The GNSS(Global Navigation Satellite System) is the worldwide navigation system that could be got the fix, the timing and so on by using the electric wave emitted from the artificial satellite at the altitude of 25,000 km. The United States has developed GPS(Global Positioning System) since 1970's, it expressed the completion of the whole world navigation system officially in July, 1995. This system has the 3-dimensional coverage wherever can be covering on the earth, so it is used widely of the world.
In the recently, the GPS is related to the ordinary life like as the navigation field, military field, communication field and the traffic field, etc. It will be expected to play an important role in the forthcoming ubiquitous era.
It was made clear that GPS services are susceptible to various types of interference, and those effects of these vulnerabilities on the applications. GPS was augmented to satisfy the various requirements for accuracy, coverage, availability, continuity and integrity. Differential GPS service provides increased accuracy and integrity of the GPS using land-based reference stations that transmit correction messages. And there are also the satellite-based GPS augmentation systems, such as WAAS, EGNOS and MSAS.
Ministry of Maritime Affairs and Fisheries of Korea has established and operated the land-based 11 DGPS stations along the coast in order to ensure the maritime traffic safety, according to the recommendation of IALA(International Association of Marine Aids to Navigation and Lighthouse Authorities) and IMO(International Maritime Organization). These DGPS stations are transmitting the correction messages(within 2m) with medium wave frequency(283.5~325㎑) that the transmission power is 300W. Its coverages are 185km of the coastal sea area of the country. Also the correction messages are transmitted from the neighboring countries, and they could get to our coastal area and interfere with our signals.
The research on the effect of mutual interference among the neighboring countries has not carried out. In the study, the condition of mutual interference was grasped and the countermeasures of it are proposed. Calculations of signal strength for DGPS stations have been carried out by using the Millington Method which is widely applied in analyzing for the medium wave characteristics. And the field data emitted from DGPS stations have been measured on the sea. The comparative analysis between the calculated results and field data has carried out and verified with coincidence.
In order to grasp the effect where the DGPS signals of the neighboring countries act on our waters, the simulations which use the medium wave characteristics have been carried out on the basis of verified data. It was known that the effective coverage of C DGPS station in China penetrated into our western coast near by Sochungdo, and the effective coverages of H and W DGPS station in Japan penetrated into our southern coast near by Youngdo.
Actually, it may raise the problem that the foreign signals with big error will be able to receive in our coast. It can cause not only the loss of reliability on positioning accuracy but also the confusion of security on state of emergency.
In the future, the result of the study will become the scientific ground data which prepares national countermeasures for foreign DGPS signal interference. Also, it may be properly used national countermeasure materials in FERNS(Far East Radio Navigation Service) Conference established to promote cooperation in operating radio navigation aids among Korea, China Japan and Russia.