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We examine the performance of the iterative soft-output Viterbi algorithm (SOVA) for high rate turbo codes on an additive white Gaussian noise (AWGN) channel and compare its performance to that of the a posteriori probability (APP) algorithm. Code rates of the form k/sub 0//k/sub 0/+1 (k/sub 0/=4, 8, 16, 92, and 64) are considered. In our simulations, we show that the SOVA algorithm yields a bit error probability (P/sub b/) performance that is only about 0.7 dB inferior to the performance of the APP algorithm and about 1.7 dB from the capacity limit at P/sub b/=10/sup -5/. We also examine SOVA performance as a function of the number of iterations and a parameter we call the reliability depth.