In this paper, we introduce a network-decomposed hierarchical cooperation (HC) protocol and completely characterize the corresponding throughput--delay trade-off for a large wireless ad hoc network formed in the context of social relationships. Instead of randomly picking source--destination pairings, we first consider a distance-based social formation model characterized by the social group density $gamma$ and the number of social contacts per node, $q$, where the probability that any two nodes in distance $d$ away from each other are socially connected is assumed to be proportional to $d^{-gamma}$, which is a feasible scenario. Then, using muiltihop and network-decomposed HC protocols under our social formation model, we analyze a generalized throughput--delay trade-off according to the operating regimes with respect to parameters $gamma$ and $q$ in both a dense network of unit area and an extended network of unit node density via a non-straightforward network transformation strategy. Our main results reveal that as $gamma$ increases, performance on the throughput--delay trade-off can remarkably be improved, compared to the network case with no social relationships. It is also shown that in the dense network, the network-decomposed HC protocol always outperforms the multihop protocol, while the superiority of the network-decomposed HC depends on $gamma$ and the path-loss exponent in the extended network.
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