D2d Data Offloading In Vehicular Environments With Optimal Delivery Time Selection

Within the framework of a Device-to-Device (D2D) data offloading system for cellular networks, we propose a Content Delivery Management System (CDMS) in which the instant for transmitting a content to a requesting node, through a D2D communication, is selected to minimize the energy consumption required for the transmission. The proposed system is particularly fit to highly dynamic scenarios, such as vehicular ones, where the network topology changes at a rate which is comparable with the order of magnitude of the delay tolerance. We present an analytical framework able to predict the system performance, in terms of energy consumption, considering concurrent requests for contents with different popularity. We validate the analytical model through simulations, and provide a thorough performance evaluation of the proposed CDMS, in terms of energy consumption and spectrum use. The proposed CDMS can be configured in two ways: (i) either use I2D transmissions only as a last resort, if it is not possible to serve request through D2D offloading within the limit of the delay tolerance; or (ii) include the possibility for the Base Stations (BSs) to transmit contents even before the deadline, if this is found to be more energy efficient from the point of view of the overall energy consumption, renouncing a portion of the offloading opportunities. The proposed scheme is benchmarked against a plain classic cellular scheme, a cellular (I2D only) scheme with optimal Infrastructure-to-Device (I2D) transmission scheduling for delay-tolerant applications, and a D2D data offloading scheme (proposed in previous works) in which the D2D transmission is performed as soon as a close-by device with the required content is found (i.e., without optimizing the transmission instant). We implemented a quite detailed simulator complete of Radio Resource Management (RRM) over the MAC layer of a multi carrier system, in a multi-cell scenario. Our results show that the proposed CDMS can induce a reduction of an order of magnitude, i.e. 90% or higher, of the energy consumed by the devices to implement D2D offloading, with respect to the benchmark D2D offloading scheme. At the same time, we observed a reduction of the energy consumption of the overall system in the order of 30%, under conservative assumptions. Finally, the system induces a remarkable degree of spatial frequency reuse, thus reducing the overall spectrum occupation.