La investigació d'aquesta Tesi Doctoral per compendi d'articles es centra en la tècnica de ràpid Posicionament de Punt Precís (Fast-PPP). La novetat radica en l'ús d'un model ionosfèric precís que, combinat amb productes estàndard de rellotge i de l'òrbita de satèl·lit, redueix el temps de convergència de les actuals tècniques de navegació precisa d'aproximadament una hora a pocs minuts. La meva primera contribució a la tècnica Fast-PPP com a estudiant de Doctorat ha estat el disseny i la implementació d'un filtre de navegació d'usuari innovador, basat en el tractament de múltiples freqüències de mesures de codi i fase sense diferenciar (absolutes). La estratègia del filltre de navegació evita l'aplicació de l'habitual combinació lineal lliure de ionosfera per a aquests observables. Així, s'explota la capacitat completa dels senyals multi-freqüència en el nous Sistemes Globals de Navegació per Satèl·lit (GNSS) i s'augmenta la robustesa del Fast-PPP en entorns difícils, on es redueix la visibilitat del cel. S'ha optimitzat per tal de prendre avantatge de les correccions necessàries per a compensar els retards (és a dir, els errors) que afecten els senyals GNSS. Les correccions de Fast-PPP i més important, les seves incerteses (és a dir, els intervals de confiança) s'afegeixen com a equacions addicionals al filltre per aconseguir Posicionat de Punt Precís (PPP) en pocs minuts. La segona contribució ha estat la consolidació del modelat ionosfèric precís de Fast-PPP i la seva extensió d'un abast regional a una escala global. La correcta determinació i ús dels intervals de confiança de les correccions Fast-PPP ha esdevingut de gran importància a l'hora de navegar en zones de baixa latitud a l'equador, on la ionosfera és més difícil de modelar amb precisió. Fins i tot en aquest escenari, s'ha aconseguit una gran consistència entre els errors de posicionament reals i els nivells de protecció dels usuaris de Fast-PPP, tal com s¿ha demostrat amb figures de mèrit similars a les utilitzades en l'aviació civil (els diagrames de Stanford). La tercera contribució d'aquesta Tesi Doctoral ha estat la caracterització de l'exactitud dels models ionosfèrics utilitzats actualment en GNSS. L'avaluació utilitza mesures de fase, sense ambigüitats i sense diferenciar, gràcies a la capacitat de modelatge centimètric emprat a la tècnica de Fast-PPP. No només els errors dels models de la ionosfera han estat quantificats en termes absoluts i relatius, sinó també, el seu efecte sobre la navegació.
Sanz, J.; Rovira-Garcia, Adrià.; Juan, J.; Gonzalez-Casado, G.; Ibañez, D.; Romero-Sánchez, J.; Alonso, M.; Shao, Y.; Escudero, M. Multi-GNSS Asia Conference p. 1 Presentation's date: 2015-12 Presentation of work at congresses
Two high-precision positioning techniques currently offer accur acy at the centimetre level: Real-Time Kinematics (RTK) and Precise Point Positioning (PPP). Both methods use carrier-phase measurements, 2 orders of magnitude more prec ise than pseudoranges. Classical single-baseline RTK (appeared in the 80’s) uses a nea rby reference station to compensate most of the delays (i.e., errors) affecting GNSS sig nals. RTK achieves centimetre-level of accuracy in seconds after the Double Differ ences of the carrier-phase ambiguities are fixed to integers. The drawbacks of RTK are: i) the bandwidth and continuity requirements to disseminate the measurements from th e reference receiver to the user and ii) the maximum distance to the reference station, which can range from 10-20 km (depending on the ionosph eric activity) to 50 km using Network-RTK. PPP (defined in the 90’s) overcomes the RTK limitations with du al-frequency measurements and orbit and clock products precise to a few cent imetres. PPP products require less bandwidth than RTK, with less continuity constrain s and allow world-wide coverage. However, PPP requires almost 1 hour to convergence th e un-differenced carrier-phase ambiguity estimation from the noisy pseudorange. This initialization is not acceptable in most professional kinematic applications (e.g. su rveying, farming) that usually rely on RTK. Recent improvements to PPP are: (i) the or bit and clock corrections are sent to users i n real-time, (ii) the user can f ix the carrier ambiguities in undifferenced mode, improving the accuracy, (iii) the multi-con stellation context. In this presentation we will review the main features of the Hi gh Accuracy Positioning techniques, from RTK to PPP. In particular we will address some the large convergence time of PPP and the lack of integrity in the user solution. Fin ally we will show how a World-Wide Ionospheric Model for Fast-PPP reduces the convergence time in PPP and, also, enables High-Accuracy navi gation with a single frequency receiver.
