Current Issue : April - June Volume : 2014 Issue Number : 2 Articles : 5 Articles
The GNSS measurements are strongly affected by ionospheric effects, due to the signal propagation through ionosphere; these\r\neffects could severely degrade the position; hence, a model to limit or remove the ionospheric error is necessary. The use of\r\nseveral techniques (DGPS, SBAS, and GBAS) reduces the ionospheric effect, but implies the use of expensive devices and/or\r\ncomplex architectures necessary to meet strong requirements in terms of accuracy and reliability for safety critical application. The\r\ncheapest and most widespread GNSS devices are single frequency stand-alone receivers able to partially correct this kind of error\r\nusing suitable models. These algorithms compute the ionospheric delay starting from ionospheric model, which uses parameters\r\nbroadcast within the navigation messages. NeQuick is a three-dimensional and time-dependent ionospheric model adopted by\r\nGalileo, the European GNSS, and developed by International Centre for Theoretical Physics (ICTP) together with Institute for\r\nGeophysics, Astrophysics, and Meteorology of the University of Graz. The aim of this paper is the performance assessment in\r\nsingle point positioning of the NeQuick Galileo version provided by ESA and the comparison with respect to the Klobucharmodel\r\nused for GPS; the analysis is performed in position domain and the errors are examined in terms of RMS and maximum error for\r\nthe horizontal and vertical components. A deep analysis is also provided for the application of the exanimated model in the first\r\npossible Galileo only position fix....
A novel ranging technique based on received signal strength (RSS) and suitable to indoor scenarios is illustrated. In the proposed\r\ntechnique, multiple power measurements, associated with the signals radiated by a cluster of nodes surrounding a given target,\r\nare jointly processed to improve the quality of RSS-based estimation of the distance between the target and an anchor. Specific\r\nalgorithms for the generation of a cluster and for the acquisition of power measurements are described. Simulation results show\r\nthat, when used in indoor positioning systems, the proposed ranging technique is substantially more accurate than noncooperative\r\nstrategies. In addition, it allows to concentrate significant processing tasks in a limited number of fixed anchors, so reducing\r\nmaintenance costs and making it possible to adopt cheap and simple portable wireless nodes....
As part of the GPS modernization, the GPS L1 C/A signal will be augmented by the L1C signal. With this improvement, for\r\nthe first time, several signals from the same constellation will be available at the same frequency. In this paper, an acquisition\r\nmethod is implemented to combine the GPS L1 C/A and L1C signals before correlation. The combined acquisition succeeds to\r\nacquire the signal at low C/N0, whereas the acquisition of the L1C data channel alone fails. Concerning the tracking, a method\r\nto combine the GPS L1 C/A and L1C signals before the discriminator is developed. This method shows better performance than\r\nthe traditional tracking using only one signal. Finally, a Kalman filter to combine the signals in the tracking is developed. It shows\r\nbetter performance than the traditional tracking in all conditions. Since the L1C signal will not be broadcast before 2013, these\r\nmethods are tested using a software signal simulator....
Global navigation satellite systems (GNSSs) can provide reliable positioning information under optimum conditions, where at least\r\nfour satellites can be accessed with sufficient quality. In critical situations, for example, urban canyons or indoor, due to blocking\r\nof satellites by buildings and severe multipath effects, the GNSS performance can be decreased substantially. To overcome this\r\nlimitation, we propose to exploit additionally information from communications systems for positioning purposes, for example,\r\nby using time difference of arrival (TDOA) information. To optimize the performance, hybrid data fusion and tracking algorithms\r\ncan combine both types of sources and further exploit the mobility of the user. Simulation results for different filter types show\r\nthe ability of this approach to compensate the lack of satellites by additional TDOA measurements from a future 3GPP-LTE\r\ncommunications system. This paper analyzes the performance in a fairly realistic manner by taking into account ray-tracing\r\nsimulations to generate a coherent environment for GNSS and 3GPP-LTE....
Underlay cognitive radios (UCRs) allow a secondary user to enter a primary user�s spectrum through intelligent utilization of\r\nmultiuser channel quality information (CQI) and sharing of codebook. The aim of this work is to study two-user Gaussian UCR\r\nsystems by assuming the full or partial knowledge of multiuser CQI. Key contribution of this work is motivated by the fact that\r\nthe full knowledge of multiuser CQI is not always available. We first establish a location-aided UCR model where the secondary\r\nuser is assumed to have partial CQI about the secondary-transmitter to primary-receiver link as well as full CQI about the other\r\nlinks. Then, new UCR approaches are proposed and carefully analyzed in terms of the secondary user�s achievable rate, denoted\r\nby C2, the capacity penalty to primary user, denoted by ?C1, and capacity outage probability. Numerical examples are provided\r\nto visually compare the performance of UCRs with full knowledge of multiuser CQI and the proposed approaches with partial\r\nknowledge of multiuser CQI....
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