By T. M. Straus, Hughes Aircraft Company
The advantages of digitized compressed video are particularly relevant to microwave transmission in that such formats permit transmission of many more than the maximum 79 channels which otherwise could be carried in the 500 MHz wide 13 GHz CARS band. A further advantage is the potential for significantly increased microwave fade margin when digitized video is utilized in place of analog VSBAM. Since under normal propagation conditions the noise contribution of AML is only a very small portion of the overall CATV system noise, the focus here must be on the performance of the digital modulation scheme under faded conditions. Transmission of the QPSK Skypix signal through AML systems has already been successfully demonstrated. Considerations relating to the carriage of higher level modulation formats such as 16 QAM through existing AML systems are explored. In this regard, the differences between CATV systems utilizing channelized transmitters and block conversion transmitters are analyzed.