## 1 Introduction  
Based on short-range communication protocols, wireless sensor networks (WSNs) have a communication range of 100 meters. If a greater range is required, multi-hop modes can be used to extend coverage. However, more routes must be deployed as distance increases, making the system costly and difficult to maintain. Monitoring systems built on WSNs can use other methods to extend their communication distance; for example [1; 2; 3; 4; 5], used a gateway with multiple communication nodes. [PERSON] et al. designed a multi-mode gateway that included wireless local area networks (WLAN) and 3G/4G mobile data networks [3], enabling healthcare professionals and the family of patients in a hospital setting to connect to the hospital monitoring system via different communication networks. Although the gateway design above provides users with greater flexibility, the remote monitoring functions fail if WLAN and mobile data networks are unstable. Military warehouses, for example,are usually located in regional areas with poor telecommunication infrastructure, making it extremely problematic to effectively build a WSN monitoring system. Wired communication systems commonly use twisted pair cabling for dial-up networking, but the problem with this approach is that the quality of the connection is often unstable. Although wireless networks have greater signal transmission range and can enable better network access in remote areas, signal quality is determined by distance to the mobile phone tower. In areas with poor coverage, therefore, it is essential that remote monitoring systems are designed with back-up capabilities for communication networks. [PERSON] et al. and [PERSON] et al. set out the communication architecture for a monitoring system that combines both WSN and wired networks [6; 7]. The advantage of this hybrid approach is that, should the wired network fail, the system can immediately switch to communicating via WSN. The disadvantage is that such systems are extremely complex and costly to build, as well as difficult to maintain. In the hybrid monitoring mechanism developed by [PERSON] et al. [8], when the wired network shows errors or irregularities, these data are conveyed back to the server via pre-allocated routes and used to enhance the transmission rate of the wireless network. According to the results of [6; 7], it is obvious that the monitoring and control system must have communication backup capabilities. However, the solution to the system backup mentioned in the above articles is achieved by using switching of wired and wireless communication networks. The monitored area is in a location where signal coverage is poor, and therefore we must consider other communication methods (such as mobile communication) to prevent system failure. The National Communications Commission (NCC) of Taiwan provides a Mobile Communications Service Information System [9], which can be used to search for the signal coverage and reception quality of 3G/4G mobile phone networks in any area (see Figure 1). In the figure, green indicates areas with high reception quality. This means that mobile phone users in these areas can place calls and transmit data over a stable and consistent connection. The yellow regions have standard reception quality. Phone calls are uninterrupted and audio is clear, but the data connection may occasionally be unstable. The orange zones have acceptable reception quality, meaning that data connections may be partially unstable. Finally, the white or transparent zones have poor reception, meaning it is difficult to successfully make calls and audio is unclear. Most of the mountainous areas in Taiwan are not covered by mobile communications, and the system does not mark additional colors, so the mountains present the dark green of the original satellite imagery. If WSNs were built in the yellow and orange zones, these would be considered communication blind spots. We would be limited to using GSM/SMS [10; 11; 12] communication for remote monitoring.