In this paper, we study the constellation design of quadrature amplitude modulations (QAMs) with odd number of bits per symbol. A square constellation, which adopts symmetrical Gray labeling, is proposed. Simplified mapping and demapping methods are also designed for it. Performance of the proposed square constellation is compared with that of conventional rectangular and cross constellations. As simulation results show, the proposed square constellation obtains better BER performance when channel coding is used in communication systems. Moreover, it achieves much lower realization complexity than cross constellation by using the proposed mapping and demapping method.
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