The optimization of sensor deployment is a challenging problem that directly affects the coverage rate of ROI and accordingly the surveillance quality of ROI.The WSNs composed of mini-robot-based mobile nodes that construct mobile sensor networks, can adjust deployment autonomously according to the location and importance of ROI, which will optimize network coverage and satisfy application requirement. A typical strategy to these kinds of deployment problems is the virtual force relationship based Algorithm(VFA) [15�C17]. Originally proposed to facilitate the movement of robots to avoid obstacles, VFA has be adopted as one of the most effective algorithms to optimize the sensor deployment in WSNs.

In this research we study the deficiencies of VFA by analyzing its convergence property, boundary effect and useless movement, and propose two effective improvements, dubbed Improved VFA (IVFA) and Exponential VFA (EVFA). Extensive simulations are carried out to evaluate the performance of the proposed approaches. The results show that our proposed algorithms get better performance in energy consumption, convergence and coverage rate.The remainder of this paper is organized as follows. Section 2 describes the background of deployment problem of mobile sensor networks and analyzes the deficiencies of original VFA. Section 3 proposes two novel schemes to improve original virtual force relationship in ROI to solve deployment problem of the mobile sensor networks. Extensive simulation experiments have been done to evaluate these deployment algorithms and the results verify the proposed algorithm in section 4.

Finally, we give some conclusions.2.?Analysis of Deficiencies of Virtual Force Algorithm2.1. Problem DescriptionWithout loss of generality, we consider the sensor deployment problem in mobile sensor networks with a N �� M rectangle ROI. We adopt the plate sensing model, where the sensor can cover every point in the circle area centered at node itself and with a detection (or sensing) radius. In other words, the sensor node can detect the target appeared in its radius area. The effective communication distance is twice of the sensing radius. Each node can obtain the location of itself (through GPS or some other localization algorithms). Initially, the mobile sensor nodes are distributed randomly in the ROI plain.

During the process of deployment, each node is able to move freely within certain range. Our main objective is to deploy the sensors and control their movement to achieve high coverage rate, low energy consumption Batimastat and fast convergence.2.2. Virtual Force AlgorithmVFA was elicited from the potential field algorithm used for avoiding obstacles in mobile robot movement. Zou originally combined the potential field algorithm and the plate coverage theory by abstracting the sensor node to be a particle in the potential field, which will exert forces on the nodes nearby [13].