The effects of time delay spread on TCM in portable radio environments

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Abstract
This paper studies the effects of time delay spread on TCM in portable radio environments. The average irreducible bit error rate (BER) of three different TCM schemes are evaluated by simulation. The results under low delay spread indicate that the performance of TCM schemes with interleaving/deinterleaving is much better than that of QPSK and good TCM schemes under flat fading also give better performance. A good TCM scheme in frequency-selective fading channel should have both large Euclidean distance and large degree of built-in time diversity. If the time delay spread is relatively high, they do not have advantages over QPSK. This paper also compares their performance with and without diversity. It is found that diversity greatly improves the performance under a low delay spread, while the diversity gain quickly diminishes as the RMS delay spread approaches 0.2 of the symbol period.