A helicopter-mounted communication apparatus encodes video data at a compression rate based on a percentage of time a transmission beam is blocked by rotor blades. When a number of video packets is less than a specified number, the helicopter-mounted communication apparatus inserts null packets to keep a packet rate constant, then deletes the null packets and attaches additional information to another packet indicating the number of deleted null packets, and after buffering modulates and transmits a signal toward a communication satellite at transmittable-time points. A terrestrial station communication apparatus receives and demodulates the transmitted signal via the communication satellite, generating a packet stream, and based on the additional information included in the generated packet stream, inserts null packets in the packet stream and buffers the packet stream, thereby keeping the packet rate constant, and then separates the video packets from the packet stream and decodes the separated video packets.