Pappenfus, E.W., Bruene, W.B. and Schoenike, E.O. (1964) Single Sideband Principles and Circuits, McGraw-Hill. Fitch, E. (1947) The Spectrum of Modulated Pulses, J. Inst. Elect. Engrs. 94, Pt. 111A, p. 556. Roberts, J.H. (1977) Angle Modulation, Peter Peregrinus. Flood, J.E. (1952), Crosstalk to Time Division Multiplex Communi- Sturley, K.R. (1965) Radio Receiver Design, (3rd edition), Chap- cation Systems Using Pulse Position and Pulse Length Modula- man & Hall. tion, Proc. Inst. Elec. Engrs., 99, Pt. IV, p. 64. Tucker, D.G. (1953) Modulators and Frequency Changes for Am- Flood, J.E. and Tillman, J.R. (1951) Crosstalk in Amplitude Modu- plitude Modulated Line and Radio Systems, Macdonald. lated Time Division Multiplex Systems, Proc. Inst. Elec. Engrs., Viterbi, A.J. (1966) Principles of Coherent Communication, 98 Pt. III, p. 279. McGraw-Hill. Digital modulation Professor J E Flood OBE DSc FInstP CEng FIEE Aston University Contents Introduction 19/3 Digital transmission 19/3 Digital modulation of a carrier 19/7 Pulse code modulation 19/11 Differential pulse code modulation 19/17 Delta modulation 19/19 Coding programme quality sound 19/21 Coding video signals 19/21 Acknowledgements 19/21 19.10 References 19/21 This page intentionally left blank Introduction 19/3 19.1 Introduction Wmin - 1 1 B (19.4) The term digital modulation is used in two senses, both of which are discussed in this chapter: This result can also be demonstrated for the case when the trans- mitted symbols are very short pulses (which approximate to im- 1. Modulation of an analogue carrier by a digital baseband signal. pulses), instead of the full width pulses considered above. The 2. Modulation of a digital carrier by an analogue baseband signal. impulse response, h(t), of the ideal low pass filter of bandwidth W is given by Equation 19.5. A digital signal may modulate an analogue carrier by using ampli- tude modulation, frequency modulation or phase modulation, as h(1)= (19.5) discussed in Chapter 18. Examples are wireless telegraphy and the use