The transmitter for the QPSK signal has low power efficiency since the output power amplifier is operated in the linear region. The power efficiency can be improved by the method to combine a pair of PM signal which is amplified by the saturated amplifier. Three methods to generate a pair of PM signal are presented in this paper. The output spectra of these methods are almost the same in comparison with the linear amplifying system.
HDTV transmission is expected to be one of the most attractive services in future broadband ISDN. However, in ATM environments, new problems occur which do not exist in conventional STM networks. In this paper, a variable bit-rate HDTV codec for ATM networks and an ATM adaptation scheme are studied. Based on the study, an experimental HDTV codec has been realized and characteristics of variable bit-rate HDTV transmission using the codec and a pseudo ATM network were examined.
It is important that we research the rain attenuation in the 12GHz band used for Broadcasting Satellite when we design the circuits for broadcasting and communication. we have observed the attenuation on the roof at NHK Hiroshima Station since July, 1988,and classified this observation data for the period of one year from March, 1989 to February, 1990. In this paper, we analyze the correlation of the attenuation with the rain intensity, and that of the time lag with the cloud.