Data-directed frequency-and-phase lock loop for decoding an offset-QAM modulated signal having a pilot
View Patent ↗A data-and-pilot directed frequency-and-phase lock loop for an offset-QAM modulated signal having a pilot signal comprising a pilot acquisition loop and a pair of data-directed acquisition loops. The pilot is extracted from the main signal by a pilot filter, then used both by the pilot acquisition loop and to remove the pilot from the signal to the data-directed acquisition loops. The outputs of the pilot and the two data-directed acquisition loops are summed and returned to the VCO to complete the feedback loop.
1. A data-and-pilot directed frequency-and-phase lock loop having a symbol rate, comprising:
a signal input;
a VCO having an in-phase and a quadrature output;
a first multiplier having as input the signal input and the in-phase and quadrature outputs of the VCO, the first multiplier further having a first output;
a second multiplier having as input the first output, the second multiplier further having a second output;
a narrow band-pass filter having as input the second output, the narrow band-pass filter further having a third output;
a third multiplier having as input the third output, the third multiplier further having a fourth output that is a convolution of the third output;
a fourth multiplier having as input the fourth output, the fourth multiplier further having a fifth output;
a first low-pass filter having as input an in-phase component of the fifth output, the first low-pass filter further having a first filtered output;
a fifth multiplier having as input the first filtered output and a quadrature component of the fifth output, the fifth multiplier further having a sixth output;
a first summer having as input the second output and the third output, the first summer further having a seventh output that is a difference between the second output and the third output;
a sixth multiplier having as input the seventh output, the sixth multiplier further having an eighth output that is a convolution of the seventh output;
seventh and eighth multipliers having as input the eighth output, the seventh and eighth multipliers further having a ninth and tenth output, respectively;
second and third low pass filters having as input in-phase portions of the ninth and tenth outputs, respectively, the second and third low pass filters having a second and third filtered output, respectively;
ninth and tenth multipliers having as inputs the second and third filtered outputs, respectively, and quadrature portions of the ninth and tenth outputs, respectively, the ninth and tenth multipliers further having an eleventh and twelfth outputs, respectively;
a second summer having as input the sixth, eleventh, and twelfth outputs, the second summer further having a thirteenth output; and
a fourth low-pass filter having as input the thirteenth output, the fourth low-pass filter further having a fourteenth output;
wherein the fourteenth output is returned to the VCO to complete a feedback loop.
2. The data-and-pilot directed frequency-and-phase lock loop of claim 1 , wherein:
the second multiplier multiplies by ¼ the symbol rate;
the fourth multiplier multiplies by ¾ the symbol rate; and
the seventh and eighth multipliers multiply by ¼ and ¾ the symbol rate, respectively.
3. The data-and-pilot directed frequency-and-phase lock loop of claim 1 , wherein the seventh and eighth multipliers multiply by fixed frequencies having a difference of ½ the symbol rate.
4. The data-and-pilot directed frequency-and-phase lock loop of claim 1 , wherein the second and fourth multipliers multiply by fixed frequencies that add up to the symbol rate.
5. The data-and-pilot directed frequency-and-phase lock loop of claim 1 , wherein the second multiplier multiplies only by 1 and −1.
6. The data-and-pilot directed frequency-and-phase lock loop of claim 1 , wherein the narrow band-pass filter is centered about an expected pilot frequency.
7. A data-and-pilot directed frequency-and-phase lock loop, comprising:
a signal input;
a VCO having an in-phase and quadrature output;
a first multiplier having as input the signal input and the in-phase and quadrature outputs of the VCO, the first multiplier further having a first output;
a narrow band-pass filter having as input the first output, the narrow band-pass filter further having a second output;
a second multiplier having as input the second output, the second multiplier further having a third output that is a convolution of the second output;
a first low-pass filter having as input an in-phase component of the third output, the first low-pass filter further having a first filtered output;
a third multiplier having as input the first filtered output and a quadrature component of the third output, the third multiplier further having a fourth output;
a first summer having as input the first output and the second output, the first summer further having a fifth output that is a difference between the first output and the second output;
a fourth multiplier having as input the fifth output, the fourth multiplier further having a sixth output that is a convolution of the fifth output;
a second low pass filter having as input an in-phase portion of the sixth output, the second low pass filter having a second filtered output;
a fifth multiplier having as inputs the second filtered output and a quadrature portion of the sixth output, the fifth multiplier further having a seventh output;
a second summer having as input the fourth and seventh outputs, the second summer further having an eight output; and
a third low-pass filter having as input the eighth output, the third low-pass filter further having a ninth output;
wherein the ninth output is returned to the VCO to complete a feedback loop.
8. The data-and-pilot directed frequency-and-phase lock loop of claim 7 , wherein the narrow band-pass filter is centered about an expected pilot frequency.
9. A data-and-pilot directed frequency-and-phase lock loop, comprising:
a pilot-directed acciuisition loop having a pilot input and a pilot output;
a data-directed phase-lock loop having a data input and a data output;
wherein the pilot output and the data output are used to produce a feedback signal that is a non- 1 inear combination of the pilot input and the data input, and the non-linear combination is performed by adding the pilot input and data input during a first half of each phase, and by inverting the in-phase portion of one of the pilot input and the data input and adding the result to the other of the pilot input and the data input during a second half of each phase.
10. A data-and-pilot directed frequency-and-phase lock loop, comprising:
a pilot-directed acquisition loop having a pilot input and a pilot output;
a data-directed phase-lock loop having a data input and a data output;
wherein the pilot output and the data output are used to produce a feedback signal that is a non-linear combination of the pilot input and the data input, further comprising a plurality of frequency shift multipliers that comprise a first multiplier and a second multiplier that multiply by fixed frequencies having a difference of ½ the symbol rate.