Mitigation of Outage Probability for All-Optical FSO System using Multipath SNR Equalization Scheme

In this paper, we consider an all-optical multi-relay FSO system and investigate its outage performance over Gamma-Gamma atmospheric turbulence channels. To avoid strict synchronization requirements among relay nodes, we employ relay selection and use only the selected relay in the relaying phase. The outage probability results indicate that relay selection demonstrates significant improvements over the conventional scheme with all relays active.

In this article, we propose an all-optical bidirectional wireless communication system for off-body sensor communication. Optical technology uses infrared (IR) for uplinks and visible light communication (VLC) for downlinks. From numerical simulations, we discuss the impact of body sensor positions on IR and VLC channels. Our goal is to evaluate the possibilities of using optical technology to transmit sensor data for extreme positions such as the ankle, for which the presence of the body creates blockages. In addition, we also consider the variations in orientation of transceivers due to random mobility of body parts during normal movement. Based on a statistical approach, we evaluate performance in terms of outage probability using channel impulse response sets corresponding to the studied scenario, which is health monitoring. Considering a given quality of service, we address trade-offs related to emitting power and data rate. We discuss the results regarding sensor node position and body reflectivity specifically for ankle sensors, corresponding to an extreme but realistic position in the health-monitoring context.

Turbulence and beam wandering are major factors that affect the performance of a laser beam traveling from a ground-to-satellite (uplink). In this paper the performance of the optical uplink with differential phase shift keying (DPSK) scheme is evaluated in order to determine the optimum beam size that minimizes the average bit error rate (BER) and outage probability. Considering the combined effect of turbulence, and beam wandering close-form expressions for BER and outage probability are derived. The accuracy of the derived close-form expressions are verified by applying appropriate simulation scenarios, and numerical results. The obtained results show that the optimum beam size is 2 with zenith angle changes from 0 to 35°. This paper also, studies the system performance on optimized beam size considering the effect of changing satellite altitude, transmit power and zenith angle.

The authors analyse a dual‐hop mixed radio frequency/free space optical (RF/FSO) communication system comprising of single‐input multiple‐output (SIMO) RF hop and a single FSO hop. The RF source is connected to an optical destination through a decode‐and‐forward relay having RF/FSO capabilities. Each link in SIMO‐RF hop is assumed to experience independent and identically distributed (i.i.d.) Nakagami‐m fading. For FSO hop, a unified novel expression for the probability density function (PDF) of irradiance has been derived which unifies Gamma–Gamma and generalised‐K () distributions with misalignment error. Moreover, we obtain a unified PDF of instantaneous signal‐to‐noise ratio (SNR) by unifying the heterodyne detection and intensity modulation/direct detection schemes. Utilising the unified PDF, we derive novel unified closed‐form expressions for average symbol error probability (for different RF modulation techniques), outage probability, and ergodic capacity for the system under consideration. We have also analysed the considered system for high SNR conditions and have analytically obtained the unified diversity order of the same. The derived results clearly show the impact of misalignment error, severe atmospheric conditions, type of detection scheme, and number of RF links on the system performance. All the analytical results are validated through simulations.

Free space optical communication (FSO) has become a popular research direction due to its high bandwidth, easy deployment, and inherent security. Its channel state is unstable because of atmospheric environment, especially in long‐distance ground transmission system. Interleaving combined with forward error correction coding (FEC) have been utilised to improve the stability of system. However, there is little detailed experimental results of deep interleaving combined with FEC under different atmospheric turbulence intensity over long‐distance FSO system. A deep interleaving with FEC method was designed and implemented on a 7 km long online experiment. The performance of different depth interleaving is analysed under weak and strong atmospheric turbulence state. The experiment results show that deep interleaving performs better under weak turbulence for the larger correlation factor of the channel and the outage probability of the system with deep interleaving can be greatly reduced.

Performance investigation of FSO communication systems with chromatic dispersion, propagation losses and truncated normal modeled time jitter

Novel approximate and asymptotic expressions of the outage probability and BER in gamma–gamma fading FSO links with generalized pointing errors

In this paper, an exact performance analysis for the hybrid radio frequency/free space optical (RF/FSO) communication system based on receiver diversity combining technique is presented. The hybrid system transmits the same data with the same data rate over the RF and FSO links simultaneously. The selection combining technique is implemented to combine the received signals from both link. New closed-form expressions for the average bit error rate and outage probability are derived in order to trace the system’s performance under the combination of the atmospheric turbulence and weather conditions variation. The analysis of the hybrid system’s performance clearly indicates that the system is advantageous as it exploits the complementary properties of the FSO and RF channels. In addition, the performance comparison demonstrates the hybrid system’s superior performance compared with the FSO and RF systems over a different variation of the atmospheric channel.

