In this section, we review the literature on energy-efficient data collection by mobile sinks in delay-tolerant WSNs. We examine direct-contact data collection methods first and study rendezvous-based data collection methods afterwards.
In direct-contact data collection, a mobile sink collects data directly from data sources by one-hop communication. Sinks may retransmit data or, if needed, physically carry the data to a fixed base station. This approach minimizes energy consumption among sensors for communication, since sensors do not need to forward messages for each other. In this scenario, the main concern is the computation of the best sink trajectory that covers all data sources and minimizes data collection delay.
Shah et al. (2003) considered stochastic sink mobility and proposed a simple data collection algorithm. In their proposal, sensors buffered their measurements locally and wait for the arrival of a mobile sink. Multisink scenario is also considered. Each sink moves randomly and collects data from encountered sensors in its communication range. Collected data are then carried by the sink to a wireless access point (e.g., a fixed base station).
In the case of stochastic sink mobility, energy consumption at sensor side is only due to sink discovery and subsequent data transfer. Assume each sink broadcasts a beacon message while moving. A straightforward ...