Performance Analysis of Hybrid FSO Systems Using FSO/RF-FSO Link Adaptation

Abstract

Free-space optical (FSO) links are considered as cost-effective, noninvasive alternative to fiber optic cables for 5G cellular backhaul networking. For FSO-based backhaul networks, we propose an additional millimeter-wavelength (MMW) radio-frequency (RF)-FSO link, used as a backup. Uninterrupted and reliable network connection is possible by switching between primary FSO link and the secondary RF-FSO link; when the primary link is under atmospheric turbulence, the secondary link maintains connectivity as the MMW RF link exhibits complementary characteristics to atmospheric effects. In order to analytically assess the improvement, we also derive concise mathematical expressions for different performance metrics, such as outage probability, average bit error rate (BER), and capacity. Our results demonstrate that the FSO/RF-FSO topology performs better than a single FSO link in terms of outage probability and BER. The dual-hop mixed RF-FSO link is realized with an amplify and forward (AF) relay that adapts an average power scaling strategy. The irradiance fluctuations in the FSO links are modeled by gamma-gamma distribution, assuming strong atmospheric turbulence while it is assumed that the RF link experiences multipath Rayleigh fading. For switching between links, a single FSO threshold is considered first, followed by a dual FSO threshold to prevent unnecessary switching.

Performance Analysis of Hard-Switching Based Hybrid FSO/RF System over Turbulence Channels

“…On the other hand, the RF link experiences Rayleigh fading as it is subjected to a multi-path effect. Accordingly, the signal to noise ratio corresponds to following exponential PDF [9]:…”

“…Another relay scheme was proposed in [7,8], where the relay system was analyzed for two nodes with the dual hop between FSO and RF link. In [9], link adaptation technique was used for a hybrid system where RF-FSO dual link activated as the threshold of FSO link went below a certain threshold. Dual FSO threshold scheme was also discussed which is effective to avoid frequent switching when the weather conditions change rapidly.…”

“…For simplicity, it is assumed that at least one link remains active at a certain time and the system does not interrupt the total Hybrid FSO/RF link. As one link remains active at a time, the transmitter will have to consume less power and receiver design would be simpler as it will not require any combination techniques to extract data like in [9,10]. Figure 1 portrays the basic idea of the hybrid system while Figure 2 shows the state transition diagram for this hard-switching between FSO and RF link of the Hybrid FSO/RF system under consideration.…”

Performance evaluation of a novel relay‐assisted hybrid FSO/RF communication system with receive diversity

“…Few works of this category investigated diversity schemes [25]. The second group examines the performance of the dual-hop structure [2,12,13,15,[30][31][32][33][34][35][36][37][38][39]; in this area, few works used diversity schemes [39]; also parallel transmission was investigated in few works [31]. The third category involves the multi-hop structure [40][41][42][43][44][45].…”

“…asymptotic Outage Probability of the proposed structure in Negative Exponential atmospheric turbulence becomes as (37). )} (38)…”