Exact and Heuristic Solutions for Energy-Aware Multihop Cooperation Over Wireless Networks

This paper addresses the problem of energy-aware multihop cooperation among the mobile terminals (MTs) that cooperatively download a common content from a wireless network. The base station (BS) unicasts or multicasts the content to selected MTs that, in turn, either unicast or multicast it to other MTs, forming a multihop ad hoc network with a predefined maximum allowed number of hops. This paper presents the optimization formulations whose solution gives the exact optimal set of receiving MTs from the BS, the optimal multihop ad hoc network, and the optimal unicasting and multicasting transmission bit rates that minimize the total energy consumption of the MTs. Second, a simplified multicasting formulation is proposed that has a close-to-optimal performance with notably lower computational complexity. Third, interference avoidance among the transmitting MTs is considered. For each presented formulation, the complexity is identified, and results show that some formulations can be efficiently solved for medium network sizes, while others are more computationally complex. Thus, polynomial-time heuristic solutions are presented that have close-to-optimal performance. Results demonstrate remarkable energy consumption reduction gains and wireless resources savings under various network scenarios.