Experimental evaluation of synchronized SS-CDMA transmission timing control method for QZSS short message communication

We have already proposed synchronized spread spectrum code division multiple access (SS-CDMA) for the Quasi-Zenith Satellite System (QZSS) safety confirmation system to be used in times of great disaster. In this system, the satellite reception timings of all uplink signals are synchronized using a transmission timing control method in order to realize high-density user multiple access. An issue that should be addressed in order for this system to be viable is the error that can occur in the satellite reception timing. This error occurs due to the terminal time deviation and the error in calculating the propagation delay to the satellite. In this paper, we measure the terminal time deviation and the propagation delay calculation error at the same time by using the same receivers and evaluate the satellite reception timing error of the uplink signal. By this measurement, it is shown that satellite reception timing error within 50 ns can be realized in 99.98% of mobile terminals. This shows that the synchronized SS-CDMA with the transmission timing control method has a potential to realize the QZSS short message system with high-density user multiple access.