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- PostAnalysis of static and dynamic GNSS multipath in rural area(2024) Behzadi, Sepehr; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Johansson, Jan; Johansson, JanPresently, the development of autonomous vehicles, particularly in construction, fo cuses extensively on excavators. This thesis examines the impact of multipath and environmental factors on GNSS signals when a single GNSS antenna is mounted on an excavator. Signal Strength Indicator(SSI) data for Galileo and GPS, along side GPS carrier phase residuals from the multi-GNSS PPP software GipsyX, were utilized to analyze the environment’s influence and the effects stemming from the excavator and its arm orientation. The experiment took place at a farm near the Onsala Space Observatory, involving the daily rotation of the excavator’s arm in different directions and simulated digging scenarios. Analysis of GPS SSI data from RINEX files and GPS post-fit residuals unveiled a systematic effect associated with the excavator’s arm orientation. The discernible impact on SSI suggests the potential for predicting the arm’s orientation even be fore data processing. Furthermore, employing residuals enables modeling of effects and errors linked to diverse arm orientations, promising enhanced data processing accuracy. Notably, superior performance was achieved using the L2L signal, demon strating higher correlations among residuals with matching arm orientations. Using the L2L signal also yielded improved repeatability in position estimations. The study suggests that concurrent consideration of RMSE values and correlation coef ficients of SSIs and residuals could effectively forecast the arm’s orientation. The measurements were done in a rather simple rural area with few objects, modelling the effects and errors linked to various arm orientations in this kind of area holds promise for enhancing position estimation, both in the same kind of area and as well in more complex areas like cities with numerous reflective objects causing multipath effects or signal blockage
- PostA comparison between low-cost and professional RTK equipment under forest conditions(2024) Wan, Yiqing; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Johansson, Jan; Isoz, Oscar; Hedekvist, Per-OlofReal time kinematic (RTK) is an important differential GNSS positioning method. It is widely used in forestry investigation. Depending on the type of reference station, RTK technique can be divided into traditional RTK and the advanced network RTK. There are also different types of GNSS receivers, for example the low-cost mapping type and the professional surveying type. The surveying type devices tend to have more accurate results, but the price difference between the two types of receivers can be dozens of times, and surveying type receivers are usually too bulky to carry and move around in the forest. Therefore, it is worthwhile to analyze if there are any situations that low-cost traditional RTK devices can achieve a comparable per formance as the professional network RTK devices do. In this project, we compared the performance of a low-cost mapping type receiver, u-blox F9P, with a professional network RTK device, Leica GS18 I. Field measure ments were taken in two days in the forests near Gothenburg. Measurements were taken in different percentages of canopy closure, different canopy directions and different tree species. Standard deviations and positional errors of the collected po sitions were calculated. Variables like dilution of precision (DOP), age of differential (AoD), sky plot and time to fix were also collected. It is found that the real time correction messages (RTCM) communication range for u-blox was at least 500 m in flat area, but terrain obstacles might reduce the range limit by half. The u-blox device performed bad when the canopy closure was over 50% or 65%, with a positional error of over 50 cm, thus it is not recommended to replace Leica network RTK with u-blox in dense forests. In most cases the standard deviation of Leica was better than that of u-blox. DOP was an important factor that had strong correlations with errors, fix status and cycle slips. Data collection with u-blox should wait for 1∼5 minutes after power-on, until DOP becomes lower and stable. AoD is found not much related with the error, but there should not be obvious break with the communication of RTCM. Canopy directions influenced the error but had less impact than canopy closure. The relationship between the error and tree species was not able to be determined.
- PostThe core mass function in the galactic center(2024) Kinman, Alva; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Tan, Jonathan; Petkova, Maya
- PostChemical diversity among asymptotic giant branch stars(2024) Brinkmalm, Johanna; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; De Beck, Elvire; De Beck, Elvire
- PostRay-tracing based atmospheric propagation simulator for a 2x2 LOS MIMO system(2023) Zhou, Yongan; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Eriksson, Patrick; Bao, Lei; Coldrey, MikaelA microwave radio system with multiple antennas is one popular technology for backhaul network deployment to reach the capability increase required for 5G and 6G. Antenna separations at transmit and receive sites should be carefully designed to ensure a proper phase relation, in this Multiple Input Multiple Output (MIMO) system with long Line-of-Sight (LoS) paths between transmitter and receiver. The LOS MIMO system may fail to operate under an extremely refractive atmosphere due to a lack of sufficient system gain which is determined by the power level and phase condition of the received sub-streams. The contribution of the thesis is to provide a simulator that can model radio’s at mospheric propagation, and it can be further used to verify real link measurement data. It is tested that the simulator has minor accuracy loss over the propagating distance concerned in this study. The simulation of electromagnetic wave propa gation is based on Forward Ray Tracing (FRT). The results demonstrate that the simulator is capable of predicting channel performance (MIMO gain, MIMO phase, etc.) for a 2-by-2 LOS MIMO system over a refractive atmosphere. The results also demonstrate that the simulator is found to be in good agreement with the lit erature and with Parabolic Equation (PE) methods, validating its potential use for predicting the outage probability for the MIMO link. This study, to the author’s best knowledge, is the first work that models the im pact of atmospheric refractivity on LOS MIMO channels using FRT. It is found that for a 2x2 LOS MIMO system the antenna separation calculated assuming free space propagation is also valid for the case of standard refractivity. For other re fraction conditions, the link will more likely experience an outage due to variation in phase condition than loss of power. In addition, atmospheric multipath may in duce random MIMO phase variation. However, the simulator cannot yet properly tackle surface-induced effects on the signals; this requires further development of the software.