Adaptive Antenna Against Multipath?

Abstract

Improvements achieved in GNSS space and control segments as well as in receiver signal processing technologies leave multipath nowadays as the main challenge to the navigation society especially in the case of differential navigation. The use of an adaptive antenna in the navigation receiver can be evidently a prospective solution to the problem of multipath. It allows to discriminate incoming signals in spatial domain and to suppress multipath signals efficiently even when common temporal and frequency domain techniques fail. The adaptive antenna is also able to produce a large gain to the line-of-sight satellite signals and therefore to improve receiver performance in unfavourable signal conditions. This paper presents investigation results for the performance of a basic navigation receiver combined with the adaptive antenna, a 5-by-5 uniform rectangular antenna array. The performance is characterised in terms of the pseudorange error. Three multipath scenarios, namely severe multipath conditions, final approach and urban car, were used with signals of GPS and signals likely to be used in coming Galileo. The signals were tracked with the commonly used non-coherent DLL and Costas PLL. The results indicate that both the multipath induced bias and the standard deviation of the pseudorange error can be reduced up to one order of magnitude. While suppressing multipath echoes, the antenna provides more than 10 dB additional gain to the line-of-sight signal when compared to the standard antenna with a hemispherical diagram. In conclusion, the user equivalent range error (UERE) budget is compared for different types of GNSS receivers (single frequency, dual frequency and differential mode) taking into account the results for multipath error with the standard and adaptive antennas. It is shown that the use of adaptive antennas is the most advantageous for dual frequency receivers and receivers with differential mode.