Some Techniques for the Instantaneous Real-Time Measurement of Multipath and Doppler Spread

The design optimization of digital communication systems using selectively fading transmission media such as HF and troposcatter requires knowledge of the selective fading characteristics of the media. A minimal characterization is provided by the gross channel parameters of multipath spread and Doppler spread. This paper presents several techniques which will allow the simultaneous measurement of multipath and Doppler spread in real time with a minimum of equipment complexity. The techniques are first divided into two classes depending upon whether measurements are made on in-phase and quadrature components of received carriers or on envelopes of received carriers. A further subdivision is made according to two different techniques of multipath spread measurement, one of which, called the SSB method, uses two transmitted carriers while the other, called the FM method, uses a frequencymodulated carrier. The envelope measurements are the simplest and should provide considerable help in any large scale testing of the selective fading properties of the HF and troposcatter media.