Opportunism vs. cooperation: Comparing forwarding strategies in multihop wireless networks with random fading

A wide range of forwarding strategies have been developed for multi-hop wireless networks, considering the broadcast nature of the wireless medium and the presence of random fading that results in time-varying and unreliable transmission quality. Two recently proposed strategies are opportunistic forwarding, which exploits relay diversity by opportunistically selecting an overhearing relay as a forwarder, and cooperative forwarding, which relies on the synchronized transmissions of relays to reinforce received signal strengths. Although these strategies are well-known in the literature, there is no comprehensive comparative analysis of their network-level performance in a realistic SINR (signal-to-interference-and-noise ratio) setting with multiple network flows. In this paper, we develop Markovian models for these protocols in the case of multiple competing flows in a general network setting; we also provide recurrence relations for the special case of linear networks. We first use these models to evaluate simple small-scale networks, and find that opportunism often outperforms cooperation - a result corroborated by simulations in larger networks. We also present a fixed-point model to efficiently estimate the throughput of large networks using these models. We identify the interference resulting from the larger number of transmissions under cooperative forwarding as a cause for mitigating the potential gains achievable with cooperative forwarding.