DWDM aspects of radio-over-fiber

Fixed wireless access provides an attractive option for 'last mile' delivery of broadband services in urban areas. The availability of spectrum in the millimeter-wave (mm-wave) band allows delivery of digital voice, video and data services. Optical transport may play an important role in point-to-multipoint (PMP) fixed wireless access systems by providing distribution backbone between the central office and base transceiver stations (BTSs). The use of radio-over-fiber transmission, where all radio processing is performed before the signal is transmitted over fiber, will minimize outdoor equipment and allow flexible siting of BTSs many kilometers from the central office. To perform optical-to-radio conversion, the detected optical signal is simply filtered, amplified and radiated. Together with the radio signal for broadcast, an unmodulated carrier may also be delivered to the BTS to allow duplex operation. Using the unmodulated carrier as a local oscillator to perform downconversion of the return signal allows optical transmission back to the central office at a convenient IF frequency. The necessary electrical functionality may be realized using MMIC technology, providing a compact, high performance BTS module.