Soft trellis slicer for improving the performance of a decision-directed phase tracker
View Patent ↗A soft trellis slicer is provided in a high definition television (HDTV) receiver. The soft trellis slicer calculates a decision value and a confidence value corresponding to a phase angle error of a signal processed by the receiver. The receiver includes an equalizer, a phase tracking loop and a trellis decoder. The equalizer provides an equalized signal to the phase tracking loop; and the phase tracking loop calculates a phase angle error for the equalized signal. The trellis decoder calculates a decision value and a confidence value. The trellis decoder provides the decision value and the confidence value to the phase tracking loop, which calculates the reliability of the phase angle error based upon the phase angle error and the decision value and the confidence value provided by the trellis decoder. The trellis decoder calculates the decision value based upon a best path metric and calculates the confidence value based upon the best path metric and a second best path metric.
1. A method of making a phase angle correction in a phase tracking loop, comprising the steps of:
calculating a phase angle error in a signal;
calculating a decision value based upon a first path metric of a plurality of path metrics corresponding to a plurality of paths through a trellis decoder
calculating a confidence value based upon the first path metric and a second path metric of the plurality of path metrics;
adjusting the phase angle error based upon the confidence value and the decision value; and
modifying the signal based upon the adjusted phase angle error.
2. The method of claim 1 , wherein the phase angle is calculated by a phase lock loop.
3. The method of claim 1 , wherein the signal is the output of a comb filter.
4. The method of claim 1 , wherein the signal is an Advanced Television Systems Committee (ATSC) signal.
5. The method of claim 1 , wherein the step of calculating the confidence value comprises the steps of:
subtracting the second path metric from the first path metric to create a distance value; and
setting the confidence metric based upon the distance value.
6. The method of claim 5 , wherein the first path metric is a best path metric and the second path metric is a second best path metric.
7. The method of claim 5 , wherein the distance value is set to a first threshold value if the distance value is greater than a second threshold value.
8. The method of claim 1 , wherein the step of calculating an confidence value is based upon a nominal trace-back length.
9. A soft trellis slicer, comprising:
logic for calculating a plurality of path metrics of a signal based upon a plurality of possible paths of the signal through a trellis decoder;
logic for setting a soft slicer decision value based upon a first path metric of the plurality of path metrics;
logic for calculating a confidence value based upon a difference between the first path metric of the plurality of path metrics and a second path metric of the plurality of path metrics;
a phase tracking loop, comprising:
logic for calculating a phase angle error of the signal; and
logic for adjusting the phase angle error based upon the soft slicer decision value and the confidence value.
10. The soft trellis slicer of claim 9 , the phase tracking loop further comprising:
a phase lock loop for calculating the phase angle error.
11. The soft trellis slicer of claim 9 , wherein the signal is the output of a comb filter.
12. The soft trellis slicer of claim 9 , wherein the signal is an Advanced Television Systems Committee (ATSC) signal.
13. The soft trellis slicer of claim 9 , wherein the confidence value is set to a first threshold value if the confidence value is greater than a second threshold value.
14. The soft trellis slicer of claim 9 , wherein the first path metric is a best path metric and the second path metric is a second best path metric.
15. The soft trellis slicer of claim 9 , wherein the logic for calculating the plurality of path metrics depends upon a nominal trace-back length.
16. A high definition television (HDTV) receiver, comprising:
a trellis decoder, the trellis decoder comprising:
a soft trellis slicer, comprising:
logic for calculating a plurality of path metrics of a signal based upon a plurality of possible paths of the signal through a trellis decoder;
logic for calculating a confidence value based upon a difference between a first path metric of the plurality of path metrics and a second path metric of the plurality of path metrics;
logic for setting a soft slicer decision value based upon the first path metric; and
a phase tracking loop, comprising:
logic for calculating a phase angle error of the signal; and
logic for adjusting the phase angle error based upon the soft slicer decision value and the confidence value.
17. The HDTV receiver of claim 16 , the phase tracking loop further comprising:
a phase lock loop for calculating the phase angle error.
18. The HDTV receiver of claim 16 , wherein the signal is the output of a comb filter.
19. The HDTV receiver of claim 16 , wherein the confidence value is set to a threshold value if the confidence value is greater than the threshold value.
20. The HDTV receiver of claim 16 , wherein the logic for calculating the plurality of path metrics depends upon a nominal trace-back length.