New Construction of OVSF-OZCZ Codes in Multi-Rate Quasi-Synchronous CDMA VLC Systems for IoT Applications

Internet of Things (IoT) has become an emerging vision for next-generation network and attracts many researchers' attention. In this paper, we propose a novel quasi-synchronous code division multiple access (QS-CDMA) visible light communication (VLC) system for IoT network. A new construction of optical zero correlation zone (OZCZ) code set with orthogonal variable spreading factor (OVSF) is presented for this system, which can meet the multi-rate requirement and tolerate time delay. After deriving the construction and properties of the proposed code set, the maximum numbers of simultaneous users and multiple access interference (MAI) characteristic are analyzed. Furthermore, the signal noise ratio (SNR) and bit error rate (BER) performance of this system are also investigated while taking into account the effects of phase-induced intensity noise (PIIN), shot noise, and thermal noise. The numerical results indicate that the new construction can eliminate MAI and PIIN, which can achieve high quality transmission in the multi-rate QS-CDMA-VLC system for IoT applications.