On optimal mobile terminal grouping in energy aware cooperative content distribution networks

This work addresses the problem of optimized content distribution over wireless networks with cooperation among mobile terminals. The mobile terminals are optimally divided into groups where each group internally cooperates by downloading and exchanging a common content from the base station in order to minimize the total energy consumed by the mobile terminals. We assume unicasting transmissions from the base station and multicasting transmissions among the mobile terminals. It is well known that the optimal content multicasting problem that minimizes the mobile terminal´s energy consumption is an NP-hard problem. Consequently, several heuristic algorithms have been proposed in the literature that take into account only few network parameters to simplify the energy minimization problem. The main contributions of this work are the following. First, we derive the optimal energy consumption expression in a grid network as a function of the optimal cooperative group size. Second, we study the effect of several important network parameters on energy consumption; these include the transmission rates and the energy consumed per unit time during data transmission and reception. Results show that cooperation leads to notable reduction in energy consumption compared to the non-cooperative case. Besides, we demonstrate that several network parameters have nearly equivalent importance; consequently, energy-aware content distribution protocols should take into account multiple network parameters to obtain more efficient solutions.