Reconfigurable Intelligent Surface Empowered Device-to-Device Communication Underlaying Cellular Networks

Reconfigurable intelligent surface (RIS) is a new and revolutionary technology to achieve spectrum-, energy- and cost-efficient wireless networks. This paper studies the resource allocation for RIS-empowered device-to-device (D2D) communication underlaying a cellular network, in which an RIS is employed to enhance desired signals and suppress interference between paired D2D and cellular links. We maximize the overall network’s spectrum efficiency (SE) and energy efficiency (EE), respectively, by jointly optimizing the spectrum reuse indicators, the transmit power, the RIS’s passive beamforming and the BS’s receive beamforming. To solve both mixed-integer non-linear programming problems, we first propose an efficient and low-complexity user-pairing scheme based on relative channel strength to determine the spectrum reuse indicators. Other variables are then optimized to maximize the SE by an iterative algorithm, based on the techniques of alternating optimization, successive convex approximation, Lagrangian dual transform and quadratic transform. The EE-maximization problem is solved by an alternating algorithm integrated with Dinkelbach’s method. Numerical results show that the proposed design achieves significant SE and EE enhancements compared to traditional underlay D2D network without RIS, relay-assisted D2D network and other benchmarks.

I. Introduction

Device-to-device (D2D) communication underlaying a cellular network allows a device to communicate with proximity devices in licensed cellular bands. It is recognized as a promising wireless technology and a competitive candidate for beyond 5th-Generation (5G) system standards [1]. Specifically, the overall network’s spectrum efficiency (SE) can be enhanced, since additional D2D links are supported by sharing the licensed cellular spectrums; the overall network’s energy efficiency (EE) can be improved by exploiting the proximity of D2D users; also, the transmission delay can be reduced by eliminating the forwarding through a cellular base station (BS). Task offloading in edge computing networks can effectively improve the mobile devices’ computation and energy efficiency [2], [3]. D2D communications is also a promising offloading solution in cellular networks with high SE and EE. However, interference management is an important challenge for underlay D2D communication [1], [4], [5]. The D2D link and the cellular link operating in the same band interfere with each other, and the interference needs to be carefully suppressed via efficient interference control [6] and resource allocation [7]. Existing interference management schemes were designed assuming that the wireless environment including interference channels is fixed. Thus the extent of interference suppression is fundamentally limited.