Characterizing the Effects of Multipath Dispersion on Digital Radios

A widely used method of estimating the performance of digital radios in the presence of multipath fading is based on the concept of Composite Fade Margin (CFM). The CFM provides a simple means of incorporating the effects of thermal noise interference, and multipath dispersion into a prediction of radio performance. As described in the literature, CFM is based on the characterization of the multipath fading on a standard hop. Over the last few years, propagation experiments on many hops have provided a basis for describing the varying character of the fading from hop to hop. In particular, the use of Dispersion Ratio has recently been proposed as a measure of the dispersiveness of the fading on a hop from an extended measurement of the fading statistics on that hop. The Dispersion Ratio is the quotient of: (1) the time that the In-Band Power Difference (IBPD), measured in a 22 MHz band, exceeds 10 dB; divided by (2) the time that the single frequency fading on a path exceeds 30 dB. The IBPD is the decibel difference between the least faded and most faded frequency in the band at a given instant.