Renato Filjar

Location-Based Services: A Road Towards Situation Awareness

With the widespread use of mobile devices and increased demand for mobile services , Location - Based - Services (LBS) represent a promising addition to service offerings of net-work operators as well as third - party service providers.Based on long-term research in LBS , our group has proposed a generic Enhanced LBS Reference Model (ELRM) , which describes the concept , the architecture and the functionalities of the LBS.In addition , an evolutionary information process has been identified within the LBS, that represents knowledge maturity from posotion awareness to situation awareness.Both the ELRM and the information evolution process in LBS are presented in this article and illustrated by a case study within the framework of the 3GPP-standardised IP Multimedia Subsystem (IMS).This case-study emphasises the opportunities for navigation and LBS related solutions development provided by modern telecommunication technologies.

The role of telecommunications in development of new-generation Intelligent Transport Systems

Transport is one of the pillars of modern society, and as such, exposed to growing demands for efficiency, security, reliability, cost-effectiveness and care for environment. Solution for satisfaction of all above-mentioned demands is generally seen in multi-layered infrastructure usually referred to as the Intelligent Transportation System (ITS). ITS is a result of synergy between several existing technological components, integrated through carefully suited process in order to reach solution for general transport control and transport information services provision.

Distributed positioning: a network-supported method for satellite positioning performance improvement

Recent studies show that basic satellite positioning is reaching its limits in terms of performance improvements. Further enhancements in positioning performance can be based almost entirely on augmentation and procedures supported by other systems. Considering the complexity of the interrelationship with additional systems, intrinsically different solutions are being developed to solve the positioning performance improvement problem. Here we present a new concept in positioning. Dubbed distributed positioning, it merges basic satellite positioning with advanced and assisted positioning procedures. The resulting complex synergy unavoidably includes the use of additional technologies in mobile communications, wireless Internet, and advanced computer systems. The real advantage from the introduction of distributed positioning lies in its capability to provide a significant improvement in overall positioning performance. Latest navigation status and up-to-date local environment models are much easier to apply on rover positioning, compared with classical assisted-GPS positioning procedures. Distributed positioning presents a completely different approach in positioning performance improvement, opening new prospects in research and development not only in the field of the satellite positioning, but also in telecommunications and computer engineering.

A Study Of Direct Severe Space Weather Effects On GPS Ionospheric Delay

Severe space weather conditions affect the performance of numerous modern technical systems, causing problems not only for national and global economies, but for everyday life as well. Satellite navigation systems are particularly vulnerable, despite the fact that systematic monitoring of space weather in general is still performed on a global scale. Space weather effect correction models applied within the standard satellite positioning service are not capable of tackling the effects of severe space weather conditions and local ionospheric characteristics. Severe space weather effects on the GPS ionospheric delay are intensely studied in order to provide advanced models of the space weather effects on GPS positioning performance. Here one study of severe space weather conditions and its consequences on the GPS ionospheric delay in Croatia is presented. The study takes advantage of the availability of the space weather indices and the GPS pseudorange measurements (taken at the reference site at Osijek, Croatia) related to a major severe space weather event lasting from early October 2003 to late November 2003. This paper presents the reconstruction of the severe space weather conditions and the development of ionospheric disturbances. Based on these reconstructions, the dynamics of the GPS ionospheric delay has been derived. The comparison of actual (measured) and modelled (according to standard GPS model) GPS ionospheric delay has been performed, with the aims of identifying actual behaviour of GPS ionospheric delay and examining the ability of standard (Klobuchar) GPS model to describe the GPS ionospheric delay in severe space weather conditions. Two interesting experimental models derived from the data analysis are presented, addressing the direct relations between the GPS ionospheric delay and the parameters of space weather activity (sunspot number and solar flux), as observed at the reference station Osijek, Croatia. The paper concludes with the plans for further research activities related to the regional GPS ionospheric delay model development for south-eastern Europe.

