Architecture and Applications of a Versatile Small-Cell, Multi-Service Cloud Radio Access Network Using Radio-over-Fiber Technologies

Small-cell systems based on cloud radio access network (cloud-RAN) architecture have been proposed as promising solutions to meet the ever-increasing capacity demand of the next-generation wireless access networks. By centralizing the processing power to reduce the complexity of conventional cell sites, the cloud-RAN architecture is ideal for large-scale small-cell system at reduced capital and operational expenses. However, high-speed, flexible, and scalable backhaul links between the centralized baseband processing unit (BBU) and the remote antenna units (RAUs) are required to support the high throughput of the small-cell cloud-RANs, and the conventional approaches are based on digital baseband signal transmission in the backhaul links. In this paper, we propose a novel multi-service small-cell wireless access architecture based on radio-over-fiber (RoF) technologies. By utilizing analog radio frequency (RF) signal transmission in the optical backhaul links, the design of RAUs can be further simplified. In addition, by combing RoF with optical wavelength division multiplexing (WDM) techniques, multiple bands, multiple services and multiple operators can coexist in a shared optical infrastructure without interference. To demonstrate the proposed system, two-operator coexistence in a shared small-cell cloud-RoF access network is implemented in an in-building testbed by using off-the-shelf optoelectronic components and commercialized WiMAX base stations and clients. In addition, the feasibility of delivering both conventional wireless services and future-proof high-RF-band services (millimeter-wave band) is also demonstrated in the proposed multi-service small-cell cloud-RoF access systems.