A Theoretical Performance Bound for Joint Beamformer Design of Wireless Fronthaul and Access Links in Downlink C-RAN

TL;DR

This paper derives a theoretical performance bound for joint beamformer design in wireless fronthaul and access links of downlink C-RAN, and proposes algorithms to approach this bound under imperfect channel information.

Contribution

It introduces a novel theoretical bound for joint beamforming in wireless C-RAN with imperfect CSI and compares multiple algorithms' performance against this bound.

Findings

Higher algorithm complexity yields performance closer to the theoretical bound.

Proposed algorithms effectively approximate optimal beamforming under realistic conditions.

Theoretical bound provides a benchmark for evaluating beamforming algorithms in C-RAN.

Abstract

It is known that data rates in standard cellular networks are limited due to inter-cell interference. An effective solution of this problem is to use the multi-cell cooperation idea. In Cloud Radio Access Network (C-RAN), which is a candidate solution in 5G and future communication networks, cooperation is applied by means of central processors (CPs) connected to simple remote radio heads with finite capacity fronthaul links. In this study, we consider a downlink C-RAN with a wireless fronthaul and aim to minimize total power spent by jointly designing beamformers for fronthaul and access links. We consider the case where perfect channel state information is not available in the CP. We first derive a novel theoretical performance bound for the problem defined. Then we propose four algorithms with different complexities to show the tightness of the bound. The first two algorithms apply successive convex optimizations with semi-definite relaxation idea where other two are adapted from well-known beamforming design methods. The detailed simulations under realistic channel conditions show that as the complexity of the algorithm increases, the corresponding performance becomes closer to the bound.