Single-frequency GPS positioning performance Around the time of the Chilean 2010 earthquake

Premda u ograničenim geoprostornim razmjerima, potresi su poznati izvori geomagnetskih i ionosferskih poremećaja. Kako navedeni poremećaji također utječu na značajke širenja radiovalova, može se očekivati utjecaj potresa na učinkovitost i kvalitetu rada satelitskih navigacijskih sustava. U radu su objavljeni rezultati analize kvalitete rada jednofrekvencijskih GPS prijemnika smještenih na odabranim položajima širom svijeta u vrijeme potresa koji je pogodio Čile 2010. godine. Analizirana je kvaliteta jednofrekvencijskog GPS pozicioniranja na odabranim referentnim stanicama u vremenskom intervalu neposredno nakon nastupa potresa. Također, ustanovljeno je vrijeme povrata funkcionalnosti GPS sustava u prvobitno operativno stanje. U istraživanju je vidljiv značajan kratkoročni poremećaj kvalitete rada GPS sustava na svim promatranim stanicama. U procesu sakupljanja podataka GPS opažanja umanjen je utjecaj raznih izvora pogrešaka u postupku određivanja položaja sustavom GPS, isključujući GPS ionosfersko kašnjenje i pomak u referentnom koordinatnom okviru. Teorijske analize pokazale su kako je utjecaj pomaka u referentnom koordinatnom sustavu zanemariv na učinkovitost GPS pozicioniranja; na ovaj način, ionosferski utjecaji izazvani potresom nastupaju kao najvjerojatniji uzrok degradacije kvalitete pozicioniranja jednofrekvencijskih GPS prijemnika širom svijeta.The earthquakes are known sources of geomagnetic and ionospheric disturbances, although on the restricted geospatial scale. Since such disturbances also affect the radio wave propagation characteristics, it is expected for the earthquakes to cause an impact on the satellite navigation systems’ performance. In this paper we have reported the results of the single-frequency GPS performance analysis at various locations around the globe at the time of the Chilean 2010 earthquake occurrence. The single-frequency GPS positioning performance at the selected reference sites in the time interval immediately following the Chilean 2010 earthquake outbreak has been analysed, and the GPS recovery time identified. Our study shows considerable short-term GPS performance disturbance observed at every location taken into consideration. The GPS observables collection process mitigates the impact of various GPS positioning error sources, excluding the GPS ionospheric delay and the reference frame shift. A theoretical analysis has shown negligible effects of the reference frame shift on the GPS positioning performance, leaving the ionospheric effects as the most probable cause of the earthquake-induced short-term single-frequency GPS performance degradation around the world

On Global Ionospheric Maps based winter-time GPS ionospheric delay with reference to the Klobuchar model: Case study of the Northern Adriatic

Modelling of the ionospheric Total Electron Content (TEC) represents a challenging and demanding task in Global Navigation Satellite Systems (GNSS) positioning performance. In terms of satellite Positioning, Navigation and Timing (PNT), TEC represents a significant cause of the satellite signal ionospheric delay. There are several approaches to TEC estimation. The Standard (Klobuchar) ionospheric delay correction model is the most common model for Global Positioning System (GPS) single-frequency (L1) receivers. The development of International GNSS Service (IGS) Global Ionospheric Maps (GIM) has enabled the insight into global TEC dynamics. GIM analyses in the Northern Adriatic area have shown that, under specific conditions, local ionospheric delay patterns differ from the one defined in the Klobuchar model. This has been the motivation for the presented research, with the aim to develop a rudimentary model of the TEC estimation, with emphasis on areas where ground truth data are not available. The local pattern of the ionospheric delay has been modelled with wave functions based on the similarity of waveforms, considering diurnal differences in TEC behavior from defined TEC patterns. The model represents a spatiotemporal winter-time ionospheric delay correction with the Klobuchar model as a basis. The evaluation results have shown accurate approximation of the local pattern of the ionospheric delay. The model was verified in the same seasonal period in 2007, revealing it successfulness under pre-defined conditions. The presented approach represents a basis for the further work on the local ionospheric delay modelling, considering local ionospheric and space weather conditions, thus improving the satellite positioning performance for single-frequency GNSS receivers

Expression of GNSS Positioning Error in Terms of Distance

This manuscript analyzes two methods for Global Navigation Satellite System positioning error determination for positioning performance assessment by calculation of the distance between the observed and the true positions: one using the Cartesian 3D rectangular coordinate system, and the other using the spherical coordinate system, the Cartesian reference frame distance method, and haversine formula for distance calculation. The study shows unresolved issues in the utilization of position estimates in geographical reference frame for GNSS positioning performance assessment. Those lead to a recommendation for GNSS positioning performance assessment based on original WGS84-based GNSS position estimates taken from recently introduced data access from GNSS software-defined radio (SDR) receivers

