Section: New Results
Participants: M. Fiore, G. Gaillard, D. Naboulsi, H. Rivano, R. Stanica, F. Valois
Bandwidth availability in the cellular backhaul is challenged by ever-increasing demand by mobile users. Vehicular users, in particular, are likely to retrieve large quantities of data, choking the cellular infrastructure along major thoroughfares and in urban areas. It is envisioned that alternative roadside network connectivity can play an important role in offloading the cellular infrastructure. We investigate  the effectiveness of vehicular networks in this task, considering that roadside units can exploit mobility prediction to decide which data they should fetch from the Internet and to schedule transmissions to vehicles. Rather than adopting a specific prediction scheme, we propose a fog-of-war model that allows us to express and account for different degrees of prediction accuracy in a simple, yet effective, manner. We show that our fog-of-war model can closely reproduce the prediction accuracy of Markovian techniques. We then provide a probabilistic graph-based representation of the system that includes the prediction information and lets us optimize content prefetching and transmission scheduling. Analytical and simulation results show that our approach to content downloading through vehicular networks can achieve a 70% offload of the cellular network.
Vehicles also produce large quantities of Floating Car Data (FCD), which consist of information generated by moving vehicles and uploaded to Internet-based control centers for processing and analysis. As upcoming mobile services based on or built for networked vehicles largely rely on uplink transfers of small-sized but high-frequency messages, FCD traffic is expected to become increasingly common in the next few years. Presently, FCD are managed through a traditional cellular network paradigm: however, the scalability of such a model is unclear in the face of massive FCD upload, involving large fractions of the vehicles over short time intervals. In  , we explore the use of vehicle-to-vehicle (V2V) communication to partially relieve the cellular infrastructure from FCD traffic. Specifically, we study the performance boundaries of such a FCD offloading approach in presence of best- and worst-case data aggregation possibilities at vehicles. We show the gain that can be obtained by offloading FCD via vehicular communication, and propose a simple distributed heuristic that has nearly optimal performance under any FCD aggregation model.
We also advocate the use of a data shuttle service model to offload bulk transfers of delay-tolerant data from the Internet onto standard vehicles equipped with data storage capabilities  . We first propose an embedding algorithm that computes an offloading overlay on top of the road infrastructure. The goal is to simplify the representation of the road infrastructure as raw maps are too complex to handle. In this overlay, each logical link maps multiple stretches of road from the underlying road infrastructure. We formulate then the data transfer assignment problem as a novel linear programming model that determines the most appropriate logical paths in the offloading overlay for a data transfer request. We evaluate our proposal using actual road traffic counts in France. Numerical results show that we can satisfy weekly aggregate requests in the petabyte range while achieving cumulative bandwidth above 10 Gbps with a market share of 20% and only one terabyte of storage per vehicle.
Energy Consumption in Communication Networks
Providing high data rates with minimum energy consumption is a crucial challenge for next generation wireless networks. There are few papers in the literature which combine these two issues. The work we propose in  focuses on multi-hop wireless mesh networks using a MAC layer based on S-TDMA (Spatial Time Division Multiple Access). We develop an optimization framework based on linear programming to study the relationship between throughput and energy consumption. Our contributions are twofold. First, we formulate and solve, using column generation, a new MILP to compute offline energy-throughput tradeoff curve. We use a physical interference model where the nodes can perform continuous power control and can use a discrete set of data rates. Second, we highlight network engineering insights. We show, via numerical results, that power control and multirate functionalities allow optimal throughput to be reached, with lower energy consumption, using a mix of single hop and multihop routes.
Another strategy with regard to energy consumption is switching off some network nodes that are not carrying any data or control traffic. In  , we tackle the problem of on-grid energy saving in cellular networks based on switch-on/off techniques for base stations and the usage of renewable energy. We aim to evaluate how much power can be saved in the network and dimension the renew able energy system according to the consumptions in real-world networks.
Service Level Agreements
The era of the Internet of Things (IoT) brings complexity and deployment costs in smart cities, particularly in WSNs. Utilities such as gas or water providers are keen on delegating the management of the communications to specialized firms, namely WSN Operators, that will share the WSN resource among their various clients. For this reason, in  we provide a guideline to write Service Level Agreements (SLAs) for IoT operation, borrowing a well studied concept from the web services domain. We extend the SLA definition with specific items that integrate the WSN constraints, and we facilitate the construction of complex metrics that express the performance of the WSN.
Furthermore. WSN operators will need a robust and reliable technology in order to guarantee QoS constraints in a wireless environment, as in the industrial world. IEEE 802.15.4e Time Slotted Channel Hopping (TSCH) is one good candidate. Moreover, the IETF experience in IP networks management is an important input for monitoring and QoS control over WSNs. In  , we give formal guidelines for the implementation of a SLA architecture for operated WSNs. We distinguish the various formal algorithms that are necessary to operate a WSN according to SLAs, and determines which functional entities are necessarily technology-dependent. Detailed examples of such entities are developed in an IPv6 over IEEE 802.15.4e TSCH context, such as advocated in the IETF 6TiSCH Working Group.