We propose a novel transport network architecture for mobile backhauling along with its tailored communication protocol to offer ultra-low latency. Results show that less than 0.5 milliseconds packet delay can be achieved for inter-base-station communications.

Low latency is of key importance for mobile networks to support emerging time-critical applications, such as road traffic safety and efficiency. Meanwhile, a passive optical network (PON) is widely recognized as a promising solution for mobile backhaul networks thanks to its high capacity and low energy consumption. In the conventional PON-based mobile backhaul network, where base stations (BSs) are co-located with optical network units, the traffic between the neighboring BSs that are mainly caused by user mobility has to be first sent to the optical line terminal and even further, e.g., edge nodes of mobile core networks, resulting in high latency, although the adjacent BSs are geographically located close to each other. In this paper, a novel PON-based architecture is proposed for mobile backhaul to enhance the connectivity between neighboring BSs. Meanwhile, a tailored medium access control protocol and dynamic bandwidth allocation algorithm are introduced to support fast inter-BS communications. The results reveal that a low latency (less than 1 ms packet delay) for communications among any adjacent BSs can be achieved in the proposed PON-based mobile backhaul network, demonstrating great potential to support future time-critical applications.

Driven by the increasing number of connected vehicles and related services, powerful communication and computation capabilities are needed for vehicular communications, especially for real-time and safety-related applications. A cellular network consists of radio access technologies, including the current long-term evolution (LTE), the LTE advanced, and the forthcoming 5th generation mobile communication systems. It covers large areas and has the ability to provide high data rate and low latency communication services to mobile users. It is considered the most promising access technology to support real-time vehicular communications. Meanwhile, fog is an emerging architecture for computing, storage, and networking, in which fog nodes can be deployed at base stations to deliver cloud services close to vehicular users. In fog computing-enabled cellular networks, mobility is one of the most critical challenges for vehicular communications to maintain the service continuity and to satisfy the stringent service requirements, especially when the computing and storage resources are limited at the fog nodes. Service migration, relocating services from one fog server to another in a dynamic manner, has been proposed as an effective solution to the mobility problem. To support service migration, both computation and communication techniques need to be considered. Given the importance of protocol design to support the mobility of the vehicles and maintain high network performance, in this paper, we investigate the service migration in the fog computing-enabled cellular networks. We propose a quality-of-service aware scheme based on the existing handover procedures to support the real-time vehicular services. A case study based on a realistic vehicle mobility pattern for Luxembourg scenario is carried out, where the proposed scheme, as well as the benchmarks, are compared by analyzing latency and reliability as well as migration cost.

With advances in the information and communication technology (ICT), connected vehicles are one of the key enablers to unleash intelligent transportation systems (ITS). On the other hand, the envisioned massive number of connected vehicles raises the need for powerful communication and computation capabilities. As an emerging technique, fog computing is expected to be integrated with existing communication infrastructures, giving rise to a concept of fog-enhanced radio access networks (FeRANs). Such architecture brings computation capabilities closer to vehicular users, thereby reducing communication latency to access services, while making users capable of sharing local environment information for advanced vehicular services. In the FeRANs service migration, where the service is migrated from a source fog node to a target fog node following the vehicle's moving trace, it is necessary for users to access service as close as possible in order to maintain the service continuity and satisfy stringent latency requirements of real-time services. Fog servers, however, need to have sufficient computational resources available to support such migration. Indeed, a fog node typically has limited resources and hence can easily become overloaded when a large number of user requests arrive, e.g., during peak traffic, resulting in degraded performance. This paper addresses resource management in FeRANs with a focus on management strategies at each individual fog node to improve quality of service (QoS), particularly for real-time vehicular services. To this end, the paper proposes two resource management schemes, namely fog resource reservation and fog resource reallocation. In both schemes, real-time vehicular services are prioritized over other services so that their respective vehicular users can access the services with only one hop. Simulation results show that the proposed schemes can effectively improve one-hop access probability for real-time vehicular services implying low delay performance, even when the fog resource is under heavy load.

Fog computing is expected to be integrated with existing communication infrastructures, giving rise to the concept of fog-enhanced cellular networks (FeCNs) to support real-time services. In such FeCNs, service migration is necessary to maintain the service continuity and satisfy stringent latency requirements of real-time vehicular services, where the service is migrated from a source fog node to a target fog node following the vehicle's moving trace. Fog servers, however, need to have sufficient computational resources available to support such a migration. Also, provisioning resource for the migrated real-time services needs to be completed as soon as possible to minimize the service interruption. This paper proposes a distributed online resource management (ORM) scheme, in which resources for real-time vehicular services are provisioned with high priority. Once resources are scarce in one fog node, services with low priority can be migrated to neighboring fog nodes and their resources can be released in a distributed fashion. We propose two algorithms tailored to reduce the negative effects on the affected services. As a case study, the Luxembourg traffic volume model has been considered to verify the performance of the proposed scheme. Simulation results show that the performance of the proposed scheme is dependent on the backhaul capacity. Compared with other schemes, the one-hop access probability for real-time vehicular services implying low delay performance can be effectively improved, while the performance of other services can also be well maintained by providing sufficient backhaul capacity.

Fog computing is expected to be integrated with communication infrastructure, giving rise to the concept of fog-enhanced radio access networks (FeRANs) to support various mission-critical applications. Such architecture brings computation capabilities closer to end users, thereby reducing the communication latency to access services. In the context of FeRAN, service migration is needed to tackle limited resources in a single fog node and to provide continuous service for mobile end users. To support service migration, high capacity and low latency are required in mobile backhaul networks. Passive optical networks can be a promising solution for such mobile back-haul, in which bandwidth is shared by both migration traffic and that which is not associated with service migration. In this paper, we propose a bandwidth slicing mechanism, in which the bandwidth can be provisioned to the migration traffic and non-migration traffic dynamically and effectively to meet their different delay requirements. Simulation results verify that the proposed delay-aware bandwidth slicing scheme can handle the migration traffic properly, i.e., sending it within a required time threshold, while limiting the impact of the migration traffic on the latency and jitter of the non-migration traffic, particularly that with high priority.