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Abstract

A drop-and-add multiplexer for receiving an incoming FDM signal with a plurality of channels, for receiving signals of additional channels, and for outputting an outgoing FDM signal. The multiplexer includes at least one single channel filter for receiving an incoming FDM signal, filtering the incoming FDM signal by blocking a selected channel frequency, and outputting a filtered FDM signal. At least one interpolating digital frequency converter receives another channel signal which is not in the incoming FDM signal, converts the other channel signal into a channel frequency which has been blocked by the at least one single channel filter or was an empty channel frequency in the incoming FDM signal, and outputs a converted other channel signal. At least one digital frequency converter is provided and includes a cascade connection of a decimating digital frequency converter and an interpolating digital frequency converter, for receiving the incoming FDM signal, frequency-converting a selected channel from an input frequency to a different outgoing frequency, and outputting a frequency-converted channel signal. An adder adds the converted other channel signal output by the interpolating digital frequency converter, the filtered FDM signal output by the single channel filter, and the frequency-converted channel signal output by the digital frequency converter, and outputs an outgoing FDM signal.

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First Claim