Hybrid Constellations for Dual-Polarized Wireless Communications

This paper considers constellation designs for 2×2 systems with a coherent dual-polarized antenna configuration. Such an architecture enables a four dimensional (4D) signal space that exploits polarization, and this paper considers hybrid constellations formed as a combination of amplitude/phase states and polarization states. For coherent detection, phase shift keying (PSK) is combined with polarization shift keying (PolSK) to produce constant-power PSK+PolSK constellations that consistently outperform PSK+PSK. Next, quadrature amplitude modulation (QAM) and amplitude phase shift keying (APSK) are combined with PolSK to construct hybrid QAM+PolSK and APSK+PolSK constellations, and constrained capacity results indicate the viability of coded modulation based on these signal spaces. For non-coherent detection, differential PSK (DPSK) is combined with PolSK to yield DPSK+PolSK signaling that does not require phase alignment at the receiver and outperforms DPSK+DPSK, both with and without the adverse effect of carrier frequency offset and symbol time offset. The methods are verified in over-the-air testing with universal software radio peripherals (USRPs) integrated in a dual-polarized testbed. Error performances of all proposed 4D hybrid constellations in an OFDM framework are analyzed under both quasi-AWGN and multipath fading scenarios.