The effect of constellation density on trellis coded modulation in fading channels

Abstract

There has been some reluctance to use dense constellations such as 16 CAM for mobile communications because of their greater peak-to-average-power ratio and their seemingly greater sensitivity to noise and channel interference. It is demonstrated that dense constellations can actually improve performance. Using a completely analytical method, three constellations are compared with the same net throughput of 2 bits/symbol: uncoded QPSK, rate 2/3 TCM 8-PSK, and rate 1/2 TCM 16 QAM. Comparison on the basis of average power puts TCM 16-QAM 5-dB ahead of TCM 8-PSK. Even comparison on the basis of peak power gives TCM 16-QAM a 2.44-dB advantage over TCM 8-PSK. QPSK is much poorer than either.<>