Waveform distortion and interference during multipath fading are dominant factors in determining the severely errored seconds in digital fixed wireless systems operating below about 10 GHz. Both factors have to be taken into account when designing digital radio systems.
The following gives a brief introduction to many methods used to estimate the effects of propagation on the performance of digital radio.
Digital fixed wireless systems are particularly affected by the frequency selective nature of multipath fading. Fading effects on a radio may be characterized by a “system signature”. Numerical methods with computer simulation could be useful for signature computation. A “system signature” is basically a static measure of the susceptibility of a particular equipment to a two ray model of the multipath channel in both minimum phase and non-minimum phase conditions. It is being used as a basis for equipment comparisons.
An important aspect of multipath fading is its dynamic nature. Therefore dynamic tests should be performed to assure satisfactory equipment performance. Dynamic multipath fading may be simulated in the laboratory by a dynamic simulator capable of simulating the time sequences of multipath fading. These tests will allow the optimization of synchronization and equalizer coefficient adaptation circuits.
Further studies are needed to define optimum test sequences for dynamic testing.
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