STATISTICS OF THE TIME DYNAMICS OF DISPERSIVE MULTIPATH FADING AND ITS EFFECTS ON DIGITAL MICROWAVE RADIOS

摘要

Dispersive multipath fading is a major cause of impairment for highcapacity digital microwave radios.Adaptive equalizers greatly improve the performance of the radio during transitions from moderate to severely dispersive fading.The performance usually is not improved as much for transitions from severely dispersive to moderate fading.This asymmetry of conditions which cause outage and those which are necessary for recovery produce a hysteresis effect.The estimates of outage seconds based on the equipment fading signatures which are measures of static performance are an order of magnitude less than outage seconds observed in the field.The performance of digital radios equipped with transversal equalizers is dominated by these hysteresis effects.Propagation data were analyzed to characterize the time dynamics of dispersive fades.Statistical results are presented and analytical expressions are derived to estimate outage time due to hysteresis.Predicted and observed outage times are compared for a 16 QAM radio system.Estimates of outage performance for 64-QAM 135 Mb/s radio systems are described.