Performance analysis of a variable‐gain amplify‐and‐forward relayed mixed RF‐FSO system

Abstract

SummaryIn this work, an amplify-and-forward variable-gain relayed mixed RF-FSO system is studied. The considered dual-hop system consists of a radio frequency (RF) link followed by a free space optical (FSO) channel. The RF link is affected by short-term multipath fading and long-term shadowing effects and is assumed to follow the generalized-K fading distribution that approximates accurately several important distributions often used to model communication channels.The FSO channel experiences fading caused by atmospheric turbulence that is modeled by the gamma-gamma distribution characterizing moderate and strong turbulence conditions. The FSO channel also suffers path loss and pointing error induced misalignment fading. The performance of the considered system is analyzed under the collective influence of distribution shaping parameters, pointing errors that result in misalignment fading, atmospheric turbulence, and path loss. The moment-generating function of the Signal power to noise power ratio measured end-to-end for this system is derived. The cumulative distribution function for the Signal power to noise power ratio present between the source and destination receiver is also evaluated. Further, we investigate the error and outage performance and the average channel capacity for this system. The analytical expressions in closed form for the outage probability, symbol and bit error rate considering different modulation schemes and channel capacity are also derived. The mathematical expressions obtained are also demonstrated by numerical plots. KEYWORDSchannel capacity, fading, free space optical communication, probability of outage, radio frequency communication, symbol error rate

Further results on the performance improvement in mixed RF‐FSO systems using hybrid DF/AF (HDAF) relaying

“…The probability density function (pdf) and the cumulative distribution function (CDF) of the instantaneous electrical SNR, ie, Υ S R , for the S R link, which is generalized‐ K distributed, can be written in terms of Meijer's G ‐function (eq. (8.2.1) in the work of Prudnikov et al) and is given in the works of Khanna et al() as and respectively, where , , with k and m being the distribution shaping parameters, Ω S R is the average electrical SNR for the S R link, Γ( n ) is the gamma function defined as , and is the Meijer's G ‐function. Furthermore, the relay to destination FSO link that is affected by path loss (attenuation), atmospheric turbulence, and misalignment fading has the CDF of the SNR Υ R D , given by Aggarwal et al as …”

“…The influence of pointing error impairments on the capacity and error performance of mixed RF‐FSO systems was further analyzed in the work of Ansari et al Since then, mixed RF‐FSO systems have been extensively researched (see related works()). In the works of Khanna et al,() the performance of a variable‐gain AF relayed mixed RF‐FSO system having a generalized‐ K ( G K ) distributed RF channel() and a gamma‐gamma distributed FSO channel was analyzed. The end‐to‐end performance of a DF relay‐assisted mixed RF‐FSO link that has a G K faded RF link and a G G distributed FSO link was analyzed by Khanna et al However, the FSO links experience several channel impairments such as path loss, atmospheric turbulence, and pointing error‐induced misalignment fading.…”

A novel project‐and‐forward relay‐assisted mixed RF‐FSO system design and its performance evaluation

“…Figure depicts the outage performance comparison for the PF relaying, and AF relaying protocols for different values of γ th considered as 0, 2, 5, and 7 dB. The outage performance of a variable‐gain AF relayed mixed RF‐FSO link has been investigated in the work of Khanna et al and closed‐form expression for the same was obtained …”

“…The free space optical (FSO) links in conjunction with RF links can provide the desirable features of high‐speed transmission in the unlicensed band, easy installation at lower costs, and resistance to RF interference. The use of FSO systems in the existing RF networks has been well investigated in literature . The transmission between multiple links is usually carried using relays.…”

“…An amplify‐and‐forward (AF) relaying protocol is a widely used protocol for data transmission due to the ease of its implementation. Khanna et al have investigated the performance of a variable‐gain AF relay‐aided asymmetric RF‐FSO link that models the RF channel's shadowing and multipath fading conditions with a Generalized‐ K ( GK ) distribution, and the atmospheric turbulence over the FSO channel is modeled by the Gamma‐Gamma ( GG ) distribution. The drawback of using the AF protocol is that the noise is also amplified along with the signal.…”