978-1-5386-3395-3/18/$31.00 ©2018 IEEE Near-Instant Link Failure Recovery in 5G Wireless Fog-Based-Fronthaul Networks Nabeel I. Sulieman, Eren Balevi, and Richard D. Gitlin Department of Electrical Engineering University of South Florida Tampa, Florida 33620, USA Email: nis@mail.usf.edu, erenbalevi@mail.usf.edu, richgitlin@usf.edu Abstract—Rapid recovery from link failures was previously demonstrated via the synergistic combination of Diversity and Network Coding (DC-NC) for a wide variety of network architectures. In this paper, the DC-NC methodology is further enhanced to achieve near-instant recovery from multiple, simultaneous wireless link failures by modifying Triangular Network Coding (TNC) to create enhanced DC-NC (eDC-NC) that is applied to 5G wireless Fog computing based Radio Access Networks (F-RANs). In addition, an explicit algorithm for the eDC-NC decoding process is provided. Our results demonstrate that applying eDC-NC coding to a F-RAN fronthaul network will provide ultra-reliability, enable near-instantaneous fault recovery, and enhance the throughput by at least 20% (for three broadcasted data streams). Keywords—5G, Diversity Coding, F-RAN, Network Coding, reliability, throughput I. INTRODUCTION Several applications in 5G wireless communication systems are required to be ultra-reliable and very efficient with ultra-low latency communications [1]. This study describes a methodology for rapid recovery from link or node failures in the fronthaul networks of 5G Fog Radio Access Networks (F- RANs). F-RANs are an enhancement and an alternative to Cloud Radio Access Network (C-RAN) [2]-[4]. The key idea of F- RAN is to employ edge nodes with the ability to store data, control signals, and communicate to each other instead of centralizing processing in the baseband unit (BBU) at the C- RAN [2]-[4]. Diversity Coding (DC) [5]-[6], an open loop coding technique, can help address this challenge and is a forward error control technology over diverse routes. With DC once the failure is detected the lost message can be rapidly recovered without performing rerouting and/or retransmission. In [7] and [8], DC is used to improve the reliability of a C- RAN network with the ability to tolerate multiple simultaneous link failures. Diversity Coding was described to improve the reliability of OFDM-based vehicular systems [9] and sensor networks [10]. Network Coding (NC) [11] has the ability to further improve 5G wireless F-RAN performance by increasing its throughput. Triangular Network Coding (TNC) [12] is another mode of NC that can be used for this purpose with less computational complexity. DC-NC coding [13], a synergistic combination of Diversity Coding (DC) and Network Coding (NC), can simultaneously enhance wireless network reliability, provide high throughput and enable low latency 5G communications systems. DC-NC coding can be easily integrated into the-state-of-art F-RAN by deploying relay nodes that are configured to enable DC-NC coding. The contributions of this paper are modifying TNC to enhance DC-NC coding and applying enhanced DC-NC coding (eDC-NC) to F-RAN wireless networks to improve their reliability with reduced computational complexity, provide extremely low recovery time for simultaneous multiple link failures, and to increase throughput for broadcasting or multicasting applications. In addition, an explicit algorithm for eDC-NC decoding process is presented. The rest of this paper is organized as follows: Section II describes the network topology based on F-RANs. Section III presents a background about Triangular Network Coding. The modification to TNC and its utilization to enhance DC-NC coding and a decoding algorithm are presented in Section IV. Section V demonstrates the ability of eDC-NC coding to enable higher throughput and faster recovery from multiple simultaneous link failures in wireless fronthaul networks. The paper ends with concluding remarks in Section VI. II. SYSTEM MODEL F-RANs were proposed in [2]-[4] to improve the performance of C-RANs by migrating a significant number of functions to the edge device and substantially upgrading the Remote Radio Heads (RRHs). These functions include controlling, communicating, measuring, managing, and storing data. In this way, an upgraded RRH is called a Fog Access Point (F-AP), and will be able to communicate and network with other F-APs and this architecture will reduce latency by performing functionality at the network edge rather than in the core [2]-[4]. The F-RAN architecture consists three layers as shown in Fig. 1 [2]. The BBU pool, network control, and centralized storage are the network layer functions. The access layer contains RRHs and F-APs. The terminal layer includes user equipment (UE) and Fog UE (F-UE) that access F-AP [2]-[3]. The F-APs can be formed into two topologies: a mesh topology and a tree-like topology. Both of topologies can significantly minimize the degrading effects of capacity-constrained fronthaul links [2]. Different transmission modes can be used in a F-RAN such as the C-RAN and Local Distributed Coordination (LDC) modes as illustrated in Fig. 1 [2]. The core mode for the F-RAN is the