Povero, G.; Deisting, B.; Kling, S.; Hai Tung, T.; Vinh, L.; Belforte, G.; Sanz, J.; Rizos, C.; Marradi, L. Ka and Broadband Communications Conference p. 1-6 DOI: 10.13140/RG.2.1.3311.4320 Presentation's date: 2015-10-14 Presentation of work at congresses
South East Asia is growing at an impressive pace with its GDP having increased by about 350% in ten years , ri sing from 650 Billion $ in 2002 to about 2300 Billion $ in 2012. Regional governments actively promote infrastructure, logistics and service development to create a favourable environment fo r sustainable growth. Within this framework, GNSS applications play a vital role. In particular, the increasing demand for better services , in both the public and private sector , and logistics is going to require increasingly reliable and trusted GNSS appl ications. South East Asia has the highest multi - GNSS coverage in the world, and is therefore the ideal place to test and compare performance and opportunities offered by the different g lobal n avigation s atellite s ystems. On the one hand, an active promotio n of E U GNSS (EGNSS) technology in this region, rising awareness on its main features while on the other hand facilitating the linking of European enterprises with South East Asian GNSS stakeholders, are extremely important so as to establish and maintain global European scientific and industrial leadership in this crucial sector. Indeed, it is also fundamental to encourage the penetration of EGNSS industry in to the South East Asian market taking into account all potential applications of EGNSS. Therefore, the BELS project exploits the opportunities presented by the NAVIS Centre, an International Collaboration Centre for Research and Development on Satellite Navigation Technology in South East Asia based in Hanoi, Vietnam, to promote visibility and to raise awareness o f EGNSS technology in the region. The next three years will be crucial for pav ing the way for Galileo services, both for European companies that can enter a new growing market and for the South East Asian countries that can discover the capabili ties of the EGNSS technology. Consequently, BELS facilitates and supports the visits of European companies for such purposes a s carrying out tests in the NAVIS Centre and hence to assist them in getting ready for the global GNSS applications market .
Rovira-Garcia, Adrià.; Juan, J.; Sanz, J.; Gonzalez-Casado, G.; Ibañez, D.; Romero-Sánchez, J. International Technical Meeting of the Satellite Division of the Institute of Navigation Presentation's date: 2015-09-18 Presentation of work at congresses
The main objective of this work is to present a methodology to assess the accuracy of any ionospheric model used in Global Navigation Satellite System (GNSS) applications. A number of global and regional models (both in realtime and post-process) will be analyzed during the entire 2014, i.e. near to the last Solar Cycle Maximum, to identify seasonal characteristics. The new method uses as reference values the unambiguous and undifferenced geometry-free combination of carrier-phase measurements from a worldwide distribution of receivers. The differences between the Slant Total Electron Contents (STECs) of the model and the measurements are fit to constant hardware delays: a receiver plus a satellite Differential Code Bias (DCB). Once such DCBs are estimated, the post-fit residual of the adjustment to the reference values is computed. It is shown that this residual is a very suitable metric to represent the error of any ionospheric model tailored for GNSS-based navigation. Any miss-modeling present in the STECs predictions which cannot be represented by a constant parameter per station and a constant per satellite degrades the user positioning. The assessment includes the comparison of the 3D navigation error of some permanent stations, being processed in singlefrequency as kinematic rovers, using different ionospheric corrections and precise satellite orbits and clocks.
