Improved union bounds on turbo codes performance

An improved union bound on the performance of turbo codes is evaluated, ext ending the preliminary results presented by Viterbi and Viterbi (1998) in c onjunction with the input-binary AWGN channel. Since, in an increasing numb er of important applications, the AWGN channel provides an entirely inappro priate model of the propagation environment, the analytical expression of t he previously derived improved union bound is extended to provide a charact erisation of turbo code performance in a more general case, namely when con sidering the multiplicative fast-fading fully-interleaved channel. A unifor m interleaver is assumed; this strategy allows one to derive the average pe rformance of the turbo coding scheme by analysis. Of interest is the improv ement of the bound for values of E-b/N-0 near and below R-0 (i.e. the 'comp utational cutoff rate'), a region where the conventional union bound become s useless. This improvement allows a better estimate of turbo code performa nce in conjunction with the fast-fading fully-interleaved channel and with the AWGN channel, which can be treated as a particular case. Moreover, it a llows one to determine a tighter bound to the actual code performance as fa r as the slow fading Rician channel is concerned.