Testing a Real Time Kinematic Service System Using FM DARC for the Nationwide DGPS Network in Korea

Transcription

1 Testing a Real Time Kinematic Service System Using FM DARC for the Nationwide Network in Korea Jong-Uk Park 1, Jeong-Ho Joh, Hyung-Chul Lim, and Pil-Ho Park Korea Astronomy Observatory, 61-1, Whaam, Taejon, South Korea, jupark@kao.re.kr 1 SangWoon Lee, and WooSung Jeon Munhwa Broadcasting Co. Ltd., 31 Yoido, Youngdungpo, Seoul, South Korea, & SeungChul Bang Bway Co. Ltd., #302 Yeyang Bldg., Yoksam, Kangnam, Seoul, South Korea, BIOGRAPHY Dr. Jong-Uk Park is a Senior Research Staff at the GPS Research Group of Korea Astronomy Observatory and a lecturer at the department of Astronomy & Space Science of ChungNam National University, Korea. He holds a B. Sc. and M. Sc. in Astronomy, and a Ph. D. in Astronomy & Space Science from Yonsei University. His current research interests are the development of GPS network for high precision GPS positioning and its application systems. Mr. Jeong-Ho Joh is a Senior Research Staff at the GPS Research Group of Korea Astronomy Observatory. He holds a B. Sc. in ChungNam University and M. Sc. in Space Science from Yonsei University, Korea. His area of expertise is the data processing and analysis of GPS tropospheric path delay. Mr. Hyung-Chul Lim is a Research Staff at the GPS Research Group of Korea Astronomy Observatory from He holds a B. Sc. and M. Sc. in Astronomy from Yonsei University, Korea. Mr. Pil-Ho Park is a manager at the GPS Research Group of Korea Astronomy Observatory. He holds a B. Sc. and M. Sc. in Astronomy & Space Science from Yonsei University in Korea, and in a Ph.D. Degree course at same university from His area of expertise is the research of geodynamics and geodesy using GPS. He is now a Korean representative of IGS (International GPS Service) as an associate member. Mr. SangWoon Lee is a Project Manager at the Technical R&D Center of MunHwa Broadcasting Corp. Seoul, Korea. He holds a B.Sc. and M. Sc. in Communication Systems from Yonsei Univ. Korea, and in a Ph.D. Degree course at the same University. His area of expertise is the development of Data/ITS/ transmission system using FM and Digital Broadcasting Network. He is a member of ISO TC 204 WG 10. Mr. WooSung Jeon is a director at the Technical R&D Center of MunHwa Broadcasting Corp. Seoul, Korea. He holds a B.Sc. in electronics from the Kwang woon Univ. and a M.Sc. in communication systems from Yonsei Univ. His main research interests are in DTV, DAB, and Data Broadcasting System. Mr. SeungChul Bang is the President of Bway co., Ltd. Seoul, Korea. He graduated at DanKook Univ. Korea. His area of expertise is semiconductor design for FM subcarrier receiver. He had participated in the development of RDS and DARC Decoder.

2 ABSTRACT In past few years several GPS networks have been established for the multiple purposes of real-time & post-time applications in Korea. Most of these networks are operated by national governments agencies, including the Korea Astronomy Observatory (KAO), Ministry Of Government Administration and Home Affairs (MOGAHA), National Geography Institute (NGI), and Ministry Of Maritime Affairs and Fisheries (MOMAF). Totally, 60 Continuously Operating Reference Stations (CORS), including two IGS sites (DAEJ & SUWN), are installed by above-mentioned agencies and the site locations are well distributed to cover the whole country. The inter-station spacing ranges from 20 to less than 50 km by location adjustment and the GPS council starts to make the nationwide network by connecting each network. The cost-effective candidate to transfer Differential GPS () and Real-Time Kinematic (RTK) data of the nationwide GPS network is to use FM sub-carrier. At the 2nd, Dec. 1999, Munhwa Broadcasting Corp. (MBC), one of the major broadcasting company in Korea, started to broadcast the data provided from KAO s GPS network (7 CORSs) via FM DAta Radio Channel (DARC). The user purchased a dedicated FM receiver can use the reference data freely. The coverage area is 70% of population, including six major cities in South Korea, and will be expanded to the nationwide in the near future. In order to check the availability and performance of FM DARC system for the nationwide RTK service in Korea, MBC started to broadcast the RTK data of KAO s reference station in Seoul. The optimal data transmission standard in DARC format should be designed to minimize bandwidth considering the transmission capacity of FM DARC (16 Kbps). In addition, it is very useful to support the RTK manufacturer s standard such as the Compact Measurement Record (CMR) format of Trimble. Therefore, DARC/RTK format is designed to represent three satellites in a triple of DARC packets (61 bytes) and to decode both the RTCM SC-104 format (Message Type 18/19) and the CMR format at a receiver unit. It is more than CMR format by 30%, but is less than RTCM SC-104 format by 44% in the case of 8 SV, L1/L2, and code/phase data validity. This paper describes the status of nationwide network and the RTK service system using FM DARC in Korea. The preliminary results of field tests are presented. INTRODUCTION In past few years several GPS networks have been established for the multiple purposes of real-time & post-time applications in Korea. Most of these networks are operated by national governments agencies, including the Korea Astronomy Observatory (KAO), Ministry Of Government Administration and Home Affairs (MOGAHA), National Geography Institute (NGI), and Ministry Of Maritime Affairs and Fisheries (MOMAF). At the end of 2000, totally 60 Continuously Operating Reference Stations (CORS), including two IGS sites (DAEJ & SUWN), had been installed for providing the reference data to the user group of Geodesy, Positional Astronomy, Surveying, Navigation, and the GPS-related applications. In recent, the GPS council of Korea started to make the nationwide network by connecting each network. The Munhwa Broadcasting Corp. (MBC), one of the major broadcasting companies in Korea, started to broadcast the data with other information using FM DARC (DAta Radio Channel) on the 2nd, Dec.