Gonzalez-Casado, G.; Juan, J.; Sanz, J.; Rovira-Garcia, Adrià.; Aragón Angel, A. International Technical Meeting of the Satellite Division of the Institute of Navigation p. 3459-3468 Presentation's date: 2015-09-17 Presentation of work at congresses
We introduce a methodology to extract the separate contributions of the ionosphere and the plasmasphere to the vertical total electron content, without relying on a fixed altitude to perform that separation. The method combines two previously developed and tested techniques, namely, the retrieval of electron density profiles from radio occultations using an improved Abel inversion technique and a two-component model for the topside ionosphere plus protonosphere. Taking measurements of the total electron content from global ionospheric maps and radio occultations from the Constellation Observing System for Meteorology, Ionosphere, and Climate/FORMOSAT-3 constellation, the ionospheric and plasmaspheric electron contents are calculated for a sample of observations covering 2007, a period of low solar and geomagnetic activity. The results obtained are shown to be consistent with previous studies for the last solar minimum period and with model calculations, confirming the reversal of the winter anomaly, the hemispheric asymmetry of the semiannual anomaly, and the existence in the plasmasphere of an annual anomaly in the South American sector of longitudes. The analysis of the respective fractional contributions from the ionosphere and the plasmasphere to the total electron content shows quantitatively that during the night the plasmasphere makes the largest contribution, peaking just before sunrise and during winter. On the other hand, the fractional contribution from the ionosphere reaches a maximum value around noon, which is nearly independent of season and geomagnetic latitude.
The project implements a set of coordinated actions to promote EGNSS technology in South East Asia (SEA), meanwhile supporting the competitiveness of EU enterprises facilitating their contacts with relevant GNSS stakeholders in SEA, a fast growing market of more than 600 million people. Exploiting the facilities offered in Hanoi by the NAVIS Centre - a strategic asset for Europe, setup with FP7 EU funding - European enterprises can increase their competitiveness conducting tests of their products in a challenging multi-GNSS environment, not available in Europe, with hard ionospheric activity conditions. Ten workshops organised in the different ASEAN States promote EGNSS technology and offer contact opportunities with local stakeholders to EU companies/institutions. Three editions of the Asia Oceania Regional Workshop on GNSS, an important event in SEA, are organized in collaboration with JAXA, MGA and other partners. To reach as many interested EU GNSS companies as possible, the project activities and collaboration opportunities offered by the NAVIS Centre are carefully advertised through different channels including clusters, social networks, websites etc. and three events are organized in Europe, possibly as side events of larger ones. So a larger network of long lasting relations between European companies and SEA GNSS stakeholders is built, allowing the NAVIS Centre to keep serving as a focal point for cooperation with Europe and as showcase of EGNSS technology. A competition to attract smart young researchers/entrepreneurs from ASEAN States to develop EGNSS-based business ideas/applications is also organized. The prize consists in a six-month incubation period in Europe to further implement the idea. Capacity building actions complete the project: they target SEA researchers/technicians with the aim to prepare a generation of SEA experts familiar with European technology, habits and culture and ready to support European industries willing to operate in SEA.
Rovira-Garcia, Adrià.; Juan, J.; Sanz, J.; Gonzalez-Casado, G. IEEE transactions on geoscience and remote sensing Vol. 53, num. 8, p. 4596-4604 DOI: 10.1109/TGRS.2015.2402598 Date of publication: 2015-03-03 Journal article
Fast precise point positioning (Fast-PPP) is a satellite-based navigation technique using an accurate real-time ionospheric modeling to achieve high accuracy quickly. In this paper, an end-to-end performance assessment of Fast-PPP is presented in near-maximum Solar Cycle conditions; from the accuracy of the Central Processing Facility corrections, to the user positioning. A planetary distribution of permanent receivers including challenging conditions at equatorial latitudes, is navigated in pure kinematic mode, located from 100 to 1300 km away from the nearest reference station used to derive the ionospheric model.
