In this paper, we developed the Realtime Ship Position Information System and the software in relation to the system, which consists of the on-board system and the shore-based system. The on-board system is composed a GPS receiver, a computer, and a modem. The shore-based system is composed of a telephone, a modem and a computer. Both systems are operated by the data communication program The system displays automatically the ship's movement on the digital chart by using the ship's position acquired by a GPS receiver via INMARSAT-A communication system. The results presented in many experiments indicate that the system in processing the position data well during the transmission and reception.

This paper is concerned with the experimental analysis of EOW(End-of-Week) rollover. The GPS EOW Rollover happens every 20 years. Because GPS time, counted in weeks, started counting Jan. 6, 1980, the GPS week will rollover from week 1023 to 0000 at midnight between Aug. 21 and 22. This is significant because it is the first EOW rollover since the GPS constellation was established and it could be interpreted as an invalid date in receivers that were not designed to meet GPS specification. We analyzed GPS data of the noncompliant receivers and the compliant receiver. It was concluded that all receivers had not serious problems during or after the rollover.

On this paper, the traditional methods for the measurement of ship's maneuverabilities during the sea-trial of newly built ship are summarized and new methods for the same measurement using Integrated Navigation System and GPS are introduced. After various sea-trials of training ship "HANNARA" which are equipped with modern INS and GPS system, the results are compared and analysed. The purpose of this paper is to present more accurate methods of measurement of ship's maneuverabilities during sea-trial using INS and GPS which are gradually becoming the basic navigational equipments on many newly constructed vessels.d vessels.

This study describes the accuracies of position fixes observed by the DGPS systems for the purpose of obtaining the utility basic data in the fishery and oceanography observation field. The circling sail experiments around a reterence point using the DGPS were made in water level point of National Fisheries University of Pusan and on the sea in Yongho day located on the southeast of that university. The main results are as follows ; 1) The number of the usable satellites in position fixing were all eighteen, SV 2, 3, 11-21, 23-26 and SV 28 etc. Each satellites could be observed for average seven hours a day, and position fixing was found to be always possible except about thirty minutes a day. 2) In the standard fixed position, the radius of 95% probability circle and the shifted distance between the position fixes by the DGPS and true position were respectively 5.7m, 0.9m. In the above case those of ordinary GPS was respectively 48.8, 54.2m. Therefore, the accuracy of the position fixes by DGPS was shown much higher the ordinary GPS. 3) At land, the shifted distance between the center of traces in the circling sail experiment of 15m ra-dius by DGPS and the reference position amounted to 5.5m and observed radius of circling traces was 17.5m. other than 15m. At sea, that distance the center of traces in circling experiment of 20m radius by the DGPS and the reference position amounted to 3.6m and observed radius of circling traces was 19.7m, other than 20m. Therefore, the utility of the circling experiment to obtain the accurate position fixes by the DGPS was found to be very high.

The NAVSTAR/GPS is a satellite-based navigation system that will provide extremely accurate three-dimensional position and velocity information to users anywhere on or near the earth. This system has been studied primarly for military use and thus the results of studies are seldom obtainable for civilian use up to date. Expecting this system to be opened to civilian use in the future, this paper aims to the collection of basic data of the PN phase modulated communication system adopted in the GPS system by computer simulation. The results of studies are as follows; 1) The PN phase modulation of the speed of 106b/s can be simulated by Fourier summation, the spectrum region which can be restricted is in the region of 0.5-1.5 MHz and spectrum number required is over than 270. 2) By computer simulation, it is verified that optimum r.f filter bandwidth is about 0.3 MHz for the case of 106b/s PN codes phase modulated in 1.575GHz carrier. 3) In case that PN rate to data rate is between 10 and 100, the allowable minimum SNR to demodulate data signal correctly by optimum LPF is about 0.3. It is also verified that the larger the frequency ratio of PN code to the data code, the lower the allowable minimum SNR required.

In this paper, author studied on the elementary data required for the design of the receiver of Pseudo Noise (PN) phase modulation communication adopted in Global Positioning System(GPS). By computer simulation technique, the phase modulator, filters, and PN generator are designed, and also required bandwidth of R-F amplifier for carrier frequency in phase modulation system is investigated. It is verified that the optimum bandwidth is about 3 times of the PN frequency and almost independent of the carrier frequency. And the low pass filter required for demodulation of slow Boolean data is also found to be about 60 times of the data signal frequency.