System for determining precise position including a chirp receiver utilizing phase precessed chirp signals

Abstract

A system for determining precise position includes a chirp receiver that processes broadcast chirp signals in the frequency domain to distinguish direct path signals from multipath signals. The chirp receiver processes the received chirp signals, which consist of respective pulsed frequency sweeps, by combining a received chirp signal with a synchronized locally generated chirp signal and phase adjusting and concatenating the results over multiple sweeps, based on estimated clock phase errors and expected phase rotations of the direct path signals, to produce a sine wave. The phase adjustment and concatenation allows the use of longer Fast Fourier Transforms (FFTs) that, in turn, provide increased accuracy of frequency estimation and separate component signals that are very close in frequency. The phase adjustment and concatenated signals are processed in the frequency domain using an FFT and a frequency corresponding to the direct path signal is identified by the lowest frequency bin in which power is above a predetermined noise threshold. The receiver then determines a time delay based on the identified frequency and uses the time delay to calculate accurate clock phase error. The system may then determine position based on associated pseudorange measurements.