# Dynamic Spectrum Access for Internet of Things Service in Cognitive Radio-Enabled LPWANs
## 1 Introduction  
In general, service providers (SPs) for public radio communication need to pay the government the high cost for licensing of radio spectrum bands in the respective country. Once the spectrum bands are assigned, the amount of available spectrum in each band is fixed. In contrast, the industrial, scientific and medical (ISM) radio bands are exceptionally unlicensed radio spectrum although they are served with fixed spectrum allocation as well. Moreover, the unlicensed ISM band is suitable for building Internet of Things (IoT) services with flexibility and low cost without any restrictions on wireless coverage and network topology [1; 2]. The traditional wireless sensor networks (WSNs) applications operate most commonly based on the 2.4 GHz unlicensed band under IEEE 802.15.4 standard. However, this band has often been overcrowded due to other wireless technologies such as WPANs (wireless personal area networks), WLANs (wireless local area networks), and WiMAX (worldwide interoperability for microwave access) operating over the same bands [1; 3]. Recently, low power wide area network (LPWAN) systems such as LoRa [2; 4; 5], SigFox [2; 5], and Wi-SUN [6], which operate most commonly under 800-900 MHz unlicensed bands, have been deployed commercially for IoT services even though the 3 GPP NB-IoT [5; 7] system still uses the licensed bands. Since many licensed spectrum bands are often either underutilized or unutilized, unlicensed users can temporarily use the unused spectrum such as spectrum hole without interfering with licensed users. Cognitive radio (CR) techniques have been used to alleviate the limitations of spectrum in wireless networks. However, cognitive radio has a critical drawback that it must not cause radio spectruminterference to the licensed band. CR can avoid spectrum interference by altering its transmission. The CR can provide a network or a wireless node with the abilities to sense its environment such as spectrum holes, and change its transmitter parameters during communication. Thus, the CR attempts to get the best available spectrum through the interaction with its spectrum environment. That is, one aim of CR is to maximize the spectrum utilization for scare radio resources [8; 9; 10; 11; 12; 13]. Until now, many researches have been done in order to cope with the coexistence of multiple wireless technologies in unlicensed spectrum bands in the WSNs [14; 15; 16; 17; 18; 19; 20; 21]. Similarly, IoT devices can also exploit the potential advantages of cognitive techniques if they are equipped with CR. That is, they can manage the radio spectrum dynamically in the aid of the cognitive radio capabilities. The cognitive radio can be one of the most promising techniques for IoT systems since it improves spectrum utilization, increases network efficiency and extends network life. Consequently, this leads to the appearance of a new radio network paradigm for the IoT systems, called Cognitive Radio-enabled Low Power Wide Area Network (CR-LPWAN). In CR-LPWANs for IoT systems, each device can sense the unused spectrum in both licensed and unlicensed spectrum bands. The unlicensed users can access the unutilized channels in licensed spectrum in the hope of improving the communication reliability and efficiency. That is, the licensed users can use the spectrum anytime, whereas unlicensed users can use the spectrum only when it is not used by the licensed user. More specifically, the cognitive radio-equipped unlicensed IoT device can select the most appropriate channel among the identified idle ones in the licensed spectrum band and can use it. If it is detected that a new licensed user arrives on the channel, the unlicensed IoT device moves to another spectrum hole and eventually vacates the channel. Hence, it becomes an important challenge for an unlicensed user to share licensed spectrum more efficiently without interfering with licensed users. Our aim is to maximize the spectrum capacity for the unlicensed CR-enabled IoT network while ensuring that it never interferes with the licensed network.