VLC-CDMA systems based on optical complementary codes

VLC performs the dual-functions of communication and lighting and will play an important role in next-generation wireless communications. Proper multiple access methods should be identified for VLC in multi-user scenarios. This article proposes a VLC-CDMA system using OCCs, which are unipolar codes with a multiple sub-codes structure. OCCs offer good autocorrelation and cross-correlation functions. The issues on encoding criteria and application of OCCs in VLC-CDMA systems are discussed. The transmitters use LEDs with different wavelengths to distinguish different sub-codes. Compensator circuits are used to achieve equal gain combining at receivers to exploit the good correlation properties of OCCs. The receivers use the filters with different center wavelengths to distinguish different sub-codes. The performance of VLC-CDMA systems with OCC is compared to OOCs and multi-carrier CDMA systems, to verify that the proposed system is robust for its applications in multi-user scenarios.