Precise Point Positioning (PPP) provides accurate absolute position information without the direct need of measurements from a reference station at the user. The current challenge of GPS L1/L2-based ...PPP is its long convergence time of more than 20 minutes being caused by the need to estimate atmospheric parameters, and the relatively large code noise and multipath errors. There are two options to reduce the convergence time of PPP: First, the Galileo wideband signals on E5 and E6 have a much lower code noise than current GPS L1 and L2 pseudoranges. Second, the satellite positions and satellite-related biases can be determined much faster and more accurately with optical inter-satellite links supporting ranging, time-transfer and intra-system communication. In this paper, we consider both options. A joint estimation of the receiver position, receiver clock offset, tropospheric zenith delay, ionospheric slant delays and carrier phase ambiguities is performed with a Kalman filter. Orbital errors and pseudo range multipath are also taken into account. The float carrier phase ambiguity estimates are mapped to integers using the famous Least-Squares Ambiguity Decorrelation Adjustment (LAMBDA) method. The simulation results show that an ambiguity fixing and, thereby, a highly-accurate PPP solution, can be achieved consistently within a few epochs. This is a quite substantial benefit and could make PPP attractive for numerous applications.
A new vector phase-locked loop (PLL) for joint tracking of carrier phase from all satellites on multiple frequencies is presented. It increases the robustness to ionospheric scintillations, carrier ...phase multipath and interference from jammer. The tracking error is split into a position error, a clock offset, ionospheric, and tropospheric errors which are filtered individually. The filter coefficients are optimized with orthogonal projections of the tracking error that eliminate the nuisance parameters. The tracking performance is determined recursively, and a significant reduction of the tracking error is observed during strong ionospheric scintillations with deep amplitude fades.
The autonomous driving of robots is coming and requires precise and reliable positioning information with low-cost sensors for the mass market. In this paper, we propose a tightly coupled sensor ...fusion of multiple complementary sensors including Global Navigation Satellite System (GNSS) receivers with Real-Time Kinematics (RTK), Inertial Measurement Units (IMUs), wheel odometry, Local Positioning System (LPS) and Visual Positioning. The focus of this paper is on the integration of LPS and vision since the coupling of GNSS-RTK, INS and wheel odometry is already state of the art. We include the positions of the LPS anchors and the bearing vectors and distances from the robot's camera towards the patch features as state vectors in our Kalman filter, and show the achievable positioning accuracies.
Precizno odre.ivanje položaja uporabom satelitske navigacije zahtjeva poznavanje satelitskog koda te fazna mjerenja. U ovom radu predložena je nova metoda za procjenu faznih pomaka signala uporabom ...rezultata mjerenja iz geodetske mreže. U prvom koraku iz mjerenja se izuzimaju poznati podaci o orbitama, satelitskim satovima i višestrukim putevima, kako bi se smanjila njihova dinamika. U drugom se koraku uporabom Kalmanovog filtra procjenjuju fazni pomaci, ionosferska kašnjenja, neodre.enost broja valnih duljina nosioca i geometrija koja uključuje sve nedisperzivne parametre. Konačno, odre.uje se korigirana geometrija u drugom Kalmanovom filtru radi proračuna orbitalnih pogrešaka, pogrešaka koda i troposferskog kašnjenja. S obzirom na to da prvi Kalmanov filtar unosi vremensku korelaciju, opći Kalmanov filtar primjenjuje se u drugom koraku. Predloženi algoritam primijenjen je u dvofrekvencijskim GPS-mjerenjima u lokalnoj geodetskoj mreži u Njemačkoj. Postignuta je visoka stabilnost rezultata uz varijacije manje od 3 cm tijekom 4 sata.
The code ionospheric bias, also known as the Differential Code Bias (DCB), is an important correction term for single-frequency receiver. This paper proposes a new method to estimate the biases as ...well as the vertical ionospheric delays using Kriging estimator with a network of receivers. Kriging estimates an unknown variable based on a set of known parameters and a variogram describing the spatial correlation. It is the best estimator in the sense of minimizing the estimation variance. Kriging method is proposed, as it could reconstruct the vertical delays based on a subset to overcome the rank deficiency. A Kalman filter is introduced, and a sub-optimum solution has been obtained based on an iterative Greedy Algorithm. Simulation results have shown cm-level accuracy on the ionospheric bias estimates. The algorithm has also been applied with real GPS data for multiple days, which showed high bias repeatability. The bias estimates have been verified by comparison with published values.
The adaption of symbol probabilities to the Maxwell-Boltzman distribution enables a shaping gain of up to 1.53 dB over uniform distributions. We assign a variable number of labels to each signal ...point to implement signal shaping. The ambiguous mapping requires a larger label alphabet that we obtain by increasing the label length. The ambiguous mappings enable an additional coding gain due to the increased label length which allows the use of a lower coding rate. We deduce the optimum MAP detector and approximate the optimum Maxwell-Boltzman distribution by a rounding based algorithm. Some optimized label distributions and extended mappings are given for 16- and 64-QAM. Extended mappings for signal shaping combine the advantages of a more powerful channel code and the increase in channel capacity. Simulation results promise a very low bit error floor with extremely simple channel codes.
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