Channel Estimation and Equalization of Fi-Wi Uplink for Multiuser Networks

Radio-over-fibre (ROF) has received increasing attention for its ability to enable broadband wireless access. This fibre-based wireless access scheme meets the demand for broadband service by integrating the high capacity of optical networks with the flexibility of radio networks (the optical and wireless channels are concatenated with one another).There is however, impairments that come with this appealing technology. The nonlinear distortion of the optical link and the multipath dispersion of the wireless channel are two of the major factors. In order to limit the effects of these distortions, estimation and subsequently equalization of the concatenated fibre-wireless (Fi-Wi) channel needs to be done. In the proposed technique, estimation of the fibre-wireless uplink in a multiuser CDMA environment is presented using pseudonoise (PN) training sequences. Estimation is done in a multiuser CDMA communication system where all users transmit their signal simultaneously. Correlation analysis is applied to identify the channel impulse response (CIR). The estimation and equalization are performed in the presence of wireless and optical channel noise. Estimation of both the linear and nonlinear systems in the presence of ten independent users is simulated. Then the fiber-wireless uplink is equalized in a single user environment using Hammerstein type decision feedback equalizer.