Irregular Euclidean Distance Constellation Design for Quadrature Index Modulation

In this letter, in order to exploit the spatial gains from signal constellations, new signal constellations called irregular Euclidean distance QAM/PSK (IEDQAM/PSK), in which the Euclidean distances between the adjacent constellation points are not uniform of equidistance, are designed for lowering the bit error probability. Through this design that is applied to both quadrature spatial modulation (QSM) and spatial modulation with spatial constellation (SM-SC), the squared minimum Euclidean distances (MEDs) between the transmit vectors are further enhanced. Furthermore, the squared MEDs, spatial gains and the energy-saving percentage are analyzed. Finally, simulation results show a close match with analytical results in the high signal noise ratio region, and demonstrate that the spatial gains are achieved to improve the bit error ratio performance.