Variable Spreading Method for MC/DS-CDMA Road to Vehicle Communication System

This paper presents a spreading method for down-link road to vehicle communication systems, which support broadcast and unicast communication in the same frequency. The proposed system is based on MC/DS-CDMA system, and uses a small spreading factor for broadcast transmission to achieve high data rate and uses a large spreading factor for unicast transmission to reduce the interference among vehicles. In the proposed system, the scrambling code, which is used for reducing the interference among cells under the multi-cell environments, is designed for unicast communication not to affect to the broadcast communication. Moreover, a space-time block coding (STBC) technique is applied to receive the site diversity gain with keeping orthogonality for broadcast transmission by using the plural access points. The performance of the proposed system is evaluated by computer simulation under additive white Gaussian noise (AWGN) and Rayleigh fading environment