A SPREAD-SPECTRUM COMMUNICATIONS CHANNEL SOUNDER

The design of a microwave channel probing analyzer is presented and di scussed, Special attention is paid to the characteristics of the trans mission path to be measured; the choice of spread spectrum probing sig nal; the signal processing methods used; modulation, demodulation, and synchronization at the transmitter and receiver sites; the path model to be fitted to the measured data and finally, the impact of all of t hese issues upon the necessary hardware and software. Following a form ulation of the channel-probing problem, transfer function regression t echniques are reviewed-to illustrate the advantages of periodic averag ing over established correlation methods. The construction of an exper imental sounder based on these methods is described, The equipment has been used to measure the time-variant frequency-selective channel dyn amics of a short (158 km) troposcatter transhorizon link at a frequenc y of 11.647 GHz over a 31.25-MHz bandwidth. Off-line, nonlinear spectr um analysis, based on Prony's method and singular value decomposition, is used to estimate parameters of a high-resolution delay model that accurately reflects the underlying ray structure of the transmission p ath.