Group delay compensation in AltBOC receivers to mitigate the effect of frequency selective propagation delay distortions

Abstract

This paper extends the Sub-carrier Phase Combination technique previously presented by the authors to mitigate the effect of frequency selective Radio Frequency (RF) propagation delay distortions in Alternate Binary Offset Carrier (AltBOC) receivers. Two major propagation delay distortion sources are considered: the ionosphere and multipath. Initial analysis shows that the ionospheric delay errors can be reduced to being comparable to the receiver impairments (when the error due to multipath is low) and the maximum multipath error (under low ionospheric distortions) can be reduced to half a meter. Under extremely high ionospheric delay distortions, the multipath delay error envelope, with the proposed technique, will suffer no change in the magnitude of the error except that the spatial characteristics are different. The underlying idea of the proposed technique is that difference in the phase delays of the E5a and E5b signal tracking is simply the slope of the phase response over the entire band and hence represents the group delay at the E5 center frequency of 1191.795 MHz. The group delay which appears as the code phase error for the E5 signal tracking, can thus be compensated except for the occurrence of higher order errors