Investigating multi-GNSS performance in the UK and China based on a zero-baseline measurement approach

GPS is the positioning tool of choice for a wide variety of applications where accurate (cm level or less) positions are required. However GPS is susceptible to a variety of errors that degrade both the quality of the position solution and the availability of these solutions. The contribution of additional observations from other GNSS systems may improve the quality of the positioning solution. This study investigates the contribution of the GLONASS and BeiDou systems and the potential improvement to the precision achieved compared to positioning using GPS only measurements. Furthermore, it is investigated whether the combination of the satellite systems can limit the noise level of the GPS-only solution. A series of zero-baseline measurements, of 1 Hz sampling rate, were recorded with different types of pairs of receivers over 12 consecutive days in the UK and in China simultaneously. The novel part in this study is comparing the simultaneous GNSS real measurements recorded in the UK and China. Moreover, the correlation between the geometry and positional precision was investigated. The results indicate an improvement in a multi-GNSS combined solution compared to the GPS-only solution, especially when the GPS-only solution derives from weak satellite geometry, or the GPS-only solution is not available. Furthermore, all the outliers due to poor satellite coverage with the individual solutions are limited and their precision is improved, agreeing also with the improvement in the mean of the GDOP, i.e. the mean GDOP was improved from 3.0 for the GPS only solution to 1.8 for the combined solution. However, the combined positioning did not show significant positional improvement when GPS has a good geometry and availability

Review of code and phase biases in multi-GNSS positioning

A review of the research conducted until present on the subject of Global Navigation Satellite System (GNSS) hardware-induced phase and code biases is here provided. Biases in GNSS positioning occur because of imperfections and/or physical limitations in the GNSS hardware. The biases are a result of small delays between events that ideally should be simultaneous in the transmission of the signal from a satellite or in the reception of the signal in a GNSS receiver. Consequently, these biases will also be present in the GNSS code and phase measurements and may there affect the accuracy of positions and other quantities derived from the observations. For instance, biases affect the ability to resolve the integer ambiguities in Precise Point Positioning (PPP), and in relative carrier phase positioning when measurements from multiple GNSSs are used. In addition, code biases affect ionospheric modeling when the Total Electron Content is estimated from GNSS measurements. The paper illustrates how satellite phase biases inhibit the resolution of the phase ambiguity to an integer in PPP, while receiver phase biases affect multi-GNSS positioning. It is also discussed how biases in the receiver channels affect relative GLONASS positioning with baselines of mixed receiver types. In addition, the importance of code biases between signals modulated onto different carriers as is required for modeling the ionosphere from GNSS measurements is discussed. The origin of biases is discussed along with their effect on GNSS positioning, and descriptions of how biases can be estimated or in other ways handled in the positioning process are provided.QC 20170922</p

Agent-Based Modeling of the Hajj Rituals with the Possible Spread of COVID-19

With the coronavirus (COVID-19) pandemic continuing to spread around the globe, there is an unprecedented need to develop different approaches to containing the pandemic from spreading further. One particular case of importance is mass-gathering events. Mass-gathering events have been shown to exhibit the possibility to be superspreader events; as such, the adoption of effective control strategies by policymakers is essential to curb the spread of the pandemic. This paper deals with modeling the possible spread of COVID-19 in the Hajj, the world’s largest religious gathering. We present an agent-based model (ABM) for two rituals of the Hajj: Tawaf and Ramy al-Jamarat. The model aims to investigate the effect of two control measures: buffers and face masks. We couple these control measures with a third control measure that can be adopted by policymakers, which is limiting the capacity of each ritual. Our findings show the impact of each control measure on the curbing of the spread of COVID-19 under the different crowd dynamics induced by the constraints of each ritual

