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

RTK-GPS is a satellite positioning system which provides instant and accura te positions. The ranging error to the satellite from a user GPS antenna de termined by the phase measurement of the carrier waves from the GPS satelli tes is of the order of mms. Thus an accuracy of a few cm can be easily obta ined. 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 Ja pan. It is necessary, however, to provide a fast data communication link fo r the transmission of carrier phase data from a reference station located a t a known position, to a user receiver. A radio communication device with l ow power, is commonly used because it requires no license. However the data transmission area is generally limited to just several hundred meters in r adius from the reference station. The authors have investigated RTK-GPS pos itioning with several different lengths of baseline using data transmission via TV audio-MPX-data broadcast, and evaluated its validity. The carrier p hase data is transmitted from the reference receiver at the Tokyo Universit y of Mercantile Marine, to the experimental station of the Asahi National B roadcasting Company, by public phone line with data rate 9,600 bps. The dat a, which when multiplexed into TV audio, was then disseminated with the rat e 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 l ength 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 baseline s less than 10 km in length.