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We consider the problem of energy-efficient transmission in delay constrainedcooperative multihop wireless networks. The combinatorial nature of cooperativemultihop schemes makes it difficult to design efficient polynomial-timealgorithms for deciding which nodes should take part in cooperation, and whenand with what power they should transmit. In this work, we tackle this problemin memoryless networks with or without delay constraints, i.e., quality ofservice guarantee. We analyze a wide class of setups, including unicast,multicast, and broadcast, and two main cooperative approaches, namely: energyaccumulation (EA) and mutual information accumulation (MIA). We provide ageneralized algorithmic formulation of the problem that encompasses all thosecases. We investigate the similarities and differences of EA and MIA in ourgeneralized formulation. We prove that the broadcast and multicast problemsare, in general, not only NP hard but also o(log(n)) inapproximable. We breakthese problems into three parts: ordering, scheduling and power control, andpropose a novel algorithm that, given an ordering, can optimally solve thejoint power allocation and scheduling problems simultaneously in polynomialtime. We further show empirically that this algorithm used in conjunction withan ordering derived heuristically using the Dijkstra's shortest path algorithmyields near-optimal performance in typical settings. For the unicast case, weprove that although the problem remains NP hard with MIA, it can be solvedoptimally and in polynomial time when EA is used. We further use our algorithmto study numerically the trade-off between delay and power-efficiency incooperative broadcast and compare the performance of EA vs MIA as well as theperformance of our cooperative algorithm with a smart noncooperative algorithmin a broadcast setting.

Algorithmic Aspects of Energy-Delay Tradeoff in Multihop Cooperative Wireless Networks