Energy method of spectrum sensing in CR networks.
Energy detection is one of the most common method of spectrum sensing in CR networks. An energy detector involves a Band Pass Filter (BPF) followed by a square law device and an integrator. The received signal is ltered by BPF and helps in reducing the noise bandwidth which in turn makes the noise at the input of square law device to have a band limited and at spectral density. The integrator integrates its input and gives an output which is equal to the energy of the signal present at the input of square law device for a time interval of T. Inorder to decide whether PU is present, the output from integrator is compared with a threshold. The block diagram of energy detection algorithm is shown in g 7 16. Fig. 7. Block diagram of energy detection The goal of energy detector is to identify the sample signal,nd its energy and then compare it with a threshold to detect the presence or absence of the PU 17. This is formulated as an hypothesis test as H0 and H1 as given by eqn(1) and eqn(2). The performance of energy detector is specied by the following parameters. 1) Probability of detection Pd It is the probability of the energy detector to make a correct decision. It indicates the level of protection provided to PUs from SUs interference. It should be high. 2) Probability of false alarms Pfa It is the probability of the occurrence of the event such that the detector makes a decision of H1 when the right decision was exactly H0 (refer eqn(1)and eqn(2)). Because of the false alarm event, the SU would miss a chance to make use of the free channel. Therefore this should be kept small inorder to avoid the underutilization of the spectrum. Pfa < 0.1 as per IEEE standard. 3) Probability of missed detection Pm It is the probability of the occurrence of an event such that the detector makes the decision H0 when the right decision was exactly H1. If this event occurs there is a chance of causing interference to PUs by SUs. Hence Pm should also be kept small 18. Flow chart of energy detection is shown in the g 8