Radio over fiber (RoF) or RF over fiber (RFoF) refers to a technology whereby light is modulated by a radio frequency signal and transmitted over an optical fiber link. Main technical advantages of using fiber optical links are lower transmission losses and reduced sensitivity to noise and electromagnetic interference compared to all-electrical signal transmission. Applications range from the transmission of mobile radio signals (3G, 4G, 5G and WiFi) and the transmission of cable television signals (CATV) to the transmission of RF L-Band signals in ground stations for satellite communications.
General Advantage Low attenuation Signals transmitted on optical fiber attenuate much less than through other media like metal cables or wireless media. By using optical fiber, the radio signals can gap larger transmission distances, reducing the need of additional repeaters or amplifiers.
Applications
Wireless Communications In the area of Wireless Communications one main application is to facilitate wireless access, such as 5G and WiFi simultaneously from the same antenna. In other words, radio signals are carried over fiber-optic cable. Thus, a single antenna can receive any and all radio signals (5G, Wifi, cell, etc..) carried over a single-fiber cable to a central location where equipment then converts the signals; this is opposed to the traditional way where each protocol type (5G, WiFi, cell) requires separate equipment at the location of the antenna. Although radio transmission over fiber is used for multiple purposes, such as in cable television (CATV) networks and in satellite base stations, the term RoF is usually applied when this is done for wireless access. In RoF systems, wireless signals are transported in optical form between a central station and a set of base stations before being radiated through the air. Each base station is adapted to communicate over a radio link with at least one user's mobile station located within the radio range of said base station. The advantage is that the equipment for WiFi, 5G and other protocols can be centralized in one place, with remote antennas attached via fiber optic serving all protocols. It greatly reduces the equipment and maintenance cost of the network. RoF technology enables convergence of fixed and mobile networks. RoF transmission systems are usually classified into two main categories (RF-over-fiber; IF-over-fiber) depending on the frequency range of the radio signal to be transported.
a) In RF-over-fiber architecture, a data-carrying RF (radio frequency) signal with a high frequency is imposed on a lightwave signal before being transported over the optical link. Therefore, wireless signals are optically distributed to base stations directly at high frequencies and converted from the optical to electrical domain at the base stations before being amplified and radiated by an antenna. As a result, no frequency up–down conversion is required at the various base stations, thereby resulting in simple and rather cost-effective implementation is enabled at the base stations. b) In IF-over-fiber architecture, an IF (intermediate frequency) radio signal with a lower frequency is used for modulating light before being transported over the optical link. Therefore, before radiation through the air, the signal must be up-converted to RF at the base station. Access to dead zones An important application of RoF is its use to provide wireless coverage in the area where wireless backhaul link is not possible. These zones can be areas inside a structure such as a tunnel, areas behind buildings, Mountainous places or secluded areas such as jungles. FTTA (Fiber to the antenna) By using an optical connection directly to the antenna, the equipment vendor can gain several advantages like low line losses, immunity to lightning strikes/electric discharges and reduced complexity of base station by attaching lightweight optical-to-electrical (O/E) converter directly to antenna.
Advantages for Wireless Communications Low complexity RoF makes use of the concept of a remote station (RS). This station only consists of an optical-to-electrical (O/E) (and an optional frequency up or down converter), amplifiers, and the antenna. This means that the resource management and signal generation circuitry of the base station can be moved to a centralized location and shared between several remote stations, thus simplifying the architecture. Lower cost Simpler structure of remote base station means lower cost of infrastructure, lower power consumption by devices and simpler maintenance all contributed to lowering the overall installation and maintenance cost. Further reduction can also be made by use of low-cost graded index polymer optical fiber (GIPOF) Future-proof Fiber optics are designed to handle gigabits/second speeds which means they will be able to handle speeds offered by future generations of networks for years to come. RoF technology is also protocol and bit-rate transparent, hence, can be employed to use any current and future technologies. New RoF techniques that support MIMO-enabled wireless services, notably 4G/5G mobile and 802.11 WLAN standards, have also been proposed.
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