International Journal of Future Generation Communication and Networking Vol. 5, No. 4, December, 2012 89 An Energy-Efficient Multi-hop Hierarchical Routing Protocol for Wireless Sensor Networks Jin Wang 1 , Xiaoqin Yang 1 , Yuhui Zheng 1 , Jianwei Zhang 2 and Jeong-Uk Kim 3 1 Jiangsu Engineering Center of Network Monitoring, Nanjing University of Information Science & Technology, Nanjing 210044, China 2 School of Math and Statistic, Nanjing University of Information Science & Technology, Nanjing 210044, China 3 Department of Energy Grid, Sangmyung University, Seoul 110-743, Korea {wangjin, xqyang, yhzheng, zhangjw}@nuist.edu.cn; jukim@smu.ac.kr Abstract Clustering provides an effective method for improving the performance of wireless sensor networks (WSNs). In this paper, we study that different number of clusters leads to different network performance on the energy consumption, energy balancing and network lifetime. We propose an Energy-Efficient Multi-hop Hierarchical Routing Protocol (MHRP) for wireless sensor networks to enhance the network lifetime and avoid the formation of energy holes. MHRP is a hierarchical routing protocol which selects sensor nodes with criterion of residual energy level to act as cluster heads and establish intra-cluster multi-hop routing based on the tradeoff between the two criteria of residual energy level and distance. Simulation results show that our MHRP can largely reduce the total energy consumption and significantly prolong the network lifetime compared to other routing algorithm like LEACH. Keywords: Wireless sensor networks, energy efficiency, clustering, multi-hop routing, network lifetime 1. Introduction Wireless sensor networks (WSNs) are usually composed of a large number of low-cost and tiny sensor nodes used for gathering information and sending it in a multi-hop manner to sink nodes. These sensor nodes have some computational power, storage and communication capability. WSNs are used broadly at military surveillance and tracking, environment monitoring and forecasting, healthcare etc. WSNs are energy-limited and application-specific. The energy of sensor nodes is usually limited and commonly non-rechargeable. Thus, how to utilize the limited energy resource of each sensor node in an efficient way is the primary research challenge [1, 2]. A typical wireless sensor network consists of densely deployed static sensor nodes with static sink node [3]. In WSNs, energy consumption and energy-balancing are one of the primary research issues. The traffic generally follows a many-to-one pattern, where sensor nodes closer to the sink node will consume more energy and deplete their energy faster for the heavier traffic loads. Namely the sensors nearer to the fixed sink node not only need to transmit their own packets, but also forward packets gathering from other sensor nodes that are far away from the fixed sink node. As a result, the uneven consumption will reduce the network performance such as network lifetime, energy consumption and so on.