TTCM decoder design

A soft-in soft-out functional block (SISO) that calculates a plurality of soft symbol decisions for a block that includes plurality of encoded symbols arranged into a plurality of sub-blocks, the SISO comprising:

• a first alpha/beta metric calculation functional block that initially processes the encoded symbols of the plurality of encoded symbols in a first direction within the block, the first direction extending from a block beginning towards a block middle, to calculate forward metrics (alphas) and selectively stores alpha check point values associated with the sub-blocks of the plurality of sub-blocks that are processed in the first direction onto a check point stack;
• wherein the first alpha/beta metric calculation functional block also initially processes the encoded symbols of the plurality of encoded symbols in a second direction within the block, the second direction extending from a block end towards the block middle, to calculate backward metrics (betas) and selectively stores beta check point values associated with the sub-blocks of the plurality of sub-blocks that are processed in the second direction;
• wherein, when the first alpha/beta metric calculation functional block substantially reaches the block middle when processing in the first direction, the first alpha/beta metric calculation functional block pushes each alpha value onto an alpha stack;
• wherein, when the first alpha/beta metric calculation functional block substantially reaches the block middle when processing in the second direction, the first alpha/beta metric calculation functional block pushes each beta value onto a beta stack;
• wherein, when the first alpha/beta metric calculation functional block reaches the block middle after processing in the first direction, a second alpha/beta metric calculation functional block skips back to a first sub-block that has been processed in the first direction by the first alpha/beta metric calculation functional block and recalculates alphas for each encoded symbol contained in the first sub-block while the first alpha/beta metric calculation functional block simultaneously calculates betas in the second direction for a sub-block adjacent to the first sub-block;
• wherein, when the first alpha/beta metric calculation functional block substantially reaches the block middle after processing in the second direction, the second alpha/beta metric calculation functional block skips back to a second sub-block that has been processed by the first alpha/beta metric calculation functional block in the second direction and re-calculates betas for each encoded symbol contained in the second sub-block while the first alpha/beta metric calculation functional block simultaneously calculates alphas in the first direction for a sub-block adjacent to the second sub-block;
• for each encoded symbol for which the second alpha/beta metric calculation functional block calculates a beta in the second direction for the sub-block adjacent to the first sub-block, an extrinsic value calculation functional block pops a corresponding alpha off of the alpha stack and calculates a corresponding soft symbol decision using the most recently corresponding calculated beta and most recently popped alpha;
• and
• for each encoded symbol for which the second alpha/beta metric calculation functional block calculates an alpha in the first direction for the sub-block adjacent to the second sub-block, the extrinsic value calculation functional block pops a corresponding beta off of the beta stack and calculates a corresponding soft symbol decision using the most recently corresponding calculated alpha and most recently popped beta.

A decoder that decodes a block that includes plurality of encoded symbols arranged into a plurality of sub-blocks, the decoder comprising:

