Measuring channel signal to noise metric using constellation data
AssigneeTektronix, Inc.
InventorsDaniel G. Baker, Lakshmanan Gopishankar, George W. Tusing
Life of this patent
Estimating the term…
Abstract
Described are systems and methods of estimating a Signal-to-Noise (S/N) ratio of an input channel carrying a QAM signal. A Modulation Error Ratio (MER) is calculated for the input QAM signal, but uses only the centermost error values of a constellation of the input QAM signal in generating this modified MER. The modified MER accurately represents the S/N ratio of the input channel carrying the QAM signal. In this way the S/N ratio may be accurately determined using only the received I and Q components of the modulated QAM input signal itself.
Claims12
A method of estimating a Signal-to-Noise (S/N) ratio of an input channel carrying a QAM signal, the QAM signal having a defined number of ideal values in demodulated I and Q components, the method comprising:
- receiving the QAM signal from the input channel;
- comparing decoded values from a constellation of a decoded QAM signal to ideal constellation values to determine error values for a selected group of constellation ideal values, the selected group of constellation ideal values having a fewer number of values than the defined number of ideal values for the QAM signal constellation;
- determining a modified Modulation Error Ratio (MER) for the input received QAM signal using error values that correspond only to the selected group of constellation ideal values;
- and
- ascribing the modified MER ratio as the S/N ratio of the input channel carrying the QAM signal.
A test and measurement device for estimating a Signal-to-Noise (S/N) ratio of an input channel carrying a QAM signal, comprising:
- an input for receiving the QAM signal;
- a demodulator for demodulating the QAM signal into a constellation of I and Q component values;
- an error value calculator structured to compare the demodulated constellation of I and Q component values to an ideal set of values for the QAM constellation and generate an error value;
- a Modulation Error Ratio (MER) calculator including a selectable window limiter, the MER calculator structured to calculate a modified MER of the input channel carrying the QAM signal based on only particular of the error values generated by the error value calculator;
- and
- an ascriber structured to ascribe the modified MER of the input channel carrying the QAM signal as the S/N ratio of the input channel carrying the QAM signal.
Dependencies are inferred from the claim text.