Modeling Multipath Fading Responses Using Multitone Probing Signals and Polynomial Approximation

Abstract

We show in quite a general way that highly accurate modeling of multipath fading responses is possible using low-order complex polynormals. This applies to all terrestrial radio systems in the channelized common carrier bands below 15 GHz, where channel widths are 40 MHz or less. The context of the study is a new multipath experiment being conducted in New Jersey over a 23-mile path at 11 GHz. The transmitted signal consists of up to nine tones in a 40-MHz bandwidth. These tones are coherently processed, sampled, and digitized in the receiver and recorded, during fading events, for later off-line reductions. Simple routines can be used to determine polynomial coefficients from these recorded data. This paper describes the signal processing and data reduction methods and analyzes them to assess the accuracy of polynomial fitting. The analysis uses a mean-square error measure and assumes a representative form for the underlying response function. Our results predict that the vast majority of multipath fading responses can be accurately approximated over bandwidths of 40 (62) MHz using first- (second-) order complex polynomials.