Rameez Ur Rahman Lighari

Bio: Rameez Ur Rahman Lighari is an academic researcher from University of Oulu. The author has contributed to research in topics: GNSS applications & Multipath propagation. The author has an hindex of 4, co-authored 6 publications receiving 25 citations.

Circularly polarized GPS antenna for simultaneous LHCP and RHCP reception with high isolation

Abstract: In this paper a compact dual-feed Global Positioning System (GPS) antenna for simultaneous left- and right hand circularly polarized wave reception is presented. The antenna structure consists of a single patch antenna on top of a printed circuit board and two aperture coupled feeds in the ground plane which are used to generate both left- and right-hand (LH and RH) circular polarizations for the patch. The feed network is implemented as a 2-section branch-line coupler underneath the ground plane. It is able to generate adequate phase shifts for both LH and RH circular polarizations simultaneously via two feed ports. Due to the aperture coupling and coupler implementation three layer printed circuit board approach is used. The measured axial ratio is < 1.35 for both polarizations over the 24 MHz bandwidth at the frequency of 1.575 GHz. The isolation between the LH and RH feed ports in reception mode is −35… −26 dB in the broadside direction. The antenna enables simultaneous direct and multipath signal measurement with equal spatial coordinates for both polarizations.

Polarization based measurement system for analysis of GNSS multipath signals

Abstract: In this paper, the principle of a polarization-based measurement system intended for the data recording of the Global Navigation Satellite System (GNSS) signals is described. The measurement arrangement includes left- and right hand circular polarized antennas with separate satellite RF recorders for both polarizations. Based on the recorded data for different antenna polarizations the Line-Of-Sight (LOS) and the reflected Non-Line-Of-Sight (NLOS) signal components can be analyzed in order to generate a three-dimensional channel model. Initial field measurements are performed for a route of one kilometer in a university campus area. The initial recorded data include digitized RF signals for all visible Global Positioning System (GPS) satellites, the National Marine Electronics Association (NMEA) data, video recording of the environment and reference velocity from a separate speed sensor. In this paper, the preliminary analysis of the recorded data is presented. Based on the recorded data it is concluded that the polarization based measurement system is able to separate LOS and NLOS signal components thus enabling first steps toward the three-dimensional GNSS channel model development.

Classification of GNSS SNR data for different environments and satellite orbital information

Abstract: In this paper, a data classification method for analyzing the aspects of Signal-to-Noise Ratio (SNR) for Global Navigation Satellite System (GNSS) in real conditions is introduced Different parts of measured environments and the orbital information of satellites are used as criteria for data classification It consists of: 1) taking fish eye images of measured routes; 2) dividing measured environments into four potential sub environments (open area, forest area, single building blockage, and street canyon); 3) classifying satellites into nine different groups as function of elevation angles; and 4) creating a table containing the information of mean and standard deviation of SNR for different environments and satellite elevation angles Results show good correlation of SNR's between same sub environments for different satellite elevation ranges which offer useful insight to regenerate a generalized set of SNR parameters in the laboratory environment for the development of 3D GNSS channel model

Analysis of the measured RHCP and LHCP GNSS signals in multipath environment

Abstract: The performance evaluation of Global Navigation Satellite System (GNSS) device in 3D laboratory measurement environment is gaining increasing importance. Even though GNSS is a mature technology the 3D channel model to be implemented in laboratory environment does not exist due to the challenges encountered in creating controllable and repeatable multipath conditions. This research work is a first step toward the one solution of these problems. In this paper, the GNSS data set recorded with the polarization based measurement system is analyzed. Both Right Hand Circularly Polarized (RHCP) and Left Hand Circularly Polarized (LHCP) antennas are employed so that direct and reflected signals can be acquired simultaneously. The goal of the study is to investigate the characteristics of polarization based reflections, path length of delayed multipath signal, position error, coverage efficiency (mean number of tracked satellites), and the impact of satellite elevation angle on received Signal-to-Noise Ratio (SNR) for a typical multipath environment. Results show that satellite elevation angle, and multipath propagation affect both the position precision measured by the receiver and SNR. Additionally, presented results will serve as basis for the development of 3D GNSS channel model to work for both static and dynamic environments.

3-D Ray Tracing Based GPU Accelerated Field Prediction Radio Channel Simulator

Abstract: A ray tracing simulator for urban and indoor environments is introduced. The simulator uses NVIDIA graphics processing unit (GPU) accelerated CUDA parallel computing platform and programming mode and the OptiX Ray Tracing Engine. As a use case, channel characteristics for Global Navigation Satellite System (GNSS) satellites are simulated and compared with measurements in an urban area. The speedup achieved by parallel processing allows computation of multiple relevant reflections characteristic of a satellite channel.

