Enhanced Bit-to-Symbol Mapping for M-ary θ-QAM

In conventional bit-to-symbol mapping for θ-QAM, the Hamming distance between the symbols with the minimum Euclidean distance is not minimized when θ <; 60°, and this undesirably increases the bit error rate (BER). In this paper, we propose an enhanced bit-to-symbol mapping for M-ary θ-QAM, which minimizes the Hamming distance between the symbols with the minimum Euclidean distance even when θ <; 60°. By adopting the conventional mapping when θ ≥ 60° and the proposed mapping when θ <; 60°, we formulate the overall bit-to-symbol mapping for θ-QAM. To validate the proposed bit-to-symbol mapping, we compare the BERs of the proposed mapping and the conventional one through computer simulations.