Turbo codes: correlated extrinsic information and its impact on iterative decoding performance

The performance of a turbo code is dependent on two properties of the code: its distance spectrum and its suitability to be iteratively decoded. The performance of iterative decoding depends on the quality of the extrinsic inputs; badly correlated extrinsic inputs can deteriorate the performance. While most turbo coding literature assumes that the extrinsic information is uncorrelated, we investigate these correlation properties. An iterative decoding suitability measure is presented, intended to serve as an indication on the degree of correlation between extrinsic inputs. The suitability measure can be used as a complement to the weight distribution when ranking interleavers