A model for the multipath delay profile of fixed wireless channels

摘要

This paper deals with the measurement and modeling of multipathndelay on fixed wireless paths at 1.9 GHz in suburban environments. Thenprimary focus is on the delay profile, which is the normalized plot ofnreceived power versus delay in response to an RT “impulse.”nWe describe measurement campaigns in the western suburbs of Chicago, IL,nand in suburban north-central New Jersey. Our analysis of the datansuggests to us that, for directive terminal antennas, the delay profilencan be modeled as having a “spike-plus-exponential” shape,ni.e., a strong return (“spike”) at the lowest delay, plus anset of returns whose mean powers decay exponentially with delay. Thisndelay profile can be characterized by just two parameters (both variablenover the terrain), namely, the ratio (K0) of the averagenpowers in the “spike” and “exponential”ncomponents and the decay time constant (Τ0) of then“exponential” component. No such simple structure appears tonapply for delay profiles using omnidirectional antennas. For a directivenantenna with a 32° beamwidth, we find that: (1) the statisticalncorrelation between the profile parameters K0 and Τ0n is negligible; (2) these parameters are relatively insensitive tonantenna height and path length; and (3) over each measured regionn(Illinois and New Jersey), K0 and Τ0 havenmedian values close to 8 dB and just below 0.2 Μs, respectively.nMoreover, we have found simple probability distributions that accuratelynportray the variability of K0 and Τ0 over thenterrain