Traditionally, the use of radio frequency bands has been regulated in most countries through the process of spectrum allocation in which the use of a frequency band is restricted to the license holders of the band. Within this framework, spectrum has often been viewed as a scarce resource in high demand. However, measurements conducted have suggested that most licensed spectrum is often under-utilized with large spectral holes at different places at different times. Cognitive radio systems have been proposed as a possible solution to the spectrum crisis. The idea is to detect times when a specific licensed band is not used at a place and use the band for transmission without causing any significant interference to the transmissions of the license holder. Considering a system of cognitive radio users who cooperate with each other in trying to detect licensed transmissions. If the cooperating nodes use identical energy detectors, the received signals are modelled as correlated log-normal random variables and study the problem of fusing the decisions made by the individual nodes. A linear-quadratic (LQ) fusion strategy based on a deflection criterion for this problem, which considers the correlation between the nodes. Matlab simulations shows that when the observations at the sensors are correlated, the LQ detector significantly outperforms the Counting Rule, which is the fusion rule that is obtained by ignoring the correlation.
Reference Paper: Cooperative Sensing for Primary Detection in Cognitive Radio
Author’s Name: Jayakrishnan Unnikrishnan and Venugopal V. Veeravalli
Source: IEEE

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