Section: New Results

Solutions for cellular networks.

Participants: Anis Ouni, Fabrice Valois, Hervé Rivano, Marco Fiore

Content downloading through a vehicular network.

We considered a system that leverages vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communication to transfer large contents to users on-board moving cars. This paradigm is intended to relieve the cellular infrastructure from the high load that such downloads would induce, once vehicles are widely equipped with infotainment devices.

We first characterized the theoretical performance limits of such a vehicular content downloading system by modeling the downloading process as an optimization problem, and maximizing the overall system throughput. Our approach allows us to investigate the impact of different factors, such as the roadside infrastructure deployment, the vehicle-to-vehicle relaying, and the penetration rate of the communication technology, even in presence of large instances of the problem [7] . We then evaluated practical protocols for vehicular downloading, devising solutions for the selection of relay vehicles and data chunks at the Road Side Units (RSUs), and evaluating them in real-world road topologies, under different infrastructure deployment strategies [8] .

Our results show that V2V transfers can significantly increase the download rate of vehicular users in urban/suburban environments, and that such a result holds throughout diverse mobility scenarios, RSU placements and network loads. Also, they highlight the existence of two operational regimes at different penetration rates and the importance of an efficient, yet 2-hop constrained, V2V relaying.

Toward green mesh and cellular networks.

On the one hand, a promising technique for minimizing the transmission power of cellular networks seems to be a dramatic densification of micro-cells coverage. On the other hand, increasing the number of micro-cells multiplies the energy consumed by the cells whatever their state, idle, transmitting or receiving. For a sustainable deployment of such micro-cell infrastructures and for a significant decrease of the overall energy consumption, an operator needs to be able to switch off cells when there are not absolutely needed. The densification of the cells induces the need for an autonomic control of the on/off state of cells. This has motivated a preliminary investigation on exploiting within the micro-cellular settings the manifold results of duty cycles for Wireless Sensor Networks where switching nodes on and off is done in a distributed or localized manner while coverage and connectivity properties are maintained [29] .

Focusing on broadband wireless mesh networks based on OFDMA resource management, and considering a realistic SINR model of the physical layer with a continuous power control and discrete transmission rate selection at each node, we have investigated the trade-off between transmission energy consumption and network capacity [24] . Correlation between capacity and energy consumption is analyzed as well as the impact of physical layer parameters - SINR threshold and path-loss exponent. We highlight that there is no significant tradeoff between capacity and energy when the power consumption of idle nodes is important. We also show that both energy consumption and network capacity are very sensitive to the SINR threshold variation. We also highlight that power control and rate selection are not expandable to an optimal system configuration.