Recently, many researchers have focused their attentions on spectrum sensing in CRNs, in which the cognitive radio (CR) nodes are able to perform the wideband spectrum sensing to detect the unoccupied frequency bands for temporal using.
The recent spectrum measurement campaigns in the United States [11] and Europe [12] show that the spectrum is under-utilized; hence, opportunistic use of unoccupied frequency bands is highly desirable.
By giving the CR users a reward to choose the unoccupied channel frequencies, if available, each pair of sensors can communicate without affecting its neighbors.
Relative to traditional approaches for accessing spectrum, OSA allows for unlicensed wireless users to temporarily "borrow" unoccupied licensed frequency bands [6].
One application for the deployment of CR systems and DSA networks is the opportunistic spectral usage of unoccupied portions of the TV frequency bands by future mobile radio systems such as long term evolution (LTE) mobile radio communication [42].
In particular, subcarriers located in the frequency vicinity of unoccupied wireless spectrum can be used for transmitting data while those sub-carriers that could potentially interfere with nearby PU signals can be deactivated or nulled.
On the contrary, some licensed frequency bands are unoccupied for most of the time and some other bands are just partially used while unlicensed users have needs to get access to the spectrum [3].
When a frequency spectrum is unoccupied by its corresponding PU, it can sell portions of the available spectrum bi (e.g., time slots in a time division multiple access (TDMA -based wireless access sysTDMA -based SU i (i = 1, 2,…, N) at the offered price p. Both PU and SUs use adaptive modulation for wireless traccesssystem
The fixed-equiprobable algorithm, appropriate for data-matrices with unoccupied sites, maintains the species occurrence frequencies and considers all sites (trees) equiprobable [39].
In [13] the behavior of the duty cycle (occupied-unoccupied behavior) of neighboring frequency bins that belong to certain parts of PU signals was practically determined as correlated through real-world experiments.
