To provide interactivity, a public wireless packet data network is combined with a broadband digital broadcast network. In the preferred embodiment, the broadcast network utilizes multiple transmitters at separately located sites simultaneously broadcasting the same multi-channel, multi-program ...http://www.google.com.tw/patents/US5729549?utm_source=gb-gplus-share專利 US5729549 - Simulcasting digital video programs for broadcast and interactive services 
