Analysis of internal data width requirements for SISO decoding modules

This paper studies the dynamic range of the forward path metrics, the backward path metrics, and the extrinsic information within a soft-input soft-output (SISO) maximum a posteriori (MAP) decoding module for parallel concatenated convolutional codes (PCCCs). Upper bounds on path metric differences and the extrinsic information are presented as explicit functions of the inputs. These bounds are employed to determine the minimum internal data width for the hardware implementation of the decoder. Simulations show that the analytic bounds on the dynamic ranges and the internal data width are accurate and tight