Four Dimensional Hybrid Constellations for Dual-Polarized Wireless Communications

This paper considers the design of signal constellations for a 2 × 2 MIMO digital communication system with dualpolarized transmit and receive antennas. Specifically, it proposes four-dimensional “hybrid” constellations formed as the direct product of an absolute amplitude/phase state and a polarization state. We begin by imposing a constant symbol power constraint and combining phase shift keying (PSK) with polarization shift keying (PolSK) to produce hybrid constellations referred to as PSK+PolSK. As a motivating example, uncoded 8PSK+8PolSK is shown to enjoy a 1.1 dB gain over more conventional 8PSK+8PSK at a symbol error rate of 10 ^-4 in additive white Gaussian noise. When the power constraint is removed to form QAM+PolSK an APSK+PolSK constellations, the resulting performance suffers relative to comparable QAM+QAM and APSK+APSK constellations due to the polarization state's sensitivity to symbol power. Capacity calculations provide insight into the viability of coded modulation based on hybrid signaling. Particular hybrid constellations based on QAM+PolSK and APSK+PolSK were shown to provide a capacity advantage over comparable QAM+QAM constellations over a range of rates of practical value.