# ScienceIoT: Evolution of the Wireless Infrastructure of KREONET
## 2 Background
### Wireless Communication Technology for IoT  
Given that the IoT is being adopted in various applications, many wireless technologies are being employed considering their performance and features. According to their wireless coverage and data rate, wireless technologies can be categorized into wireless wide area networks (WWANs), wireless local area networks (WLANs), wireless personal area networks (WPANs), and LPWANs as shown in Figure 2. WWANs, WLANs, and WPANs are suitable for mobile device communication, building/office networks, and home/industrial dedicated networks, respectively. However, we focus on LPWAN technologies, which are suitable for collecting data from sensors located over distributed and possibly hostile areas. This is required in various research fields, including environmental, energy, and agricultural research. Table 1 shows a comparison of the three representative LPWAN technologies: Narrowband IoT (NB-IoT), SigFox, and LoRaWAN. Many studies have been conducted to investigate their similarity and the distinctive characteristics among them [3; 4; 5; 6]. NB-IoT uses licensed frequency bands standardized by 3 GPP and provides long-range communication and a high data rate. Therefore, it incurs high costs due to the expense of dedicated communication frequency bands and requires a considerable amount of battery power. By contrast, SigFox and LoRaWAN are operated in the unlicensed Industry-Science-Medical (ISM) frequency bands, thereby circumventing the cost for dedicated communication spectra. Although these technologies provide a lower data rate than cellular technology, they support very long-range communication with low energy consumption. Among the unlicensed LPWAN technologies, LoRaWAN offers advantages in terms of security, adaptability, and privacy. Thus, ScienceLoRa was built based on the LoRaWAN technology to provide data transmission in research and education. \begin{table}
\begin{tabular}{l l l l} \hline \hline  & **NB-IoT** & **Sigfox** & **LoRaWAN** \\ \hline Standardization & 3 GPP & ETSI and Sigfox Alliance & LoRa Alliance \\ \hline Technology & LTE (rel.13) & Proprietary & Proprietary \\ \hline Topology & Star & Star & A Star of stars \\ \hline Frequency & Licensed LTE frequency band & Unlicensed ISM bands & Unlicensed ISM bands \\ \hline Duty cycle restriction & No & Yes (typically 1\%) & Yes (typically 1\%) \\ \hline Modulation & QPSK/BPSK (DL), GFSK (UL) & DBPSK (UL), GFSK (DL) & CSS/FSK \\ \hline Bandwidth & 200 kHz & 100 Hz & 125/250/500 kHz \\ \hline Transmission technique & FDD & UNB & Aloha \\ \hline Maximum data rate & 200 kbps & 100 bps & 50 kbps \\ \hline Bidirectional & Yes/Half-duplex & Limited/Half-duplex & Yes/Half-duplex \\ \hline Maximum messages/day & Unlimited & 140 (UL)/4 (DL) & Unlimited \\ \hline Maximum payload length & 1600 bytes & 12 bytes (UL)/8 bytes (DL) & 243 bytes \\ \hline Coverage/Range & 1 km (urban), 10 km (rural) & 10 km (urban), 40 km (rural) & 5 km (urban), 20 km (rural) \\ \hline Maximum TX power & 20 dBm/23 dBm & 14 dBm/22 dBm & 14 dBm/27 dBm \\ \hline Interference immunity & Low & Very high & Very high \\ \hline Security & LTE encryption & MAC verification & AES 128 \\ \hline Adaptive data rate & No & No & Yes \\ \hline Handover & End-device joins a single base station & End-device does not join a single base station & End-device does not join a single base station \\ \hline Localization & No (under specification) & Yes (RSSI) & Yes (TDOA) \\ \hline Private network & No & No & Yes \\ \hline Module cost & \textless{}$5$ & \textless{}$5$ & \textless{}$510 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of various LPWANs. Figure 2: Wireless technologies categorized according to their data rate and coverage. LoRa/LoRaWAN is composed of a physical layer (LoRa) and a network layer (LoRaWAN). The protocol stack of LoRa/LoRaWAN comprises the physical, media access control (MAC), and application layers.