Efficiency data transmission technique
First Claim
1. A data transmission system comprised of:
- (a) means for receiving a digital input signal characterized by a predetermined transmission rate,(b) a half-cosine filter for receiving and filtering said received digital input signal and for providing a filtered output signal, characterized by a transfer function having a transmission null at Nyquist frequency, and(c) a very steep low-pass filter connected in series with said half-cosine filter, and having a cut-off frequency which is less than the Nyquist frequency by a predetermined amount, for receiving and further filtering said filtered output signal, thereby limiting intersymbol interference and enabling digital signal transmission at a transmission rate greater than the Nyquist rate by said predetermined amount.
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Accused Products
Abstract
Partial response and quadrature partial response data transmission system characterized by increased transmission rate, lower signal-to-noise ratio, low cost and simpler hardware implementation than prior art systems. A steep filter (almost rectangular) is connected to the output of a cosine filter, forming a composite filter, wherein the cut-off frequency of the rectangular filter is less than the Nyquist frequency by a predetermined amount which is inversely proportional to the amount in percentage by which the data transmission rate exceeds the Nyquist rate. The system is thus capable of signalling at the Nyquist rate and greater, without requiring that channel filter parameters or the basic clock rate be adjusted. A smaller number of signal levels can be selected (as compared to previously existing methods) for spectrally efficient applications, and the resulting more robust system can also be used to transmit PAM, QAM, and other baseband or modulated signals.
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Citations
28 Claims
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1. A data transmission system comprised of:
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(a) means for receiving a digital input signal characterized by a predetermined transmission rate, (b) a half-cosine filter for receiving and filtering said received digital input signal and for providing a filtered output signal, characterized by a transfer function having a transmission null at Nyquist frequency, and (c) a very steep low-pass filter connected in series with said half-cosine filter, and having a cut-off frequency which is less than the Nyquist frequency by a predetermined amount, for receiving and further filtering said filtered output signal, thereby limiting intersymbol interference and enabling digital signal transmission at a transmission rate greater than the Nyquist rate by said predetermined amount. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A data transmission system comprised of:
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(a) means for receiving a digital input signal characterized by a predetermined transmission rate, and generating an analog input signal in response thereto, (b) a first filter for receiving and filtering said analog input signal, and characterized by a first transfer function H1 (f), wherein H1 (f)=Cos (π
f/2fN), fN =Nyquist frequency, and f=the frequency of the input signal,(c) a second filter connected in series with said first filter for further filtering said analog input signal, and characterized by a second transfer function H2 (f), wherein H2 (f)=1 for f=fN /1+b, where b=amount in percentage by which said predetermined rate exceeds the Nyquist rate RN, where RN =2fN, and wherein H2 (f)=0 otherwise, whereby said first and second filters generate a band-limited partial response signal transmitted at said predetermined transmission rate in response to receiving and filtering said analog input signal, and (d) means for receiving and demodulating said partial response signal and generating said digital input signal in response thereto. - View Dependent Claims (23, 24, 25, 26, 27)
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28. A data transmission method comprising the steps of:
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(a) receiving a digital input signal characterized by a predetermined transmission rate, and generating a first multi-level analog signal in response thereto, (b) transforming said first multi-level analog signal into a further multi-level analog signal having infinite bandwidth and a greater number of levels than said first multi-level analog signal, and (c) band limiting said further multi-level analog signal to a maximum frequency which is less than Nyquist frequency by a predetermined amount, and generating a partial response output signal in response thereto, whereby said predetermined amount is equal to the amount in percentage by which said predetermined transmission rate is greater than the Nyquist rate.
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Specification