Embedding the Dimensions of Sustainability into City Information Modelling

The purpose of this paper is to address the functions of sustainability dimensions in city information modelling and to present the required sustainability criteria that support establishing a sustainable planning framework for enhancing existing cities and developing future smart cities. The paper is divided into two sections. The first section is based on the examination of a wide and extensive array of cross-disciplinary literature in the last decade and a half to conceptualize the terms ‘sustainable’ and ‘smart city’, and map their associated criteria to city information modelling. The second section is based on analyzing two approaches relating to city information modelling, namely statistical and dynamic approaches, and their suitability in the development of cities’ action plans. The paper argues that the use of statistical approaches to embed sustainability dimensions in city information modelling have limited value. Despite the popularity of such approaches in addressing other dimensions like utility and service management in development and action plans of the world cities, these approaches are unable to address the dynamics across various city sectors with regards to economic, environmental and social criteria. The paper suggests an integrative dynamic and cross-disciplinary planning approach to embedding sustainability dimensions in city information modelling frameworks. Such an approach will pave the way towards optimal planning and implementation of priority actions of projects and investments. The approach can be used to achieve three main goals: (1) better development and action plans for world cities (2) serve the development of an integrative dynamic and cross-disciplinary framework that incorporates economic, environmental and social sustainability criteria and (3) address areas that require further attention in the development of future sustainable and smart cities. The paper presents an innovative approach for city information modelling and a well-argued, balanced hierarchy of sustainability criteria that can contribute to an area of research which is still in its infancy in terms of development and management

An enhanced calibration method of GLONASS inter-channel bias for GNSS RTK

A user of heterogeneous GPS and GLONASS receiver pairs in differential positioning mode will experience ambiguity fixing challenges due to the presence of inter-channel biases. These biases cannot be canceled by differencing GLONASS observations, whether pseudorange or carrier phase. Fortunately, pre-calibration of GLONASS pseudorange and carrier phase observations can make ambiguity fixing for GPS/GLONASS positioning much easier. We propose an effective algorithm that transforms an RTK (real-time kinematic) solution in a mixed receiver baseline from a float to a fixed ambiguity solution. Carrier phase and code inter-channel biases are estimated from a zero baseline. Then, GLONASS both carrier phase and code observations are corrected accordingly. The results show that a mixed baseline can be transformed from a float (~100 %) to a fixed (more than 92 %) solution

Proc 5th Int. Navigation Conference – Melaha 2010

This paper aims to investigate variousfunctional models of the Ordinary Kriging(OK) technique in order to preciselyestimate epoch-by-epoch atmosphericcorrections for real-time kinematic (RTK)positioning. A network of ContinuouslyOperating Reference Stations (CORS) inNew South Wales (NSW), known asCORSnet-NSW, is utilised to: 1) obtainatmospheric residuals per referencestation, 2) construct an empiricalvariogram over the network, 3) determineKriging parameters for three differentmodels: a spherical-, an exponential-, anda Gaussian model; and 4) optimise theatmospheric corrections for RTK users.Applying the atmospheric correctionsbased on the Kriging functional models,“synthetic” measurements at a givenvirtual reference station (VRS) aregenerated and used for RTK positioning. Atest with a 21km baseline VRS-RTKindicates that less than 2cm of horizontalerrors (1 sigma) and 7cm of vertical errors(1 sigma) are achieved. This isapproximately a 33% improvement whencompared with the results fromcommercially available software packages.This study has demonstrated the usefulnessof a number of OK functional modelswhere ionospheric and tropospheric delayssignificantly degrade the positioningquality

ION GNSS 2011 : 24th International Technical Meeting of the Satellite Division of the Institute of Navigation 2011

As it is anticipated that the full operational capability of GLONASS will be achieved in the very near future, GLONASS is now attracting surveyors’ attention, with questions being asked on how much improved accuracy can be obtained if GPS and GLONASS were used together. Such a performance assessment has been undertaken in the past; however, most of the tests were conducted with a limited number of available (at the time) GLONASS satellites. It is timely to re-assess the performance because most networks of continuously operating reference stations (CORS) are now equipped with receivers that can track both GPS and GLONASS satellites, and therefore network-based positioning with combined GPS and GLONASS observations is possible. This paper compares the network-based positioning results with GPS measurements only versus the use of combined GPS and GLONASS measurements, under various sky view conditions. The benefit of adding GLONASS measurements to GPS measurements is more obvious when a limited number of satellites are available due to the fact that sky view is partially blocked. Comparing the GPS-only solution with the GPS+GLONASS solution, the accuracy improves by approximately 2mm and 3mm in the 2-dimensional and 3-dimensional coordinates, respectively. However, the combined solution shows its clear advantage when GLONASS-only solutions are considered

Proc 23rd Int. Tech. Meeting of the Satellite Division of the U.S. Inst. of Navigation

