Automatic VSB/QAM modulation recognition method and apparatus

A method of determining whether a received signal is a vestigial sideband signal comprising the steps of:

• filtering the received signal using a sliding passband filter to generate a filtered signal corresponding to the portion of the received signal passed by the passband filter;
• controlling the center frequency of the sliding passband filter to sweep across a preselected frequency region corresponding to the region of a vestigial sideband signal in which a pilot tone is located;
• estimating the power of the filtered signal as the sliding passband filter sweeps across the preselected frequency region;
• comparing the estimated power of the filtered signal to a preselected upper threshold detection value and a preselected lower threshold value, the preselected upper threshold value corresponding to a power level which will be exceeded when a VSB pilot tone is located within the passband of the sliding passband filter, the lower threshold value corresponding to a power level which will not be exceeded when a quadrature amplitude signal is received;
• generating a modulation type signal, the modulation type signal having a first value indicative of the vestigial sideband signal when the upper threshold value is exceeded by the estimated power of the filtered signal and having a second value indicative of the quadrature amplitude modulated signal when the estimated power of the filtered signal is below the lower detection threshold.

A method of determining whether a received signal is a vestigial sideband signal comprising the steps of:

• filtering the received signal using a sliding passband filter to generate a filtered signal corresponding to the portion of the received signal passed by the passband filter;
• controlling the center frequency of the sliding passband filter to sweep across a preselected frequency region corresponding to the region of a vestigial sideband signal in which a pilot tone is located;
• estimating the power of the filtered signal as the passband filter sweeps across the preselected frequency region;
• comparing the estimated power of the filtered signal to a preselected pilot tone detection threshold;
• maintaining a count of the number of times the estimated power of the filtered signal exceeds the preselected pilot tone detection threshold;
• generating a modulation type signal, as a function of the count and an analysis period detection threshold value.

A modulation type recognition apparatus for determining if a signal is a vestigial sideband signal, the apparatus comprising:

• means for receiving and frequency translating the signal;
• a fixed frequency passband filter coupled to the receiving and frequency translating means for filtering the received signal;
• a power estimation circuit coupled to the fixed frequency passband filter for generating an estimate of the power of the filtered signal;
• a frequency control circuit coupled to the receiving and translating means for controlling the translating means to sweep the received signal across a frequency range;
• and
• a modulation type decision means coupled to the power estimation circuit for generating a modulation type decision signal, as a function of a comparison of the estimated power of the filtered signal to a detection threshold.