Enhanced Zero Correlation Code-based Timing Synchronization for DCO-OFDM Systems

Optical wireless communication (OWC) is one of promising technologies to improve the reliability of vehicular communications. In this correspondence, we investigate that the previous zero correlation code (ZCC)-based timing synchronization method is vulnerable to inter-symbol interference (ISI) in real-and-positive signals, caused by wireless reflected channels and light emitting diode (LED)'s limited bandwidth, leading to performance degradation in OWC. Thus, we propose an enhanced ZCC (eZCC) timing synchronization approach for direct current biased optical-orthogonal frequency division multiplexing (DCO-OFDM) OWC systems, which is theoretically proved to be robust against ISI. There are a pool of training symbols and a pool of local symbols in ZCCs. We design a non-repetitive pilot structure, and use the cross-correlation between two pools to formulate a timing metric. The timing synchronization is conducted by maximizing the formulated timing metric. The proposed non-repetitive structure enables the cross-correlation higher than the hybrid auto-correlation and cross-correlation between ZCCs in a repetitive pilot structure that generates two identical parts in the previous ZCC method. We prove that the proposed timing metric is Gaussian distribution, and derive the probability of false detection in a closed form. Also, we build an experiment testbed to validate the proposed eZCC approach superior to the existing works in terms of bit error rate (BER).