This investigates various functional models ofthe Ordinary Kriging technique, applied toprecisely estimate epoch-by-epochatmospheric corrections for real-timekinematic positioning. A network ofContinuously Operating Reference Stations inNew South Wales, known as CORSnet-NSW,is utilised to: 1) obtain atmospheric residualsfor each reference station, 2) construct anempirical variogram over the network, 3)determine Kriging parameters for threedifferent models: a spherical-, an exponential-,and a gaussian model; and 4) optimise theatmospheric corrections for real-timekinematic positioning.Applying the atmospheric corrections obtainedby the Ordinary Kriging functional models,“synthetic” measurements at a virtualreference station are generated and used forreal-time kinematic positioning. Field testswith baselines ranging from 21km to 62kmindicate that 1.9cm up to 4.4cm of horizontalaccuracy (1 sigma) is achieved. Results showapproximately 53% or higher improvementwhen compared with the results fromcommercially available software packages.This study has demonstrated the usefulness ofa number of Ordinary Kriging functionalmodels where ionospheric and troposphericdelays significantly degrade the positioningquality

Addressing some remaining challenges of integrated high precision GPS/GLONASS positioning

The multi-GNSS era is attracting more attention with the declaration of full operational capability of the Russian Federation's GLONASS, with 24 satellites being declared &#145;healthy&#146; on December 8th 2011. This brings benefits for GNSS users in areas where the number of visible satellites is limited because of shadowing effects (e.g. &#145;urban canyon&#146; environments or in deep open cut mines). In such areas adding more functioning satellites, which is one possible aiding solutions, becomes an attractive option. The inclusion of GLONASS observations in positioning solutions will increase the available number of satellites and thus positioning accuracy may improve as a result of enhanced overall satellite geometry. However, adding GLONASS observations to GPS solutions is not a straight forward process. This is attributable to differences in signal structures. One of the challenges is that relative receiver clock errors cannot cancel as in the case of GPS-only observation modelling. Several approaches have been suggested to address this challenge, which can be grouped into two main classes: receiver clock error estimation or receiver clock error elimination. Approaches used to address the relative receiver clock error modelling challenge for high accuracy users in static and kinematic modes have been compared and evaluated. Several data quality measures were used to compare the different processing strategies. The influence of system selection on ambiguity resolution was assessed using some of the commonly used measures for ambiguity validation. A user of heterogeneous GPS and GLONASS receiver pairs in differential positioning mode will experience ambiguity fixing challenges due to the presence of inter-channel biases. These biases cannot be cancelled by differencing GLONASS observations, either pseudorange or carrier phase measurements. Fortunately, pre-calibration of GLONASS pseudorange and carrier phase observations can make ambiguity fixing for integrated GPS/GLONASS positioning much easier. An effective algorithm which transforms an RTK (real-time kinematic) solution in a mixed receiver baseline from a &#145;float&#146; to a &#145;fixed&#146; ambiguity solution has been proposed. Another challenge for high precision GPS and GLONASS surveying and navigation techniques is that the baseline between two receivers (distance between the reference station, known coordinates, and the user station, required coordinates) is typically constrained to short ranges (<10-20km). This adversely impacts on RTK productivity. Fortunately this limitation has been addressed by the so-called Network-based RTK (NRTK) techniques. Comprehensive investigation of several approaches to implementing NRTK techniques, which requires the estimation of atmospheric corrections on an epoch-by-epoch basis,, has been carried out in order to identify the optimal method for mitigating atmospheric effects for real-time kinematic applications for different network geometries. Most networks of continuously operating reference stations (CORS) are now equipped with receivers that can track both GPS and GLONASS satellites and, therefore, it is common for a CORS network having to support heterogeneous user receivers. As a result, users of such networks will face ambiguity fixing challenges in mixed receiver scenarios when both GNSS systems are used for positioning. In this study, data from the CORSnet-NSW network located in the Sydney region, Australia, were used to examine and validate the proposed GPS and GLONASS Network RTK algorithm for mixed baselines. It has been demonstrated that the pre-calibration of both GLONASS carrier phase and pseudorange observations can assist NRTK users seeking cm-level positioning accuracy by improving the success rate of GPS/GLONASS ambiguity fixing