GNSS Vulnerabilities and Existing Solutions: A Review of the Literature

Abstract: This literature review paper focuses on existing vulnerabilities associated with global navigation satellite systems (GNSSs). With respect to the civilian/non encrypted GNSSs, they are employed for proving positioning, navigation and timing (PNT) solutions across a wide range of industries. Some of these include electric power grids, stock exchange systems, cellular communications, agriculture, unmanned aerial systems and intelligent transportation systems. In this survey paper, physical degradations, existing threats and solutions adopted in academia and industry are presented. In regards to GNSS threats, jamming and spoofing attacks as well as detection techniques adopted in the literature are surveyed and summarized. Also discussed are multipath propagation in GNSS and non line-of-sight (NLoS) detection techniques. The review also identifies and discusses open research areas and techniques which can be investigated for the purpose of enhancing the robustness of GNSS.

Retrieval of Snow Water Equivalent, Liquid Water Content, and Snow Height of Dry and Wet Snow by Combining GPS Signal Attenuation and Time Delay

Abstract: For numerous hydrological applications, information on snow water equivalent (SWE) and snow liquid water content (LWC) are fundamental. In situ data are much needed for the validation of model and remote sensing products; however, they are often scarce, invasive, expensive, or labor‐intense. We developed a novel nondestructive approach based on Global Positioning System (GPS) signals to derive SWE, snow height (HS), and LWC simultaneously using one sensor setup only. We installed two low‐cost GPS sensors at the high‐alpine site Weissfluhjoch (Switzerland) and processed data for three entire winter seasons between October 2015 and July 2018. One antenna was mounted on a pole, being permanently snow‐free; the other one was placed on the ground and hence seasonally covered by snow. While SWE can be derived by exploiting GPS carrier phases for dry‐snow conditions, the GPS signals are increasingly delayed and attenuated under wet snow. Therefore, we combined carrier phase and signal strength information, dielectric models, and simple snow densification approaches to jointly derive SWE, HS, and LWC. The agreement with the validationmeasurements was very good, even for large values of SWE (>1,000 mm) and HS (> 3 m). Regarding SWE, the agreement (root‐mean‐square error (RMSE); coefficient of determination (R)) for dry snow (41 mm; 0.99) was very high and slightly better than for wet snow (73 mm; 0.93). Regarding HS, the agreement was even better and almost equally good for dry (0.13 m; 0.98) and wet snow (0.14 m; 0.95). The approach presented is suited to establish sensor networks that may improve the spatial and temporal resolution of snow data in remote areas.

Circularly polarized GPS antenna for simultaneous LHCP and RHCP reception with high isolation

Abstract: In this paper a compact dual-feed Global Positioning System (GPS) antenna for simultaneous left- and right hand circularly polarized wave reception is presented. The antenna structure consists of a single patch antenna on top of a printed circuit board and two aperture coupled feeds in the ground plane which are used to generate both left- and right-hand (LH and RH) circular polarizations for the patch. The feed network is implemented as a 2-section branch-line coupler underneath the ground plane. It is able to generate adequate phase shifts for both LH and RH circular polarizations simultaneously via two feed ports. Due to the aperture coupling and coupler implementation three layer printed circuit board approach is used. The measured axial ratio is < 1.35 for both polarizations over the 24 MHz bandwidth at the frequency of 1.575 GHz. The isolation between the LH and RH feed ports in reception mode is −35… −26 dB in the broadside direction. The antenna enables simultaneous direct and multipath signal measurement with equal spatial coordinates for both polarizations.

Global positioning system processing methods for GPS passive coherent location

Abstract: This study addresses processing methods for the use of the global positioning system (GPS) as a signal of opportunity in a multistatic passive coherent location (PCL) system The signal properties of the GPS signal are designed for position estimation, which makes it particularly suited for GPS PCL applications The signal specifications are examined and the potential limitations of a proposed system are explored Conventional GPS processing techniques are implemented in the framework of multistatic GPS PCL GPS specific methods are developed for target position estimation of a multistatic PCL system in a three-dimensional plane The PCL system has comparable performance metrics to conventional GPS positioning Two methods are developed utilising measurements available in a conventional GPS system The first involves a short time scale, which is in the order of milliseconds The second involves a long time scale method, which is on the order of seconds Simulation and analysis are performed to verify the methods Experimental validation was also conducted using a hardware in the loop approach, as well as, an active radar calibrator

Classification of GNSS SNR data for different environments and satellite orbital information

Abstract: In this paper, a data classification method for analyzing the aspects of Signal-to-Noise Ratio (SNR) for Global Navigation Satellite System (GNSS) in real conditions is introduced Different parts of measured environments and the orbital information of satellites are used as criteria for data classification It consists of: 1) taking fish eye images of measured routes; 2) dividing measured environments into four potential sub environments (open area, forest area, single building blockage, and street canyon); 3) classifying satellites into nine different groups as function of elevation angles; and 4) creating a table containing the information of mean and standard deviation of SNR for different environments and satellite elevation angles Results show good correlation of SNR's between same sub environments for different satellite elevation ranges which offer useful insight to regenerate a generalized set of SNR parameters in the laboratory environment for the development of 3D GNSS channel model