Hi
A high sample rate for such ns times of arrival resolution is impractical. Same holds for high SNR and longer times of measurement. GPS and most other high resolution positioning systems stitch the information together from the signal time of arrival with the carrier phase of arrival. Since carrier frequencies are incredibly high, their phase can provide such ns accuracy because the phase information is preserved across the downconversion stages with sufficient linearity. For this purpose, the algorithms also need to determine the integer number of arriving wavelengths.