Digital quality index for QAM digital signals
First Claim
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1. A method of determining an indication of the quality on a quadrature amplitude modulated (QAM) digital signal on a cable network with forward error correction comprising the steps of:
- a) determining a first bit error rate (BER) of the digital signal prior to forward error correction (FEC);
b) determining a second bit error rate after forward error correction (FEC);
c) determining a digital quality index (DQI) on a predetermined scale based on the first and second bit error rates; and
d) displaying the DQI to provide an indication of the quality of the QAM digital signal on the cable network.
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Abstract
The present invention relates to a system for calculating a digital quality index (DQI), which provides a rating on a predetermined scale, indicative of the impairments in a received quadrature amplitude modulated (QAM) signal in a CATV cable system. The DQI system utilizes bit error rates prior to and after forward error correction to calculate the DQI value. To increase the calculation rate, the bit error rates can be estimated using voltage errors, signal to noise ratios and/or average corner error metrics.
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Citations
25 Claims
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1. A method of determining an indication of the quality on a quadrature amplitude modulated (QAM) digital signal on a cable network with forward error correction comprising the steps of:
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a) determining a first bit error rate (BER) of the digital signal prior to forward error correction (FEC); b) determining a second bit error rate after forward error correction (FEC); c) determining a digital quality index (DQI) on a predetermined scale based on the first and second bit error rates; and d) displaying the DQI to provide an indication of the quality of the QAM digital signal on the cable network. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A testing device for generating an indication of the quality on a quadrature amplitude modulated (QAM) digital signal on a cable network with forward error correction (FEC) comprising:
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an input port for receiving the QAM digital signal; first bit error rate (BER) generating means for determining the BER of the QAM digital signal prior to FEC; second first bit error rate (BER) generating means for determining the BER of the QAM digital signal after FEC; digital quality index generating means for determining a digital quality index (DQI) of the QAM digital signal on a predetermined scale based on the first and second BER; and a display for displaying the DQI to provide an indication of the quality of the QAM digital signal on the cable network. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24)
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25. A method of determining a bit error rate of a quadrature amplitude modulated (QAM) digital signal on a cable network with forward error correction (FEC) comprising the steps of:
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a) determining an error voltage VERR of the digital signal once every 5 to 50 microseconds; b) determining a first bit error rate prior to FEC based on a predetermined statistical relationship between the VERR and the first BER once every 5 to 50 microseconds; and c) averaging the first BER every 0.5 to 2 seconds.
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Specification