Improved time and frequency synchronization for dual‐polarization OFDM systems

This article presents techniques for improved estimation of symbol timing offset (STO) and carrier frequency offset (CFO) for dual‐polarization (DP) orthogonal frequency division multiplex (DP‐OFDM) systems. Recently, quaternion multiple‐input multiple‐output OFDM has been proposed for high spectral efficiency communication systems, which can flexibly explore different types of diversities such as space, time, frequency, and polarization. This article focuses on synchronization techniques for DP‐OFDM systems using a cyclic prefix, where the application of quaternion algebra leads to new improved estimators. Simulations performed for DP system methods show faster reduction of STO estimator variance with a double‐slope line in the log‐variance line versus signal‐to‐noise ratio (SNR) plot compared with single‐polarization (SP) counterparts, and simulations for CFO estimates show a 3‐dB gain of DP over SP estimates for same SNR values defined, respectively, for quaternion‐valued or complex‐valued signals. Cramer–Rao bounds for STO and CFO are derived for the synchronization methods, correlating with the observed gains of DP over SP OFDM systems.