Analog Radio Over Fiber Aided C-RAN: Optical Aided Beamforming for Multi-User Adaptive MIMO Design

Yichuan Li,Mohammed El-Hajjar,Salman Ghafoor,Muhammad Fasih Uddin Butt

doi:10.3389/frcmn.2021.725976

Abstract

Given the increasing demand for high data-rate, high-performance wireless communications services, the demand on the radio access networks (RAN) has been increasing significantly, where optical fiber has been widely used both for the backhaul and fronthaul. Additionally, advances in signal processing such as multiple-input multiple-output (MIMO) techniques, have improved the performance as well as transmission rate of communications networks. Beamforming has been used as an efficient MIMO technique for providing a signal to noise ratio (SNR) gain as well as reducing the multi-user interference. However, beamforming requires the employment of phase-shifters, which suffers from reduced phase resolutions, degraded noise figures as well as beam-squinting in addition to the implementation challenges. Hence, in this paper we employ an analogue radio over fiber (A-RoF) aided architecture for supporting the requirements of the current and future mobile networks, where we design a photonics aided beamforming technique in order to eliminate the bulky electronic phase-shifters and the beam-squinting effect, while also providing a low-cost RAN solution. Additionally, this photonics aided beamforming is combined with a reconfigurable multi-user MIMO technique, where users can communicate with one or multiple remote radio heads (RRHs), while employing stand-alone beamforming, beamforming combined with diversity or with multiplexing depending on the available resources and the user channel information as well as the quality of service requirements.

Highlights

The United Nation’s Sustainable Development Goals (UN SDGs) include 17 goals in the Agenda 2030, which are framed to address global challenges including climate change, poverty and inequality (UN2, 2015; 6G Flagship White paper, 2020)
It is worth noting that beamforming requires the employment of phase-shifters (Cao et al, 2016), which suffers from reduced phase resolutions, degraded noise figures as well as beamsquinting in addition to the implementation challenges such as the synchronization of the phase shifters (Poon and Taghivand, 2012; Zhang et al, 2018)
In (Hemadeh et al, 2018) we presented a flexible multi-functional multiple-input multiple-output (MIMO) technique and compared in details the performance of the different configurations, where we have shown that the diversity aided MIMO has the best performance at the expense of reduced throughput as opposed to the multiplexing techniques, which have a higher throughput and reduced bit error rate (BER) performance compared to the diversity techniques

Summary

Introduction

The United Nation’s Sustainable Development Goals (UN SDGs) include 17 goals in the Agenda 2030, which are framed to address global challenges including climate change, poverty and inequality (UN2, 2015; 6G Flagship White paper, 2020). In the fourth Generation (4G) mobile network, the concept of centralised RANs (C-RAN) was employed, where the central unit (CU) employs several baseband units (BBUs) connected to several remote radio heads (RRHs) by fiber. In this case, each RRH supports an individual cell (Li et al, 2020 (accepted).

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