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Since the birth of wireless sensor networks (WSNs), researchers make lots of works on this area. This promotes the technology development and let it mature gradually. WSNs can be applied to the military, bio-medical, industry and agriculture, urban management, environmental monitoring, remote control of hazardous areas, scientific research, and space exploration and so on.WSN usually consists of a large number of sensor nodes. Constrained by the small size and very limited hardware resources, the nodes cannot share the existing routing protocols in wireless networks. So in WSN, the routing protocol is a core technology, which has become one of the hottest research areas.This article focused on the hierarchical routing protocols, and analyzed the scene of their applications, as well as their advantages and disadvantages. Also, we studied some representative routing protocols of this type, including LEACH, PEGASIS, and EEUC. LEACH protocol is a self-organizing, adaptive and energy-efficient cluster-based routing protocol. Many other typical hierarchical routing protocols such as PEGASIS, TEEN, are evolved from LEACH.LEACH uses random methods to select cluster head, and nodes choose a cluster head only considering local optimization of the area in cluster, which leads to energy imbalance of the whole network. While LEACH is a single-hop network, sensor nodes which are further from the base station will run out of energy earlier, because they need more power to send packet and this will shorten the network lifetime. We learned the idea of unequal clustering from EEUC. Since the communication between the cluster head and base station (BS) in LEACH is single-hop, we compute the cluster size according to the distance between the cluster head and the BS:the closer the bigger; the further, the smaller. In this way, we balanced the energy consumption of the whole network and achieved the purpose of prolonging the network lifetime. What’s more, we did a certain amount of optimization on the cluster head selection algorithm, using link energy consumption and distance threshold to make further improvement of the performance.In order to check the improved unequal LEACH protocol’s performance, we did simulations on NS2simulation platform. First, experimentations were required to determine the optimum cluster heads’percentage of network in unequal LEACH as well as some other parameters. And then we found out the influence of unequal metrics on the performance of the protocol. Finally, we compared unequal LEACH with LEACH and LEACH-C protocols through simulation. The results showed that unequal LEACH makes certain improvements of LEACH and prolongs the lifetime of wireless sensor network. And compared to LEACH, the improved protocol had better scalability, so it is more suitable for WSN.
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