Network RTK GNSS Quality Assessment Yiming Quan, Xiaolin Meng, Lei Yang, and Scott Stephenson Nottingham Geospatial Institute, The University of Nottingham, UK mail: xiaolin.meng@nottingham.ac.uk Abstract Network RTK (Real-Time Kinematic) is a technology that is based on GNSS (Global Navigation Satellite System) providing centimetre- level accuracy positioning in real-time by making use of observations from multiple Continuously Operating Reference Stations (CORS) to precisely model local errors. The objective of this paper is to assess the quality of Network RTK with a specific attention towards the correction dissemination processes. A series of static tests have been conducted using Leica SmartNet and Nottinghan Geospatial Insitution (NGI) testbed server under Master Auxiliary Concept (MAC). The results present a satisfactory performance of Network RTK with over 90% availability and millimetre accuracy of Easting and Northing, but centimetre accuracy of Height. Three types of unexpected correction messages (message duplication, emptiness, and loss) were found and concretely analysed in relevant experiments, indicating that overload of server may be the causal factor. BIOGRAPHIES Xiaolin Meng is Associate Professor, Theme Leader for Positioning and Navigation Technologies, and MSc Course Director for GNSST & PNT at the Nottingham Geospatial Institute of the University of Nottingham. Dr Meng’s main research interests include ubiquitous positioning, location based services, intelligent transportation systems and services, network real-time kinematic GNSS positioning, etc. He is author of more than 200 papers and founding Director of the Sino-UK Geospatial Engineering Centre. He also holds a few Professorships in renowned academic organisations in China. Yiming Quan received a BEng degree from the University of Nottingham in 2012. This paper is based on his undergraduate dissertation. He is now a PhD candidate at the Horizon Doctoral Training Centre of University of Nottingham. His current research interest is concerned with Multi-Constellation Integration. Lei Yang is a Research Fellow at the Nottingham Geospatial Institute, The University of Nottingham. He attained his PhD degree in Department of Electrical and Electronic Engineering from the same university in 2006. Scott Stephenson is a PhD student at the Nottingham Geospatial Institute within the University of Nottingham. He holds a BSc degree in Surveying and Mapping Science from the University of Newcastle-Upon-Tyne. After completing his degree, he was a Senior Engineering Surveyor working in the UK. Scott’s postgraduate research is sponsored by MIRA Ltd through an EPSRC CASE studentship. I. INTRODUCTION Currently Network RTK (Real-Time Kinematic) technology is increasingly being used for its high accuracy, operational feasibility, and commercial viability. In the UK, a network of more than 100 reference stations is operated by the Ordnance Survey. These networked reference stations provide nationwide GNSS correction services with centimetre-level positioning accuracy achieved in real-time. It serves various applications including surveying and mapping, construction, Intelligent Transport System (ITS), precision agriculture, and fisheries. Also, Network RTK for the upcoming positioning systems such as Galileo, GPS L5C, and GLONASS CDMA, is being developed and will be brought into operation in future. Although it is widely recognized that Network RTK has been commercialized and will continue to bring about a profitable business, relevant quality control issues are vitally important for the implementation of this technology. Many previous researches indicate that Network RTK, particularly for commercialized application like Leica SmartNet, can achieve a centimetre-level accuracy [1], [2]. The factors influencing Network RTK solution have been identified and studied. Meng et al, quoted by Aponte et al. [3], considered the factors like accessibility of satellite signals, deployed Continuously Operating Reference Stations (CORS), and stability of correction message dissemination would directly influence the quality of Network RTK solutions. Furthermore, Aponte et al. [3] looked into several key parameters, demonstrating that a low number of satellites in view, high HDOP and VDOP, and a high Age of Correction (AoC) can result in an obvious accuracy degradation. While the importance of correction transmission has been recognized, there are still few researches thoroughly looking into the issues in transmission processes of correction messages. This paper will study relevant quality issue raised in Network RTK positioning with an emphasis placed on the corrections dissemination. With the access to the