Towards Carrier-Grade Quality in Heterogeneous Wireless Mesh Networks

Towards Carrier-Grade Quality in Heterogeneous Wireless Mesh Networks

Johannes Lessmann (NEC Europe Ltd., Germany), Paulo Loureiro (NEC Europe Ltd., Germany), John Fitzpatrick (University College Dublin, Ireland), Sebastian Robitzsch (University College Dublin, Ireland), Pablo Serrano (University Carlos III of Madrid, Spain) and Albert Banchs (University Carlos III of Madrid, Spain)
DOI: 10.4018/978-1-4666-0017-1.ch008
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Current backhaul networks typically comprise a wired middle mile and a wireless last mile part. The wireless part is almost exclusively based on tree topologies. However, a lot could be gained by deploying mesh-based backhauls. Meshes allow better network capacity exploitation due to load balancing and offer inherent resilience to link degradations or failures. Yet meshes come with increased complexity in terms of radio configuration, routing, or mobility management. This chapter proposes architecture and mechanisms for carrier-grade mesh-based wireless backhauls. One special focus is that it supports heterogeneous backhauls, which encompass multiple different wireless technologies. The proposition has been successfully deployed in a test network.1
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Providing backhaul solutions for radio access networks with mobility support is very costly. Current solutions have significant limitations which will become even more pronounced with increased use of mobile data applications. New networking paradigms can result in a number of advantages when it comes to realizing such networks: mesh networks provide lower-cost solutions with greater flexibility, something that is highly desirable for operator deployments. The focus of the approach in this chapter, then, is on realizing backhaul mesh networks which can be used to deliver carrier-grade services to users, some of which are mobile.

Current backhaul solutions are largely divided into two categories: wired backhaul via leased lines (copper, fiber) or point-to-point, high capacity radio links. Both of these solutions have their limitations - in the first case, provisioning of the wired connection can take some time, be expensive and, in some cases, there are issues with availability of wired connectivity, especially in remote areas; in the second case, expensive radio engineers are required to install and maintain costly point-to-point backhaul links. Both of these solutions lack flexibility when it comes to deployment of new base stations in a radio access network.

Mesh networking technology represents a cost-effective and efficient alternative for realizing backhaul networks to provide mobile users with high quality services. The multi-hop wireless network architecture of mesh networks enables them to efficiently cover large areas without requiring many interconnections to a wired infrastructure. Further, mesh networks offer better capacity exploitation via statistical multiplexing effects as well as inherent resilience to link failures via higher path diversity, which ultimately results in reduced up-front cost (CAPEX) and lower network maintenance costs (OPEX) for the operator.

While mesh-based solutions can be highly beneficial for fixed backhaul scenarios, their usage is also advantageous in situations where the network infrastructure is only needed for short time periods, as is the case for large public events or emergency scenarios. In these situations, the deployment of a traditional backhaul infrastructure would require a very high investment which is usually uneconomical for such a short duration; a solution based on low-cost technologies such as Wi-Fi, deployed in mesh topologies, provides a much more cost-effective way of satisfying this short-term demand.

A critical concern for operators is to provide access to the typical service bundle via all the radio access networks offered by the operator. Specifically, access to typical voice, video and data services must be provided. This imposes some constraints on the performance of the mesh backhaul: it must support carrier-grade service provisioning. While carrier grade, in general, has many aspects, including equipment reliability, security, AAA, QoS, management, standard's compliance, mobility support, service integration, etc., the contribution in this chapter will focus on those aspects that are most related to reliable service delivery: specifically, on issues related to ensuring that typical carrier service offerings, such as voice, video and data, are delivered with appropriate service quality to diverse mobile devices. This is a real challenge which is not supported by current mesh network technology. Hence, we call our system approach a Carrier-grade Wireless Mesh Network (CARMEN).

Generally, there is no single optimal wireless technology for all use cases at the same time. Backhauls for mobile cellular networks are well served with point-to-point microwave radios. Communication coverage in emergency scenarios is probably better provided with WiMAX of Wi-Fi meshes. Hence, in this chapter, we propose a mesh solution that is able to combine different technologies in order to realize a heterogeneous mesh backhaul solution (see Figure 1).

Figure 1.

CARMEN's heterogeneous wireless mesh network scenario

In our considered scenario in Figure 1, we distinguish between CARMEN Access Points (CAPs) which are nodes that (in addition to relaying traffic within the mesh backhaul) provide wireless access to user terminals (UTs), CARMEN Mesh Points (CMPs) that are pure backhaul router nodes and CARMEN Gateways (CGWs), that connect the mesh backhaul to the operator core network or the Internet.

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