Multi-Wavelength WiMAX–PONs With Overlapping Cells

An access network architecture integrating standard wireless signal formats over multi-wavelength splitter passive optical networks (PONs) based on radio-over-fiber (RoF) technology is demonstrated. Frequency division multiplexing (FDM) is applied to address individual base stations sharing a single wavelength. The extended wavelength band overlay overcomes the need for complex dispersion compensation techniques as it avoids the use of high frequency subcarriers in the FDM window. Also, it achieves enhanced network scalability compared with previously reported converged architectures as well as reduced component cost. Significantly, extended features of wireless networks have been presented through the application of overlapping cells to overcome the wireless spectrum congestion beyond current deployment scenarios and provide resilience for legacy PONs. To evaluate the network transmission characteristics, multiple IEEE802.16d channels, with 70 Mbits/s downstream and 40 Mbits/s upstream data rates, are frequency shifted around the same RF carrier and transmitted on two different wavelengths. The obtained results have demonstrated error vector magnitudes (EVMs) of -31 dB at optical network unit/base-station (ONU/BS) remote antenna inputs and minimum 10^-4 bit error rates (BERs) bidirectionally over combined 20 km and faded 330 m overlapping micro-cell circumferences without any error coding or relay techniques. The application of a low-cost long-wavelength vertical cavity surface emitting laser (VCSEL) array in upstream for colorless transmission demonstrated 0.7 dB power penalty to the received worldwide interoperability for microwave access (WiMAX) channels in the optical line terminal (OLT).