Distance Dependence of Microwave Delay Spreads Measured in Urban Quasi Line-of-Sight Environments

Measurements of delay spread were performed at microwave frequencies of 3.35, 8.45 and 15.75GHz along quasi line-of-sight streets in metropolitan Tokyo. It is found that the delay spreads increase with the measurement distance and reach around 600 ns up to 1 km. It is also confirmed that a cumulative probability of the delay spreads follows a log-normal distribution. The gradients of delay spreads against the distance are greater for a lower mobile antenna height hm = 1.6m than for hm = 2.7m in these measurements because of blocking effect by the traffic of vehicles and pedestrians on the road. When the mobile antenna height is 2.7m, the delay spreads within the range before the break points are observed relatively small: 90 ns (3.35GHz), 140 ns (8.45GHz) and 150 ns (15.75GHz) at the cumulative probability of 90%. The gradients of delay spreads against the distance are greater for wider streets in our measurements. key words: mobile communication, radio propagation, delay