---

Positioning in road network environment requires a process with which can be able to match the raw coordinates, obtained from the positioning sensor(s), to the links of the network. Such matching process is necessary for two obvious reasons. First, positional data is not definite, and second, map coordinates are not absolute. Hence, there is a need for a process, known as map-matching, to reconcile two groups of coordinates. Accordingly, to provide some location-based services in network areas, performing a map-matching process seems inevitable. In this paper, after discussing several types of geometric map-matching methods, which is the most basic form of map-matching, a weighted-base map-matching algorithm is developed.The participating parameters’ weights are optimized experimentally. The algorithm takes three parameters as input: ‘Distance’, ‘Heading Convergency’, and ‘Relational Position’. Four types of modelling for ‘Relational Position’ are presented. The most effective type is then recognized after executing tests on algorithm performance. Also, comparing the performance of the suggested map-matching algorithm to the map-matching algorithms of the same complexity developed in other studies shows that the suggested algorithm is more efficient. This paper's suggested algorithm provided 95.5 percent of true link selection during the performance assessment.

---

Earth’s upper atmosphere, called the ionosphere, is a highly variable region with complex physical characteristics in which the density of free electrons are large enough to have considerable effects on signals’ propagation travelling through this dispersive medium. As GPS signals travel through the ionosphere, they may experience rapid amplitude fluctuations or unexpected phase changes. This is referred to as ionospheric scintillation. Ionospheric scintillation which caused by small scale irregularities in the electron density, is one of the dominant propagation disturbances in radio frequency signals. These irregularities severely affect the accuracy and reliability of GPS measurements. Therefore, it is necessary to investigate ionospheric scintillation and its effects on GPS observations. Hence, the focus of this paper is to detect ionospheric scintillations over Iran’s region and to investigate these effects on GPS observations in more details. The results will show the occurrance of this phenomenon and its effects on GPS observations.

---

Tropospheric delay is always considered as one of the factors limiting the accuracy of GPS. In this paper, the three-dimensional ray tracing technique is proposed to calculate the tropospheric delay. The ability of the MODIS mission to calculate the tropospheric delay is also examined. For this purpose, an area in central Europe was selected and a MODIS acquisition on 2008/08/01 was studied. In addition, the radiosonde observations as well as ERA-Interim meteorological data were used to evaluate the obtained results. After applying corrections to the MODIS acquisition, the three-dimensional ray tracing method was implemented at the location of a GPS station using all three types of data to extract the tropospheric delay. The RMS of difference between the results of MODIS and results of radiosonde and ERA-Interim data was 1.11 and 0.89 cm respectively. Then, precise point positioning was done using the Bernese software and tropospheric correction from MODIS, radiosonde and ERA-Interim data and compared with precise coordinate of station. The accuracy of position with MODIS tropospheric correction is less than ones corrected with radiosonde and ERA-Interim tropospheric data. The results show the low efficiency of MODIS data for tropospheric correction of GPS observations compare to radiosonde and ERA-Interim data.

---

Today, the global positioning systems (GPS) do not work well in buildings and in dense urban areas when there is no lines of sight between the user and their satellites. Hence, the local positioning system (LPS) has been considerably used in recent years. The main purpose of this research is to provide a four-layer artificial neural network based on nonlinear system solver (NLANN) for local positioning problem. To evaluate the performance of artificial neural network, three methods of gauss-newton (GN), genetic algorithm (GA) and hybrid particle swarm optimization (HPSO) have been used. The results indicate that the proposed model has high accuracy. The accuracy of the artificial neural network on the simulated data is 0.05 m, while the best accuracy in other algorithms is about 0.45 meters. In the data of Italy's GPS network, the artificial neural network has been reached to accuracy below 10 cm in one minute. Also, artificial neural network has better accuracy in different dimensions of study area and different signal to noise ratio (SNR), and by increasing the number of stations, it has achieved good results in less time. Whereas other algorithms have not get well accuracy. However, the HPSO has better results related to GA and GN algorithms.

---

Ocean navigation relies heavily on the determination of the position of the  floating units. In the past, as there was no satellite navigation system, all the floating units in the ocean calculated their position using celestial bodies and the Sun. With the advent of the satellite navigation system, astronomical positioning using celestial bodies has faded and is only limited to the  emergency cases where the floating units are unable to use the  satellite equipment. On the other hand, we know that one of the biggest weaknesses in determining the astronomical position in the intersection method and the other vector and drawing methods is related to the approximate position or at least the approximate latitude. In this research, the algorithm for determining the position of a moving or stationary observer by measuring two consecutive heights from the Sun has been developed. One of the prominent points in this algorithm is that it does not need the approximate or initial position of the observer to calculate the position. On the other hand, the difference between this research and the other similar researches is how we calculate the Sun position and how accurate our calculation is. The results of this study show that the best results of positioning can be obtained by measuring two consecutive altitudes of the Sun in about 10 to 20 minutes, and the accuracy of this method is about 10^-1  minutes. If the applied theoretical method is used and the accuracy of the calculations of the Sun location is increased, it is possible to achieve the optimal accuracy in the astronomical navigation, which paves the way for future research in obtaining the height of the Sun with very accurate methods (except  for the sextant).