On Hierarchical Routing Protocols Of Wireless Sensor Networks

Recent advances in wireless communication, MEMS, low-power analog and digital electronics, low-power RF design have motivated the development of low-cost, low-power, multifunctional sensors. These sensors can possess sensing, data processing and wireless communication capabilities in extremely small size. Many of these sensors can be deployed in the monitoring areas, form into self-organized network, accomplish complex monitoring tasks, this is called Wireless Sensor Networks(WSN). WSN is randomized deployed, self organized, environment adapted and low cost, so it has wide application foreground, it can be used in many fields such as military, industry monitoring, environment monitoring, medical treatment and health, intelligent home, commerce, etc. It has attracted high attention in academia and industry fields, it is considered as one of the most important technology of the 21st century.Because of the restriction of size and cost, the computing ability, memory and communication bandwidth of the sensors are limited, they can only take limited batteries as energy sources. In order to accomplish special tasks, the sensors are usually deployed in the enemy area or in the foul environment, their energy can't be supplied or replaced, so how to reduce the energy dissipation, make the lifetime of the network as long as possible is a key problem. The data transmission of the network can't leave the routing protocols, designing energy-efficient routing protocols so as to prolong the network lifetime is high important.Routing protocols can be classified into plane and hierarchical protocols in the point of the network logic view. All the sensors have equal status in the plane protocols. In the opposite, sensors are organized into hierarchical structure in hierarchical protocols. The plane protocols may cause much latency even the paralysis of WSN which has so many sensors, and their extensible ability is not so good. However, the hierarchical protocols are more fit.The hierarchical routing protocols are main clustering routing protocols. The basic idea of clustering is dividing all the sensors in the network into several clusters, each cluster is made up of a cluster head and many cluster members. Cluster members only communicate with their cluster head, the cluster head aggregates and fuses the sensing data of its members, and then transmits to the base station. The clustering structure localizes the wireless communication into each cluster, reduces the long distance wireless communication. At the same time, it can adopt data fusion methods, reduce the data quantity which need to be transmitted. So clustering can save energy greatly. Moreover, it has better extensible ability. This paper researched the hierarchical routing protocols of WSN specially. The main research contents are as follows:1. Analyzing and performance estimating of the typical routing protocols. This paper classified the existing routing protocols of WSN in the point of the network logic view. Introduced and analyzed the representative routing protocols of WSN, including Flooding, SPIN, Directed Diffusion, LEACH, PEGASIS. Introduced the Min-ID and Max-Degree algorithms which are the representative clustering protocols of the Ad Hoc. In the end, compared and analyzed all of the above representative protocols in many quality terms, found out the typical ideas and protocols which have guidance meaning for this paper.2. Researching and improving of the Low-Energy Adaptive Clustering Hierarchy-LEACH. LEACH is the first clustering routing protocol of WSN, also the most typical clustering routing protocol. The cluster heads are charged with the many tasks of data aggregation and fusion, so their reliability and stability have large influence on the whole capability of the network, their energy dissipation are more. In order to overcome this problem, in addition to possessing the advantages of the common clustering protocols, LEACH takes the dynamic clustering technology. It utilizes randomized rotation of cluster heads and distributes the energy load among all the sensors evenly, so it can banalce energy dissipation and prolong the network lifetime greatly. But it also has some shortages, such as doesn't consider the energy level of the sensors when clustering. Each sensor can't has equal energy, Apparently, we ought to make the higher-level energy sensors have more chance to be cluster head, at the same time decrease the chance to be cluster head of the lower-level energy sensors. This paper improved LEACH and proposed an energy-considered clustering routing protocol: Considered the node's energy when clustered, increased the probability to be cluster head of higher-level energy nodes, decreased the probability to be cluster head of the lower-level energy nodes, so the nodes could adjust their probability to be cluster head as to their energy. This paper proved the coherence of the produced cluster head numbers between the modified algorithm and LEACH.3. The simulation testing of the modified algorithm. Network simulation is the forceful method of the theory analyzing, the evaluating and the fault diagnosis of the network design scheme. This paper simulated LEACH and the modified algorithm E-LEACH useing the network simulator NS2, designed typical experimental scene, run them respectively. Simulation results show that the modified algorithm balance the energy distribution of the network and achieve better performance than LEACH in terms of the network lifetime.4. Hierarchical routing protocols researching based on the GAINS real WSN platform. Because of the restriction of the real hardware conditions, it is difficiult to realize the theory protocols on the real palform, so this paper researched the hierarchical routing protocols which suit the real platform, having no front knowledge and completely self-organized. This paper proposed a Min-Depth-Based Tree Routing Protocol, this algorithm is simple, applied and high efficient, it can minimize the hops from the sensors to the base station. Using the typical idea of the Min-ID and Max-Degree clustering algorithms which are the algorithms of Ad Hoc, considering the energy sensitive of WSN, and adopting the"round"concept of LEACH, this paper proposed a Integration Wight Clustering Protocol. The real experimental results prove that this protocol dissipates network energy evenly. This two protocol have been realized on the GAINS platform.In the end, some problems for further study are proposed.