## 4 Low-Cost Experimental Implementation Using on-Premises LTE/4G Network
### Experimental Implementation  
To implement a low-cost open-source monitored Emergency Evacuation System, based on smart signage, we have built a scalable LTE/4G sensor network, which is composed of low-cost LTE/4G modules (Figure 7a) and digital LED strips (Figure 7b). The LED strips are used in the current project both as a low-cost signage tool, as well as a durable and flexible digital signage component. We use a LILYGO TTGO T-SIM/000G development board with a SIMCOM7000G (Figure 7a) modem installed, and an LTE/4G sim card (Figure 7a), which is connected to a cellular network, to control the digital LED strips. We have chosen the LILYGO TTGO T-SIM/000G module, which is very compact, with a 16850 battery holder. It is also a low-power global cellular module which supports LTE CAT-M1 and NB-IoT technology. It can also be used for location tracking, as it has integrated a high-speed multi-GNSS (GPS, GLONASS, and BeiDou/Compass, Galileo, QZSS standards) chipset [42]. It can be programmed through Arduino IDE, which is a user-friendly IoT tool for node programming. With the most recent SIMCOM7000G modem, the LILYGO TTGO T-SIM/7000G gives us a combination of power, friendliness, and adaptability that enables us to connect our nodes and create IoT industrial applications for energy metering, asset tracking, monitoring, digital signage, etc. In Power Save Mode (PSM) and Extended Discontinuous Receptions (eDRX), the LTE/4G modem can extend battery life up to 10 years [43]. The SIMCOM 7000G modem is powerful and expansible with many interfaces, such as UART, GPIO, PCM, and I2C. Compared to GSM modems, it provides deeper coverage enhancement. It has been designed for applications where low latency is required, along with low-throughput data communication in a variety of propagation use cases. It combines performance and security with flexibility, and therefore it suits Machine-To-Machine (M2M) applications, such as asset tracking, remote monitoring, health monitoring, digital signage, etc. [43]. Table 4 depicts SIMCOM 7000G modem details. Industrial IoT systems have been grown rapidly, and the pervasiveness of smart nodes enables the foundation of more interactive things and users, with the hope to improve industrial procedures and system monitoring. To face the growing complexity of industrial IoT systems, where specialized resources are missing, several industrial and academic approaches have been proposed to improve the end-user experience and allow them to implement and configure their IoT applications. The most common solutions are based on Visual Programming Languages (VPLs), which have been used to develop theProgrammable Logic Controllers (PLCs) systems. Thus, many IoT implementations are created and controlled with the usage of VPLs, where Node-RED is one of the most well-known. Node-RED is an open-source software that enables the mashup of IoT devices, APIs, and third-party services, all together in a hybrid text-visual programming solution [44]. It  
Figure 7: (**a**) Low-cost 4G/LTE module; (**b**) Digital LED strips. also provides a browser-based editor that makes the connections easy. Our network uses a Node-RED IoT platform and a Node-RED IoT dashboard, which were installed along with an MQTT broker on an Ubuntu 20.04 LTS machine (Figure 8). We built flows to control the Digital LED strips by using palette nodes, which can be deployed to its runtime in a single click. Figure 9 represents an experimental flow that directs passengers of deck 8 to the safest direction. The Node-RED dashboard is a front-end web application that was developed to control the digital LED strips that were installed on the ship. We controlled them by publish/subscribe messages through the MQTT Broker to specific topics that represent the decks of the ship inside the MVZs. Figure 10 depicts the experimental Node-RED dashboard, which controls the \"SECURE\" (Figure 10a) and \"NOT SECURE\" (Figure 10b) digital signage on \"deck 8\" into an MVZ. In Figure 9 we see a \"SWITCH\" node and an \"MQTT OUT\" node, connected via an MQTT connection.