| Coal mine accidents occurred frequently in our country. Construction of WSN (wireless sensor network) based intelligent monitoring system will effectively improve the capabilities of incident detection and post-disaster emergency response, making it be the focal part of coal mine production security and informationization. Energy limited is a serious problem in WSN, therefore, how to design routing protocol of high energy efficiency in order to prolong the network lifetime and monitoring quality is very important for WSN in coal mine. The topology of WSN in coal mine is long band type, bringing problems such as unbalanced power consumption, data redundancy and data latency. Cluster-based routing technology can significantly reduce data latency, improve energy efficiency and enhance network scalability, therefore is more suitable for mine application than flat routing protocols.Clustering scheme can dramatically decrease energy consumption, However, it can't avoid energy-imbalance among nodes. First, cluster heads consumes more energy due to data fusion, cluster management and the responsibility of communication with sink node, which leads to unbalanced energy consumption between cluster heads and cluster members. Second, when cluster heads transmit data to sink node via multi-hop communication, those cluster heads closer to sink node have a higher load of relay traffic and consume more energy. Third, when the data is transmitted through a optimal path to sink node, the nodes in that path will consume much more energy than other nodes for frequently involved in data relay. In the scenario of coal mines, cluster heads approximately distribute in a straight line, thus the choice of next hop is even a single in multi-hop communication, making the situation worse.Aiming to mitigate the problem of energy-load imbalance mentioned above among nodes to some extent, the UCEBRP (Uneven Cluster-based Energy-balanced Routing Protocol for Wireless Sensor Networks in Coal Mines) is proposed. The core of UCEBRP is an energy-balanced adaptive clustering scheme EBACS and an energy-efficient inter-cluster routing EEICR. In EBACS, the cluster heads will be reelected and rotated in next round in order to evenly distribute the energy load among all the nodes. To avoid the node having low energy level being cluster head and die early, the mechanism of tentative cluster head will be used, ensuring that the node going to be cluster head have higher energy level relatively. The main factors affecting energy balance among cluster heads are distances to sink node and energy level. Different values of these factors leads to unequal size clusters, which adaptively adjust energy consumption between intra-cluster and inter-cluster. In competing cluster head, tentative cluster head decides whether to become a cluster head according to the relative energy level compared with neighbor tentative nodes, further avoids the nodes having low energy level being cluster heads. The EEICR is designed according to the theoretical analysis of optimal hop and optimal forwarding distance in linear sensor network. It takes account both the minimum transmit energy consumption of the path and energy balance among forwarding nodes to protect those low-energy nodes. The feasibility of the proposed protocol is demonstrated with simulation results. It is shown that the UCEBRP effectively balances the energy consumption among cluster heads and achieves an obvious improvement on the network lifetime. |
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