System for signal path characterization with a reference signal using stepped-frequency increments
First Claim
1. A system for measuring a linear frequency response of a transmission medium, the system comprising:
- a transmitter for transmitting an unimpaired reference signal into the transmission medium, the unimpaired reference signal comprisinga major time interval comprising at least two minor time intervals, anda sine wave operating at a constant frequency during each minor time interval wherein the constant frequency for each time interval is different from the constant frequency of any other adjacent minor time interval,a receiver connected to the transmission medium, at a location different from the location wherein the transmitter is connected, for receiving an impaired reference signal from the transmission medium;
a processor connected to an output of the receiver for computing a linear frequency response from the impaired and unimpaired reference signals.
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Accused Products
Abstract
A system that utilizes a reference signal for testing signal paths for complex frequency response (linear distortion), and non-linear distortion. This reference signal, which is also known as a ghost canceling reference signal or a training waveform, has excellent properties for channel characterization. The reference signal is a waveform that operates for a major time interval that is subdivided into multiple minor time intervals. During each minor time interval, a sine wave oscillates at a constant angular velocity or frequency. The sine wave frequency may take uniform steps between the minor time intervals, or it may skip a group of frequencies. The phase of the waveform may optionally be continuous between the end of one minor time interval and the start of the next minor time interval. This waveform is generated by loading the time sample values from a digital memory into a digital to analog converter (D-A), or by rapidly reprogramming a numerically-controlled oscillator. The reference signal can also be analyzed for the presence of non-linear distortion. Broadband RF channels, such as cable television channels, or baseband channels, such as telephone channels may be characterized using this waveform.
38 Citations
14 Claims
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1. A system for measuring a linear frequency response of a transmission medium, the system comprising:
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a transmitter for transmitting an unimpaired reference signal into the transmission medium, the unimpaired reference signal comprising a major time interval comprising at least two minor time intervals, and a sine wave operating at a constant frequency during each minor time interval wherein the constant frequency for each time interval is different from the constant frequency of any other adjacent minor time interval, a receiver connected to the transmission medium, at a location different from the location wherein the transmitter is connected, for receiving an impaired reference signal from the transmission medium; a processor connected to an output of the receiver for computing a linear frequency response from the impaired and unimpaired reference signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A system for measuring a non-linear distortion of a transmission medium, the system comprising:
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a transmitter for transmitting an unimpaired test signal into the transmission medium, the unimpaired test signal comprising a major time interval having at least two minor time intervals, and a sine wave operating at a constant frequency during each minor time interval wherein the constant frequency for each time interval is different from the constant frequency of any other adjacent minor time interval, a receiver connected to the transmission medium, at a point different from a location wherein the transmitter is connected, for receiving the reference signal; a processor connected to an output of the receiver for computing non-linear distortion from the received test signal; and a spectral notch filter located between the transmitter and the signal path wherein non-linear distortion of the transmission medium is determined by the amount of additional energy measured in the spectral notch.
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14. A system for measuring a non-linear distortion of a transmission medium comprising
a transmitter for transmitting an unimpaired reference signal through the transmission medium, the unimpaired reference signal comprising a major time interval having at least two minor time intervals, and a sine wave operating at a constant frequency during each minor time interval wherein the constant frequency for each time interval is different from the constant frequency of any other adjacent minor time interval, a receiver connected to the transmission medium, at a point different from a location wherein the transmitter is connected, for receiving the reference signal; a processor connected to an output of the receiver for computing an impulse response of the reference signal, wherein the non-linear distortion of the transmission medium is determined by an amount of uncorrelated energy in the impulse response.
Specification