Abstract
This paper aims to make a comparison between decode-and-forward (DF) relays and reconfigurable intelligent surfaces (RISs) in the case where only one relay or RIS is selected based on the maximization of the signal-to-noise-ratio (SNR). Our study accounts for the spatial distribution of RISs and relays, which is assumed to follow a Poisson point process (PPP). It considers two different path loss models corresponding to RIS/relays randomly located in the near-field and the far-field of the transmitter. Based on the Gamma distribution moment matching method and tools from stochastic geometry, we derive approximations for the outage probability (OP) as well as the energy efficiency (EE) of the RISs-assisted system in the near-field and the far-field scenarios separately. Under the same conditions as RIS, the expressions for OP and EE of the half-duplex and the full-duplex DF relays-assisted systems are also derived. Simulation results are presented to corroborate the proposed analysis and compare between the three technologies. Our results show that RIS is the best choice in the near-field case, regardless of the OP or EE criterion. Compared to half-duplex relays and full-duplex relays, the RIS based system is the most energy-efficient solution to assist communication. Moreover, RIS allows for an improvement in both OP and EE when equipped with more reflecting elements or more densely deployed.
Highlights
A S THE 5G standard is starting its implementation phase, it is critical to look for new communication technologies catering to the ever-increasing demand for traffic rate [1] in the future 5G beyond or even 6G generation
Empowered by the recent advances in metamaterial [2], Reconfigurable intelligent surfaces (RISs) are equipped with a large number of low-cost passive elements that allow for the modification of the radio waves, in that they reflect, refract, and scatter radio signals in a controllable fashion to counteract the destructive effect of multipath fading
We account for the spatial distribution of RISs and Relays in this work, which we model by Poisson point process (PPP)
Summary
A S THE 5G standard is starting its implementation phase, it is critical to look for new communication technologies catering to the ever-increasing demand for traffic rate [1] in the future 5G beyond or even 6G generation. Like relays, RISs aim to assist communication by enabling higher efficiency gains This principally motivated the emergence of a series of works aiming to compare between RIS and relay-assisted technologies from outage performance [23] and EE standpoints [26]. In this line, it was shown in [27] that large reflecting elements are needed for the RIS to outperform decode-and-forward (DF) relaying, both in terms of minimizing the total transmit power and maximizing EE, while in [28], it was shown that RIS-assisted single user system is more cost-efficient than amplify-and-forward (AF) relaying.
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