Adaptive CDMA scheme as a rain fade countermeasure in Ka-band geosynchronous satellite communications

To achieve high link availability at Ka-band geosynchronous satellite communication systems, an adaptive CDMA scheme as a rain fade countermeasure is proposed. The proposed adaptive CDMA scheme reserves and shares orthogonal sequences to countermeasure a rain fade. In the adaptive CDMA scheme, the base station allocates a set of orthogonal sequences to each user, and the number of sequences in a set is determined by the amount of rain attenuation. A symbol repetition technique is also used to compensate signal energy loss due to the rain fade. Our results show that when the base station has 64 free orthogonal codes, the adaptive CDMA scheme can save on its power by 4.2 dB compared to conventional CDMA scheme. The occupation rate of codes also shows that the adaptive CDMA can support multiple users simultaneously in even severe rain fade condition.