1. A method for transmitting a data bit stream in a communication system using a first and a second 16-QAM (Quadrature Amplitude Modulation) constellation each having 16 modulation symbols representable in four rows and four columns in a complex coordinate plane, each modulation symbol of the 16-QAM constellations being representable by a combination of four data bits, and the first and second 16-QAM constellation each obeying the following mapping rules: a first one of the four data bits representing a modulation symbol selects one of two contiguous symbol regions of the 16-QAM constellation based on its logical value, each of the two contiguous symbol regions being formed by two rows adjacent to each other, a second one of the four data bits representing the respective modulation symbol selects one of two contiguous symbol regions of the 16-QAM constellation based on its logical value, each of the two contiguous symbol regions being formed by two columns adjacent to each other, a third one of the four data bits representing the respective modulation symbol selects one of two non-contiguous symbol regions of the 16-QAM constellation based on its logical value, each of the two non-contiguous symbol regions being formed by two rows not adjacent to each other, and a fourth one of the four data bits representing the respective modulation symbol selects one of two non-contiguous symbol regions of the 16-QAM constellation based on its logical value, each of the two non-contiguous symbol regions being formed by two columns not adjacent to each other, the method comprising: forming a sequence of data words from the data bit stream, mapping each data word to a modulation symbol of a first 16-QAM constellation to obtain a first diversity arrangement version obeying said mapping rules, mapping each data word to a modulation symbol of a second 16-QAM constellation to obtain a second diversity arrangement version obeying said mapping rules, wherein the first and second 16-QAM constellation is obtained additionally obeying the following rearrangement rules: a modulation symbol of the first 16-QAM constellation having two nearest neighbors is rearranged such that it has four nearest neighbors in the second 16-QAM constellation a modulation symbol of the first 16-QAM constellation having three nearest neighbors is rearranged such that it has three nearest neighbors in the second 16-QAM constellation a modulation symbol of the first 16-QAM constellation having four nearest neighbors is rearranged such that it has two nearest neighbors in the second 16-QAM constellation, and transmitting the modulation symbol of the first 16-QAM constellation and the modulation symbol of the second 16-QAM constellation according to a transmit diversity scheme.