Capacity Improvement in Reconfigurable Intelligent Surface Assisted MIMO Communications

Jun Yang,Yijian Chen,Mengnan Jian,Min Fang,Jianwu Dou

doi:10.1109/access.2021.3113917

Abstract

Reconfigurable intelligent surface (RIS) is thought to be a potential key technique for future wireless communications due to its ability for manipulating the electromagnetic environment smartly. This paper focuses on the rank and capacity analysis when a RIS is introduced into a multiple-input multiple-output (MIMO) system. By establishing a system model for this communication system, various simulations are conducted for identifying the characteristics of the channel. The simulations of different distance between the access point (AP) and user equipment (UE) show that the condition number of the channel is worsen when the distance increases and the role of the RIS in rank improvement is weaken. The spatial distributions of the reciprocal condition number of the channel which corresponds to the RIS locations are obtained and rank-deficient zones are found in different AP, UE and RIS configurations, which depicts the spatial characteristics of the RIS-assisted MIMO channel. The simulations also indicate that the condition number of the channel not only varies with the RIS location, but is also affected by the antenna array size and orientation of AP and UE. In addition, when the AP has a larger amount of antennas than UE, it is advantageous to place the RIS near the UE rather than the AP to achieve better channel condition. Modulation and coding schemes are applied in the simulations for comparison and capacity improvement is witnessed. Beneficial suggestions for RIS deployment in the MIMO system are concluded according to the simulation results.

Highlights

R ECONFIGURABLE intelligent surface (RIS), known as intelligent reflecting surface (IRS) [1], large intelligent surface (LIS) [2], among others [3], [4], has become a hot topic in wireless communication community as it brings in new opportunity for fading and blockage settlement in high frequency for beyond-5G and future 6G communications
RECIPROCAL CONDITION NUMBER VERSUS access point (AP)-TO-user equipment (UE) DISTANCE This section investigates the rcond of the RIS-assisted multiple-input multipleoutput (MIMO) channel with different AP-to-UE distances
If the rcond is used as the metric of the MIMO channel, it is difficult to foretell the optimal location for the RIS placement when the AP and UE are fixed

Summary

INTRODUCTION

R ECONFIGURABLE intelligent surface (RIS), known as intelligent reflecting surface (IRS) [1], large intelligent surface (LIS) [2], among others [3], [4], has become a hot topic in wireless communication community as it brings in new opportunity for fading and blockage settlement in high frequency for beyond-5G and future 6G communications. With the tunable electronic circuit embedded in the element, for example [7], [8], a reflection-type RIS is able to steer the incident wave of a specific frequency band to the desired reflecting direction in real time, generating an anomalous reflection [9] rather than a specular reflection, and is capable of creating an intelligent electromagnetic environment for wireless communications [10], [11] When it comes to high frequency regime, path loss and signal blockage become severe in wireless communications, which seriously limits the service range of an access point (AP) and lowers the transmission energy efficiency. In a spacious public square where only the LOS signal is significant, the MIMO channel is rank-deficient Based on these rank-deficient scenes, this paper investigates the rank and capacity improvement by introducing RIS to the MIMO system.

SYSTEM MODEL

H21 H22

CAPACITY UNDER MODULATION AND CODING SCHEMES

CONCLUSION