# Integrating Cognitive Radio with Unmanned Aerial Vehicles: An Overview
## 3 Background
### Cognitive Radio Networks  
The European Telecommunications Standards Institute (ETSI) defines CR as a radio that can sense and understand the radio environment and policies, and monitor usage patterns and users' needs; autonomously and dynamically adapts according to the radio environment, so that it can achieve predefined objectives, such as efficient utilization of spectrum; and learn from the environment and the results of its own actions, so it can further improve its performance [18].  
CR is also able to operate as a secondary user (SU) within a spectrum band of a licensed user or primary user (PU). In [12; 19], the Resolution ITU-R 58-2 of the International Telecommunications Union (ITU) states that \"the introduction of CRSs in any radiocommunication service needs to ensure that coexistence within radiocommunication services and the protection of other radiocommunication services sharing the band and in the adjacent bands are maintained or improved\" [20]. In practice, clearer parameters on how that action is done is usually defined by local regulatory agencies.  
CR is described as an intelligent SDR with the following components:  
1. spectrum sensing: identifies the available spectrum and detects PUs when operating in a licensed band,
2. spectrum management: selects the best available channel,
3. spectrum sharing: coordinates accessibility to the available channel with other users, and
4. spectrum mobility: vacates the channel when a PU arrives.  
Figure 2 shows the interaction among the CR components. First, the spectrum sensing component is responsible for collecting data from the radio environment, and it keeps sending the gathered radio data to the spectrum management component. When a PU is detected, it also notifies the spectrum mobility component, then a spectrum handover must be executed. The spectrum management component is responsible for submitting the channel with higher availability to the mobility component of the spectrum, because when the current channel needs to be vacated, a new channel is used. Finally, to organize the allocation of spectrum bands, the spectrum sharing portion is responsible for interacting with the radio environment.  
In practice, CR consists of a hardware associated with an intelligent software. Usually, the hardware consists of a radio platform, generally an SDR, and a computational platform. Most computational platforms used for CR applications are single-board computers, such as the ODROID [22], the Raspberry Pi [23], and the BeagleBoard [24]. The Universal Software Radio Peripheral (USRP) from Ettus Research [25] and the Wireless Open-Access  
Figure 2: The interaction among CR components. Adapted from the work in [21].  
Research Platform (WARP) from Rice University are both SRDs and the most common radio platforms used in CR [26; 27].  
Figure 3 shows one of the most usual SDR hardware in research experiments: the USRP B200 by Ettus Research. It provides full-duplex wireless communication within a frequency range starting from 70 MHz varying up to 6 GHz. Its architecture offers compatibility with a variety of software and frameworks, such as C++, Python, GNU Radio, Amarisoft LTE 100, and OpenBTS.