There has been significant recent interest within the networking research community to characterize the impact of mobility on the capacity and delay in mobile ad hoc networks. In this paper, the fundamental trade-off between the capacity and delay for a mobile ad hoc network under the Brownian motion model is studied. It is shown that the 2-hop relaying scheme proposed by Grossglauser and Tse (2001), while capable of achieving a per-node throughput of is the variance parameter of the Brownian

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... tion model. It is then shown that an attempt to reduce the delay beyond this value results in the throughput dropping to its value under static settings. In particular, it is shown that under a large class of scheduling and relaying schemes, if the mean packet delay is