Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Automatic Modulation Recognition For Cognitive Communication Systems

The automatic recognition of the modulation format of a detected signal, the intermediate step between signal detection and demodulation, is a major task of an intelligent receiver. The recognition of modulation type of a received signal is performed automatically in civil and military applications as in many areas. Automatic Modulation recognition is extremely important in military electronic counter/counter-counter measures such as target detection, monitoring and jamming operations. Generally the developed recognizers / classifiers are divided into two groups. Although the likelihood based classifiers which rely on the likelihood function of the received signal give the optimum solution, they have highly computational complexity.

Thus, feature based classifier methods which have less computational complexity and give suboptimal solution, have been used. Feature based classification of modulation consists feature extraction and decision making steps. Statistics of complex envelope of the signal and the examples of frequently are obtained features by Wavelet transform of the signal and Fourier transform of the signal. At decision making stage, decision tree, artificial neural networks and support vector machines are frequently utilized.

In this thesis study, a feature based automatic modulation classifier is developed which guarantees the automatic recognition of modulation type of a received signal for civil and military applications. The features which are to be used at classification are composed from high-order statistical moments of complex envelopes of the signals. The classification process consists of M-ASK, M-FSK and M-PSK modulated signals that are subjected to AWGN channel. In the study, The classification accuracy of proposed simulation method for automatic modulation recognition problem were obtained about %100 at 3 dB SNR. Therfore by using the proposed modulation classifier, the modulation scheme of unmodulated received signal can be estimated automatically without any aid of human being.