Optimal power allocation and harvesting duration for mixed RF/FSO using Non Orthogonal Multiple Access
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Optimal power allocation and harvesting duration for mixed RF/FSO using Non Orthogonal Multiple Access Nadhir Ben Halima1 · Hatem Boujemaa2 Received: 21 March 2020 / Accepted: 18 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this paper, we suggest to optimize power allocation coefficients and harvesting duration in mixed Radio Frequency (RF)/Free Space Optical (FS0) communications using Non Orthogonal Multiple Access (NOMA). The system model contains three time slots. In the first time slot, relay node R harvests energy from RF signal received from node H. Node H can be any node transmitting RF signals. In the second time slot, an FSO transmitter T transmits a linear combination of symbols of K users to relay node R using NOMA. In the third and last slot, relay R detects the receive symbols and sends a linear combination of detected symbols to K users using NOMA. We show that power allocation and harvesting duration optimization allow to increase the throughput of RF/FSO communications. We consider two users’ ranking techniques using average or instantaneous channel gains. Keywords FSO · Mixed RF/FSO · NOMA · Energy harvesting · Optimal power allocation
1 Introduction In mixed Radio Frequency (RF) Free Space Optical (FSO) systems, there are two hops using RF and FSO communications (Abou-Rjeily 2020; Kamga et al. 2019; Wang et al. 2019; Upadhya et al. 2019). Different relaying techniques were suggested for mixed RF/ FSO such as Amplify and Forward (AF) and Decode and Forward (DF) protocols (Labghough et al. 2019; Al-Ebraheemy et al. 2019; Petkovic and Trpovski 2018; Ansari et al. 2013). Relaying allows to benefit from cooperative diversity since the best relay can be activated (Ashrafzadeh et al. 2019; Anees et al. 2017). Mixed RF/FSO with multihop relaying can be used to increase the coverage and reduce outage events (Yi et a. 2019). In hybrid FSO/RF, there are both RF and FSO links and the receiver selects the link with largest Signal to Noise Ratio (SNR) (Lee et al. 2019; Alathwary and Altubaishi 2019; Al-Eryani et al. 2018). Mixed RF/FSO with energy harvesting allows to recharge the battery of relay * Nadhir Ben Halima [email protected] Hatem Boujemaa [email protected] 1
Higher Colleges of Technology, Sharjah, UAE
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COSIM Lab, SUPCOM, Aryanah, Tunisia
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nodes using the received RF signals (Chen et al. 2019; Abd El-Malek et al. 2019). Energy harvesting allows to increase network life-time since no recharging of transmitter’s battery is required (Chen et al. 2019; Abd El-Malek et al. 2019). Non Orthogonal Multiple Access (NOMA) has been suggested for RF communications to increase data rates (Zhong and Zhang 2016; Liu et al. 2016; Sun et al. 2019). NOMA users share the same spectrum and time slot. Therefore, interference cancelation is mandatory (Zhong and Zhang 2016; Liu et al. 2016; Sun et al. 2019). Weak user detects only its symbol. However, strong user detects first
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