# IoT Sensor Challenges for Geothermal Energy Installations Monitoring: A Survey
## 3 IoT Devices and Cloud Processing
### Cloud Services  
Cloud services involve infrastructure, platforms and software delivered on demand to companies and customers via the internet. Cloud services employ cloud computing solutions and do not encumber the hardware or software of devices accessing the service. The variety of available cloud services may disguise the level of an organization's ownership of the stack [98]. For clarity, cloud service models can be grouped into four main categories according to how they are managed (Figure 7).  
* On Premises (Private Cloud)--This cloud model is in fact not a genuine cloud service. It is suitable for users who require data protection and security and are willing to pay more for the service. Because data and all infrastructure, including software and hardware, are on the premises, the system is managed by the user's own IT team. In-house maintenance requirements and fixed scalability mean that this type of deployment is the most expensive.
* Infrastructure as a Service (IaaS)--IaaS allows customers to outsource equipment such as storage, servers and network resources. The remainder of the stack is managed by the customer. The disadvantage of IaaS is the potential for vendor outages and the cost of training personnel to manage new infrastructure.  
\begin{table}
\begin{tabular}{l r r r} \hline \hline  & **LoRaWAN** & **Sigfox** & **NB-IoT** \\ \hline Range & 5–20 km & 10–40 km & 1–10 km \\ Band & Unlicensed ISM & Unlicensed ISM & Licensed LTE \\ MAC layer & ALOHA-based & ALOHA-based & LTE-based \\ Payload & 242 B [86] & 12 B (UL), 8 B (DL) & 1600 B \\ Authentication and & AES-128 & No & LTE encryption \\ encryption & Adaptive data rate & Yes & No \\ Modulation & LoRa (CSS) & DBPSK, GFSK & QPSK \\ Transmission speed & 50 kbps & 100 bps & 200 kbps \\ Deployment model & Provider, private & Provider & Provider \\ Adaptive data rate & Yes & No & No \\ Topology & Star, mesh, P2P & Star & Star \\ Standardization & LoRa Alliance & Sigfox company with ETSI & 3 GPP \\ Power consumption & Low & Low & High \\ Interference immunity & Very high & Very high & Low \\ \hline \hline \end{tabular}
\end{table}
Table 6: Summary of LPWAN parameters [95; 97; 85].  
Figure 7: Cloud model types: on premises, infrastructure as a service, platform as a service and software as a service.  
* Platform as a Service (PaaS)--The provider manages everything as in IaaS but is also responsible for the base software and operating system, middleware and database. The drawback of PaaS is potential security problems and greater dependency on the vendor.
* Software as a Service (SaaS)--This model completely transfers the management of all components to the vendor service provider [99; 100].  
Table 7 summarizes the features of three widely used cloud services: Amazon Web Services (AWS), Microsoft Azure IoT, Google Cloud Platform [101; 102; 103], and IBM cloud [104]. Generally, these state-of-the-art cloud providers dedicate broad support to services and applications designed for the IoT and standard communication interfaces for connecting IoT devices to a cloud. They also feature powerful scalable data storage and support for big data analysis.