J. M. Walsh, P. A. Regalia, and C. R. Johnson, Jr.
Many previous attempts at analyzing the convergence behavior of turbo and iterative decoding, such as EXIT style analysis and density evolution, ultimately appeal to results which become valid only when the block length grows rather large, while still other attempts, such as connections to factor graphs and belief propagation, have been largely unsuccessful at showing convergence due to loops in the turbo coding graph. The information geometric interpretation presented in this paper allows us to relate the quantities of interest in the turbo decoder. Using it, we point out a measure which will be key in studying convergence.