  In this paper, we investigate in detail the performance of turbo codes in
quasi-static fading channels both with and without antenna diversity. First, we
develop a simple and accurate analytic technique to evaluate the performance of
turbo codes in quasi-static fading channels. The proposed analytic technique
relates the frame error rate of a turbo code to the iterative decoder
convergence threshold, rather than to the turbo code distance spectrum.
Subsequently, we compare the performance of various turbo codes in quasi-static
fading channels. We show that, in contrast to the situation in the AWGN
channel, turbo codes with different interleaver sizes or turbo codes based on
RSC codes with different constraint lengths and generator polynomials exhibit
identical performance. Moreover, we also compare the performance of turbo codes
and convolutional codes in quasi-static fading channels under the condition of
identical decoding complexity. In particular, we show that turbo codes do not
outperform convolutional codes in quasi-static fading channels with no antenna
diversity; and that turbo codes only outperform convolutional codes in
quasi-static fading channels with antenna diversity.
