Frequency Offset Compensation and Carrier Phase Recovery for Differentially Encoded 16-QAM Vector Signal in a 60-GHz RoF System

Differentially encoding and frequency offset compensating for a 16-quadrature amplitude modulation (16-QAM) vector signal in 60-GHz millimeter-wave radio-over-fiber (RoF) systems are experimentally investigated. The fourfold phase ambiguity issue in a non-data-aided signal communication transmission system with conventional square 16-QAM constellations is successfully tackled based on the differentially encoding scheme. Experimental results show that frequency offset compensation and carrier phase recovery are simultaneously achieved by utilizing the decision-directed carrier phase recovery algorithm. Up to
$\sim\! \pm 1.3 \times 10^{-3}$
frequency offset times symbol rate product
$\Delta f \cdot T_{s}$
is well compensated at the given bit-error-ratio (BER) value of
$\sim\!\!10^{-3}$
.