Research On Modulation Recognition Of MQAM Signals

Modulation recognition for communication signals is an important part of signalanalysis, which is widely used in the military and civilian fields such as communicationcountermeasure, technical investigation, spectrum management and so on. With the recentdevelopment of digital communication technology, various modulation types have alreadybeen applied to communication systems. Among all the modulation types, M-aryquadrature amplitude modulation (MQAM) as an advanced digital modulation techniquewith high spectrum efficiency is well fit for satellite communication, networkcommunication and microwave communication. Therefore, the research on theclassification of MQAM signals has become a hotspot of technical issue.In this thesis, we endeavor to classify MQAM signals based on statistical patternrecognition method. The approaches of MQAM modulation classification are analyzedwith the use of signal’s constellation diagram and phase diagram features. The main workof this thesis is as follows:1. This dissertation studies the modulation classification algorithm based on constellationfeatures of MQAM signals. On the basis of signal preprocess including down conversation,symbol rate estimation, timing estimation, etc, clustering classification algorithm onconstellation is researched. Aiming at the limitation of directly using subtractive clusteringalgorithm, an improved method based on symmetrical characteristics of constellation isproposed, and the simulation results show that this method is feasible and effective.2. A Düffing oscillator model is designed for modulation recognition via the analysis ofthe Düffing system state properties by using different parameters. It is illustrated that thesystem is not only effective for MQAM signal filtering, but also advantageous to extractthe phase diagram feature from MQAM signal. In addition, the feasibility of using phasediagram to recognize the MQAM signal is analyzed according to the phase diagramprinciples.3. Noise-reduction performance of Düffing system is analyzed by comparing with the FIRdigital band-pass filter. Anti-jam capability of phase diagram is discussed under the influence of multipath. Finally, the algorithms on the basis of the constellation diagram andphase diagram are compared. The analysis results demonstrate that the process of featureextraction based on phase diagram algorithm is simpler, and the classification result issuperior to that of constellation diagram method in the case of insufficient symbols. Butwhen the quantity of symbols is enough, the recognition rate of phase diagram approach islower than the rate obtained from constellation diagram approach in the condition of lowersignal to noise ratio (SNR), and the recognition rates of the both are similar with highSNR.