A study of the communication systems using the low-altitude nongeostationary satellites

Satellite communication systems with low-altitude orbits are considered. In low-altitude orbital satellite communication systems, signals suffer a larger Doppler shift. The effects of the shift are examined from the viewpoint of carrier recovery and multiple access schemes. Some typical features of the systems for relatively small service area are also shown. The necessity of intersatellite link for domestic continuous service has been confirmed by numerical examples. The receiver with phase-locked loop (PLL) is found to be available only for wideband signal systems, and a receiver with a block demodulator is proposed for relatively narrow signals. It is shown that code division multiple access (CDMA) systems can provide greater capacity than frequency division multiple access (FDMA) for Doppler shifted signals