Synchronization symbol re-insertion for a decision feedback equalizer combined with a trellis decoder
View Patent ↗A digital equalizer for interpreting a digital signal including convolutionally encoded symbols and synchronization symbols outside the convolutional code comprises a combined trellis encoder and DFE. The synchronization symbols are re-inserted into the input of the DFE in order to restore time domain continuity created by removal of the synchronization symbols.
1. A synchronization symbol re-inserter for use in a symbol decoder, comprising:
a trellis decoder, including;
a plurality of decoding stages for decoding encoded data symbols, each decoding stage having as output intermediate decoded symbols; and
a mirrored symbol delay line, including;
a plurality of multiplexers, each multiplexer providing multiplexer output symbols, and each multiplexer receiving as input the intermediate decoded symbols from a following stage of the trellis decoder and the intermediate decoded symbols from a current stage of the trellis decoder; a plurality of delay devices, each delay device receiving as input the multiplexer output symbols from a selected one of the multiplexers and providing corresponding delayed multiplexer output symbols, the delayed multiplexer output symbols of each delay device other than the multiplexer output symbols from a final one of the plurality of multiplexers being fed to a following multiplexer; and
where when the delayed multiplexer output symbol of one of the plurality of delay devices is a synchronization symbol a following one of the plurality of multiplexers selects the synchronization symbol delayed by the corresponding delay device at the output of the mirrored symbol delay line, and otherwise the plurality of multiplexers provide the intermediate symbol from each of the current stages of the trellis decoder at the output of the mirrored symbol delay line.
2. The synchronization symbol re-inserter of claim 1 , where each of the multiplexers comprises a pair of 2:1 multiplexers.
3. The synchronization symbol re-inserter of claim 1 , further comprising a composite synchronization indicator that determines whether the output of one of the plurality of delay devices is a synchronization symbol.
4. The synchronization symbol re-inserter of claim 1 , further comprising a decision feedback equalizer (DFE) following the trellis decoder.
5. The synchronization symbol re-inserter of claim 4 , where the decision feedback equalizer (DFE) comprises a filter having a transposed structure.