Improving network lifetime with mobile wireless sensor networks

Sensors are used to monitor and control the physical environment. In mobile sensor networks, nodes can self-propel via springs, wheels, or they can be attached to transporters, such as vehicles. Sensors have limited energy supply and the sensor network is expected to be functional for a long time, so optimizing the energy consumption to prolong the network lifetime becomes an important issue. In static sensor networks, if sensors are uniformly deployed, sensors near the sinks die first. This is because besides sending their own sensed data, they also participate in forwarding data on behalf of other sensors located farther away from the sink. This uneven energy consumption results in network partitioning and limitation of the network lifetime. In this paper, we survey mechanisms that utilize nodes' mobility to extend the network lifetime. We divide these mechanisms into three groups: mechanisms using mobile sinks, mechanisms using mobile sensors redeployment, and mechanisms using mobile relays. Using mobile sinks, energy is saved by using shorter multi-hop data delivery paths and the set of sensors located near a sink changes over time, thus the energy consumption is balanced in the whole network. Using mobile sensors, the initial deployment can be improved through sensor relocation such that to balance energy consumption and to extend network lifetime. Mobile nodes can also be used as relays, which can inherit the responsibilities of the co-locating static sensors or they can carry data to the sink to reduce the cost of long distance communication. We provide overviews and comparisons among different mechanisms.