IMO WORLDWIDE RADIONAVIGATION SYSTEM (WWRNS) Study on Communication Techniques for High Accuracy DGPS in the Republic of Korea

Transcription

1 INTERNATIONAL MARITIME ORGANIZATION E IMO SUB-COMMITTEE ON SAFETY OF NAVIGATION 52nd session Agenda item 12 NAV 52/INF.8 12 May 2006 ENGLISH ONLY WORLDWIDE RADIONAVIGATION SYSTEM (WWRNS) Study on Communication Techniques for High Accuracy DGPS in the Republic of Korea Submitted by the Republic of Korea SUMMARY Executive summary: This document provides information regarding nationwide DGPS to provide a high positioning service Action to be taken: Paragraph 4 Related documents: None 1 Currently, GPS is one of the most widely used positioning systems. The Republic of Korea provides more accurate positioning system for seafarers sailing along the coast of the Republic of Korea with the DGPS (differential GPS). 2 The attached study result is aimed to design the data acquisition system of the Republic of Korea NDGPS (Nationwide DGPS) so as to provide a high positioning service and to find the best optimized GNSS (Global Navigation Satellite System) data transfer format and transmission media. 3 This study will contribute to maritime safety by enhancing accurate positioning. Action requested of the Sub-Committee 4 The Sub-Committee is invited to note the information provided (DGPS). *** For reasons of economy, this document is printed in a limited number. Delegates are kindly asked to bring their copies to meetings and not to request additional copies.

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3 A STUDY ON COMMUNICATION TECHNIQUE FOR HIGH ACCURACY DGPS IN THE REPUBLIC OF KOREA 1.0 INTRODUCTION The objectives of this study are to plan the data acquisition system of the MOMAF (Ministry of Maritime Affairs and Fisheries) NDGPS (Nationwide Differential GPS) to provide a high positioning service and to find the best optimized GNSS (Global Navigation Satellite System) data transfer format and transmission media. The reference stations and monitoring stations of MOMAF NDGPS are providing a real-time DGPS service via beacon transmitters for the safe maritime. To provide an in-land GNSS high positioning service, three in-land reference stations are constructed and three more stations are planned. Currently positioning of few meters is maintained when the real-time data provided by the MOMAF NDGPS reference station is used. However, end should carry a specific beacon receiver to use the correction data. Also, the practical application of this system is limited. MOMAF is on track to improve and construct a GPS reference station network to expand the effectiveness of this system, to create various applicable areas, and to provide a high quality GPS data. MOMAF, KORDI (Korea Ocean Research and Development Institute) and KASI (Korea Astronomy and Space Science Institute) Space Geodesy Research Group suggested several real-time data acquisition methods for the MOMAF NDGPS reference stations and data processing system. Also KASI team investigated a feasible data transfer formats compatible with the international standard and available data transmission media to lay a stone for an independent high NDGPS system. 2.0 FORMAT AND MEDIA REVIEW AND TEST RESULTS 2.1 Data Standard Format for the Application of HA-DGPS! DGPS Standard Format (RTCM SC-104)! RTCM 3.0 format to support DGNSS NMEA (National Marine Electronics Association) and RTCM (Radio Technical Commission for Maritime Service) are widely used for the GPS data transfer standard. RTCM 3.0 format was released to response to DGNSS (Differential GNSS) on February of This RTCM 3.0 format was developed to improve and update the capability of previous version. RTCM 3.0 has several messages for the RTK (Real-Time Kinematic) applications. Also, RTCM 3.0 supports the new GPS operation (L2C, L5) as well as the GLONASS and future Galileo operations. Table 2.1 show the characteristic difference between RTCM 2.3 and 3.0 versions.

4 Page 2 Table 2.1 Characteristic Analysis of Message Type of RTCM Format RTCM Message Size, Bytes, Ver.Survey where n is #satellite n=6 1 GPS Correction 2.3 DGPS 60 3 GPS Ref. Station 2.3 DGPS GLONASS Correction 2.3 DGPS 60 18/20 RTK Carrier Phases 2.3 RTK 75 19/21 RTK Pseudoranges 2.3 RTK Extended Ref. Station 2.3 RTK SAPOS 2.3 VRS GPS Observation L1 3.0 RTK Extended GPS Obs. L1/L2 3.0 RTK Ref. Station with Antenna 3.0 RTK Antenna and Ser. Number 3.0 RTK Data broadcasting Method! FM DARC (FM DAta Radio Channel)! WiBro (Wireless Broadband)! DMB (Digital Multimedia Broadcasting) Table 2.2 describes the current status of KASI and MOMAF networks and broadcasting service providers. And Table 2.3 shows the brief descriptions of current available broadcasting media and its services. Table 2.2 Existing equipments and necessary equipment in each institute MOMAF KASI Service Provider 9 GPS permanent obs. site MOMAF Beacon 22 GPS permanent obs. IGS GDC system site Existing Intranet + Internet FM Broadcasting DGPS Network Equipments Trimble t-dmb system Intranet NetRS s-dmb system Trimble 4000 fast internet WiBro to be ready connection Equipment to be acquired R&D real-time data Intranet or Internet connection Data server Analysis and process Integrated Data server server Integrated data providing server Real-time fast Internet connection Real-time data transfer data analysis data processing correction data providing fast internet connection if needed Data compression technique or packet technology

