Impact of Imperfect Channel Estimation on the Performance of M-QAM Hierarchical Constellations with Diversity

In this paper we derive general expressions for the performance of hierarchical multilevel quadrature amplitude modulation constellations (M-QAM), over flat Rayleigh fading environments with imperfect channel estimation. Cases of diversity reception with identical channels and with dissimilar channels, employing maximal ratio combining (MRC) are considered. Since hierarchical constellations are usually employed to achieve unequal bit error protection, the individual bit error rate (BER) of each bit stream is analyzed and it is shown that poor channel estimation has a more severe impact in the performance of the least protected bit streams.