Recognition of Analogue & Digital Modulations
Some of the modulation recognisers for both analogue and digital modulations discussed in Chapter 1 utilise the pattern recognition approach, which requires long signal duration and strong SNR to decide about the modulation type of an RF signal. So, these recognisers are mainly used in off-line analysis. Furthermore, none of these recognisers considered VSB and combined modulation signals. In this chapter a set of fast algorithms for the recognition of both analogue and digital modulations without any a priori information about the nature of a signal, whether it is analogue or digital, is introduced. Moreover, the AMRAs introduced in Chapter 2 and Appendix C.1 are concerned with only analogue modulated signals. Also, the DMRAs introduced in Chapter 3 and Appendix C.2 are concerned with digitally modulated signals only. So, for these algorithms, there is a priori information about the nature of the signal under consideration. Sometimes, there is no a priori information about the nature of a signal. In this case the modulation recognition algorithms introduced in Chapter 2, Chapter 3, Appendix C.1, and Appendix C.2 cannot discriminate between some types of modulations such as MASK and AM, MFSK and FM, PSK2 and DSB, and PSK4 and combined moduktted signals. It is worth noting that the only difference between such modulation types is in the nature of the modulating signal used to generate these modulation types. In the analogue modulated signals a speech signal is used as modulating signal while a digital symbol sequence is used as a modulating signal in the digitally modulated signals.
KeywordsSpeech Signal Modulation Type Instantaneous Frequency Digital Modulation Modulation Recognition
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