System and method for determining parity bit soft information at a turbo decoder output

A method for computing parity bit soft information, comprising:

• receiving a plurality of input parity bit soft information values corresponding to a plurality of parity bits;
• receiving a plurality of output systematic bit soft information values that are derived in part from the input systematic bit soft information value in a decoding operation;
• determining a plurality of initial forward metrics and a plurality of initial backward metrics;
• determining a plurality of branch metrics as a function of the plurality of input parity bit soft information values and the plurality of output systematic bit soft information values;
• determining a plurality of output parity bit soft information values in a processor for the plurality of parity bits, respectively, based on the plurality of initial forward metrics, the plurality of initial backward metrics and the plurality of branch metrics;
• and
• providing the plurality of output parity bit soft information values to a portion of a receiver circuit.

A decoding circuit, comprising:

• a backward metric calculator configured to receive an input trellis termination soft information value relating to an encoder that employs a plurality of parity bits, and to generate a plurality of initial backward metrics;
• a turbo decoder configured to receive an input systematic bit soft information value, a plurality of input parity bit information values, and the plurality of backward metrics, and to generate an output systematic bit soft information value and a hard decoded bit according to a turbo decoding operation;
• a trellis termination soft information calculator configured to receive the input trellis termination soft information value and the plurality of initial backward metrics, and to generate an output trellis termination bit soft information value;
• and
• a parity bit soft information generation circuit configured to receive the plurality of backward metrics, the plurality of input parity bit soft information values, and the output systematic bit soft information value, to generate a plurality of initial forward metrics, to generate a plurality of branch metrics based on the plurality of input parity bit soft information values, and the output systematic bit soft information value;
• and to generate a plurality of output parity bit soft information values based on the plurality of initial forward metrics, the plurality of initial backward metrics, and the plurality of branch metrics.