3 1999. The EYEDIO (EYE radio), the nickname of FM DARC system operated by MBC, broadcasts now the data provided by KAO s 7 stations. At the end of last year, MBC expanded the coverage area to the 70% of population, including six major cities in Korea. This service will cover the nationwide area in the second half of In order to check the availability and performance of DARC system for the nationwide RTK service, MBC start ed to broadcast the RTK data of KAO s reference station in Seoul. This service system will start to broadcast the nationwide RTK data in the near future. NATIONWIDE NETWORK IN KOREA As shown in figure 1, The inter-station spacing ranges from 20 to less than 50 km inland and the site locations are well distributed to cover the whole country. Each of the CORS has the same design except two IGS sites. The unmanned reference station is equipped with a dual-frequency GPS receiver, a choke-ring antenna, communication units, and a control system for the electric power and the temperature in the special shelter within a GPS tower. Most of the CORSs use a Trimble Navigation Ltd. 12 channel, dual-frequency 4000SSi TM geodetic surveyor as a reference receiver. The reference station receives and processes signals from visible GPS satellites and sends the observation raw-data to the GPS data center of each network in real-time or post-time. From early 1999, several GPS networks have been established for the multiple purposes of real-time & post-time applications in Korea. At the end of 2000, totally 60 Continuously Operating Reference Stations (CORS), including two IGS sites (DAEJ & SUWN), had been installed by the national governments agencies (Figure 1). Recently, the GPS council of Korea started to make the nationwide network by connecting each network. Figure 2 shows the basic concept of the nationwide network of Korea. It consists of the several GPS networks, a center for nationwide network (CFND), a GPS solution provider, and communication link systems as shown in figure 2. GPS Networks Center for National Communication Link Applications Control Center Control Center Broadcast LAN Frame-Relay Dedicated Line ISDN/PSTN Reference Interface Inverted Solution Terminal Interface Network Adjustment Reference Monitoring Data Managing Virtual Reference System GSP Interface GSP Interface Post Processed Solution GPS Solution Provider Real-Time User Interface Interface Radio Beacon DARC DAB Mobile Phone Internet Mobile Phone Internet Real-Time User Interface User Interface L1K R T K I Static Survey Pseudolite ITS, GIS CNS, PNS CNS, PNS Survey I GIS, LIS Science m dm cm m cm Figure 1. Coverage map of the nationwide network of Korea Figure 2. Basic concept of the nationwide Network of Korea.

