Mobile base station position optimization for network lifetime maximization in wireless sensor networks

The success of widespread deployment of and associated research efforts on the Wireless Sensor Networks (WSNs) is undisputed. Yet, there is still room for exploring and improving many aspects of WSNs as well as fully grasping intricate performance related details of some less-than-completely charted topics. WSNs are ad-hoc networks usually used for monitoring a particular area by a large number of sensor nodes. The most important factor making this possible is indisputably the removal of restrictions on the production costs of the sensor nodes in high quantities due to the help of innovations and developments in semiconductor technologies, wireless communications, networking and materials science. In WSNs sensor nodes usually have limited resources such as energy, communication distance, bandwidth, computing power and memory size. After the limitations related to the cost and hardware are met by the progress on semiconductor, network, and materials science; energy becomes the most critical resource for WSNs. Therefore, as one of the most crucial design goals of WSNs, network lifetime maximization through efficient utilization of energy is quite necessary. Although it is understood that balancing the energy in multi-hop data relaying towards a static sink prolongs network lifetime, some nodes usually end up with dissipating their energy unevenly and suffer from a problem generally known as the hot-spot problem. Base station position in WSNs has a significant impact on the network lifetime. The network's lifetime is inversely proportional to the total energy spent in the sensor nodes. The energy consumption for the communication which forms the largest portion of this energy is directly related to the base station location in the network. Therefore, sink mobility has been proposed in the literature to mitigate the suboptimal energy dissipation and the hot-spot problem. Sink mobility increases the sensor network lifetime, significantly, in certain network configurations. However this increase is shown to be limited if only a single mobile sink is used. In this study, our goal is to gain some more insight about the performance of base station mobility under different mobility patterns, to counter the sub-optimal energy dissipation. Also, an optimum base station mobility pattern is developed and the results are compared with the already known mobility routines such as grid, random, and spiral mobilities. Additionally, we develop a novel Mixed Integer Programming (MIP) framework to model and characterize achievable WSN lifetime trends for static and dynamic mobile sink trajectories. The effects of base station mobility on the network lifetime are characterized by solving the models within a wide parameter space. Our results shed more light into the energy efficiency characteristics of the optimal multiple sink mobility patterns, the efficacy of multiple sinks as opposed to a single one, and the tradeoff between static versus dynamic sink trajectories.