# A Routing Protocol for Multisink Wireless Sensor Networks in Underground Coalmine Tunnels
## 2 Related Studies
In this respect, the use of the competitive mechanism of the cluster head and unequal competitive radius within the long-strip structure of the coalmine area was optimized by [1]. In [23], the LEBUC (Liner Energy-Balanced Uneven Cluster) algorithm was proposed to optimize the competitive mechanism of the cluster head by considering the distance between the sensor node and the sink, the residual energy of the sensor node, and the sensor node density in coalmine. Moving objects in a coalmine tunnel have very-strong temporal and spatial correlations in path selection, and these are considered in [24], where a routing algorithm is proposed on the basis of Bayesian decision by analyzing the probability of path selection by the moving objects in the tunnel. Other partition strategies, including energy balance and cluster head selection according to the tunnel characteristics of the coalmine, were introduced in [25; 26; 27]. Some novel algorithm is proposed in [28; 29]: in [28] a model for underground mines is generated by adopting a performance-based approach, while, in [29] a green MAC algorithm is proposed for smart home sensor networks. These strategies effectively extend the network lifetime and improve network performance. However, many of the aforementioned studies on multisink routing protocols have not been conducted in accordance with coalmine tunnel characteristics and are therefore not suitable for use in underground coalmine tunnels. Most of the multisink studies as represented by [10; 11; 12] focused on prolonging the network lifetime by optimizing the number and deployment location of sinks in the network. However, the sensor nodes are usually deployed in a place where it is very difficult to conduct manual maintenance within the coalmine tunnel. Some studies [14; 15; 16; 17; 18; 19; 20; 21; 22] have proposed methods relating to load balance and effectiveness of energy consumption with the aim of avoiding packet loss caused by congestion and collision in the data transmission process. However, these studies are not directly related to the special structure of the coalmine tunnel and therefore cannot be applied here. In addition, although other studies [1; 23; 24; 25] have investigated energy consumption in accordance with the special coalmine tunnel structure, such studies have unfortunately been based on a single-sink structure, which has evident application limitations. It is thus evident that the previous studies are not applicable for use in underground coalmine tunnels, because they are either based on the single-sink network structure or they do not consider the special shape of underground tunnels. However, because the CNP algorithm is based on a no-grid-cell multisink structure, sensor nodes are deployed randomly in its simulation, and the algorithm consumes less energy and has a longer lifetime, we compare the CNP algorithm with the algorithm presented in our study. Furthermore, the CNP algorithm uses the one hop rule and has a similar calculation method to our algorithm. Our paper focuses on transmission power control and combines the multisink network structure with clustering routing technology to propose a new routing protocol known as PCEB-MS for underground coalmine tunnels, focusing particularly on the haulage roadway. This protocol obtains an optimal communication radius by negotiating the sink transmission power control to guarantee the coverage area of a network. The unequal clustering algorithm is also used to ensure the energy balance of the network to obtain the best connectivity, prolong the network lifetime, and rapidly transmit monitored data.