Browsing by Author "Daneshmand, Saeed"

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    Assessment of Measurement Distortions in GNSS Antenna Array Space-Time Processing
    (2016-02-17) Marathe, Thyagaraja; Daneshmand, Saeed; Lachapelle, Gérard
    Antenna array processing techniques are studied in GNSS as effective tools to mitigate interference in spatial and spatiotemporal domains. However, without specific considerations, the array processing results in biases and distortions in the cross-ambiguity function (CAF) of the ranging codes. In space-time processing (STP) the CAF misshaping can happen due to the combined effect of space-time processing and the unintentional signal attenuation by filtering. This paper focuses on characterizing these degradations for different controlled signal scenarios and for live data from an antenna array. The antenna array simulation method introduced in this paper enables one to perform accurate analyses in the field of STP. The effects of relative placement of the interference source with respect to the desired signal direction are shown using overall measurement errors and profile of the signal strength. Analyses of contributions from each source of distortion are conducted individually and collectively. Effects of distortions on GNSS pseudorange errors and position errors are compared for blind, semi-distortionless, and distortionless beamforming methods. The results from characterization can be useful for designing low distortion filters that are especially important for high accuracy GNSS applications in challenging environments.
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    GNSS Interference Mitigation Using Antenna Array Processing
    (2013-04-19) Daneshmand, Saeed; Lachapelle, Gérard; Broumandan, Ali
    Although hundreds of millions receivers are used worldwide, the performance of location-based services provided by GNSS is still compromised by interference which can range from unintentional distortion due to multipath propagation to intentionally menacing spoofing signals. Hence, the requirement for proper mitigation techniques becomes a must in GNSS receivers for robust, accurate and reliable positioning. Recently, interference mitigation techniques utilizing antenna arrays have gained significant attention in GNSS communities. Although at the time of this thesis, employing antenna array in GNSS applications is mostly limited to academic research and possibly sophisticated military applications, it is expected that in the near future, antenna array-based receivers will become widespread in civilian markets as well. Rapid advances in electronic systems and antenna design technology make previously hardware and software challenging problems easier to solve. Furthermore, due to the significant effort devoted to miniaturization of RF front-ends and antennas, the size of antenna array-based receivers will no longer be an issue. Given the above, this thesis investigates the use of antenna arrays in GNSS interference mitigation applications. It starts by proposing a new spatial processing technique capable of mitigating both high power interference and coherent and correlated GNSS multipath signals. It then follows by introducing three new methods that take advantage of spatial and temporal processing in three different GNSS applications. In the first method, the use of spatial-temporal processing for multipath mitigation in the form of a synthetic array is studied. A new method utilizing a moving antenna array is proposed to deal with highly correlated multipath components and also to increase the degree of freedom of the beamformer by synthesizing a larger antenna array. Thus, the array’s degree of freedom is not limited to the number of physical antenna elements. This method can be employed to mitigate multipath signals in vehicular navigation applications. The second method investigates benefits of spatial-temporal processing algorithms for improving narrowband interference mitigation performance. The limitations of previous space-time filters are analyzed and a new approach that employs the inherent periodic feature of GNSS signals in conjunction with the spatial-temporal processing to improve the performance of existing space-time filters is proposed. It is shown that in some interference scenarios, a space-time filter subject to the distortionless constraint may cause a significant degradation to the signal-to-noise ratio (SINR), which can be alleviated by employing the periodicity in the structure of the filter. In the third method the advantage of spatial-temporal processing for the purpose of GNSS spoofing mitigation is studied. A new mitigation approach, which removes the spoofing signal LOS component as well as its multipath reflections before the despreading process of GNSS signals, is introduced. This in turn decreases the computational complexity and processing time. Therefore, this method can be either employed as an inline standalone pre-processing unit for conventional GNSS receivers or it could easily be integrated in the next generation of receivers. Several simulations and real data analyses are used to evaluate and show the effectiveness of the proposed methods.