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Modeling of Ionospheric Delay for SBAS Using Spherical Harmonics Functions

Han D., Yun H., Kee C.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2013

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Vol. 7, no. 2

205--209

EN

In SBAS (satellite‐based augmentation system), it is important to estimate ionospheric delay accurately to guarantee userʹs accuracy and integrity. Grid based ionospheric models are generally used to estimate ionospheric delay for SBAS. In grid based model, SBAS broadcasts vertical ionospheric delays at the grid point, and users get their ionospheric delay by interpolating those values. Ionospheric model based on spherical harmonics function is another method to estimate ionospheric delay. This is a function based approach and spherical harmonics function is a 2‐D fourier series, containing the product of latitude dependent associated Legendre functions and the sum of the longitude dependent sine and cosine terms. Using ionospheric delay measurements, coefficients for each spherical harmonics functions are estimated. If these coefficients are known, user can reconstruct ionospheric delay. In this paper, we consider the spherical harmonics based model and propose a ionospheric delay estimation strategy for SBAS that can be used to mitigate ionospheric delay estimation error, especially in storm condition. First, coefficients are estimated under initial order and degree. Then residual errors for each measurement are modeled by higher order and degree terms, then coefficients for these terms are estimated. Because SBAS message capacity is limited, in normal condition, initial order terms are only used to estimate ionospheric delay. If ionospheric storm is detected and there is need to mitigate the error, higher order terms are also used and error can be decreased. To compare the accuracy of spherical harmonics based model with grid based model, some post‐processing test results are presented. Raw observation data is obtained from RINEX format and the root mean square(RMS) and max value of residual errors are presented.

2

Korean WA-DGNSS User Segment Software Design

Shah S. T., Choi W.S., Han W.Y., Yun H., Kee C.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2013

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Vol. 7, no. 1

69--74

EN

Korean WA‐DGNSS is a large scale research project funded by Ministry of Land, Transport and Maritime Affairs Korea. It aims to augment the Global Navigation Satellite System by broadcasting additional signals from geostationary satellites and providing differential correction messages and integrity data for the GNSS satellites. The project is being carried out by a consortium of universities and research institutes. The research team at Electronics and Telecommunications Research Institute is involved in design and development of data processing softwares for wide area reference station and user segment. This paper focuses on user segment software design. Korean WA‐DGNSS user segment software is designed to perform several functions such as calculation of pseudorange, ionosphere and troposphere delays, application of fast and slow correction messages, and data verification. It is based on a layered architecture that provides a model to develop flexible and reusable software and is divided into several independent, interchangeable and reusable components to reduce complexity and maintenance cost. The current version is designed to collect and process GPS and WADGNSS data however it is flexible to accommodate future GNSS systems such as GLONASS and Galileo.

3

Flexible Software Design for Korean WA-DGNSS Reference Station

Choi W.S., Chhattan S.S., Kye J.E., Han W.Y., Yun H., Kee C.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2013

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Vol. 7, no. 1

75--78

EN

In this paper, we describe the software design results of WA‐DGNSS reference station that will be constructed in Korea in the near future. Software design of the WRS (Wide area Reference Station) is carried out by applying object oriented software methodology in order to provide flexibilities: easy of model change (namely ionospheric delay model etc) and system addition (Galileo, GLONASS in addition to GPS etc). Software design results include the use case diagrams for the functions to be executed, the architecture diagram showing components and their relationships, the activity diagrams of behaviors and models among them, and class diagrams describing the attribute and operation.