Novel Scheme of Multi-Rate Quasi-synchronous Coherent Time-spreading OCDMA System

Abstract

We propose a novel scheme of multi-rate quasisynchronous coherent time-spreading OCDMA system, employing orthogonal variable spreading factor (OVSF) codes with a zero-correlation zone. Within permissible time delay, the aperiodic cross-correlation of OVSF with a zero-correlation zone equals zero. Therefore, multipleaccess interference and beat noise can be removed in multirate quasi-synchronous coherent time-spreading OCDMA system, and the near-far problem can also be eliminated. Simulation of eight simultaneous users with 2.5 Gbit/s, 1.25 Gbit/s and 0.625 Gbit/s is demonstrated, where the fiber link consists of 20 km single-mode fiber, plus 2 km Dispersion Compensating Fiber. The results show that OVSF codes with a zero-correlation zone can be employed to multi-rate quasi-synchronous coherent time-spreading OCDMA system.

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

“…Based on above analysis, the new construction of OVSF-OZCZ code set satisfies the ideal auto-correlation and cross-correlation properties within Zcz, which is helpful to reduce the effect of time delay between different users compared with the construction in [21], [32]. The transmitter and receiver both employ the unipolar code set for the intensity modulation directly in VLC system compared with the construction in [28], [29]. Furthermore, compared with the construction in [24], [25], the proposed code set with different spreading factors can enhance the multi-rate system performance significantly.…”

“…Optical zero correlation zone (OZCZ) codes with ideal correlation properties in the zero correlation zone have been designed for QS-CDMA-VLC system, which can effectively tolerate the inevitable time delay and eliminate multiple access interference (MAI) and phase-induced intensity noise (PIIN) [24]- [26]. Some reported OVSF-ZCZ code sets such as Zcomplementary set [27], [28] and ternary complementary pair (TCP) [29], [30] can both support multi-rate transmission and tolerate time delay, but three polar sequences do not fit for intensity modulation of VLC system [31].…”