Interference dynamics considerations in digital radio performance estimation

Digital radio performance degradation due to interference is significant in the latest 64 QAM technology and must be considered during the path design of a digital radio facility. A route engineering tool, based on a model that considers radio interference to be time-varying has been developed for designing rugged digital radio paths in a radio interference environment. The long-term statistics of interference dynamics during multipath fading is modeled as a lognormal distribution with a standard deviation dependent on terrain roughness. Analysis of multipath fading data obtained from a distance experiment has shown a linear relationship between the standard deviation of the interference and the fade depth of the desired signal. When this interference dynamics model is used to calculate the expected outage in a 64 QAM digital radio system equipped with space diversity (at a junction station with average terrain roughness, a free space C/l of 60 dB, and a standard deviation of 4 dB), a 200% increase in outage is predicted over the outage predicted by the constant interference model.<>