RTK-GPS positioning by TV audio-MPX-data broadcast in Japan

Abstract

RTK-GPS is a satellite positioning system which provides instant and accurate positions. The ranging error to the satellite from a user GPS antenna determined by the phase measurement of the carrier waves from the GPS satellites is of the order of mms. Thus an accuracy of a few cm can be easily obtained. The system is easier to operate than a traditional survey system such as the ‘Total Station’. Hence it has been used for many applications in Japan. It is necessary, however, to provide a fast data communication link for the transmission of carrier phase data from a reference station located at a known position, to a user receiver. A radio communication device with low power, is commonly used because it requires no license. However the data transmission area is generally limited to just several hundred meters in radius from the reference station. The authors have investigated RTK-GPS positioning with several different lengths of baseline using data transmission via TV audio-MPX-data broadcast, and evaluated its validity. The carrier phase data is transmitted from the reference receiver at the Tokyo University of Mercantile Marine, to the experimental station of the Asahi National Broadcasting Company, by public phone line with data rate 9,600 bps. The data, which when multiplexed into TV audio, was then disseminated with the rate of about 8 kbps from the Tokyo Tower. The data transmission delay in this system appeared random between 0.740 and 1.317 s, of which the difference (0.577 s) corresponds to the transmission time of 32 blocks of multiplexed data. Positioning was tried at several fixed points with different lengths of baseline (0–21 km). Tests proved that the accuracy became worse as the length of baselines became longer. The 2drms height are less than the 2.5 cm, and ‘Fix’ solution success rates are more than 98%, for shorter baselines less than 10 km in length.