Analog network coding (ANC) can effectively improve the outage performance and increase its spectrum efficiency for two-way relay systems. An adaptive analog network coding strategy (AVSN-ANC strategy) was proposed in this paper, which dynamically adjusts the number of timeslots according to the instantaneous channel information. In this manner, the outage probability can be significantly reduced. We describe the detailed realization of the strategy, derive the closed-form expression for the lower bound of the outage probability, analyze the achievable diversity order, and discuss the power allocation issue. Simulation results validate the theoretical analysis. Compared to conventional ANC protocol with fixed slot numbers, the proposed AVSN-ANC strategy offers better outage performance. In addition, it is shown from our study that, the equal power allocation scheme, despite its simplicity, can obtain the near-optimal performance in terms of the outage probability.

Network coding can improve the information transmission rate, which is an effective technology to improve the performance of wireless relay network. Based on cooperative diversity and network coding, the paper propose a two-way communication system model of vehicle and study the three-slot amplification and forwarding network coding scheme with direct link. The optimal power allocation scheme is obtained by analyzing the optimal power allocation based on the system outage probability. We analyze the influence of distance, speed and time on the probability of interruption. Simulation results show that the power optimization scheme proposed in this paper can obtain a lower outage probability than the equal power allocation scheme.

In this letter, a novel approach for outage probability analysis of the multinode amplify-and-forward relay network is provided. It is shown that the harmonic mean of two exponential random variables can be approximated, at high signal-to-noise ratio (SNR), to be an exponential random variable. The single relay case considered before is a special case of our analysis. Based on that approximation, an outage probability bound is derived which proves to be tight at high SNR. Based on the derived outage probability bound, optimal power allocation is studied. Simulation results show a performance improvement, in terms of symbol error rate, of the optimal power allocation compared to the equal power-allocation scheme

In this paper, we study the power allocation for two-way amplify-and-forward relay networks with asymmetric traffic requirements in cognitive radio. The proposed power allocation scheme is achieved by minimizing the weaker link's individual outage probability under the sum-power constraint and interference power threshold (IPT) constraints of the primary user (PU). Particularly, for the purpose of accomplishing the power allocation more realistically, the interference to each other between PU and secondary user (SU) and relay is taken into consideration. And the closed-form solution is derived for the optimum power allocation scheme of each case. Numerical results confirm that the proposed scheme improves the system performance compared with the equal power allocation scheme under various traffic requirements. The outage probability of SU communication is limited by the IPT constraints of PU and is affected significantly by the IPT level of PU. Furthermore, regardless of the symmetric or asymmetric traffic requirements, the proposed power allocation scheme is more suitable for cognitive two-way relaying networks.

In this paper, we consider a mixed dual-hop RF-FSO communication system, where RF link is subjected to Rice fading, while FSO link experience double generalized Gamma (GG) turbulence with pointing errors. The double GG distribution is a newly developed turbulence model, which contains commonly used turbulence models as its special case and matches excellently with the existing experimental data. The Rician fading model represents propagation conditions which include the presence of the line-of-sight component and also, it includes the Rayleigh fading model as its special cases. Here we first derive a novel, analytical closed-form expression for the cumulative distribution function for the end-to-end signal-to-noise ratio of the considered system. We show that our derived result contains the existing results presented in the literature as its special case. Then, relaying on the developed analytical results, we derive a closed-form expression for the outage probability and using it, we analyze the outage performance of the mixed dual-hop RF_FSO system and investigate the impact of the pointing errors. Numerical results are further demonstrated to confirm the analytical results.

Physical layer security in SWIPT-based cooperative vehicular relaying networks

The last years, FSO technology has demonstrated an increasing scientific and commercial interest. However, due the signal’s propagation through the atmosphere, the operation of FSO links depends strongly on the weather conditions and mostly by atmospheric turbulence effect. A common way for the maximization of the effective radius of FSO systems operating through the atmosphere is the employment of DF relays. However, by employing multiple relays and depending on the adopted fading model for turbulence, the complexity of the expressions used for the performance estimation of such systems can be significant increased. Motivated by the latter, in this work we minimize the mathematical complexity of these expressions by emulating the multi-hop system as dual-hop and by using an approximation for the turbulence-induced fading.