Читать книгу The Smart Cyber Ecosystem for Sustainable Development - Группа авторов - Страница 53

The fundamental objective of sensing methods is to increase the positive detection probability and decrease the false detection probability of PUs. This leads to more protection of PUs and at the same time more utilization of the available spectrum. In this section, we present the main sensing methods. However, several other methods can be found in the literature.

 1. Energy Detection

 The most commonly adopted method because of its simplicity and the associated computation overhead. It requires short sensing interval. An energy detector is used to detect a narrowband channel. The detected energy is compared to a predefined threshold. If the measured energy is found to be larger than the threshold, then PU is judged to be active. The selection of the threshold is a challenge because the noise level is normally unknown.

 2. Cyclostationary Feature Detection

 This method aims at distinguishing between PUs’ signals, interference, and noise. This is achieved by identifying the cyclostationary features of signals, including modulation type, carrier frequency, and data rate. The implementation of this method needs sufficient prior information about these features of the PUs’ signals so that the method can use this knowledge as a base during the matching of measured features with those belong to PUs’ signals. Hence, sufficient number of samples is needed for accurate performance, leading to long sensing intervals.

 3. Matched Filtering

 This method is considered to be the most accurate method that achieves higher detection probability in short sensing intervals. The basic idea of this method is that the sensed signal is passed thought a filter that is matched to the PUs’ signals. Despite its accuracy, the method is considered to be impractical in cases wherein PUs transmit signals of different features.