Digital Modulation—Baseband Techniques
B Sundareshan · IETE Journal of Education · 1992
Digital modulation is the process which transforms an input bit stream into a digitally encoded waveform. Similarly digital demodulation is the process by which we extract the bit stream from the received digital waveform. The digital modulation/demodulation process form an essential and integral part of any digital communication system. The different techniques involved in this process can be broadly classified into two groups viz the base band techniques and bandpass techniques. In baseband modulation the information is formated so that it is represented by digital symbols. Then pulse waveforms are assigned that represent these symbols. These waveform can then be transmitted over a cable. Baseband signals are not appropriate for propagation through many transmission media. Baseband signals whose spectrum has been shifted to a frequency band that is more appropriate for propagation through a medium are called bandpass modulation signals. The first part of this two part article explains the important concepts and techniques employed for baseband modulation.