Estimation of radio-over-fiber uplink in a multiuser CDMA environment using PN spreading codes

Two of the major issues with radio-over-fiber (ROF) technology for wireless communications are the nonlinear distortion of the optical link and the multipath dispersion of the wireless channel. In order to limit the effect of these distortions, estimation, and subsequently equalization of the concatenated fiber-wireless channel should be done. The estimation of the fiber-wireless uplink was done in a single user CDMA environment. This paper focuses on estimation in a multiuser CDMA environment by utilizing the properties of pseudonoise (PN) spreading codes. We also consider both wireless channel and optical receiver noise. Furthermore, we propose a new iterative technique to mitigate the adverse effect of multiple access interference (MAI) on the identification process. Numerical evaluations of the developed algorithm show a good estimation of both the linear and nonlinear systems with 10 users, an SNR of 25 dB between the mobile user and RAP, and an optical noise power equalling the wireless noise power