Eksperimentalna studija točnosti određivanja položaja diferencijskim GPS postupkom za potrebe lokacijskih usluga

The importance of differential satellite positioning has been intensively questioned in recent times, especially after ceasing of the selective availability (SA) in standard GPS positioning service. Almost without exception, experimental studies have confirmed the improvement in satellite positioning given by differential corrections still exists. In this article, the improvement of positioning accuracy for LBS obtained by differential GPS (DGPS) positioning method is addressed, based on experimental data analysis. Differential GPS positioning accuracy is discussed in relation to satisfaction of LBS positioning accuracy requirements and comparison with standard GPS positioning. While the implementation of DGPS positioning method still does not lead to satisfaction of the high-level LBS positioning performance requirements, it still improves and stabilises standard-level positioning accuracy for LBS.Značaj diferencijskog satelitskog određivanja položaja intenzivno se istražuje, napose od vremena gašenja selektivne dostupnosti GPS sustava. Gotovo bez izuzetaka, eksperimentalne studije potvrđivale su poboljšanje kvalitete satelitskog određivanja položaja kad je ono bilo podržano primjenom diferencijskih korekcija. U ovom radu istražuje se poboljšanje kvalitete satelitskog određivanja položaja primjenom diferencijskih korekcija u svjetlu zahtjeva koje postavljaju lokacijske usluge. Točnost diferencijskog GPS određivanja položaja analizira se u svjetlu zahtjeva za točnošću određivanja položaja određenih specifikacijama lokacijskih usluga. Dobiveni rezultati eksperimentalne provjere uspoređuju se s rezultatima standardnog GPS određivanja položaja i sa zahtjevima na točnost koji određuju kvalitetu lokacijskih usluga. Iako primjena diferencijskih korekcija još uvijek ne zadovoljava najstrože zahtjeve koje postavljaju specifikacije lokacijskih usluga, DGPS u zamjetnoj mjeri poboljšava i održava standardnu razinu kvalitete lokacijskih usluga

Conveying and Handling Location Information in the IP Multimedia Subsystem

The IP Multimedia Subsystem (IMS), specified by the 3rd Generation Partnership Project (3GPP), is a key element in the next-generation network (NGN) converged architecture. Extending the IMS towards provisioning support for location based services (LBS) will enable enhanced services and offer new revenues to the operator. Conveying location information in the IMS and connecting the IMS with a positioning system are still open issues. This paper presents the design and implementation of an IMS Location Server (ILS) integrating IMS with a positioning system. From the IMS perspective, the ILS serves as a service enabler for LBS. In order to demonstrate proof-of-concept in enhancing IMS-based services, two prototype service scenarios have been implemented: Location-aware Messaging (LaM), and Location-aware Push-to-Talk over cellular (LaPoC). Some work has been done by the IETF in the area of location information transport based on the Session Initiation Protocol (SIP). This paper proposes improvements in this area, primarily related to reducing the necessary amount of signaling with the specification of a new type of location filter. We have conducted measurements in a laboratory environment in order to illustrate our proposed solution and verify the benefits compared to existing solutions in terms of traffic load and session establishment time. Furthermore, we present a case study integrating the ILS with the Ericsson Mobile Positioning System (MPS)

