## 2 Radio Communication Technologies
### The Main Characteristics of LPWAN Technologies
#### 2.2.2 Deployment Bandwidth, Scalability, and Coverage  
SigFox was created to ensure connection over huge areas from a couple of meters to several kilometers, although the speed of the data transfer is as low as 100 bps for 4-, 8-, or 12-byte packets. In Europe, however, SigFox is still under construction. The aim is to provide greater coverage for further areas than those covered nowadays [11]. Sigfox also uses 100 Hz bandwidth ultra-narrow band (UNB) modulation to achieve ultra-low noise levels [13]. Therefore, the benefit of Sigfox is its large coverage of a city with one base station at a range of over 40 km, in contrast to LoRaWAN, which has a lower range for rural areas. An example of the great coverage of Sigfox is in Belgium, a country with a total surface area of nearly 45,000 km\({}^{2}\), which is entirely covered by 7 Sigfox base stations [10]. Sigfox signals can delve underground; however, some tests showed a low level of performance due to a huge number of collisions in a 5000-node scenario [11]. In the LoRaWAN architecture, several devices communicate with one or more gateways in a star-of-stars topology. In fact, the devices and the gateway are bridged using a centralized intelligence server or a NetServer. The gateway-NetServer connection is either wired or wireless and manages excessive packets, configures the package parameters, and adjusts the security parameters. The NetServer is connected to another application server outside the LoRaWAN, where the IoT applications are deployed [14]. LoRaWAN has a dynamic data rate that is obtained based on the usage of different spreading factors. In Europe, the default channels are 868.10, 868.30, and 868.50 MHz. Therefore, the data rate can shift up to 9.375 kbps [15]. Utilizing a bandwidth that is not too narrow to broadcast a signal, which is usually 125 kHz, allows LoRaWAN to be robust against negative channel features such as frequency selectivity and the Doppler effect [16]. The Sigfox coverage area is better than that of LoRaWAN, but the reason that may make LoRaWAN a better choice is that it is an open protocol [17]. Random Phase Multiple Access (RPMA) is another technology allowing a higher linking capacity in comparison to LoRa or Sigfox by working on a 2.4 GHz band, while the majority of LPWAN technologies use sub-gigahertz frequencies. This is beneficial since RPMA can be regulated around the globe, but 2.4 GHz is also used in many of the other technologies such as Bluetooth and WiFi, making interference more probable [9]. The NB-IoT channels follow a reused and extended model based on the LTE design. For instance, an NB-IoT carrier uses twelve 15 kHz sub-carriers for a total of 180 kHz [15]. NB-IoT can coexist with GSM (Global System for Mobile Communications) and LTE systems in licensed frequencies (e.g., 700 MHz, 800 MHz, and 900 MHz). NB-IoT's frequency bandwidth of 200 kHz corresponds to one resource block in GSM and LTE. There are three operation modes regarding the bandwidth in NB-IoT. In a stand-alone type of operation, the utilization of the GSM frequencies that are currently used is possible. In guard-band operation, the unused resource blocks within an LTE carrier's guard-band are supported and the in-band operation utilizes resource blocks within an LTE carrier [18]. The next chapter gives a more detailed view of the operation modes of NB-IoT and its architecture. NB-IoT applications are expected to be deployed in areas with poor cellular coverage and penetration, such as in underground parking garages and elevators. The narrow-band (NB-IoT) protocol technology has many of LoRaWAN's features, such as having a high frequency, but it is not an open protocol [17]. NB-IoT's design includes 20 dB coverage and working on a single battery charge for over 15 years. It is also compatible with the LTE cellular network infrastructure that currently exists, providing the same level of security [5]. Sigfox, LoRaWAN, and NB-IoT technologies enable high-scalability features supporting the connection of thousands of end devices.