Spatially Correlated Dual Hop RIS Aided Next Generation Wireless Systems: An Outage Perspective

Renjith Ravindran Unnithan Jalaja,Sundarrajan Jayaraman Thiruvengadam,Vetrivel Chelian Thirumavalavan,Periakarupan Gurusamy Sivabalan Velmurugan

doi:10.1109/access.2021.3072294

Renjith Ravindran Unnithan Jalaja, Sundarrajan Jayaraman Thiruvengadam + Show 2 more

Open Access

https://doi.org/10.1109/access.2021.3072294

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Journal: IEEE Access	Publication Date: Jan 1, 2021
Citations: 36	License type: CC BY 4.0

Abstract

Design and analysis of Reconfigurable Intelligent Surfaces (RIS) assisted new wireless communication systems have attracted much attention among the 6G technology researchers. Recently, studies were made to compare the use of RIS and Decode and Forward (DF) relaying when a weak direct path exists between the transmitter and receiver. Amalgamating the merits of both RIS and DF relay technologies, an RIS assisted DF relay-based cooperative wireless system with energy harvesting is proposed in this paper. A Lambertian model of reflectance is employed in the analysis of the reflecting nature of RIS. Further, the impact of spatial correlation which arises due to the tightly-packed planar RIS array geometry is also considered for performance analysis. By varying inter-element distances and transmit power, the performance of the proposed system is analyzed in terms of outage probability and energy harvesting capability. Numerical expressions are derived for the outage probability of the proposed system and verified using Monte-Carlo simulations. Based on the high performance, the concept of joint use of RIS and DF Relay is extended to the Index Modulation (IM) based wireless system.

Highlights

Futuristic 6G wireless technologies will supposedly accomplish the expectations not met with 5G
Using (5), the variations in spatial correlation between the first and second elements are shown in Fig. 9 with respect to the change in inter-element spacing
Two algorithms are given in Appendix B to generate correlated Rayleigh envelopes

Summary

Introduction

Futuristic 6G wireless technologies will supposedly accomplish the expectations not met with 5G. The key enablers of 6G are envisioned to be Reconfigurable Intelligent Surfaces (RIS), ultra-massive Multiple Input Multiple Output (MIMO) communications, and user-centric networking [1]–[3]. Controllable intelligent channels, enabled by RIS, are utilized to adjust the phase of incident signals such that the signals are added constructively at the end-user. In RIS, arbitrary incident waves are phase tuned by the discrete reflecting elements, and the reflected waves out of RIS, reach the end-user as a coherent wave [6]. In this way, operators can have certain control over the random channel behavior. In [7], it is proved that the RIS aided

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