GPS PERFORMANCE DEGRADATION CAUSED BY SINGLE SATELLITE OUTAGE: A GPS PRN24 CROATIA CASE STUDY

Prekidi rada pojedinačnih satelita općenito imaju veliki utjecaj na kvalitetu određivanja položaja satelitskim sustavima. Privremeni prekid GPS satelita PRN24 predviđen za 12. rujna 2009. godine postao je motivom pokretanja analize utjecaja na sveukupnu dostupnost ikvalitetu određivanja položaja sustavom GPS. Temeljena na simulaciji, analiza je usmjerena ka definiranjui utvrđivanju degradacije kvalitete GPS satelitskog određivanja položaja uslijed prekida rada satelita u Hrvatskoj, s obzirom na sve veću upotrebu satelitskih navigacijskih sustava kao sastavnog dijela nacionalne infrastrukture. Za utvrđivanje prepreka satelitskoj vidljivosti na otvorenom nebu simulirane su dvije GPS referentne lokacije u ruralnim područjima. Isto tako, za razdoblje prije i poslije planiranog prekida rada satelita definirana je vidljivost satelita i odgovarajuća prostorna degradacija točnosti (PDOP) za obje referentne lokacije. Izvršena je usporedba rezultata dobivenih simulacijom na referentnim lokacijama korištenjem emitiranog GPS almanaha s rezultatima koji se odnose na neometanu vidljivost nebeskog svoda. Analiza je pokazala kako u situacijama neometane vidljivosti nebeskog svoda privremeni prekid rada jednog GPS satelita nije prouzročio značajniju degradaciju kvalitete određivanja položaja satelitskim sustavom GPS.Međutim, zamjetan utjecaj uočen je u slučaju određivanja položaja u okruženju s prirodnim preprekama na južnom dijelu nebeskog svoda.Navigation satellite outage has a profound effect on the satellite navigation systems performance. A programmed temporal outage of the PRN24 satellite scheduled for 12thSeptember 2009 motivated a simulation-based study of the satellite outage effects on the overall GPS positioning performance and signal availability. The study was focused on the identification of the GPS performance degradation due to satellite outages in Croatia due to the growing utilization ofthe satellite navigation systems as a component of the national infrastructure. Two GPS reference sites in rural areas were simulated for the determination of open sky view obstructions. The satellite visibility and the corresponding positioning dilution of precision (PDOP) for both sites prior and after the planned temporal outage of GPS PRN24 satellite were determined. The results obtained from simulation using broadcast GPS almanac were compared with those related to the un-obstructed view of the sky. The analysis revealed no significant disruption for the un-obustructed sky view, but a significant impact was identified particularly to sites with natural southward sky-view obstruction

Ionospheric component of satellite positioning error due to extreme space weather disturbances

U radu se analizira utjecaj ekstremnih ionosferskih poremećaja prouzročenih promjenama svemirskog vremena na vrijednosti ionosferskog kašnjenja signala za satelitsko određivanje položaja. Definira se pojam svemirskog vremena i parametri koji opisuju njegovo stanje. Opisuje se tvorba ionosferskih slojeva uslijed djelovanja svemirskog vremena, te definiraju parametri stanja ionosfere. Prikazuju se ionosferski modeli, koji povezuju parametre stanja ionosfere s parametrima stanja svemirskog vremena, te standardni model GPS ionosferskog kašnjenja. Identificiraju se ograničenja postojećih modela, posebno obzirom na stanje i dinamiku svemirskog vremena. Na konkretnom primjeru ekstremnih poremećaja svemirskog vremena i ionosfere tijekom listopada i studenog 2003. godine, analizira se utjecaj svemirskog vremena i ionosfere na vrijednosti ionosferskog kašnjenja GPS signala na području Republike Hrvatske. Vrijednosti GPS ionosferskog kašnjenja određuju se iz eksperimentalnih podataka prikupljenih na referentnoj stanici Osijek, Hrvatska. Promatra se dinamika GPS ionosferskog kašnjenja, te njena korelacija s dinamikom promjena svemirskog vremena i ionosfere. Rezultati analize koriste se za definiranje novog modela GPS ionosferskog kašnjenja, utemeljenog na praćenju dinamike GPS ionosferskog kašnjenja. Na kraju, predlaže se opći kompozitni model za određivanje vrijednosti GPS ionosferskog kašnjenja, koji uvažava regionalne posebnosti stanja ionosfere. Predloženi model primjenjiv je u svim uvjetima svemirskog vremena.Here the problem of the impact of space weather and ionospheric conditions on ionospheric delay of the satellite navigation system signals is addressed. First, the space weather term is defined, along with the parameters describing its conditions. The process of ionospheric layer generation is presented, and related parameters describing the conditions of the ionosphere defined. The ionospheric models describing the relationship between the space weather and the ionosphere are discussed. The existing standard GPS ionospheric delay model is presented. Limitations and drawbacks of existing models in relation to the impact of the conditions and dynamics of space weather are analysed. The impact of extreme space weather and ionospheric disturbances on GPS ionospheric delay is analysed, based on particular case of extreme space weather and ionospheric disturbances observed during October and November 2003, as experienced in Republic of Croatia. The true values of GPS ionospheric delays for the period in question are extracted from raw GPS pseudorange measurements taken at the reference station Osijek, Croatia. The GPS ionospheric delay dynamics is analysed, and the correlation comparison with the space weather and the ionospheric conditions development examined. The results of the analysis form the foundation for a new GPS ionospheric delay model definition, established upon the monitoring of true GPS ionospheric delay dynamics. Finally, the general composite model for GPS ionospheric delay estimation is proposed, which takes into account the local and the regional characteristics of the ionosphere. Proposed model uses a present state of the space weather conditions as an input, and is completely applicable in all space weather conditions