# Monitoring Perishable Commodities Using Cellular IoT:
## 1 Introduction
These allow for communicating wirelessly through broadband networks, such as Wi-Fi or mobile networks such as GSM, GPRS or LTE, which entails high power consumption, or through narrowband networks, highlighting Low Power Wide Area Networks (LPWAN), such as NB-IoT, LTE-M, LoRaWAN or Sigfox, with very low power consumption and a large range, at the cost of limiting the amount of data that can be sent [33; 34; 35]. Using IoT devices, perishable products can be tracked and traced throughout the food supply chain in real time, which would help to know more accurately where quality losses take place and propose corrective actions to mitigate them and extend their shelf life [36; 37; 38]. Moreover, the use of LPWAN communication technologies will allow IoT devices to have greater autonomy to cover the entire postharvest supply chain [39; 40]. Passive sensors can be found on the market, including simple time-temperature indicators (TTI) or sensors that employ USB, RFID or Bluetooth for data transmission [41; 42; 43; 44]. This presents the major drawback of not providing real-time data, as mentioned before. Readings must be taken manually, which is labor-intensive, prone to human error and precludes live monitoring. Moreover, some passive sensors are single-use, which creates waste and ongoing costs associated with replacement. An improvement could lie in the use of gateways to collect sensor measurements via protocols such as Bluetooth Low Energy (BLE), LoRaWAN or Zigbee, for instance, and send the data wirelessly to a server in real time via mobile networks such as GSM, GPRS or LTE or via Wi-Fi. This forms a WSN capable of live remote monitoring [45; 46; 47; 48; 49]. However, this implies the use of at least two different devices to make it possible, and the multi-device architecture increases complexity and points of failure. Troubleshooting connectivity across separate sensor, gateway and base station components also proves challenging for many users. In contrast, a few companies have attempted to integrate the entire system into a single device with embedded sensors and 4G wireless communication built in [50; 51]. But these single-unit solutions remain products targeting large enterprises and are unattainable for most applications and smaller organizations. Thus, the state of the art lacks accessible options to unlock the power of real-time sensor data. While existing options can enable real-time sensor monitoring, they present barriers such as high costs, design complexity or a lack of user-friendliness. So, there is a need in the market for an affordable, compact datalogger that integrates sensors and wireless communication in one device for real-time data collection. Taking into account the monitoring needs of the commodities during the postharvest stage and the available technology, a portable instrumentation system has been designed and manufactured with a very small and compact size, low cost and high autonomy thanks to energy consumption optimization strategies and hardware design optimization. The system incorporates, in a single device, high-precision sensors and a gateway with wireless communication to send data to a server in real time and to be able to access them from any device through the Internet. A cloud platform has also been programmed to record and visualize the data. The device is capable of measuring temperature, relative humidity, CO\({}_{2}\) concentration, luminosity and vibrations. Furthermore, it provides location information. It allows the inclusion of a SIM card of the desired operator and performs wireless communication using the NB-IoT LPWAN, being able to use the LTE-M low power network if it is not available. Moreover, it can also use GSM or EGPRS if none of the above are available. The system, in addition to sending data to the server, has a backup of the data in a flash memory, being able to access this data at any time through a USB connection.