Method and apparatus for path metric processing in telecommunications systems
View Patent ↗An apparatus and a method for calculating in-place pat metric addressing far a trellis processing arrangement are provided. An arrangement of cascaded multiplexers and stores receives a known input sequence of path metrics. The input sequence of path metrics is manipulated such that certain of the path metrics are delayed in the stores by a clock cycle, whilst the remaining path metrics are presented to the cascaded banks of multiplexers. In this manner, the input sequence of path metrics is continuously processed to produce a desired output sequence of path metrics. Advantageously, embodiments of the apparatus and method may be practiced on either a forward trellis or a reverse trellis.
1. An apparatus for performing in-place path metric addressing for a trellis processing arrangement on an input sequence of a plurality of pairs of path metrics, each path metric being associated with one of a plurality of trellis states having a known order, to form a desired output sequence of path metrics corresponding to a desired older of the associated trellis states, the apparatus comprising:
a plurality of first multiplexers, each first multiplexer for receiving one of said pair of path metrics and providing a first selected one of the received pair of path metrics based on a first signal;
a plurality of latches, each latch coupled to a corresponding one of the first multiplexers for receiving the first selected one of the received pair of path metrics and configured to delay the first selected one of the received pair of path metrics based upon a delay signal;
a plurality of second multiplexers, each second multiplexer for receiving said one of said pairs of path metrics and providing a second selected one of the received pair of path metrics based on a second signal; and
a plurality of third multiplexers, each third multiplexer for receiving the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics, and wherein each of the third multiplexers is configured to present one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics based upon a third signal.
2. The apparatus of claim 1 , wherein each of the third multiplexers is configured to present said one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics such that the output sequence of path metrics provided by the third multiplexers is not the same as the input sequence of path metrics.
3. The apparatus of claim 2 , wherein each of the third multiplexers is configured to present said one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics such that the output sequence of path metrics provided by the third multiplexers corresponds to a sequence of path metrics formed in a Viterbi mode when the input path metrics correspond to a trellis formed by a non-systematic convolutional code.
4. The apparatus of claim 2 , wherein each of the third multiplexers is configured to present said one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics such that the output sequence of path metrics provided by the third multiplexers corresponds to a sequence of path metrics formed by reverse trellis switching in a LogMAP decoding mode.
5. The apparatus of claim 1 , wherein each of the third multiplexers is configured to present said one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics such that the output sequence of path metrics provided by the third multiplexers corresponds to a sequence of path metrics formed by trellis switching in a recursive systematic mode.
6. The apparatus of claim 5 , wherein each of the third multiplexers is configured to present said one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics such that the output sequence of path metrics provided by the third multiplexers corresponds to a sequence of path metrics formed by trellis switching in a Turbo decoding mode.
7. The apparatus of claim 1 , wherein each of the third multiplexers is configured to present said one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics such that the output sequence of path metrics provided by the third multiplexers is the same as the input sequence of path metrics.
8. The apparatus of claim 1 , comprising a first plurality of gates ( 1920 a–d ) for receiving a first selector signal and at least one of a first and a second enable signal, each first gate being capable of Conning the first signal based on the first selector signal and at least one of the first and the second enable signals.
9. The apparatus of claim 8 , comprising a second plurality of gates ( 1925 a–d ) for receiving the first signal and a third enable signal, each second gate being capable of forming the second signal based on the first signal and the third enable signals.
10. The apparatus of claim 9 , wherein the first and second pluralities of gates are exclusive-OR gates.
11. A method for performing in-place path metric addressing for a trellis processing arrangement on an input sequence of a plurality of pairs of path metrics, each path metric being associated with one of a plurality of trellis states having a known order, to form a desired output sequence of path metrics corresponding to a desired order of the associated trellis states, the method comprising;
receiving one of said pairs of path metrics;
providing a first selected one of the received pair of path metrics based on a first signal;
receiving the first selected one of the received pair of path metrics;
delaying the first selected one of the received pair of path metrics based upon a delay signal;
receiving said one of said pairs of path metrics;
providing a second selected one of the received pair of path metrics based on a second signal;
receiving the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics; and
providing one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics based upon a third signal.
12. The method of claim 11 , comprising providing said one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics such that the output sequence of path metrics is not the same as the input sequence of path metrics.
13. The method of claim 12 , comprising providing said one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics such that the output sequence of path metrics corresponds to a sequence of path metrics formed in a Viterbi mode when the input path metrics correspond to a trellis formed by a non-systematic convolutional code.
14. The method of claim 12 , comprising providing said one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics such that the output sequence of path metrics corresponds to a sequence of path metrics formed by reverse trellis switching in a LogMAP decoding mode.
15. The method of claim 11 , comprising providing said one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics such that the output sequence of path metrics corresponds to a sequence of path metrics formed by trellis switching in a recursive systematic mode.
16. The method of claim 15 , comprising providing said one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics such that the output sequence of path metrics corresponds to a sequence of path metrics formed by trellis switching in a Turbo decoding mode.
17. The method of claim 11 , comprising providing said one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics such that the output sequence of path metrics is the same as the input sequence of path metrics.
18. The method of claim 11 , comprising receiving a first selector signal and at least one of a first and a second enable signal and forming the first signal based on the first selector signal and at least one of the first and the second enable signals.
19. The method of claim 18 , comprising receiving the first signal and a third enable signal and forming the second signal based on the first signal and the third enable signals.
20. An apparatus for performing in-place path metric addressing for a trellis processing arrangement on an input sequence of a plurality of pairs of path metrics, each path metric being associated with one of a plurality of trellis states having a known order, to form a desired output sequence of path metrics corresponding to a desired order of the associated trellis states, the apparatus comprising:
means for receiving one of said pairs of path metrics;
means for providing a first selected one of the received pair of path metrics based on a first signal;
means for receiving the first selected one of the received pair of path metrics;
means for delaying the first selected one of the received pair of path metrics based upon a delay signal;
means for receiving said one of said pair of path metrics;
means for providing a second selected one of the received pair of path metrics based on a second signal;
means for receiving the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics; and
means for providing one of the delayed first selected one of the received pair of path metrics and the second selected one of the received pair of path metrics based upon a third signal.