It is shown that satellite orbits and clocks accurate to few centimeters
and few tenths of nanoseconds, used in conjunction with an ionosphere with an accuracy better than 1 Total Electron Content Unit (16 cm in L1) reduce the convergence time of dual-frequency Precise Point Positioning, to decimeter-level (3-D) solutions. Horizontal convergence times are shortened 40% to 90%, whereas the vertical components are reduced by 20% to 60%. A metric to evaluate the quality of any ionospheric model for Global Navigation Satellite System is also proposed. The ionospheric modeling accuracy is directly translated to mass-market single-frequency
users. The 95th percentile of horizontal and vertical accuracies is shown to be 40 and 60 cm for single-frequency users and 9 and 16 cm for dual-frequency users. The tradeoff between the formal and actual positioning errors has been carefully studied to set realistic confidence levels to the corrections.
The scope of the proposal is to strengthen the interaction between the areas of education-research-industry in Europe, leveraging on past activities already undertaken in this field, in order to consolidate a strong EGNSS knowledge triangle, i.e. a solid network for the creation of a critical mass involving the relevant actors in the three areas with the final objective of supporting the European economy development.
The project approach is in line with the general policy of the H2020 programme, for the capacity building and critical mass creation in strategic areas, so to increase Europe competitiveness and attract investments from outside Europe. In GNSS this can only be realized by investing on a strong coordination between science and industry to fill the gap with respect to other areas of the world. Indeed the poor links between Industry and Research in Europe versus e.g. the US is permanently quoted as one of the reason of the constraints on innovation
With respect to previous projects in the field (ERIG, G-TRAIN, GENIUS), the focus will be more on the innovation transfer to the industry field, the support to the creation of innovative downstream applications and the consolidation of the links and of the initiatives beyond the project duration.
Rovira-Garcia, Adrià.; Juan, J.; Sanz, J. International Technical Meeting of the Satellite Division of the Institute of Navigation p. 2533-2543 Presentation's date: 2014-09-11 Presentation of work at congresses
The ionosphere plays an important role in satellite-based navigation, either in standard navigation, with single frequency mass-market receivers, or in precise navigation, with dual frequency receivers.
In this work, the requirements of a real-time ionospheric model suitable for GNSS applications are explored, in terms of accuracy and confidence bounds. Key factors for an ionospheric determination better than 1 Total Electron Content Unit (TECU) (16 centimeters in L1) are shown to be whether the model has been derived using an ambiguity-fixing strategy and the number of layers used to reproduce the ionospheric delay. Different models are assessed both in mid-latitudes and equatorial regions, near the Solar Cycle maximum.
It will be shown how dual-frequency users take benefit from a precise modelling of the ionosphere. If accurate enough, the convergence of the navigation filter is reduced to achieve high accuracy positioning quickly, (i.e., the Fast Precise Point Positioning technique). Satellite orbits and clocks computed for Fast-PPP will be shown to be accurate to few centimeters and few tenths of nanoseconds, respectively.
Single-frequency users correct its measurements with the predictions provided by any ionospheric model. Thence, the accuracy of the Fast-PPP ionospheric corrections is directly translated to the measurements modelling and, consequently, to the user solution.
Horizontal and vertical 95% accuracies are shown to be better than 36 and 63 centimeters for single-frequency users and 11 and 15 centimeters for dual-frequency users. The assessment is done for several locations, including the equatorial region, for a month of data close to the last Solar Maximum. The trade-off between the formal and actual positioning errors has been carefully studied by means of the Stanford plots to set realistic confidence bounds to the corrections.
