Читать книгу Intelligent Security Management and Control in the IoT - Mohamed-Aymen Chalouf - Страница 18

In a CRN context, according to the analytical model defined in Song and Xie (2012), the predicted probability that a candidate channel i is inactive at time t can be expressed as follows (equation [1.1]):

[1.1]

where represents the arrival time of the kth packet and designates the length of the kth PU packet (data from one primary user) on the channel i. Ni(t) represents the state of the channel, which is a random binary variable with values 0 and 1 representing, respectively, the inactive and the occupied states.

The probability that the channel i is in active at an instant t can be obtained by equation [1.2]:

[1.2]

where represents the interarrival of the PU packets. Supposing that the PU packets arrive following a Poisson process (Wang and Wang 2008), distributed exponentially with the average packet arrival rate per second λi, the length of the PU packet following fLi (l).

Based on the prediction above, the candidate channel i is considered inactive for the following time interval when Pr (Ni (t) = 0) ≥ τ_H, where τ_H is the probability threshold for a channel to be considered inactive at the end of the current frame.