The effect of long multipath on digital transmission

When transmitting compressed digital video and audio over both cable and wireless systems, adaptive equalization is used to compensate for the intersymbol interference caused by multipath in the transmission channel. However, in some cases the echoes encountered in the transmission medium can exceed the length of the adaptive equalizer. This is most likely to occur in MMDS environments which employ beam benders since these can produce relatively severe multipath at some receive sites. When an echo exceeds the range of the equalizer, adaptive equalization is no longer effective and the burden of compensation for long multipath must fall upon the digital demodulator's error correction. This paper presents the results of studies on 64QAM transmission.