Frequency division multiplex system using comb filters

A frequency division duplexed transmission system comprising:

• first and second input signal channels;
• a first comb filter in each of said first and second input signal channels;
• the attenuation bands of said first comb filter in said first input signal channel coinciding with the pass bands of said first comb filter in said second input signal channel;
• combiner means for combing the outputs of said first and second input signal channels;
• means for applying the output of said combiner means to a transmission medium;
• means for receiving such combiner means output;
• first and second output signal channels, each having its input connected to the output of said receiving means;
• and
• a second comb filter in each of said first and second output signal channels, each said second comb filter having the same response characteristic as that of said first comb filter in a corresponding one of said first and second input signal channels, wherein said first and second comb filters each comprise a pair of n-stage delay positive and negative feed-forwarding circuits having complementary response characteristics, and wherein each stage of said delay positive feed-forward circuit comprises a delay unit for delaying an input signal, and an arithmetic unit for summing such delayed signal and undelayed input signal.

A frequency division duplexed transmission system comprising:

• first and second input signal channels;
• a first comb filter in each of said first and second input signal channels;
• the attenuation bands of said first comb filter in said first input signal channel coinciding with the pass bands of said first comb filter in said second input signal channel;
• combiner means for combing the outputs of said first and second input signal channels;
• means for applying the output of said combiner means to a transmission medium;
• means for receiving such combiner means output;
• first and second output signal channels, each having its input connected to the output of said receiving means;
• and
• a second comb filter in each of said first and second output signal channels, each said second comb filter having the same response characteristic as that of said first comb filter in a corresponding one of said first and second input signal channels, wherein said first and second comb filters each comprise a pair of n-stage delay positive and negative feed-forward circuits having complementary response characteristics, and wherein each stage of said delay negative feed-forward circuit comprises a delay unit for delaying an input signal, and an arithmetic unit for subtracting such delayed signal from the undelayed input signal.

A transmitter for transmitting a comb frequency division multiplex signal, comprising:

• first and second input signal channels, each including means for converting applied analog signals into digital signals;
• digital filter means provided in each of said first and second input signal channels for processing said digital signals, said digital filter means having a comb signal characteristic, the attenuation bands of said digital filter means in said first input signal channel coinciding with the pass bands of said digital filter means in said second input signal channel;
• means for converting each of said processed digital signals into analog signals;
• analog filter means for filtering each of said analog signals;
• means for combining the outputs of said analog filter means;
• and
• means for applying said combined signals to a transmission medium;
• said digital filter means comprising a pair of nonrecursive digital filters of the tapped-delay-line type.

A receiver for receiving a comb frequency division multiplex signal, comprising:

• means for receiving a comb frequency division multiplex signal;
• first and second signal channels, each having its input connected to the output of said receiving means and including means for converting applied analog signals into digital signals;
• digital filter means provided in each of said first and second signal channels for processing said digital signals, said digital filter means having a comb signal characteristic, the attenuation bands of said digital filter means in said first signal channel coinciding with the pass bands of said digital filter means in said second signal channel;
• means provided in each of said first and second signal channels for converting said processed digital signals into analog signals;
• and
• analog filter means provided in each of said first and second signal channels for filtering said analog signals;
• said digital filter means comprising a pair of nonrecursive digital filters of the tapped-delay-line type.