4 The CFND of Korea has been designed to have following missions: reference data collection & management, network monitoring & adjustment, data distribution for real-time and post-time user group, communications with GPS solution provider, and system maintenance & monitoring. The Virtual Reference System (VRS) technique for the reliability & integrity improvement is included in the missions. provided by KAO s 7 stations. At the end of last year, MBC expanded the coverage area to the 70% of population, including six major cities in Korea. This service will cover the nationwide area in the second half of 2001 (Figure 3). FM DARC SYSTEM IN KOREA (EYEDIO) FM DARC is one of the powerful methods for broadcasting the digital data. FM stereo broadcasting is allowed to use 100 KHz baseband to transmit stereophonic signals, but it uses only 53 KHz bandwidth. Therefore, the redundant KHz band can be used for digital data or other stereophonic services. FM DARC use this redundancy band (76KHz) with the data transmission rate of 16 Kbps and the Level-controlled Minimum Shift Keying (LMSK) modulation scheme on stereophonic signal. Because of high transmitting power and optimal transmission post, FM broadcast has the excellent propagation characteristics and wide area coverage. In addition to these characteristics, FM broadcast has some advantages in providing the digital data such as no upper limit on the number of receivers, low cost receiver, and good quality for mobile reception. FM DARC is in commercial service in Japan, U.S., European countries but free of charge in Korea (Lee et. al., 1998). The Munhwa Broadcasting Corp. (MBC), one of the major broadcasting companies in Korea, started to broadcast the data with other information using FM DARC on the 2nd, December The EYEDIO (EYE radio), the nickname of FM DARC system operated by MBC, broadcasts now the data Figure 3. Service Area of EYEDIO (2001) In order to check the availability and performance of FM DARC system for the nationwide RTK service in Korea, MBC started to broadcast the RTK data of KAO s reference station in Seoul. The optimal data transmission standard in DARC format should be designed to minimize bandwidth considering the transmission capacity of FM DARC. Figure 4 shows the dedicated FM DARC receiver unit (PM-10) developed by Bway co., Korea. It is designed to receive the FM DARC signal ranges from 87.5 to 108 MHz with 100 KHz step. This powerful FM receiver module has the capability of receiving the EYEDIO data such as /RTK, traffic information, text, and others. It has a high sensitivity FM front end, a DARC decoder, and two serial ports in a single-board. Because of its compact size (35mm 35mm 5.5mm), this module can be used for car audio, Car Navigation

5 System (CNS) and Personal Navigation System (PNS). Figure 4. Dedicate FM DARC receiver unit /RTK SERVICE SYSTEM USING EYEDIO The RTCM Special Committee No. 104 (RTCM SC- 104) recommended the standards to transfer /RTK data and the link methods (RTCM, 1998). This standard provides the 64 messages related with differential GPS and addresses the communication link methods such as radio beacon and FM sub-carrier. The cost-effective candidate to transfer data of reference stations is to use FM DARC system. Figure 5 shows the configuration of DARC data packet (layer 2 & 3) in accordance with 7-layer reference model described in ITU-R Recommendation 807 (ITU, 1992). As shown in figure 5, FM DARC has the (272, 190) product code, and can be loaded 21 data bytes in each packet bits BIC1 Prefix Data Packet BIC2 Prefix Data Packet CRC Parity Figure 5. A configuration of DARC data packet KAO adopted the self-defined, compressed algorithm as data transmission format to provide the 11 satellites maximum in three packets (61 data bytes & 2 CRC bytes) for considering the data transfer capability and the performance of DARC system. This algorithm eliminates parity data that consists of 6 bits and a large framing overhead at the broadcasting unit. It is possible to encode the received data as RTCM SC-104 message format at a receiver unit. These procedures are capable because RTCM SC-104 formats was patterned after the GPS data format like as GPS word size, word format and parity algorithm (ARINC Research Corp., 1997). In the case of RTCM SC-104 format for 11 GPS satellites, it has to broadcast totally 105 bytes including the 21 parity bytes. The received data are converted to the RTCM SC-104 message types (1 & 2) at a dedicated FM receiver unit, and can be transferred to the users through the communication port The optimal data transmission standard for RTK using FM DARC should be designed to minimize bandwidth considering the transmission capacity of FM DARC (16.7 Kbps). In addition, it is very useful to support the RTK manufacturer s standard such as the Compact Measurement Record (CMR) format of Trimble. The data transmission format for RTK data using FM DARC is more complicated than the DARC/ case. Therefore, KAO designed the new DARC/RTK format to represent three satellites in a triple of DARC packets (61 bytes) and to decode both the RTCM SC-104 format (Message Type 18/19) and the CMR format at a receiver unit. It is more than CMR format by 30%, but is less than RTCM SC-104 format by 44% in the case of 8 SV, L1/L2, and code/phase data validity. The transmitted data format for one satellite in EYEDIO service is presented in table 1. It has the minimum requested data for converting to the message type 18/19 of RTCM-SC104 and the CMR format of Trimble.

