Novel Satellite Digital Video TDMA System for Business Video Communications

This paper proposes an integrated satellite digital video (ISDV) time division multiple access (TDMA) system for business video communications which employs only one transponder for video and backward voice signal transmission and allows multipoint-to-(multi) point video signal transmission. The proposed system employs a demand-assignment TDMA scheme for various bit-rate video signal transmissions and a superposed code division multiple access (CDMA) transmission scheme for voice transmission to establish both-way voice communication channels for economized video conferences which employ only one transponder for full system implementation with one/two way video and both-way voice channels. More-over, the employment of a rate seven-eighth convolutional encoding and Viterbi decoding as forward error correction (FEC) coupled with a QPSK modulation scheme for digital video transmission enables us to reduce the required protection ratio for cochannel interference by more than 10 dB and the proposed system has far less restriction on radio frequency choice. Furthermore, the employment of a rate one-half convolutional encoding and Viterbi decoding for CDMA signal transmission and the development of a cochannel interference cancelation technique have made it possible to transmit CDMA signals over high-power and high-speed QPSK-modulated digital video signals which are transmitted and nonlinearly amplified in the same transponder. The performance of the proposed system has been experimentally evaluated and the results show the proposed scheme can transmit about 20 CDMA voice channels simultaneously. The proposed system can employ only 100 mW solid-state amplifiers for voice signal transmission for video-signal-reception-only earth stations to have both-way voice communication capability and video signals can be transmitted from various locations.