Comments on “Optimal Constellation Labeling for Iteratively Decoded Bit-Interleaved Space-Time Coded Modulation”

Having developed an optimization criterion, the authors of the commented paper used the Reactive Tabu Search algorithm to find several optimal labeling maps of bit-interleaved space-time coded modulation with iterative decoding, one per each considered system diversity order. However, they might have overlooked the fact that some of the contributed 16-QAM labelings are equivalent to one another. It is shown in this paper by means of spectral analysis and reinforced by computation of the asymptotic coding gain. Thus, there is no need to switch 16-QAM labeling maps when reconfiguring the system from one diversity scheme to another, which makes the results of Huang and Ritcey´s contribution even more valuable from a practical point of view.