Research On Digital Modulation Recognition Based On Wavelet Transform

Modulation recognition is of significance in both military and civil fields. In military field, it is used in Electronic Warfare and Electronic Scouting. In civil field, it is one of the core techniques used in non-cooperative communications, such as signal affirmance, disturbance recognition, spectrum management, etc.At first, the wavelet transformation theory was introduced in this paper. Wavelet transform has good characteristics of localizing time and frequency and multi-resolution performance, it is also an effective technique for extracting the transient characteristics from different digital modulation signals. The wavelet transformations of PSK, FSK , QAM and ASK signals deduced theoretically and the modulation identifier was constructed based on the transformation results. The interclass and intraclass modulation type classification was investigated in kinds of signal-to-noise ratio environments.Then, this thesis discussed the methods to identification of digital modulation types. At last, this paper presented an algorithm for modulation recognition of received signals in the presence of additive white Gaussian noise with the use of the wavelet transform without any prior knowledge. The decision was given based on the extraction of some special features of the continuous wavelet transform of the received signals. It was able to classify the types of signals, as well as to identify the modulation order. Effort was made in order to reduce the computational workload, so that the algorithm could be applied for real-time recognition.