# Study of Data Transfer in a Heterogeneous LoRa-Satellite Network for the Internet of Remote Things
## 3 Heterogeneous Network Architecture
### Long-Range Technology for Hybrid Terrestrial-Satellite Networks  
When choosing data transfer technologies and protocols in the heterogeneous IoRT setup, we consider the following key criteria:  
* energy efficiency;
* area coverage from a single base station;
* cost of service;
* possibility of using unlicensed radio frequency ranges. Low Power Wide Area Networks (LPWANs) [34] are usually considered as the best last mile technology for the Internet of Remote Things. The main distinctive features of LPWANs are:  
* long data transmission distance. In many implementations it can reach 10 km or even more;
* higher energy efficiency compared with standard data transfer protocols. The limitations of the technology are low speed and possible significant delays in data transmission. One of the commonly used LPWAN specifications is LoRa [32], with the Long Range Wide Area Network (LoRaWAN) [32] protocol being based on it. LoRa uses linear frequency modulation in the unlicensed frequency range up to 1 GHz (the exact range depends on the country). An adaptive spread spectrum technology allows one to dynamically change the bandwidth depending on the range of frequencies used. Thus, the LoRa specification allows for maximum transmission distance and energy efficiency compared with many other data transfer technologies for the Internet of things. The LoRaWAN protocol defines the primary network architecture for LoRa, in which a network gateway plays the role of a transparent bridge, passing LoRa packets onto the network and vice versa. LoRa and LoRaWAN are very often considered as a single joint technology covering several network layers. An alternative technology used in transmission of IoT data is Narrowband-IoT (NB-IoT) [35]. The technology was developed by the 3 rd generation partnership project (3 GPP) consortium and is now integrated into the long-term evolution (LTE) standard [36]. It is a subset of LTE to be used in energy-efficient stand-alone devices. Compared with LTE, the NB-IoT technology does not support roaming between base stations and channel aggregation to improve performance. In addition, it requires cellular communications and cannot be used in hard-to-reach areas. As a result, we will not consider NB-IoT as an equal alternative, and will focus on LoRaWAN as the primary technology for sensor data acquisition. With respect to satellite backhaul, there are two main providers of digital data transmission as of today: Inmarsat [37] and Iridium [33]. Inmarsat satellites belong to the class of GEO systems, providing coverage up to 70\({}^{\circ}\) north and south latitude, that is, they reach almost the entire globe except for \"snow caps\". The satellite system offers an Internet connection at speeds of up to 384 Kbps. A key feature of the platform is the presence of a controller, which allows implementing applications in a short time. There are ready-made Machine to Machine (M2M) [38] solutions, the choice of which depends on the complexity, speed and volume of the transmitted and received information. Among such solutions are IsatM2M [39], IsatDataPro [40] and BGAN M2M [41]. The Iridium satellite system, in turn, is a LEO constellation that provides data rates of up to 128 Kbps. The operator company offers M2M equipment based on Short Burst Data (SBD) 9602, 9603N and 9523 satellite modems, which allow transmitting short data messages. The key features of SBD satellite modems are their low power consumption and text messaging capabilities. The requirement to provide communication services in remote areas leads to the need for a coverage zone in the regions of the Far North and the Arctic. The only SATCOM that meets this criterion is the Iridium satellite system. Connecting an SBD Iridium modem to each IoT sensor is not feasible both in terms of cost and energy consumption. Thus, to organize the connection of IoT sensors via satellite communication channels, it is necessary to provide a gateway between the LPWAN networkand the satellite communication channels.