Choosing the Optimum Type of Modulation--A Comparison of Several Communication Systems

The engineer designing a new communications system often has available a choice between several different types of RF modulation. The four main methods considered here are standard amplitude (AM), double-sideband suppressedcarrier (DSBSC), single-sideband (SSB), and frequency (FM) modulations. Some of their basic system performance characteristics are evaluated on a comparative basis for the transmission of voice and pulsed data. Factors considered include: compatibility, effective range, bandwidth, signal-to-noise performance, interference rejection capabilities, distortion characteristics, required stability, required transmitter power, and resulting circuit complexity. The choice of the best type of modulation for a particular communications system requires the simultaneous consideration of many such factors evaluated for the basic requirements of that system. Because these factors vary with system parameters and because they may be of differing relative importance, it is not possible to say that any one type of modulation is best for all uses. The practical manner in which the choice may be made is illustrated by examples drawn from several types of communication systems.