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Radio over fiber (RoF) refers to a technology whereby light is modulated by a radio signal and transmitted over an optical fiber link to facilitate wireless access, such as 3G and WiFi simultaneous 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 (3G, 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 (3G, 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, 3G 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 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. == Advantages == Low attenuation It is a well known fact that signals transmitted on optical fiber attenuate much less than through other media, especially when compared to wireless medium. By using optical fiber, the signal will travel further, reducing the need of repeaters. 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)〔A. Ng'oma, (“Radio-over-Fibre Technology for Broadband Wireless. Communication Systems” ), PhD Thesis, Eindhoven University of Technology, Eindhoven, 2005〕 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.〔〔Hoon Kim (2005) (Radio-over-Fiber Technology for Wireless Communication Services ), Samsung Electronics〕 New RoF techniques that support MIMO-enabled wireless services, notably 4G/5G mobile and 802.11 WLAN standards, have also been proposed.〔G.S.D. Gordon, ("Feasibility Demonstration of a Mode-Division Multiplexed MIMO-enabled Radio-over-Fiber Distributed Antenna System" ), IEEE Journal of Lightwave Technology, vol. 32, no. 20, pp. 3521-3528, Oct. 2014〕 The most popular use for (RF over fiber ) is for cable TV systems. It is impossible to run RF signals over copper cable to more than few hundred feet. They are transporting their entire CATV channel lineup over a single-fiber optic cable, because this way they can transport the signal for hundreds of km. It works like this: An electrical RF signal usually in the range of 54–870 MHz is converted to modulated light using RF 1310 nm or 1550 nm laser optics. The light travels over single-mode fiber to the fiber optic RF receiver where is converted back to electrical RF. Electrical RF is directly connected to a TV or set-top box. 1550 nm is more popular because it has less losses in the fiber and by using fiber-optic amplifier known as EDFA it is possible to extend the transport distance. 1310 nm is losing about 0.35 db/KM of optical signal, 1550 nm is losing only 0.25 db/km. Optical budget between transmitter and receiver varies, depending on the transmitter power and receiver sensitivity. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Radio over fiber」の詳細全文を読む スポンサード リンク
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