Abstract
In recent years, with the rapid development of microelectronics technology, sensing technology, and wireless communication technology, as an emerging technology, Wireless Sensor Networks (WSNs) have become a hot research field at home and abroad. WSNs have outstanding advantages of easy configuration, flexible networking, and strong fault-tolerance and mobility. Therefore, they play an increasingly important role in unfamiliar and unexplored environmental monitoring, emergency rescue, healthcare, industrial monitoring, target location, and so on. Wireless Underground Sensor Networks (WUSNs) are the extension of the application of WSNs in underground environment. Compared with the above-ground environment, due to the complex and uncertain factors of underground environment, limited communication range and hard energy supplement, the application of WUSNs is more challenging. The application of WSNs in underground environment is extremely wide, such as the monitoring of coal mining equipment, subways, oil pipelines, and natural gas pipelines. Once these equipments fail, it is easy to cause casualties, which is a waste of resources, and would lead to economic losses. For the reasons above, many scholars launched research on WUSNs.
This special collection aims to contribute to the literature by pushing the state of the art in all facets of WUSNs and lays the foundation of enlarging the scope of application of WUSNs hopefully. Responding to our call, scholars from all over the world submitted many papers on different research directions of WUSNs for us. After several rounds of serious and rigorous review, five high-quality papers were selected for publication in this special collection finally.
In the first paper, “Channel state information-based multi-level fingerprinting for indoor localization with deep learning,” Tao Li, HaiWang, Yuan Shao, and Qiang Niu propose a multi-level fingerprinting approach for indoor localization. The approach is composed of two-level methods: the first layer is achieved by deep learning and the second layer is implemented by the optimal subcarriers filtering method. Also, this method using channel state information is termed multi-level fingerprinting with deep learning.
The paper, with the title of “Time synchronization for long-chain-type wireless sensor networks”, is contributed by Zhenping Chen, Yourui Huang, Zheng Wang, and Feng Tao. As the name implies, it is a paper that talks about one feasible time synchronization algorithm in view of the requirement on time synchronization for a kind of typical WSNs with long-chain-type topologies. By analyzing the distribution characteristics of different kinds of nodes, with the introduction of the pairwise broadcast synchronization and the series multi-hop synchronization protocol, the estimation of the clock offset and the clock skew of all the nodes in the WSNs is performed based on virtues of the joint maximum likelihood and the least-squares method. Therefore, the authors solve the problems of time synchronization of the WSNs with long-chain-type topology.
In “One energy-efficient random-walk topology evolution method for underground wireless sensor networks,” Yourui Huang, Zhenping Chen, Tao Han, and Xiaotao Liu propose one energy-efficient random-walk scale-free topology model considering the limited energy supply and imperfect topological tolerance for WUSNs. Meanwhile, a power network topology structure with adjustable rate index gets generated. The nodes that in this topology model with larger residual energy present higher connectivity probability to get an energy balance of network, taking into account both the residual energy of the node and the distance among nodes.
The paper titled “Routing algorithm for supporting data-differentiated service in hybrid wireless mesh networks in underground mines” by Haifeng Jiang, Liansheng Lu, Guangzhi Han, HeWang, Shanshan Ma, and Renke Sun proposes a routing algorithm to support data-differentiated service in hybrid wireless mesh networks, using virtual potential field. Based on network parameters, the hybrid wireless mesh networks are abstracted as potential fields. The hop count is used to build the depth potential field and the buffer space and residual energy of nodes are primarily considered when constructing the resource potential field.
In the last paper titled “An emergency rescue communication system and environmental monitoring subsystem for underground coal mine based on wireless mesh network”, Haojiang Zhao and Wei Yang study an underground emergency rescue communication system based on wireless mesh network and its corresponding environmental monitoring subsystem. In this paper, the authors design the structures of the emergency rescue communication system and the wireless mesh nodes. They also develop wireless multi-parameter environmental monitoring terminals and set up the software platform for the environmental monitoring subsystem.
If these papers can bring help of research or idea inspiration to readers, we will be greatly honored. Finally, we would like to express our gratitude to all the authors who submitted papers to us and the experts who reviewed the papers.