Abstract
The use of Space-Time Processing (STP) in Global Navigation Satellite System (GNSS) applications is gaining significant attention due to its effectiveness for both narrowband and wideband interference suppression. However, the resulting distortion and bias on the cross correlation functions due to space-time filtering is a major limitation of this technique. Employing the steering vector of the GNSS signals in the filter structure can significantly reduce the distortion on cross correlation functions and lead to more accurate pseudorange measurements. This paper proposes a two-stage interference mitigation approach in which the first stage estimates an interference-free subspace before the acquisition and tracking phases and projects all received signals into this subspace. The next stage estimates array attitude parameters based on detecting and employing GNSS signals that are less distorted due to the projection process. Attitude parameters enable the receiver to estimate the steering vector of each satellite signal and use it in the novel distortionless STP filter to significantly reduce distortion and maximize Signal-to-Noise Ratio (SNR). GPS signals were collected using a six-element antenna array under open sky conditions to first calibrate the antenna array. Simulated interfering signals were then added to the digitized samples in software to verify the applicability of the proposed receiver structure and assess its performance for several interference scenarios.
Highlights
Global Navigation Satellite System (GNSS) is used worldwide, the performance of location-based services provided by receivers can still be compromised by interfering signals
In practice and in a dynamic operation environment, a receiver should constantly select among satellite signals with lower Cr values for estimating attitude parameters
Two types of space-time filtering were employed in the structure of the receiver, namely blind and distortionless Space-Time Processing (STP) methods
Summary
GNSS is used worldwide, the performance of location-based services provided by receivers can still be compromised by interfering signals. Even if the filter completely nullifies interfering signals, the non-linearity behavior of its frequency response may result in biased measurements, distortion or broadness of the cross correlation functions during receiver acquisition and tracking stages This may not be tolerable especially for high precision GNSS applications. One effective approach is to incorporate the satellite signal steering vector, which contains all the spatial information of the incoming signal, in the structure of the space-time filter as a constrained optimization problem [19,20,21,22,23] These methods are extended versions of MVDR and MPDR beamformers for space-time processing. To evaluate the performance of the proposed space-time filter, it was compared to the well-known space-only MPDR and space-time MPDR beamformer methods
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