6 Table 1. DARC/RTK data for one satellite Parameters Number of bits Satellite ID 5 L1 P/CA code flag 1 L1 Phase valid 1 L2 data included 1 L1 pseudorange 32 L1 carrier code 32 L1 Signal to Noise Ratio 4 L1 Cycleslip 8 L2 P/CA code flag 1 L2 Phase valid 1 L2-L1 pseudorange 13 L2-L1 carrier code 13 L2 Signal to Noise Ratio 4 L2 Cycleslip 8 Total 124 FIELD TESTS In order to compare the accuracy of positioning between link methods, we adopted the radio beacon service that is operated by the Ministry of Maritime Affairs and Fisheris (MOMAF), Korea. Each observations continued 5 minutes at 1-second sampling rate. The observed mask angle was set to 10. Table 2 and figure 6 show one of the testing results in static positioning. Table 2. Summary of statistics for test results. (a) (b) Methods 2D 2drms 3D GPS only 1.70 m 0.91 m 1.90 m DARC 0.18 m 0.12 m 0.25 m GPS only 1.65 m 0.77 m 1.93 m Beacon 0.77 m 0.13 m 1.07 m Baseline 4 km 200 km We carried out several field tests to check the accuracy and the reliability of /RTK service system using FM DARC. Trimble 4000SSi TM geodetic surveyor observed GPS signals with /RTK data received from DARC /RTK receiver unit. The high precision coordinates of selected posts were computed using GPSurvey TM (Trimble, 1996) with the code and On the behalf of turning off Selective Availability (SA) from May 2000, the accuracy of stand-alone GPS positioning can reach the meter level with high precision GPS receiver. However, positioning dramatically improves the positioning accuracy both FM DARC and radio beacon services as shown in table 2 and figure 6. carrier-phase data of reference stations. (a) (b) Figure 6 (a) & (b). A test results of static positioning with FM DARC and radio beacon

7 The results show the decimeter level accuracy of 2D and 3D from precise positions when using FM DARC/ service. Moreover, the 2drms values are less than 1 meter in both cases. Considering the long baseline of radio beacon site of MOMAF, it seems that the same positioning accuracy could be provided by radio beacon system. The results show that technique using FM DARC has a capability of providing the decimeter level positioning in static GPS application fields. Table 3 and figure 7 show the result of DARC/RTK static positioning. The centimeter level accuracy of 2D and 2drms values from precise positions can be achieved using the DARC/RTK service. In addition, 3D has the 12cm accuracy. This result shows the same positioning accuracy as general RTK positioning using the radio modem. Table 2. Summary of statistics for RTK test result. Methods 2D 2drms 3D GPS only m m m DARC/RTK m m m GPS vs. RTK When the DARC service system is applied to the /RTK applications, the delay time of broadcasting /RTK data is less than one second. The accuracy of positioning can be achieved to the decimeter level and centimeter level in /RTK cases in Korea. CONCLUSION & FUTURE WORK At the end of 2000, totally 60 CORSs had been installed by the national governments agencies in Korea. These networks provide the reference data to the user group of Geodesy, Positional Astronomy, Surveying, Navigation, and the GPS-related applications. For the purpose of improving the efficiency of GPS-related resources, the GPS council of Korea will organize the nationwide network by connecting each network in the near future. The Korea Astronomy Observatory is now providing the nationwide data using FM DARC system in Korea. This system broadcasts the data within one second to users and provides the decimeter level accuracy in the case of GPS static positioning. In addition, KAO is preparing to broadcast the RTK data for the nationwide area. At the end of 2001, when the RTK service system using FM DARC is in fully operational, KAO will support concurrently highprecision GPS positioning in both and RTK applications in Korea ACKNOWLEDGEMENTS The first author would like to express his sincere thanks 210 GPS RTK to the members of Bway Co. Ltd. for their efforts to the development of the dedicated FM DARC receiver and the field tests. Figure 7. A test result of DARC/RTK static positioning

8 REFERENCES ARINC Research Corporation, 1997, NAVSTAR GPS SPACE SEGMENT/ NAVIGATION USER INTERFACES, IRN-200C-002, Navtech Seminar & Navtech GPS Supply, VA, USA International Telecommunication Union, 1992, ITU-R BT Recommendation No Lee S. W., Jeon W. S. and Whang K. C., 1998, A Study On FM Sub-Carrier Broadcasting System for The Effective Transmission of Traffic and Data, Special Sessions of the 5 th World Congress on Intelligent Transportation System, Seoul, Korea. Radio Technical Commission for Maritime Services, 1998, RTCM Recommended Standards for Differential GNSS (Global Navigation Satellite System) Services Version 2.2, RTCM Special Committee No. 104, VA, USA. Trimble Navigation Limited, 1996, GPSurvey Software User s Guide, CA, USA.