Double-spread radio-over-fiber system for next-generation wireless technologies

The main challenge for present and future personal communication systems and personal communication networks stems from the exponentially growing user demand. Radio over fiber (RoF), the combination of optical and wireless technologies, has many advantages and a wide range of applications. The 3G wireless communication technology uses wideband code division multiple access (WCDMA) standards to support the broadband services, and RoF technology will be an appropriate candidate in such environments. This paper presents what is believed to be a novel double-spreading mechanism, both in the wireless and optical domains for the cascaded RoF systems. Although a star configuration is the most popular because of its easy maintenance, the cascade or bus configuration can reduce the fiber counts and is hence cost-effective. Simulation studies on bit-error-rate performance for different numbers of users using orthogonal variable spread factor (OVSF) codes in the wireless domain and Walsh-Hadamard codes for optical code division multiple access (OCDMA) in the optical domain have been carried out. Hence, in view of less system complexity and cost, the proposed double-spreading technique would be an ideal solution for WCDMA-based wireless systems and the upcoming 4G with backbone cascaded RoF networks.