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Precise Performance Analysis of Dual-Hop Mixed RF/Unified-FSO DF Relaying with Heterodyne Detection and Two IM-DD Channel Models
摘要： This paper provides precise performance analysis of the dual-hop mixed radio frequency (RF)/unified free space optical (FSO) decode-and-forward (DF) relaying system, in which the heterodyne detection (HD) and the intensity modulation-direct detection (IM-DD) are taken into account for FSO detection. To this end, we derive closed-form expressions for the outage probability, average bit error rate (BER), and the ergodic channel capacity of this system. In this analysis, we utilize, for the first time as per our knowledge, a precise channel capacity result for the IM-DD channel. Moreover, this is the first time that not only the (IM-DD input-independent) but also the (IM-DD cost-dependent) AWGN channel is considered in such system analyses. Additionally in this study, we assume that the first hop (RF link) follows Nakagami-m fading, and the second hop (FSO link) follows Málaga (M) turbulence with pointing errors. These fading and turbulence models contain other models (such as Rayleigh and Gamma-Gamma) as special cases, thus our analyses can be seen as a generalized one from the RF and FSO fading models point of view. Also, in BER derivation, we assume that the modulation schemes in the two hops can be different, since not all modulation schemes are suitable for IM-DD FSO links. In addition, the system performance is investigated asymptotically at high signal to noise ratios (SNRs). This investigation leads to new non-reported coding gain and diversity order analyses of such system. Interestingly, we find that in the FSO hop, at high transmitted powers, all the considered FSO detectors result in the same diversity order. Furthermore, we provide simulation results that verify the accuracy of the obtained analytical and asymptotic expressions.
关键词： Nakagami-m fading,Málaga (M) fading,HD,DF,heterodyne detection,Mixed RF/FSO relay network,IM-DD,decode-and-forward,intensity modulation-direct detection
更新于2025-09-23 15:22:29
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Impact of transmission techniques in asymmetric RF/FSO system over Nakagami- <i>m</i> and gamma-gamma fading channels with pointing errors
摘要： In this paper, the performance of transmission techniques on the fixed‐gain amplify‐and‐forward–based asymmetric radio frequency/free space optical (RF/FSO) communication system is studied. The RF link and FSO link are, respectively, modeled by the Nakagami‐m and Gamma‐Gamma fading channels under the effect of zero boresight and non‐zero boresight pointing errors subject to heterodyne detection. Maximum ratio transmission (MRT) and orthogonal space‐time block coding (OSTBC) techniques are the transmission scenarios considered at the system source while selection combining is used for reception at the relay and destination for the signal detection. Moreover, a unified cumulative density distribution (CDF) of end‐to‐end signal‐to‐noise ratio is derived for the system. By utilizing this channel statistical CDF, the closed‐form expressions for the outage probability and average bit error rate for the M‐ary phase shift keying modulation are then obtained for the system. The analysis presented illustrates that both the atmospheric turbulence and pointing error significantly degrade the system performance. Based on this, the MRT transmission technique offers a better performance compared with the OSTBC techniques under the same system conditions. The accuracy of the analytical results is verified by Monte‐Carlo simulations.
关键词： transmit diversity,free space optical,Nakagami‐m fading,pointing errors,atmospheric turbulence
更新于2025-09-09 09:28:46