Performance analysis of adaptive combining based hybrid FSO/RF terrestrial communication

Abstract

This study deals with the performance analysis of adaptive combining-based hybrid free-space optics (FSO)/radiofrequency (RF) system in a terrestrial communication scenario with and without pointing errors. Here, outage probability and average symbol error rate (SER) are used as the performance metrics. Adaptive combining is a switching scheme in which the FSO link is active throughout, whereas the RF link is activated based on the transmission reliability of the FSO link and maximal-ratio-combining (MRC) of RF and FSO links is performed at the destination. The small-scale fading in RF and atmospheric turbulence induced fading in FSO links have been characterised by Nakagami-m and Gamma-Gamma distributions, respectively. In addition, the radial displacement between the beam centre and detector centre, which induces pointing errors, is modelled using Rayleigh distribution. The exact closed form expressions for the outage and average SER have been derived along with their corresponding asymptotic expressions. Diversity gain of the system has also been determined using the asymptotic expressions. Further, the variation in the performance of the system has been analysed with respect to various parameters including link distance, fading severity parameter, average signal-to-noise of the RF link, and the pointing errors parameter.

On the Capacity Performance of Hybrid FSO/RF System With Adaptive Combining Over Generalized Distributions

“…• In literature, a very few works are available on the adaptive-combining-based hybrid FSO/RF system and the performance metrics like outage and average SER were investigated over the Gamma-Gamma and Nakagami-m fading distributions [26]- [27]. Mixed FSO/RF DH with AF relay Gamma-Gamma Nakagami-m Zero boresight [13] Mixed FSO/RF DH with DF relay Gamma-Gamma Nakagami-m Zero boresight [14] Mixed FSO/RF Fixed and variable gain relay Gamma-Gamma Rician Zero boresight [15] Mixed FSO/RF AF and DF relay Double generalized Gamma EGK shadowed fading Non-zero boresight [16] Hybrid FSO/RF Soft-switching Gamma-Gamma Rician Not included [17] Hybrid FSO/RF Hard-switching Log-normal Nakagami-m Not included [19] Hybrid FSO/RF Hard-switching Malaga α-η-κ-µ Zero boresight [20] Hybrid FSO/RF Multi-hop with hard-switching Gamma-Gamma Nakagami-m Zero boresight [24] Hybrid FSO/RF MRC and SC Gamma-Gamma Rician Not included [25] Hybrid FSO/RF MRC and SC Gamma-Gamma κ-µ Zero boresight [26] Hybrid FSO/RF Adaptive combining Gamma-Gamma Nakagami-m Not included [27] Hybrid FSO/RF Adaptive combining Gamma-Gamma Nakagami-m Zero boresight computationally less exhaustive. Further, the Monte-Carlo simulations are performed to confirm the accuracy of the analytical results.…”

“…Moreover, the capacity performances of both adaptive combining and hardswitching schemes are nearly identical and the capacity values are equal to the single-link FSO system, especially in the high-SNR region. However, both the hybrid systems achieve better reliability in terms of outage and average SER with high SNR gains compared to the single-link FSO system [27]. The reason for the inferior performance of adaptive combining and hardswitching hybrid systems is that the probability of usage of the RF link is high in the low-SNR region and also, the bandwidth of the RF link is lesser than the FSO link.…”

“…The outage probability analysis of the adaptive-combining-based hybrid FSO/RF system was presented in [26]. In [27], the outage and average symbol error rate (SER) of the adaptive combining system were investigated with and without pointing errors. In existing works [26]- [27], the turbulence-induced fading of the FSO link was modeled using the Gamma-Gamma distribution and for modeling the fading of RF channel, the Nakagami-m distribution was assumed.…”

“…In [27], the outage and average symbol error rate (SER) of the adaptive combining system were investigated with and without pointing errors. In existing works [26]- [27], the turbulence-induced fading of the FSO link was modeled using the Gamma-Gamma distribution and for modeling the fading of RF channel, the Nakagami-m distribution was assumed. It is to be noted that the adaptive combining scheme offers the benefits of both switching and spatial diversity systems.…”

Outage Probability Analysis of Free Space Communication System Using Diversity Combining Techniques

“…It is well known that although RF communications have a low risk of link failure, beam-directivity lags far behind that of FSO communications. Hence, most research on the hybrid FSO-RF systems assume a link-distance of no greater than a few kilometers to maximize the merits of additional RF links [47]. It is important that all the above-mentioned studies never focus on the optimization of the hybrid FSO-RF systems using the receive diversity combining techniques.…”