Deploying long-lived and cost-effective hybrid sensor networks

In this paper, we consider the problem of network deployment in hybrid sensor networks, consisting of both resource-rich and resource-impoverished sensor devices. The resource-rich devices, called micro-servers, are more expensive but have significantly greater bandwidth and energy capabilities compared to the low-cost, low-powered sensors. Such hybrid sensor networks have the potential to support the higher bandwidth communications of broadband sensor networking applications, as well as the fine-grained sensing that is made possible by smaller sensor devices. However, care must be taken to ensure that such systems are cost-effective to the end user. We investigate some fundamental questions for hybrid sensor network deployment—for a given number of micro-servers, what is the maximum lifetime of a sensor network and the optimal micro-server placement? What benefit can additional micro-servers add to the network, and how financially cost-effective is it to introduce these micro-servers? We propose a cost model and an integer linear programming (ILP) problem formulation for minimizing energy usage in a hybrid sensor network. Then, we prove that the integer linear optimization problem is NP-hard and introduce an efficient approximation algorithm using tabu-search technique. Our studies show that network lifetime can be increased dramatically with the addition of extra micro-servers; and the placement of micro-servers can affect the lifetime of network significantly. Moreover, we propose a network performance-cost ratio model to analyze the cost-effectiveness of the network and show that a hybrid sensor network is financially cost-efficient for a large case. Our optimization algorithm, together with the performance-cost ratio model, can be used to estimate the lifetime and financial cost of a hybrid sensor network before actual deployment.