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SESAME - Software Defined Wireless Backhaul for Small Cells

Final Report Summary - SESAME (SESAME - Software Defined Wireless Backhaul for Small Cells)

The forecasted traffic growth in mobile networks is one of the biggest challenges faced by the mobile industry. In addition, declining average revenues per user (ARPUs) and rising costs of ownership increase the difficulties for service providers to fulfill this upcoming demand. Densifying mobile networks by means of adding small cells, which have a limited footprint but offer high data rates, is seen as the most promising way to cope with this increasing demand. However, one of the biggest challenges to be solved for a successful deployment of such small cells is the question of backhauling, especially when in many cases the backhaul network is expected to be wireless.

The goal of the SESAME project is to study how such a small cell wireless backhaul should be designed. In particular, we propose to apply software defined networking (SDN) techniques to the design of the wireless backhaul, which should allow service providers to: i) have a common management framework for a potentially heterogeneous backhaul network, ii) allow a flexible and dynamic deployment of network services running on top of the backhaul network, and iii) enable new business models such as those involving the sharing of the backhaul network among different service providers, hence reducing capital and operational expenditures. It is worth noting that densifying access networks and applying SDN techniques to the transport domain is an architectural vision fully aligned with the candidate technologies considered for 5G.

Within this context SESAME addresses the following goals:
- Design extensions to the OpenFlow protocol, which is the most prominent south-bound protocol used in SDN, that allow an SDN controller to manage and optimize wireless nodes. For instance, a controller could be allowed to set a different wireless channel or transmit power for different flows. In addition, a wireless node could report to its SDN controller about the received signal strength indication (RSSI) from neighboring backhaul nodes. Such an extended API should accommodate the various technology families that will be present in the wireless backhaul, e.g. LOS and NLOS.
- Design the wireless abstractions that an SDN controller should provide to the applications built on top of it (northbound interface in SDN terminology). For instance a controller could maintain a network wide interference matrix between the small cell nodes that would then be used by traffic engineering applications running on top of it.
- Develop traffic engineering algorithms for the small cell wireless backhaul, e.g. load balancing, energy efficiency, mobility and network sharing, running on top of the backhaul SDN controller.
Evaluate the designed technologies by means of simulations and experimental testbeds.

SESAME has achieved the following technical results that fulfill the stated objectives:
- Design a control plane able to operate with a multiple radio technologies. In this regard, the reference architecture builds on the IEEE 802.11 radio stack that support NLoS radio technologies operating below 6 GHz, such as 802.11ac and mm-wave technologies, offering high data rates but requiring LOS, such as 802.11ad.
- Extended the OpenFlow protocol to report wireless statistics, and demonstrated feasibility extending an open source implementation of a software switch supporting OpenFlow.
- Design of abstractions in an SDN controller that allow an external application hosted by an operator, to provision new paths in the wireless backhaul, or query status information about the installed paths. In addition, a REST based management abstraction has also been proposed that allows to instantiate virtual Access Points on demand, in a multi-tenancy scenario, where multiple operators share physically installed Small Cells. This abstractions have been implemented in an open source SDN controller.
- Design of Traffic Engineering algorithms required to offer a carrier grade service in dense deployments of Small Cells with wireless backhauling. Two algorithms have been designed, one to steer flows in the wireless backhaul, in an interference-aware manner, and another one to load balance users in the wireless access. Both algorithms have been implemented in the SESAME SDN controller.
- Evaluating experimentally the architectures, protocols and algorithms proposed in SESAME in the NITOS wireless testbed built for remote research and experimentation.

The work carried out in SESAME has resulted in five peer-reviewed publications, and another one currently under submission.

SESAME has contributed technology innovations in the area of mobile networks, mainly aimed at assisting the deployment of future 5G networks. 5G networks are expected to have a key societal and economic impact in Europe, by means of enabling more digital services to the end users, as well as serving multiple vertical industries.

Finally, SESAME has also impacted other research efforts in the H2020 space. Among them, the most representative is the H2020 5G-XHAUL project ( which belongs to the 5G-PPP initiative, and targets the design of a 5G transport infrastructure able to carry backhaul and fronthaul services. The SESAME fellow is the technical coordinator of the 5G-XHAUL project.

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