Radio over fiber technology is a growing part of many cellular communications network plans. As broadband services, such as high-speed data and streaming video, become more prevalent in cellular networks, the available bandwidth of those networks will be quickly consumed. In order to conserve or increase capacity, many network planners are looking to millimeter-wave links or optical cables between a base station (BS) and a central control station (CS) in order to route large-bandwidth signals without overtaxing the lower-frequency wireless channels within the system.
In this architecture, the CS performs switching, medium access control (MAC), and other frequency-management functions, taking the burden for this processing from the BS units. Although millimeter-wave bands at 71 to 76 GHz and 81 to 86 GHz have been allocated by the United States Federal Communications Commission (www.fcc. gov) for point-to-point communications applications such as between the BS units and the CS, the connection can also be made physically, through the use of optical fiber. The technique involves simple electrical-to-optical and optical-to-electrical conversions, and takes advantage of the large bandwidths afforded by optical fibers as well as its low signal loss and immunity to electromagnetic interference (EMI).
By using this radio over fiber approach in a cellular network, the main function of the BS is to convert optical signals to wireless signals to optical signals and optical signals to wireless signals, while the complex signal process and frequency management chores are handled by the CS. This simplifies the design of the BS and allows the CS to perform dynamic capacity allocations based on changing customer demands.
Optical communications does not involve the antenna boresighting required of millimeter-wave links, and does not suffer atmospheric effects, fading, and propagation losses. Of course, optical links must be installed over the full coverage area while millimeter-wave links work from point to point. Most network planners view practical solutions involving multiple technologies, including cellular frequencies, millimeterwave, and radio over fiber components.