Modem communication system having main and secondary channels
First Claim
1. A data modem communication system comprising;
- a transmission medium having a main data channel whereon data signals are transmitted at a relatively high bit rate and a secondary data channel whereon data signals are transmitted at a relatively low bit rate;
modem transmitter means coupled to said transmission medium for transmitting data signals on said transmission medium;
a remote modem receiver means coupled to said transmission medium and including a main channel receiver and a secondary channel receiver for receiving the same data signals transmitted over the transmission medium;
first filter means coupled to said main channel receiver and second filter means coupled to said secondary channel receiver for suppressing the main channel data signals by processing samples of the data signals a number of times; and
an analog-to-digital converter coupled to said transmission medium and having an output connected to said first filter means which is adapted to suppress the secondary channel data signals in said main channel receiver, said analog-to-digital converter further having an output coupled to said second filter means, wherein said second filter means includes a low-pass digital filter adapted to process samples of the data signals in said secondary channel receiver at successively decreasing sample rates.
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Abstract
A data modem communication system includes a data modem transmitter adapted to transmit data on a main channel at a relatively high bit rate and to transmit data at a relatively low bit rate on a secondary channel. At the receiver, a single analog-to-digital converter (54) supplies digital signals via a notch filter (58) to the main channel receiver (60) and to the secondary channel receiver (62) wherein a single IIR low-pass digital filter (110) is utilized for processing at three different sample rates to eliminate the main channel signal with frequency conversion taking place between processing at the first and second sample rates. The invention enables the provision of a reliable secondary channel while using a minimum amount of circuitry for complex-valued digital signal processing.
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Citations
10 Claims
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1. A data modem communication system comprising;
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a transmission medium having a main data channel whereon data signals are transmitted at a relatively high bit rate and a secondary data channel whereon data signals are transmitted at a relatively low bit rate; modem transmitter means coupled to said transmission medium for transmitting data signals on said transmission medium; a remote modem receiver means coupled to said transmission medium and including a main channel receiver and a secondary channel receiver for receiving the same data signals transmitted over the transmission medium; first filter means coupled to said main channel receiver and second filter means coupled to said secondary channel receiver for suppressing the main channel data signals by processing samples of the data signals a number of times; and an analog-to-digital converter coupled to said transmission medium and having an output connected to said first filter means which is adapted to suppress the secondary channel data signals in said main channel receiver, said analog-to-digital converter further having an output coupled to said second filter means, wherein said second filter means includes a low-pass digital filter adapted to process samples of the data signals in said secondary channel receiver at successively decreasing sample rates. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A data modem communication system comprising;
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a transmission medium having a main data channel whereon data is transmitted at a relatively high bit rate and a secondary data channel whereon data is transmitted at a relatively low bit rate; modem transmitter means coupled to said transmission medium for transmitting data on said transmission medium; modem receiver means coupled to said transmission medium and including a main channel receiver and a secondary channel receiver; first filter means coupled to said main channel receiver and second filter means coupled to said secondary channel receiver; an analog-to-digital converter coupled to said transmission medium and having an output connected to said first filter means which is adapted to suppress signals in said main channel receiver, said analog-to-digital converter further having an output coupled to said second filter means, wherein said second filter means includes a low-pass digital filter adapted to process signal samples at successively decreasing sample rates; and a frequency converter coupled to said secondary channel receiver connected to the output of said low-pass digital filter whereby, after processing at a first one of said sample rates, said digital filter output is subject to a frequency conversion in said frequency converter to effect a negative frequency shift, prior to effecting processing at a second one of said sample rates. - View Dependent Claims (8)
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9. A data modem communication system comprising;
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a transmission medium having a main data channel whereon data is transmitted at a relatively high bit rate and a secondary data channel whereon data is transmitted at a relatively low bit rate; modem transmitter means coupled to said transmission medium for transmitting data on said transmission medium; modem receiver means coupled to said transmission medium and including a main channel receiver and a secondary channel receiver; first filter means coupled to said main channel receiver and second filter means coupled to said secondary channel receiver; an analog-to-digital converter coupled to said transmission medium and having an output connected to said first filter means which is adapted to suppress signals in said main channel receiver, said analog-to-digital converter further having an output coupled to said second filter means, wherein said second filter means includes a low-pass digital filter adapted to process signal samples at successively decreasing sample rates; and detector means connected to an output of said second filter means, said detector means including first and second correlators adapted to determined the correlation with respect to first and second predetermined frequencies of the output of said low-pass digital filter. - View Dependent Claims (10)
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Specification