آشكار سازي سيگنال هاي طيف گسترده با نرخ هشدار كاذب ثابت

چكيده انگليسي :

Abstract Activity detection of communication signals is one of the most important tasks of unauthorizedrecievers Detection is to derive the optimum receiver structure based on a criterion that isdetermined by the application The Neyman Pearson criterion is the well known criterion foractivity detection Optimal ideal detectors require an essentially complete statistical description ofthe input signals and noise In practice this information may not be available a priori and thestatistics of the input data may also vary with time These variations yield to change of false alarmprobability of the detector So we need to employ some methods to keep the false alarmprobability to be constant In this situation the detector is called a constant false alarm rate CFAR detector In order to achieve CFAR property in varying environments a basic approach is using anadaptive threshold Heretofore so many detectors and algorithms have been introduced to reachCFAR property in radar applications but CFAR detectors have not been much considered fordetection of communication signals specially spread spectrum signals Therefore the CFARprinciples in radar systems should be tailored for detection of communication signals Time frequency cells are the subjects that have been introduced for this reason In this research we review the principles of detection in communication systems and survey someof the most important classes of the detectors Also we investigate some advantages anddisadvantages of these processors and introduce some of its newest CFAR detectors Among allkind of communication signals we focus on the spread spectrum signals because of their wideapplications Linear Frequency Modulated LFM Signal is one of spread spectrum signals that wesurvey some of its most important detectors Amongst the LFM detectors Fractional foureirtransform FrFT is chosen as a suboptimal detector because of its simple structure and high qualityof detection for LFM signal Because of the sensitivity of this detector to the noise and interferencepower the false alarm rate is varied for this detector We propose some methods for making thisdetector as a CFAR detector Comparison of proposed methods with ideal method and investigatinof them in different interference situations have done in this research Frequency hopping signal is another spread spectrum signal that we review and survey some of itsmost important detectors Among all kind of detectors channelized radiometer is selected as themost important detector for detection of FH signals The performance of a channelized radiometeris studied when different CFAR strategies are used to set the detection threshold Since thechannelized radiometer can be used in spectrum sensing in cognitive radio we introduce cognitiveradio systems and survey spectrum sensing methods We propose a CFAR method for channelizedradiometer which has a better performance comparing with other CFAR processors Key Words presence signal detection Constant false alarm rate CFAR Linearfrequency modulated LFM Frequency Hopping FH Channelized Radiometer

نادر طهراني، محسن

آشكار سازي سيگنال هاي طيف گسترده با نرخ هشدار كاذب ثابت

سيگنالLFM , سيگنالFH , راديومتركاناليزه