In this work, the performance and the capacity analysis of a fixed-gain amplify-and-forward (AF)-based dual-hop asymmetric radio frequency-free space optical (RF-FSO) communication system is performed. The RF link experiences Nakagami-m fading and the FSO link experiences Gamma-Gamma turbulence. For this mixed RF-FSO cooperative system, novel and finite power series-based mathematical expressions for the cumulative distribution function, probability density function, and moment generating function of the end-to-end signal-to-noise ratio are derived. Using these channel statistics new finite power series-based analytical expressions are obtained for the outage probability, the average bit error rate (BER) for various binary and M-ary modulation techniques, and the average channel capacity of the considered system. The same analysis is also performed for the scenario when the FSO link undergoes significant pointing errors along with the Gamma-Gamma distributed turbulence. As a special case analytical expressions for the outage probability, BER, and channel capacity are also presented for a dual-hop asymmetric RF-FSO system where the RF link is Rayleigh distributed. Simulation results validate the proposed mathematical analysis. The effects of fading, turbulence, and pointing error are studied on the outage probability, average BER, and the channel capacity.
In this study, the error performance and the capacity analysis is performed for the decode-and-forward based dual-hop asymmetric radio frequency-free space optical communication (RF-FSO) system. The RF link is characterised by Nakagami-m fading and the FSO link is characterised by path loss, Gamma-Gamma distributed turbulence and pointing error. For this mixed RF-FSO cooperative system, novel closed-form mathematical expressions are derived for cumulative distribution function, probability density function and moment generating function of the equivalent signalto-noise ratio in terms of Meijer-G function. Using these channel statistics, new finite power series based analytical expressions are obtained for the outage probability, the average bit error rate for various binary and M-ary modulation techniques and the average channel capacity of the considered system in terms of Meijer-G function. As a special case, the analytical framework can also be obtained for channel statistics and performance metrics of dual-hop mixed Rayleigh-Gamma-Gamma system. Simulation results validate the proposed mathematical analysis. The effects of fading, turbulence and pointing error are studied on the outage probability, average bit error rate and channel capacity of the asymmetric RF-FSO system.
The error performance of the free space optical (FSO) link suffers from the atmospheric turbulence. By employing an additional transmit aperture at the transmitter along with Alamouti code, the error rate of the FSO communication system can be significantly improved. However, the pointing errors, generated because of the building sway, has the potential to eradicate the benefits of the Alamouti scheme. Therefore, for a general and realistic study of the FSO based Alamouti scheme, the effect of pointing errors in the Gamma-Gamma fading atmospheric fluctuations is considered in this paper. Specifically, we derive the symbol error rate and the average capacity of the Alamouti scheme over the Gamma-Gamma fading FSO links with pointing errors. The moment generating function (MGF) of the scheme is derived in terms of the Meijer-G function. An MGF based approach is used to derive the ergodic capacity of the scheme. The effect of pointing errors over the performance of the scheme is analyzed under different scenarios and it is observed that the pointing errors significantly degrade the diversity of the considered FSO system. Index Terms-Alamouti code, free space optical links, Gamma-Gamma fading, symbol error rate.
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