System stability of SS-CDMA location and short message communication using QZSS

Highly-dependable wireless communication using satellites has been getting much attention for emergency use. In order to achieve direct access between numerous personal terminals and satellite, we have proposed spread spectrum code division multiple access (SS-CDMA) communication system. It adopts long spreading code and high accuracy positioning signal from Quasi-Zenith Satellite System (QZSS). SS-CDMA has to provide the high reliable short message communication to several million terminals in limited time with limited frequency band. Thus high multiplexing rate CDMA in uplink is employed. Keeping orthogonality among all terminals using the QZSS positioning service is a fundamental requisite. However, terrestrial terminals do not always keep the suitable situation for positioning. In this paper, system stability is evaluated in the case of the part of terminals loses the orthogonality in time and frequency domain. We show transmit performance degradation in such case and reveal that the system stability can be kept.