Distributed Deployment Strategies for Improved Coverage in a Network of Mobile Sensors With Prioritized Sensing Field

Efficient deployment strategies are proposed for a mobile sensor network, where the coverage priority of different points in the field is specified by a given function. The multiplicatively weighted Voronoi (MW-Voronoi) diagram is utilized to find the coverage holes of the network for the case where the sensing ranges of different sensors are not the same. Under the proposed strategies, each sensor detects coverage holes within its MW-Voronoi region, and then moves in a proper direction to reduce their size. Since the coverage priority of the field is not uniform, the target location of each sensor is determined based on the weights of the vertices or the points inside the corresponding MW-Voronoi region. Simulations validate the theoretical results

Deployment Strategies for Target Monitoring and Coverage Improvement in Mobile Sensor Networks

Efficient sensor deployment strategies are developed in this work for target monitoring and coverage improvement in collaborative wireless mobile sensor networks. The objective of the target monitoring problem is to compute the desired sensing and communication radii of sensors as well as their location at every time instant such that a set of prescribed specifications such as connectivity preservation and low energy consumption are satisfied. An energy-efficient strategy is also proposed for tracking a moving target in a sensing field, using a grid of sufficiently small rectangular cells. The grid is converted to a graph with properly weighted edges. A shortest-path algorithm is subsequently used to route information from target to destination by a subset of sensors. In the problem of coverage improvement in mobile sensor networks, on the other hand, the objective is to place each sensor in the field using available local information about its neighbors in such a way that the area covered by sensors is as large as possible, while some important criteria are taken into consideration. Both cases of identical and nonidentical sensors (in terms of sensing radii) are considered, and different iterative algorithms are developed which are shown to be convergent. The relocation algorithms are based on the relative position of each sensor w.r.t. the boundaries of its cell or the corresponding corner point. The algorithms are extended to the case of limited communication range of sensors (leading to inaccurate Voronoi cells), an environment with prioritized sensing (mathematically characterized by a weighting function for different points), and an environment with obstacles (leading to some invisible areas). Simulation results are provided to validate the effectiveness of the proposed algorithms

Cooperative Coverage Control of Multi-Agent Systems

In this dissertation, motion coordination strategies are proposed for multiple mobile agents over an environment. It is desired to perform surveillance and coverage of a given area using a Voronoi-based locational optimization framework. Efficient control laws are developed for the coordination of a group of unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs) with double-integrator and non-holonomic dynamics. The autonomous vehicles aim to spread out over the environment while more focus is directed towards areas of higher interest. It is assumed that the so-called ``operation costs'' of different agents are not the same. The center multiplicatively-weighted Voronoi configuration is introduced, which is shown to be the optimal configuration for agents. A distributed control strategy is also provided which guarantees the convergence of the agents to this optimal configuration. To improve the cooperation performance and ensure safety in the presence of inter-agent communication delays, a spatial partition is used which takes the information about the delay into consideration to divide the field. The problem is also extended to the case when the sensing effectiveness of every agent varies during the mission, and a novel partition is proposed to address this variation of the problem. To avoid obstacles as well as collision between agents in the underlying coverage control problem, a distributed navigation-function-based controller is developed. The field is partitioned to the Voronoi cells first, and the agents are relocated under the proposed controller such that a pre-specified cost function is minimized while collision and obstacle avoidance is guaranteed. The coverage problem in uncertain environments is also investigated, where a number of search vehicles are deployed to explore the environment. Finally, the effectiveness of all proposed algorithms in this study is demonstrated by simulations and experiments on a real testbed

Improving Group Integrity of Tags in RFID Systems

Checking the integrity of groups containing radio frequency identification (RFID) tagged objects or recovering the tag identifiers of missing objects is important in many activities. Several autonomous checking methods have been proposed for increasing the capability of recovering missing tag identifiers without external systems. This has been achieved by treating a group of tag identifiers (IDs) as packet symbols encoded and decoded in a way similar to that in binary erasure channels (BECs). Redundant data are required to be written into the limited memory space of RFID tags in order to enable the decoding process. In this thesis, the group integrity of passive tags in RFID systems is specifically targeted, with novel mechanisms being proposed to improve upon the current state of the art. Due to the sparseness property of low density parity check (LDPC) codes and the mitigation of the progressive edge-growth (PEG) method for short cycles, the research is begun with the use of the PEG method in RFID systems to construct the parity check matrix of LDPC codes in order to increase the recovery capabilities with reduced memory consumption. It is shown that the PEG-based method achieves significant recovery enhancements compared to other methods with the same or less memory overheads. The decoding complexity of the PEG-based LDPC codes is optimised using an improved hybrid iterative/Gaussian decoding algorithm which includes an early stopping criterion. The relative complexities of the improved algorithm are extensively analysed and evaluated, both in terms of decoding time and the number of operations required. It is demonstrated that the improved algorithm considerably reduces the operational complexity and thus the time of the full Gaussian decoding algorithm for small to medium amounts of missing tags. The joint use of the two decoding components is also adapted in order to avoid the iterative decoding when the missing amount is larger than a threshold. The optimum value of the threshold value is investigated through empirical analysis. It is shown that the adaptive algorithm is very efficient in decreasing the average decoding time of the improved algorithm for large amounts of missing tags where the iterative decoding fails to recover any missing tag. The recovery performances of various short-length irregular PEG-based LDPC codes constructed with different variable degree sequences are analysed and evaluated. It is demonstrated that the irregular codes exhibit significant recovery enhancements compared to the regular ones in the region where the iterative decoding is successful. However, their performances are degraded in the region where the iterative decoding can recover some missing tags. Finally, a novel protocol called the Redundant Information Collection (RIC) protocol is designed to filter and collect redundant tag information. It is based on a Bloom filter (BF) that efficiently filters the redundant tag information at the tag’s side, thereby considerably decreasing the communication cost and consequently, the collection time. It is shown that the novel protocol outperforms existing possible solutions by saving from 37% to 84% of the collection time, which is nearly four times the lower bound. This characteristic makes the RIC protocol a promising candidate for collecting redundant tag information in the group integrity of tags in RFID systems and other similar ones