# Low-Cost COTS GNSS Interference Monitoring, Detection, and Classification System +
## 3 Hardware Design
### Alternative Hardware Setups  
A large selection of COTS components can improve some aspects of the monitoring node. These alter the cost, energy consumption, or performance. Some improvements are considered in this section. Due to the current Raspberry Pi shortage [88], the selected SBC is challenging to obtain--especially at a reasonable price. There are many COTS SBC alternatives [89], but these often do not have the large Raspberry Pi community and abundant resources that facilitate rapid prototyping. However, the other communities and resources could improve in the future. Many GNSS pHats could be used, as described in the previous section. Many of these provide superior performance (especially when multi-band GNSS is used), but are more expensive. Therefore, a cost-to-performance trade-off exists. Other pHats also combine GNSS reception with mobile communications, such as LTE. Figure 6 shows several pHats used for different prototyping approaches in the monitoring station. The default communication protocol in the monitoring station is WiFi, which is practical and straightforward for small-scale deployments and tests. Furthermore, WiFi is already available on the SBC, so no extra components are required. Currently, evaluations to replace the WiFi communication are in process. However, several other communication protocols are considered for the monitoring station. Mobile communications, such as LTE or 5G, benefit in that the monitoring station only needs a connection to the mobile network. It allows the platform to be deployed anywhere it has access to a network, and modern mobile networks are ubiquitous, but some dead zones often occur. The limitation is that an extensive network of monitoring nodes can incur high costs over the mobile network for data transmission, increasing operational costs. For example, the current monitoring system requires about 3.3 GByte/month (approximately 10.2 kBit/s) to report all data, which costs 10 E  per month [90], or 120 E  per year. Comparing these costs to Equation (6) demonstrates that the network costs are considerably more than the power costs. Limiting how often data are sent could minimize these costs. Another approach is integrating the GNSS monitoring into a mobile network, such as 5G, as this could create a beneficial interdependency between the network and the monitoring stations [91]. Tests with pHats with combined Long-Term Evolution (LTE) and GNSS modules have been done. LTE integration in the pHats yields the significant challenge that the GNSS NMEA protocol and the LTE data have to share the same serial connection. Sharing the  
Figure 6: Alternative hardware designs. The top left is a high bandwidth LTE and GNSS pHat. Top right is a low-cost GNSS pHat with a uBBox MAX-M8Q. Bottom left Septentrio MOSAIC pHat. Bottom center uBBox F9R pHat. Bottom right NB LTE and GNSS pHat. same serial link significantly increases the software development effort, as additional care must be taken to identify each data byte as part of the GNSS or LTE data. Hence, an extra LTE USB stick is used to lower the development complexity. This aspect is still under further development. Low-throughput long-range protocols are applicable, such as LPWAN, LoRa, RPMA, MIOTY, or DASH7 [92]. These offer larger coverage areas, lower power consumption, the possibility to self-administrate, and an abundance of open networks (e.g., The Things Network ([[https://www.thethingsnetwork.org/](https://www.thethingsnetwork.org/)]([https://www.thethingsnetwork.org/](https://www.thethingsnetwork.org/)), accessed on 23 March 2023) or LoRa-Alliance ([[https://lora-alliance.org/](https://lora-alliance.org/)]([https://lora-alliance.org/](https://lora-alliance.org/)), accessed on 23 March 2023). However, they have significantly lower throughput rates, which is not a limitation of the current monitoring system requirements. Lastly, other SDR RFFEs can be used.