# Development of a Multi-Radio Device for Dry Container Monitoring and Tracking
## 3 Materials and Methods
### Hardware Design  
This subsection shows the CTD's electronic features used in order to meet the function requirements specified in Section 3.1. A preliminary analysis of the characteristics of development platforms most suitable for prototyping the device of interest has been carried out. Starting from the IoT device prototyping platforms available off-the-shelf, two possible approaches have been identified:  
1. Using Nordic devices and, more precisely, the Nordic Thingy:91 (already equipped with BLE, NB-IoT and GPS radios and a set of sensors) for the SW prototyping and the NRF9160 DK (which has the same processors as the Thingy:91) for the HW prototyping (adding sensors, etc. );
2. Using devices with ESP32 as the main controller and BLE Mesh coupled to a Quectel BG 95 cellular modem. For this approach, the ESP32 dev kit from Adafruit (HUZZAH32 ESP32 FEATHER STACK HDR) combined with a compatible Quectel BG95 modem shield has been selected. The information and specifications on the datasheets were used to compare the two approaches concerning their ability to meet the functional requirements. From this initial analysis, it was found that both approaches are feasible, in principle, although each has advantages and disadvantages. In general, Nordic is less power-demanding but more expensive, whereas ESP32 + Quectel is cheaper but more power-demanding. Then, the devices for both approaches were purchased (see Figures 5 and 6) and preliminary tests were performed: (1) set up the NB-IoT communication; (2) set up BLE Mesh. Regarding NB-IoT communication, using both Nordic and ESP32 + Quectel BG95 with SIM cards provided by TIM/Olivetti, it was possible to send position and sensor data to the cloud. It is important to emphasize that the CTD is SIM agnostic, as standard cellular technology is integrated into the system; notably, the authors also tested SIMs from other mobile virtual network operators (e.g., 1 NCE--DE, Telenor--NO, Arkessa--UK) offering NB-IoT SIMs that work globally. The market is evolving rapidly in this regard; other companies are claiming global roaming agreements, including TIM, ORBCOMM, Things Mobile and even Satelliot. Regarding BLE Mesh, with the Nordic approach, it was impossible to implement a BLE Mesh network. We have found that although the nRF52840 chip is included in the list of those that support BLE Mesh, in reality, this is not allowed in the current version of the firmware that Nordic makes available for the Thingy:91, nor is an upgrade planned. On the other hand, with the ESP32, it was possible to set up a BLE Mesh network. We verified that once the mesh was established, it was possible to (a) send data requests from the provisioner node toward the source sensor nodes and (b) send sensor data from the source node toward the provisioner/GW node. The insights we received from comparing the two approaches can be summarized as follows. 1. Nordic approach: BLE Mesh is not feasible with Nordic Thingy:91/NRF9160 DK. On this route, it is necessary to address the Nordic Thingy:53/nRF5340 DK (new product, not yet available on the market and not yet fully documented). An NB-IoT modem will need to be integrated into this platform (which, however, is already present on the Nordic Thingy:91). 2. ESP32 + Quectel BG95 approach: we built a BLE Mesh network with the SGI sensor node model; we configured the BG95, tested the connection to the TIM cellular network and successfully sent JSON messages to the ICON platform (TIM/Olivetti). In summary, the preliminary tests showed that the ESP32 + Quectel BG95 approach is suitable for the CTD prototype development. The Nordic approach certainly remains valid, in perspective, but requires further developments of new products that are not yet consolidated. As shown in Figure 7, the final choice for designing the CTD is to use the ESP32-WROOM-32 module as the board controller and application processor. It is a generic multi-radio module that targets a wide variety of applications, including low-power sensor networks.