Design of LEO Navigation Signal System Based on Variable Period Spread Spectrum Code

Abstract

AbstractIt is an important development direction to take advantage of low-earth-orbit (LEO) satellites to establish a LEO satellite navigation system as a supplement to Global Navigation Satellite Systems (GNSSs) in the future. The movement speed of LEO satellites is very fast, which leads to a significant and fast change in the Doppler frequency of LEO navigation signals. At the same time, due to the large number of LEO satellites, the number of signals that need to be searched increases greatly. If the LEO navigation signal still adopts the traditional Code Division Multiple Access (CDMA) technology, it will bring high computational complexity to the acquisition of LEO navigation signals, resulting in a great increase in acquisition time. Therefore, according to the high landing power of LEO navigation signals, a novel navigation signal system based on variable period spread spectrum code is proposed to realize the rapid acquisition of LEO navigation signal, which is named by Variable Period Code Division Multiple Access (VP-CDMA) technology. In this technology, different LEO satellites broadcast navigation signals generated by different spread spectrum codes with different periods. The receiver carries out delayed autocorrelation on the received navigation signals, and current satellite numbers can be acquired by the interval of correlation peaks, which means it does not need to search all satellites in turn. The simulation results show that compared with CDMA, VP-CDMA technology can significantly reduce the acquisition complexity and shorten the acquisition time to P/M (here M is the number of all satellites, P is the number of current visible satellites). There is a high application prospect for VP-CDMA in future LEO navigation systems.KeywordsGNSSLEO navigationSignal acquisitionDelayed correlation