Hybrid Optical–Wireless Access Networks
Next-generation access networks are expected to provide mobility, large data bandwidth, high quality of service (QoS), and ubiquitous coverage. Hybrid optical-wireless access networks will support these complementary features through high-capacity fiber subnetworks and flexible wireless subnetworks. As wireless access technologies progress, increased demand for access bandwidth and QoS will require a rapid evolution of fiber subnetworks and a tighter integration of the two technologies. This paper presents both radio-over-fiber transport technologies and novel architectures and technologies for hybrid optical-wireless networking. Basic optical systems for radio signals' transport use intensity modulation and direct detection. Advanced transport systems may utilize amplified links, coherent links, subcarrier transport, and digitized transport. They can be used to support powerful access solutions. On the networking side, diverse alternatives for hybrid access architectures are presented. Two wavelength division multiplexing (WDM)-based architectures, MARIN and GROWNet, are analyzed in detail. Both architectures dynamically support next-generation wireless access network traffic employing reconfigurable WDM technologies. MARIN is more technologically conservative and so is more suitable for near-future implementation. GROWNet is more technologically aggressive and is substantially more flexible and more powerful. Using hybrid network simulations, we demonstrate these architectures' capabilities to dynamically balance wireless traffic and to coordinate wireless transmission. We also review other research efforts in this field including ACCORDANCE, FiWi, FUTON, and WOBAN. Remaining challenges and research topics are also discussed to motivate further investigations into optical-wireless access networks.