Research On Connectivity Weakness Of Wireless Sensor And Actor Networks (Ph.D Dissertation)

Wireless sensor and actor networks (WSANs) is a new type of information acquisition and processing technology. In WSANs, coordination mechanisms are required among sensors and actors to gather information about the physical world and then perform appropriate actions upon the environment. In particular, new networking phenomena called sensor-actor (SA) and actor-actor (AA) coordination may occur. Due to the application scenario and characteristics of the network node, the node failure is inevitable, so the weak connection will appear among nodes in the network. Current research in WSANs face a serious challenge that is how to keep connection of network, complete processing event by means of coordination among nodes, and fulfil the requirement of real-time, coverage and service quality at the same time.Facing weak connection of WSANs, aiming at connection detection and recovery mechanism of actor, coverage sensors number, service discovery of actor, relevant theories and algorithms are carried out in this thesis. The main contributions of our work include the following:The first part of the work committed to actor node failure detection and recovery. Considering nodes’ traffic problem, the article proposes an application-oriented fault detection and recovery algorithm (AFDR). The cut-vertex was detected by using AMM in AFDR algorithm. The backup nodes of vertexes were assigned according application characteristics of the network. The backup node detects any failure to select a suitable node (leaf node or itself) to replace the failed node. When the best position is figured out, the alternative node moves to the best position to manage multiple sensors. Compared with the typical algorithms, this algorithm has a better performance in mobile distance, coverage, etc.The second part of our work is that coverage problem brought by actor node failure is analyzed. Through the actor node mobile positioning methods, under the premise that guaranteeing the existing actor network connection, realize the maximization of sensor nodes coverage and minization of sensor nodes moving distance, the problem is a NP hard problem. In the article, by binary addressing count, exchanging packets between neighbors, moving the heuristic search for the actor node to a new position, the binary addressing mobile search algorithm (SMR) is put forward. Besides, the pros and cons of three kinds of deployment mechanism are compared. Simulation and analysis results show that compared with the typical algorithms, SMR algorithm performs well in both nodes moving distance and network overhead, and achieve the best coverage.Aiming at mobile coverage put forward in this article, in the third part, approximate solution methods are given. Through the introduction of hexagon partition structure and specific addressing method, a kind of node failure recovery algorithm based on hexagonal clumping is proposed, which has a good performance in mobile coverage recovery of actor node. Approximate error of this algorithm is given in theory. The algorithm has advantages in actor coverage number and moving distance compared with the existing algorithm.In forth part we introduce the problem of service discovery in WSANs. A multi-center addressing service discovery algorithm based on hexagon partition (MASD) is put forward. Taking the node communication overhead and storage burden into account, we design a multi-center addressing scheme. This scheme uses local computation so that it has the advantages of small amount of calculation. Sensor nodes can use address or local search algorithm to look for the next-hop node which arrives at the actor node. Analyzing algorithm through the experiment, MASD algorithm has shorter search distance and less communication overhead.