• a soft-in soft-out functional block (SISO) that, based on a plurality of trellis metrics, calculates a first plurality of extrinsic values for each encoded symbol of the plurality of encoded symbols;
• an interleaver/de-interleaver, communicatively coupled to the SISO, that interleaves the first plurality of extrinsic values to generate a first “a priori probability” (app) information;
• wherein the SISO, based on the plurality of trellis metrics, calculates a second plurality of extrinsic values for each encoded symbol of the plurality of encoded symbols;
• wherein the interleaver/de-interleaver, that is communicatively coupled to the SISO, de-interleaves the second plurality of extrinsic values to generate a second “a priori probability” (app) information;
• wherein the first “a priori probability” (app) information is fed back to the SISO during a first SISO operation;
• wherein the second “a priori probability” (app) information is fed back to the SISO during a second SISO operation;
• wherein the SISO performs the first SISO operation and the second SISO operation during at least one iteration of iterative decoding to generate a plurality of soft symbol decisions, each soft symbol decision of the plurality of soft symbol decisions corresponds to an encoded symbol of the plurality of encoded symbols;
• wherein the SISO initially processes the encoded symbols of the plurality of encoded symbols in a first direction within the block, the first direction extending from a block beginning towards a block middle, to calculate forward metrics (alphas) and selectively stores alpha check point values associated with the sub-blocks of the plurality of sub-blocks that are processed in the first direction;
• wherein the SISO also initially processes the encoded symbols of the plurality of encoded symbols in a second direction within the block, the second direction extending from a block end towards the block middle, to calculate backward metrics (betas) and selectively stores betas check point values associated with the sub-blocks of the plurality of sub-blocks that are processed in the second direction;
• wherein, when the SISO substantially reaches the block middle when processing in the first direction and in the second direction, the SISO pushes each alpha value onto an alpha stack, and the SISO pushes each beta value onto a beta stack;
• wherein, when the SISO reaches the block middle after processing in the first direction, the SISO skips back to a first sub-block that has been processed in the first direction and re-calculates alphas for each encoded symbol contained in the first sub-block while simultaneously continuing to calculate betas in the second direction for a sub-block adjacent to the first sub-block and popping alphas off of the alpha stack and calculating soft symbol decisions for each encoded symbol within the sub-block adjacent to the first sub-block;
• and
• wherein, when the SISO substantially reaches the block middle after processing in the second direction, the SISO skips back to a second sub-block that has been processed in the second direction and re-calculates betas for each encoded symbol contained in the second sub-block while simultaneously continuing to calculate alphas in the first direction for a sub-block adjacent to the second sub-block and popping betas off of the beta stack and calculating soft symbol decisions for each encoded symbol within the sub-block adjacent to the second sub-block.

A received block processing method that decodes a block that includes plurality of encoded symbols arranged into a plurality of sub-blocks, the method comprising:

• during a first time period, successively calculating check point values for forward metrics (alphas) of sub-blocks within a first half of the block;
• during the first time period, successively calculating check point values for backward metrics (betas) of sub-blocks within a second half of the block;
• during a second time period, upon reaching a final sub-block of the first half of the block, calculating an alpha for each encoded symbol contained therein and storing the calculated alphas;
• during the second time period, upon reaching a final sub-block of the second half of the block, calculating a beta for each encoded symbol contained therein and storing the calculated betas;
• wherein a third time period occurs after completing the processing of both the final sub-block of the first half of the block and the final sub-block of the second half of the block;
• during the third time period, successively calculating alphas for each symbol of the final sub-block of the second half of the block;
• during the third time period, successively calculating betas for each symbol of the final sub-block of the first half of the block;
• during the third time period, performing skip-back processing to successively re-calculate alphas for each encoded symbol of a sub-block that precedes the final sub-block within the first half of the block and storing the re-calculated alphas;
• and
• during the third time period, performing skip-back processing to successively re-calculate betas for each encoded symbol of a sub-block that precedes the final sub-block within the second half of the block and storing the re-calculated betas.

A received block processing method that decodes a block that includes plurality of encoded symbols arranged into a plurality of sub-blocks, the method comprising:

• processing the encoded symbols of the plurality of encoded symbols in a first direction within the block, the first direction extending from a block beginning towards a block middle, to calculate forward metrics (alphas) and selectively storing alpha check point values associated with the sub-blocks of the plurality of sub-blocks that are processed in the first direction;
• processing the encoded symbols of the plurality of encoded symbols in a second direction within the block, the second direction extending from a block end towards the block middle, to calculate backward metrics (betas) and selectively storing betas check point values associated with the sub-blocks of the plurality of sub-blocks that are processed in the second direction;
• when substantially reaching the block middle when processing in the first direction and in the second direction, storing each alpha value and each beta value;
• when reaching the block middle after processing in the first direction, skipping back to a first sub-block that has been processed in the first direction and recalculating alphas for each encoded symbol contained in the first sub-block while simultaneously continuing to calculate betas in the second direction for a sub-block adjacent to the first sub-block, retrieving the stored alphas, and calculating soft symbol decisions for each encoded symbol within the sub-block adjacent to the first sub-block;
• and
• when reaching the block middle after processing in the second direction, skipping back to a second sub-block that has been processed in the second direction and re-calculating betas for each encoded symbol contained in the second sub-block while simultaneously continuing to calculate alphas in the first direction for a sub-block adjacent to the second sub-block, retrieving stored betas, and calculating soft symbol decisions for each encoded symbol within the sub-block adjacent to the second sub-block.