# MB-OFDM-UWB Based Wireless Multimedia Sensor Networks for Underground Coalmine: A Survey
## 1 Introduction  
Safety production of coalmines is a task of top priority which plays an important role in guaranteeing, supporting and promoting the continuous development of coal industry. It is also a key part of the state work safety. Implementing the strategy of \"Prospering the nation, the coal industry and the safety production by science\" and establishing the long-term mechanism of coalmine safety production are essential for China's coalmine industry [1]. In recent years, China has made considerable progress in coalmine safety production, but the situation is still severe which draws higher demands for the coalmine industry. To ensure the safe operation of coalmines and reduce the number of accidents and casualties to the maximum, the systems for coalmine monitoring, early warning and disaster relief have urgent demands for wireless video surveillance, wireless voice communication, underground environment monitoring and personnel positioning [2]. Video surveillance for belt conveyers and other removable heavy-duty manufacturing facilities, along with different kinds of temporary video monitoring tasks such as regional mine drainage surveillance, is an effective way to avoid accidents. Unfortunately, the existing Cable Monitoring System (CMS) cannot fully meet the requirements of these applications, due to the complex working conditions in underground mines and the limitations of the CMS. Thus, by using wireless method, the areas that are difficult to monitor for the CMS can be effectively, instantly and flexibly monitored. Wireless sensor networks (WSNs), which have outstanding advantages of easy configuration, flexibility to shrink or expand the monitoring range, strong fault-tolerance and mobility, are going to play an important role in monitoring and analyzing the dynamic, hostile, unfamiliar and unexplored environment [2]. However, the monitoring environments in coalmine are very complicated and ever-changing, and simple scalar data collected by traditional WSNs cannot meet the requirements of comprehensive environment monitoring of underground coalmine, leading to a urgent need for the introduction of information-intensive multimedia content such as video and audio streams, and still images into the sensor network based monitoring tasks in coalmines. On the basis of WSNs, wireless multimedia sensor networks (WMSNs) are new types of sensor networks which enable perception of multimedia content such as video and audio streams, and images [3; 4; 5]. The sensor nodes of WMSNs are usually equipped with inexpensive hardware such as complementary metal-oxide semiconductor (CMOS) cameras, microphones and other sensors with the ability to retrieve simple environment data. Compared with WSNs, WMSNs enable the retrieval of multimedia streams that are typically informative and can be used to realize fine-grained and precise environment surveillance. Therefore, it is an ideal and effective way to achieve multimedia surveillance on environments like underground coalmines [6]. Using WMSNs to monitor the environment of coalmines attracts interests of many researchers in recent years. For instance, strategies of deploying WMSNs in underground coalmine have been put forward by [PERSON] and [PERSON] [7; 8]. [PERSON] et al. [9] proposed a wireless multimedia sensor network self-organization protocol for mine rescue that showed the schedules for establishing a self-organization network quickly and prolonging the lifetime of network. [PERSON] et al. [10] showed an ultra-wide band (UWB) transmitting and receiving strategy with complicated and low bit rate performances in different mine roadway environment. However, most of these works are theoretical research focusing on certain technology, from which we cannot get a comprehensive understanding of the overall structure and developments of WMSNs for underground coalmine.