The invention relates to a
signal transmission method applicable to a
satellite communication
system, which belongs to the technical filed of mobile
satellite communication. The invention is characterized in that the method comprises the following steps: setting the down frequency from a
satellite transponder to a user terminal as f1, and setting the up frequency from the user terminal to the satellite
transponder as f2 which is different from f1; adopting a
time division multiplexing mode for distinguishing N different user groups by the satellite
transponder, wherein each
user group can contain a plurality of users; sequentially dividing a
down link frame into N time slots to be distributed to users of corresponding user groups to use; setting the time intervals beyond the time slots ofthe
down link frame occupied by the up link frame, and adopting a multiple access mode of CDMA or FDMA; after the up link frame to be transmitted to users positioned in f2 is received and processed by the satellite transponder, transmitting the up link frame to be transmitted to users to the user terminal in f1 at the corresponding time interval; and receiving the
down link frame corresponding part positioned in f1 by the user terminal at the corresponding time interval. When in use, a
time division switching switch realizes the switching between the receiving of the down link frame and the sending of the up link frame and the
signal insulation.