On the Performance of Low Complexity Multiple Turbo Codes∗

In this paper, we study the convergence properties of low-complexity (2and 4-state) multiple turbo codes on an AWGN channel. An analytical approach to determine the extrinsic information transfer characteristics of 2-state codes is presented. This is then used to compute the convergence thresholds of several rate 1/2, 2-state multiple turbo codes. The convergence thresholds predicted by the analytical method match those based on transfer characteristics derived from Monte Carlo simulations. Both the analytical and simulation-based approaches are then used to search for rate 1/2, 2and 4-state multiple turbo codes with low convergence thresholds for different constituent encoders and puncturing patterns. Finally, BER simulations are presented verifying the convergence thresholds predicted by the analysis.