A tandem queueing model for delay analysis in disconnected ad hoc networks

Ad hoc network routing protocols may fail to operate in the absence of an end-to-end connection from source to destination. This deficiency can be resolved by so-called opportunistic networking which exploits the mobility of the nodes by letting them operate as relays according to the store-carry-and-forward paradigm. However, the efficiency of this approach will depend to a large extent on the contact and inter-contact times of node pairs. In this work, we analyze the delay performance of a small opportunistic network by considering a tandem queueing system. We present an exact packet-level analysis by applying ideas from the polling literature. Due to the state-space expansion, this analysis cannot efficiently be applied for all model parameter settings. For this reason, an analytical approximation is constructed and its excellent performance has extensively been validated. Numerical results on the mean end-to-end delay show that the inter-contact time distribution impacts this metric only through its first two moments. Finally, we study delay optimization under power control.