# An Accurate Probabilistic Model for TVWS Identification
## 2 Background  
The term CR was coined by [PERSON] in his 1999 work [6]. The author described therein how CR could enhance the flexibility of personal wireless services through the so-called Radio Knowledge Representation Language (RKRL). CR is often described as a \"disruptive, but unobtrusive technology\" [7]. It is disruptive because it allows a SU to access the PU bands, and it is unobtrusive due to the control of different parameters, such as access or transmission power, which dramatically reduces any harmful interference with the PU. Looking at the current spectrum scenario, we find that the use of unlicensed bands are seen almost everywhere, especially because of the numerous services available to hand-held wireless devices, including Industrial, Scientific, and Medical (ISM) band at 2.4 GHz and the National Information Infrastructure (U-NII) band at 5.2 GHz. This is actually a reflection of how much today's society is dependent on wireless spectrum [8]. To access and use these open bands, the user does not need to pay any fee or to ask for a license with the local regulator, and more, these bands have similar counterparts around the world, with international regulatory bodies working to align bands and regulations [9]. Figure 1: Block diagram of the proposed model. The common use of unlicensed bands and the development of new devices and technologies led regulatory bodies like the FCC to consider opening further bands for unlicensed use. As stated by the Journal of Communications, _\"Whereas, spectrum occupancy measurements show that licensed bands, such as the TV bands, are significantly underutilized\"_[8]. In simple words, what CR is allowing an unlicensed user is to use licensed bands in the very same manner the user would use unlicensed bands, i.e., no fee or no license required. As an alternative to using unlicensed bands, CR is considered the solution to the spectrum wastage due to low usage of the licensed radio spectrum [7]. This technology works on the principle of adapting the operating parameters of the radio according to the conditions of the environment. Thereby it facilitates smart, efficient, and reliable spectrum usage through identifying and exploiting a large amount of unused or underused spectrum bands. In May 2004, the Federal Communications Commission (FCC) of the United States, proposed the creation of the 802.22 workgroup (WG) for Wireless Regional Area Networks (WRAN). The WG's goal was to develop the PHY and MAC air interfaces to allow unlicensed users or SUs to operate in the TV broadcast bands without interfering with the PU [10]. During this time, researchers developed spectrum sensing techniques and simulation models, and the idea of smart spectrum gained much interest [5; 11]. In 2011, the IEEE 802.22 WRAN standard was approved, which defined a worldwide standard air interface based on CR techniques for the TV broadcasting band [8; 12]. Following these guidelines, researchers are considering nowadays different methods to identify idle channel within TV bands or in general within any band. In [13], a detailed list is given with works that use different parameters to identify occupied vs. available channels. These include, for example, statistics with power detection, occupation and duty cycle, Probability Density Function (pdf) or Cumulative Density Function (CDF) with power detection, Markov chains, linear regression, and spectrum prediction, among others. In [14], the authors proposed a spectrum scanning method based on Bayesian inference to estimate the channel occupancy rate, by considering the false alarm and detection probabilities. This approach showed better accuracy compared to other works considering only energy detection to define the presence or absence of a PU.