Fractional lags in alternating codes: Improving incoherent scatter measurements by using lag estimates at noninteger multiples of baud length

摘要

Alternating codes are nowadays a standard measurement technique in the incoherent scatter observations. In most conditions they give the best accuracy for the plasma autocorrelation function estimates in the E and F region measurements. We explain here how oversampling can be used to further increase the speed of the experiments. In an oversampled alternating code the sampling interval and the length of the postdetection filter are a fraction of the baud length, and autocorrelation function estimates are calculated both for integer lag values, which are multiples of the baud length, and for the intermediate values, which are called fractional lags. We show that alternating codes with fractional lags give data for multiple range resolutions and that the experiments are always more efficient than the standard alternating code experiments. Finally, we study how the oversampling affects the signal processing.