Quadrature Index Modulation With Three-Dimension Constellation

Abstract

Quadrature spatial modulation (QSM) is a novel index modulation technology, which extends the antenna index (AI) to two dimensions of both in-phase AI and quadrature AI. In order to further make full use of the idle transmit antennas (TAs) resource and to exploit the signal constellation domain, taking advantage of the spatial dimension of QSM, we propose a new three-dimension (3D) structure of quadrature index modulation (QIM), which is capable of not only transmitting directly a 3D constellation symbol but also carrying more extra information bits, named as quadrature index modulation with three-dimensional constellation (QIM-TDC). More specifically, a 3D framework of QIM-TDC is designed for transmitting a 3D constellation symbol that is constructed by the $X$ -axis, $Y$ -axis and $Z$ -axis components. In the proposed QIM-TDC scheme, by utilizing an in-phase AI vector, two active TAs are activated simultaneously to transmit the $X$ -axis and $Y$ -axis components of the 3D symbol, respectively. Similarly, by utilizing the quadrature AI vector, an active TA is activated to transmit the $Z$ -axis component of the 3D symbol. Then, for further achieving the better bit error probability (BEP) performance, the design of a modified 3D constellation for maximizing the squared minimum Euclidean distance (MED) between the transmitted spatial vectors (TSVs) is illustrated. Moreover, the squared MEDs for QIM-TDC are analyzed and compared with the squared MEDs of the conventional spatial modulation schemes. Finally, The average BEP is analyzed in this paper. Numerical results with comparison among the other schemes demonstrate the QIM-TDC scheme achieves the improved performance.