5 NAV 52/INF.8 Page 3 Table 2.3 Existing equipments and necessary equipment in available broadcasting media media Beacon Beacon 2 FM DARC t-dmb s-dmb WiBro Transfer 200 bps 1 Kbps 16Kbps 300Kbps 300Kbps 1Mbps rate broadcast broadcast broadcast broadcast broadcast internet observation observation observation stations observation observation stations station observation Existing DGPS stations stations FM local stations system network DGPS WiBro broadcasting DMB Tu-media Beacon network ISP station provider transmitter Necessary equipment upgrading equipments real-time data network data analysis MOMAF Data management & Analysis Projected ship, a few receiver, difficult to find new new beacon transmitter real-time real-time data network data data network analysis data analysis MOMAF & Brodcasting station Data centre & Analysis centre car customer low profile t-dmb + customer s-dmb + MOMAF & ISP Data centre & Analysis centre car customer customer low profile low profile low profile Economical Has Has Has limited limited limited impact potential potential potential R&D period 3 yr 3 yr 3 yr 3 yr 3yr 3yr 2.3 Real-time GPS Data Acquisition Large number of GNSS receiver can handle the RTCM-104 correction messages and RTK receivers use the RTK messages. These messages can be received or relayed to end-s by various transmission media. The adaptation of the wireless internet creates a new horizon to DGNSS end-s and service providers. A new data transfer format based on HTTP is standardized and helps the connection directly between relay hosts and PC, laptop, PDA, GSM phone, GPRS, EDGE, UMTS via IP networks. It was named as Ntrip and under control of TCP/IP rules.

6 Page Application of Ntrip (Networked Transport of RTCM via Internet Protocol) Real-time GPS Data Acquisition Test After preliminary check of MOMAF central satellite office in Daejeon, KASI team configured a real-time GPS data acquisition system. The physical system was installed in Muju in-land reference station by using an industrial rated networkable PC with NtripServerWindow and NtripClient software. 3.0 CONCLUSIONS 3.1 Application of Standard Data Transfer Format The characteristics and the information transfer rules of RTCM SC-104 format as a DGPS service standard, are investigated and reviewd. The type of each data message, the additional information, and several formats are considered. The RTCM 3.0 is reviewed as a DGNSS service standard considering the introduction of a new satellite system and request from service s. RTCM 3.0 consists of messages mainly for the real-time application, and is designed for the additional signals of L2C and L5 and especially for the integration of the European Galileo system. This standard will be applied to the future Korean HA-DGPS data transfer format. Table 3.1 shows the RTCM message types for the GPS applications. Table 3.1 RTCM Message Types Message Type Message Contents Message applications DGPS Beacon HA-DGPS 1 Differential GPS Corrections 3 Reference Station Parameters 5 GPS Constellation Health 7 DGPS Radiobeacon almanacs 9 GPS Partial Correction Set 16 GPS Special Message 18 RTK Uncorrected Carrier Phases 19 RTK Uncorrected Pseudorange 3.2 Analysis and the Application of DGPS Data transfer method Current DGPS systems help the improvement of positioning by using WAAS, FM DARC, Beacon transmission, wireless internet, and radio modem. These systems are providing only correction information, thus are not restricted to the data transmission speed. However, in case of the HA-DGPS all of the observation data should be transmitted. So, it depends on the size of data and the speed of transmission. Thus, several practical data transmission methods for a high positioning service are suggested with an excellent data transfer quality. First, FM DARC which can provide any information data through existing FM broadcasting system is chosen. Second, WiBro has a high data transmission rate by using high speed wireless internet. Third, HSDPA has a high speed mobile capability with relatively high speed transmission rate. At last, satellite-dmb and terrestrial-dmb launched on late 2005 can be considered as a data transmission media of HA-DGPS.

7 Page 5 Each data transmission method has its advantages and disadvantages. We plan to use it as an ideal data transmission system in the future. Figure 3.1 shows a feasible data route to use the s-dmb system. 3.3 Application of a Real-time GPS data acquisition plan There are several ways to receive the correction data from a GPS reference station by the purpose of use. Currently most countries including Korea use a dedicated data line to use the real-time data application. The dedicated data line does not have transfer speed due to its one-toone connection but has high cost problem. To overcome this disadvantage, using Ntrip or RTIGSA softwares via internet is good alternative. These two program can control the data flow in real-time through internet. Ntrip is designed to collect and distribute the GNSS data over the internet. We established a real-time data transfer system by using Ntrip software at the Muju in-land reference satellite station office operated by MOMAF. We have successfully run several real-time data receiving experiments of GPS data from Muju by using a data server in KASI. Also we tested the connection by accessing KASI server from Muju with the NtripClient software. The real-time data acquisition method via the internet becomes an international standard. Thus its will be applied to the MOMAF NDGPS reference stations connected to the internet and will be used to download the GPS data in real-time. 3.4 Application of a National GPS Data Sharing System Strategy Sharing and integrating the GPS data from different institutes with different purposes can take important roles in the filed of data management and application. International institute operating a network of GPS permanent observation stations tends to integrate and manage their local networks to expand the scope of service like application area, global aeronomy (ironospher, troposphere) research, low Earth orbit satellite application etc. In this study, we provide the methods of data sharing for real-time application and post-processing case. In the case of data sharing via internet, we suggest the use Ntrip software with the necessary equipment at the local GPS reference stations. With this data integration system strategy MOMAF NDGPS reference station network and KASI reference network can be managed as an integated network to expand the application area and to increase the effectiveness.