# A Comprehensive Study of the Use of LoRa in the Development of Smart Cities
## 2 Background
### IoT Technologies for Smart Cities  
It is known that IoT applications for smart cities require an adequate network connectivity with large area coverage and efficient resource consumption, especially in terms of energy, since most IoT devices use battery for their operation. The low-power wide-area network (LPWAN) was created to satisfy these requirements. LPWAN is a group of technologies that allow long range communications with low power consumption, long battery life (approximately 10 years), acceptable transmission rates, good penetration characteristics, and reduced cost of installation [12]. There are different technologies that represents LPWAN (see Figure 3). Among these, LTE-M, EC-GSM, NB-IoT are considered as 3 rd Generation Partnership Project (3 GPP) standards, whereas SIGFOX, LoRa, and Weightless are classified as non-3 GPP standards. NB-IoT (narrow-band IoT) was released in June 2016 and was developed by the 3 GPP consortium; it is compatible with LTE and has a coverage range of 15 km and a transmission speed of around 150 kbps. NB-IoT is a licensed technology which has been deployed in 79 countries with an investment of $598 billion. NB-IoT uses OFDMA modulation. On the other hand, LoRa was developed by Cycleo and was released in 2012 as a non-licensed technology. It has a range of 11 km and a transmission speed of around of 10 kbps. LoRa networks have been implemented in 34 countries with an investment value of $241 billion. Finally, Sigfox is a non-licensed technology which was developed in Toulouse and released in 2009. It has a coverage range of 13 km and a transmission speed of 100 bps [16].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Smart City Subcategory** & **2015** & **2016** & **2017** \\ \hline Healthcare & 9.7 & 15 & 23.4 \\ Public Services & 97.8 & 126.4 & 159.5 \\ Smart buildings & 206.2 & 354.6 & 648.1 \\ Smart homes & 294.2 & 586.1 & 1.067 \\ Transport & 237.2 & 298.9 & 371 \\ \hline \hline \end{tabular} Source: Gartner 2015.  
\end{table}
Table 2: Connected devices in the smart city subcategory (in millions).  
Figure 3: Classification of Internet-of-Things (IoT) communication technologies from the 3 rd Generation Partnership Project (3 GPP) perspective [17].  
Among the different LPWAN technologies, LoRa was considered for this study since it operates efficiently in unlicensed bands. Other technologies have various limitations in terms of research. For example NB-IoT must be setup within a cellular network [18], Sigfox is a non-licensed technology that operates on the basis of subscription; therefore, to connect devices to the Sigfox network, the usage of application programming interfaces (APIs) of the Sigfox cloud platform is required. Other advantages of LoRa are that it is supported by many worldwide technology leaders, it has two model services, i.e., a provider network service and a private network, and the number of messages that can be sent in the LPWAN infrastructure is not limited (whereas Sigfox only allows 140 messages per day and per device) [19].  
Other important characteristics of LoRa are: (1) LoRa presents robustness against multi-path fading or Doppler effect; (2) LoRa also uses a proprietary chirp spread spectrum (CSS) modulation to archive distances greater than 700 km, and the CSS modulation provides robustness against interference and a very low signal-to-noise ratio (SNR) that allows the receiver to demodulate the signal; (3) LoRa is suitable for applications that require a very long battery lifetime and has a reduced installation cost; (4) LoRa allows tuning several physical transmission properties, such as bandwidth (BW), central frequency, coding rate (CR), spreading factor (SF), and transmission power [18]; (5) LoRa uses a long-range start architecture (see Figure 4) in which gateways are used to relay messages between end nodes; (6) LoRa uses an adaptive data rate (ADR) algorithm to estimate the CR and SF parameters under a specific channel.