Assisted satellite positioning

Although standard satellite positioning provides unbeatable performance, compared with other available positioning methods it still suffers from many environment-related issues. One of them is disruption of continuity of positioning service, usually caused by temporal inability to collect navigation data due to poor satellite visibility. This problem is particularly noticeable in urban areas, where high buildings often considerably decrease the satellite visibility. A number of GPS-based systems and services (among them the location-based services - LBS) rely upon continuous provision of satellite positioning service. In order to decrease as much as possible the time to first fix (TTFF) after temporal unavailability of standard positioning service, auxiliary communications systems deploy the functionality of assistance data provision to satellite positioning receiver. This article examines the content of satellite positioning assistance, the impact of assistance data on position estimate calculation algorithm and the means for assistance data distribution. Special emphasis is given on satellite positioning assistance for LBS, and the mechanisms for assistance data delivery through the mobile communication network are presented. In conclusion, assistance data are identified as the major contributor to satellite positioning performance improvement, with a brief list of related future activities given

Satellite Positioning for LBS: A Zagreb Field Positioning Performance Study

Recent studies confirm the importance of satellite positioning in location-based services (LBS) development. A field study was conducted in suburban and rural areas near Zagreb, Croatia in order to examine the real-time data compliance with recently established positioning performance requirements for LBS quality of service (QoS). Data analysis was based on comparison between actual positioning performance and pre-specified positioning parameter values using defined comparative procedures. The results presented here confirm a good correlation between the actual and required positioning performance, even without implementation of any of augmentation or assistance positioning methods.

The Role of Position Reporting Frequency in LBS QoS Establishment

Position reporting frequency (PRF) is among the main parameters that determine the quality of service (QoS) of location-based services (LBS). Well established PRF provides scalable location awareness for the LBS subject in question. The best description of particular objects location would be obtained if he/she/it were reporting the positioning in very small steps. However, this would soon overburden the network with mostly unnecessary traffic. In order to overcome the limitations of an ideal reporting scheme and preserve acceptable level of location awareness quality, the PRF requirements should be optimised in relation to both available resources and solution performance. This paper addresses a case-related approach for PRF requirements establishment. Three LBS solution paradigms has been chosen for an analysis aimed to yield PRF requirements parameters. PRF parameters have been identified as applicable for a general guidance in more detailed definition of PRF for location-based services

Differential Satellite Positioning Accuracy for LBS: A Zagreb Case Study

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 LBS positioning accuracy obtained by differential satellite positioning is discussed, 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 differential GPS positioning still does not lead to satisfaction of the high-level LBS positioning performance requirements, it still improves and stabilises standard-level LBS positioning accuracy

Horizontal GPS positioning accuracy during the 1999 solar eclipse

Although GPS positioning errors are now well described, there are still some uncertainties regarding the impact of some rare space weather phenomena on GPS positioning accuracy. Solar eclipses have been considered as one source of such rare events, so the 1999 solar eclipse gave the opportunity to collect horizontal GPS positioning data for further analysis. The results of statistical analysis show no deterioration of horizontal GPS positioning accuracy. Space weather, ionospheric and geomagnetic conditions were also carefully analysed and showed no significant activity. In conclusion, the experiment confirmed negligible impact of the 1999 solar eclipse on horizontal GPS positioning accuracy, and opens discussion concerning application of satellite positioning systems in space and ionospheric weather monitoring.

An Experimental Identification of Multipath Effect in GPS Positioning Error

The analysis of the GPS multipath effects in maritime environment is constrained with the practice of traditional GPS receiver design, that prevents access to GPS signals in Base‐band Processing Domain. Here we propose and validate a simple method for experimental identification of multipath effect in Navigation Processing Domain, based on spectral characterisation of time series of GPS positioning errors. http://www.transnav.eu the International Journal on Marine Navigation and Safety of Sea Transportation Volume 12