space optical (FSO) communication systems using on-off keying modulation. The study considers correlated log-normal FSO channels as well as path losses due to weather effects using intensity modulation and direct detection schemes. An approximated moment generating functions (MGF) for the joint probability density function of correlated log-normal channels are considered. Using MGF approximation, BER expressions for repetition codes (RCs) and orthogonal space time block codes (OSTBCs) in correlated lognormal channels are derived. Results show that RCs outperform OSTBCs in correlated channel conditions. In addition, the effect of different weather conditions (e.g., haze, rain and fog) on the BER performance of the FSO links are studied. Monte Carlo simulation results are further provided to demonstrate the validity of the proposed mathematical analysis.

MIMO techniques for high data rate free space optical communication system in log-normal channel

Multiple input multiple output (MIMO) technique with equal gain combining (EGC) is considered in this work to enhance the data rate of free-space optical communication (FSO) system in log-normal channel. In FSO system, light propagating in free space is used to transmit data for communication system. 256-ary pulse position modulation (PPM) using intensity modulation with direct detection (IM/DD) as a power efficient system is employed using PIN receiver. Obtained results demonstrate that significant boost of data rate can be achieved using MIMO techniques. Data rate enhances from 350 Mbps to 800 Mbps when using 2 × 2 MIMO configuration. As well, 1 Gbps is reported for 4 × 4 MIMO system. These enhancements are achieved without any bandwidth or power expansions and the bit error rate (BER) at the receiver is maintained below 10-3.

Relay selection for full-duplex FSO relays over turbulent channels

This paper investigates the performance of the best relay selection, based on the max-min signal-to-noise ratio criterion for dual-hop free-space optical (FSO) full-duplex (FD) relays communication system. Decode-and-forward relays over log-normal (LN) channels for weak-to-moderate turbulence and gamma-gamma (G-G) channels for strong turbulence are considered. We assume that the relays have full channel knowledge and the channel is symmetrical. Considering path loss effects and misalignment errors, the outage probability (OP) of the selection is obtained for both half-duplex (HD) and FD relays using the cumulative distribution function (CDF) of the best selection for LN and G-G random variables. Moreover, the average bit error rate (ABER) expressions for FSO communication system over LN channels are derived with the help of Gauss-Laguerres quadrature rule for HD relays, FD relays and direct link. Our results show that FD relays have lowest ABER and OP compared with the direct link and HD relays. Monte Carlo simulations corroborate the correctness of the obtained analytical results.