  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.
