Realization of OSW/AWG-based bipolar wavelengthtime optical CDMA for wiredwireless transmissions
This study proposes a novel radio-over-fiber (RoF) system using two-dimensional (2-D) optical code-division multiple-access (OCDMA) scheme using pseudorandom (PN) codes for the time-spreading and wavelength-hopping (t-spreading/?-hopping) codes. The 2-D system is implemented using optical switches (OSWs) and arrayed-waveguide grating (AWG) routers. By constructing 2-D codes using bipolar PN codes rather than unipolar codes provides a significant increase in the maximum permissible number of active radio base stations (RBSs). In general, the phase-induced intensity noise (PIIN) generated at high optical intensities significantly degrades the performance of a conventional multi-wavelength scheme. However, the OSW-based time-spreading method employed in the current 2-D OCDMA scheme effectively suppresses the PIIN effect. Additionally, multiple-access interference (MAI) is suppressed by the use of a wavelength/time balanced detector structure in the network receivers. The numerical evaluation results demonstrate that under PIIN- and MAI-limited conditions, the proposed system outperforms a conventional multi-wavelength OCDMA scheme by using the spectral spreading scheme to suppress beating noise. Especially, the t-spreading encoder/decoder (codec) groups share the same wavelength codec and the overall complexity is reduced and system network becomes more compact.
radio-over-fiber (rof) optical code-division multiple-access (ocdma) optical switch (osw) arrayed-waveguide grating (awg) router multiple-access interference (mai)