5G Backhaul Challenges and Emerging Research Directions: A Survey

TLDR

5G promises unprecedented data rates and IoT support, yet the ultra‑dense, high‑traffic cells create a backhaul bottleneck demanding extreme capacity, low latency, high availability, energy efficiency, and cost effectiveness. This survey examines 5G backhaul technologies, critically analyzes legacy and emerging solutions, and proposes a consolidated framework that integrates radio access and backhaul perspectives. The authors review and evaluate legacy, cutting‑edge, and trend‑setting backhaul approaches within a unified framework that jointly considers radio access and backhaul requirements. The study reveals hidden strengths and weaknesses of backhaul solutions, identifies essential catalysts, and outlines lessons learned, unsolved challenges, and a new vision for beyond‑2020 backhauling.

Abstract

5G is the next cellular generation and is expected to quench the growing thirst for taxing data rates and to enable the Internet of Things. Focused research and standardization work have been addressing the corresponding challenges from the radio perspective while employing advanced features, such as network densification, massive multiple-input-multiple-output antennae, coordinated multi-point processing, inter-cell interference mitigation techniques, carrier aggregation, and new spectrum exploration. Nevertheless, a new bottleneck has emerged: the backhaul. The ultra-dense and heavy traffic cells should be connected to the core network through the backhaul, often with extreme requirements in terms of capacity, latency, availability, energy, and cost efficiency. This pioneering survey explains the 5G backhaul paradigm, presents a critical analysis of legacy, cutting-edge solutions, and new trends in backhauling, and proposes a novel consolidated 5G backhaul framework. A new joint radio access and backhaul perspective is proposed for the evaluation of backhaul technologies which reinforces the belief that no single solution can solve the holistic 5G backhaul problem. This paper also reveals hidden advantages and shortcomings of backhaul solutions, which are not evident when backhaul technologies are inspected as an independent part of the 5G network. This survey is key in identifying essential catalysts that are believed to jointly pave the way to solving the beyond-2020 backhauling challenge. Lessons learned, unsolved challenges, and a new consolidated 5G backhaul vision are thus presented.