Sanz, J.; Juan, J.; Gonzalez-Casado, G.; Prieto-Cerdeira, R.; Schlüter, S.; Orús, R. International Technical Meeting of the Satellite Division of the Institute of Navigation p. 1173-1182 Presentation's date: 2014 Presentation of work at congresses
This work introduces a novel ionospheric activity indicator useful for identifying disturbed periods affecting performance for GNSS users, at regional level. This indicator is based in the “Along Arc TEC Rate (AATR) and can be easily computed from GNSS data. The AATR indicator has been assessed over more than one Solar Cycle (2002-2013) involving 140 receivers distributed world-wide. Results show that it is well correlated with the ionospheric activity and, unlike other global indicators linked to the geomagnetic activity (i.e. DST, Ap), it is sensitive to regional behaviour the ionosphere and identifies specific effects on GNSS users. Moreover from a devoted analysis of EGNOS performances in different ionospheric conditions, it follows that the AATR indicator is able to predict SBAS user availability anomalies linked to the ionosphere. The AATR indicator has been chosen as the metric to characterise the ionosphere operational conditions in the frame of EGNOS activities. This indicator has been also proposed for joint analysis in the International SBAS-Ionosphere Working Group.
Juan, J.; Sanz, J.; Prieto-Cerdeira, R.; Schlueter, S. International Conference on Space, Aeronautical and Navigational Electronics p. 203-206 Presentation's date: 2013-12-03 Presentation of work at congresses
A SBAS Ionospheric Activity indicator, based in the RMS of Along Arc TEC Rate (AATR) computations has been defined by the gAGE/UPC authors in the context of previous studies on EGNOS Ionosphere. This indicator can be easily computed from GNSS data and, unlike other global indices which are related with the geomagnetic activity, it is sensible to the regional behaviour of the ionosphere.
After a deep assessment done over Europe and Africa during the last Solar Cycle, this AATR indicator has been chosen as the metric to characterise the ionospheric operational conditions in the frame of ESA EGNOS activities (EGNOS V3 Mission Requirements).
In this work we summarise the results of the application of the AATR indicator to the analysis of the ionospheric activity during an entire Solar Cycle in the South of Asia (SEA) Region. This region has special interest from the ionospheric point of view, because the larger Slant Total Electron Content (STEC) values and gradients experienced due to its proximity to the ionospheric equatorial anomaly.
Hernandez, M.; Aragon-Angel, M.A.; Defraigne, P.; Bergeot, N.; Prieto-Cerdeira, R.; Sanz, J. International Colloquium Scientific and Fundamental Aspects of the Galileo Programme p. 1-9 Presentation's date: 2013-12 Presentation of work at congresses
Blanch, E.; Altadill, D.; Torta, J. Miquel; Hernandez, M.; Juan, J.; Sanz, J.; Orús, R.; Prieto-Cerdeira, R. International Beacon Satellite Symposium p. 1 Presentation's date: 2013-07 Presentation of work at congresses
In this work, an ionospheric activity indicator is defined based in the “weighted” Along Arc TEC rate (AATR). It is shown that this indicator, which can be easily computed from the GPS carrier phases, is well correlated with the ionospheric activity and, unlike other global indicators linked to the geomagnetic activity, can be sensitive to regional behaviours of ionospheric activity
Hernandez, M.; Aragon-Angel, M.A.; Defraigne, P.; Bergeot, N.; Prieto-Cerdeira, R.; Sanz, J.; Garcia-Rigo, A. International Beacon Satellite Symposium p. 1 Presentation's date: 2013-07 Presentation of work at congresses
The significance of higher order ionospheric
terms (I2+) and the performance of
realistic mitigation strategies are analyzed. After confirming the unfeasibility of removing second order ionospheric term (I2) with combinations of actual data of three -
frequency measurements (in coincidence with the theoretical expectations), we focus on
the I2+ correction modelling from electron density and geomagnetic models, and empirical bending approximations.
Using realistic simulated GNSS global observations with actual geometry (by using the IRI2012 and IGRFv11 for electron density and geomagnetic field), the impact of I2+ on high precision GNSS processing has been
quantified by using independently the GIPSY and BERNESE software which provides equivalent results. The main general conclusion is that the modeling of I2+ (mainly in terms of I2, the predominant term at all the elevations, and bending corrections) can mitigate most of I2+ signature in GNSS precise geodetic products (receiver position, clock and zenith non - hydrostatic delays, satellite orbits and clocks, and geocenter estimate), which, otherwise can be significant from mm to cm level during solar cycle maximum conditions.
A similar conclusion can be extended consistently to Precise Point Positioning (PPP)