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

Abstract

One of the main problems in mobile communication systems is the degradation of Radio Frequency (RF) connection when mobile user is far from base station. One way to solve this problem is to increase the transmitter power, but the mobile transmitter is not able to supply much power. Another way is to use a relay; among relay schemes, amplify and forward is better for long range communications. Amplify and forward relay is not affordable in terms of power consumption and performance, because it consumes a lot of power inefficiently and enhances the noise. Therefore, in other cases, except in the case of long range links, other relay protocols, such as decode and forward, as well as demodulate and forward, are preferable. In this paper, a novel multi-hop hybrid Free Space Optical (FSO) / RF link is presented; it is made up of two main parts. The first part establishes the connection between the mobile user and source base station, and the second part establishes the connection between the source and the destination base stations. In the first part, a mobile user wants to connect to the source base station via a long range link; therefore, a fixed gain amplify and forward relay with multiple receive antennas is used for communication establishment. In the second part, the source and the destination base stations are connected via a multi-hop hybrid parallel FSO / RF link with demodulate and forward relaying. Considering the FSO link in Gamma-Gamma atmospheric turbulence with the effect of pointing error in moderate to strong regime and the Negative Exponential atmospheric turbulence in saturate regime, and the RF link in Rayleigh fading, new closed form exact and asymptotic expressions are derived for the Outage Probability and Bit Error Rate of the proposed structure. Derived expressions are verified with MATLAB simulations. The results show that the performance of the proposed structure does not change with changing channel conditions; therefore, this structure is reliable and does not require more processing or power consumption in order to maintain system performance in poor channel conditions. Hence, the proposed structure is particularly suitable for mobile communications with limitations in power, processing and latency. The innovations and contributions of this paper, which are first introduced in the multi-hop hybrid FSO / RF hybrid structure, include the novelty of the proposed structure, the presentation of new exact and asymptotic mathematical solutions, the use of receive diversity, Bit Error Rate analysis, using amplify and forward as well as decode and forward protocols, taking into account a wide range of atmospheric turbulences with the effect of pointing error, using opportunistic selection and selection combining schemes.The atmospheric turbulence causes the random oscillation of the received signal intensity [5]. Many statistical models have been presented to investigate the effects of atmospheric turbulence including Log-Normal [6], Gamma-Gamma [7], K [8], M [9], and Negative Exponential [10]. Am...

Novel suboptimal approaches for hyperparameter tuning of deep neural network [under the shelf of optical communication]

“…where 𝐼 is the atmospheric turbulence intensity, Γ(. is the scaling parameter that characterize the irradiance fluctuation in Gamma-Gamma model, where 𝜎 𝑅 2 = 1.23𝑐 𝑛 2 𝑘 7/6 𝑙 11/6 , where 𝑘 = 2𝜋/𝜆 is wave number, and 𝑙 is FSO link distance [25].…”

A novel hybrid FSO / RF communication system with receive diversity

“…At the receiver side (Base Station), receive diversity technique gathers different copies of the transmitted signal, which are encountered with different fading channels. Combination of these copies could really help better recovery of the transmitted signal [2]. Maximum Ratio Combiner (MRC), Equal Gain Combiner (EGC) and Selection Combiner (SC) are some of the well-known combiners.…”

Performance analysis of hybrid FSO/RF communication systems with Alamouti coding or antenna selection

“…To the best of the authors’ knowledge, there is no other work in hybrid FSO/RF dealing with transmit diversity and other papers published on FSO/RF just focused on different atmospheric turbulences or relaying protocols. The authors, in this paper and some other papers [17–20], have tried to combine various space diversity schemes with hybrid FSO/RF system. Authors thought that it might be interesting to show what happens when these two techniques are combined.…”