Theoretical Fundamentals of Pulse Transmission - I

Pulse transmission is a basic concept in communication theory and certain methods of modulating pulses to carry information approach in their characteristics the ideal performance allowed by nature. In certain applications, such as telegraphy, pulse signalling and data transmission, it has the advantage of great accuracy, since the information is transmitted in digital form by "on-off" pulses. This at the same time facilitates regeneration of pulses to avoid accumulation of distortion from noise and other system imperfections, together with the storing, automatic checking and ciphering of messages, as well as their translation into different digital systems or transmission at different speeds, as may be required in extensive communication systems. Another characteristic of pulse systems is that improved signal-to-noise ratio can be secured in exchange for increased bandwidth, as in pulse code, pulse position and certain other methods of pulse modulation. Finally, pulse modulation systems permit multiplexing of communication channels on a time division basis, which under appropriate conditions may have appreciable advantages over frequency division in the design of multiplex terminals. In pulse modulation systems, pulses are applied at the transmitting end in various combinations, or in varying amplitude, duration or position, depending on the type of system. Pulses thus modulated to carry information may be transmitted in various ways, or undergo a second modulation process suitable to the transmission medium.