Radio-over-fiber networks

Radio-over-fiber networks RoF networks Optical fiber is medium of choice in wide, metro, access, and local area (wired) networks PONs might be viewed as final frontier of optical wired networks interfacing with a number of wireless technologies One interesting approach to integrate optical fiber networks & wireless networks are so-called radio-over-fiber (RoF) networks In RoF networks, radiofrequencies (RFs) are carried over optical fiber links to support various wireless applications

Radio-over-fiber networks Fiber-optic microcellular radio To increase frequency reuse & thereby support growing number of mobile users in cellular radio networks, cells may be subdivided into smaller units called microcells Beside increased capacity, microcells also reduce power consumption & size of handset devices Distributed antenna system connected to base station via optical fibers avoids base station antenna with high-power radiation => fiber optic microcellular radio system Radio signals in each microcell are transmitted & received to & from mobile users by using a separate small canister attached to base station via optical fiber Each canister is equipped with optical-to-RF & RF-to-optical converters, laser, and optical receiver Subcarrier multiplexed radio signals directly modulate laser Radio signals are recovered from optical signal by means of direct detection

Radio-over-fiber networks Fiber-optic microcellular radio

Radio-over-fiber networks Dynamic channel assignment Spectrum delivery scheme (SDS) is a centralized dynamic channel assignment applied at central station SDS dynamically assigns one or more subcarriers to any base station according to current traffic demands SDS helps improve flexibility of fiber optic microcellular radio networks by assigning more subcarriers to heavily loaded base stations & fewer subcarriers to lightly loaded base stations As a result, SDS effectively reduces call blocking probability in fiber optic microcellular radio networks whose traffic loads vary over time

Radio-over-fiber networks Remote modulation Remote modulation avoids equipping each radio port with a laser & associated circuit to control laser parameters such as temperature, output power, and linearity Remote modulation allows design of cost-effective radio port architecture for fiber optic microcellular radio networks using a single high-power laser at base station that is shared among many microcells

Radio-over-fiber networks Remote modulation

Radio-over-fiber networks Radio-over-SMF networks Apart from microcellular radio signals, optical fibers can be used to support wide variety of other radio signals RoF networks provide transparency against modulation techniques & support various digital formats and wireless standards in cost-effective manner Experimental demonstration of RoF network able to simultaneously transmit following four wireless standards in downstream direction using a single antenna WCDMA IEEE 802.11 WLAN PHS GSM Electroabsorption modulator (EAM) based method used to combine various radio signals onto common single-mode fiber (SMF) => radio-over-SMF networks

Radio-over-fiber networks Radio-over-SMF networks

Radio-over-fiber networks Radio-over-MMF networks Many buildings have preinstalled multimode fiber (MMF) cables rather than SMF links => radio-over-MMF networks Cost-effective MMF-based networks can be realized by deploying low-cost vertical-cavity surface-emitting lasers (VCSELs) operating in 850-nm transmission window Experimental demonstration of indoor radio-over-MMF networks using different kinds of MMF in conjunction with commercial off-the-shelf (COTS) components for in-building coverage of following four wireless standards GSM UMTS IEEE 802.11 WLAN DECT PRS

Radio-over-fiber networks WDM RoF networks Introduction of wavelength dimension not only increases capacity of WDM RoF networks but also increases number of base stations serviced by a single central station Experimental demonstration of WDM RoF ring network based on ROADMs WDM fiber loop connects multiple remote nodes with central office Each remote node deploys array of tunable FBGs A remote node is able to locally drop one or more wavelengths by tuning its FBGs accordingly Several so-called radio access units (RAUs) are attached to each remote node Each RAU may serve one or more mobile users ROADMs used at remote nodes allow add-drop wavelengths to be dynamically assigned to remote nodes & attached RAUs in response to given traffic loads

Radio-over-fiber networks RoF & FTTH networks Future multiservice access networks can be realized by integrating RoF systems with existing optical access networks, (e.g., FTTH networks) To achieve this, both wireless RF & wired-line (FTTH) baseband signals should be simultaneously modulated & transmitted on a single wavelength over a single fiber

Radio-over-fiber networks RoF & WDM PON networks Given that WDM PONs become rapidly mature, it is desirable to integrate WDM PONs with RoF systems Experimental demonstration of seamless integration of eight 2.5 Gb/s WDM signals with RoF system Simultaneous frequency upconversion of the eight WDM signals was done all-optically by means of FWM FWM is independent of signal bit rate & modulation format => FWM can be used for simultaneous frequency upconversion of different optical WDM signals

Radio-over-fiber networks RoF & rail track networks Fast-moving users (e.g., train passengers) suffer from frequent hand-overs in cellular networks => numerous packet losses & significantly decreased network throughput So-called moving cell concept solves this problem RoF network is installed along rail tracks High-capacity wireless services provided to high-speed-train passengers by using hierarchical approach Wireless link between railway & train using RoF network Separate wireless link between train & users deploying one or more WLAN access points in each train carriage Concept of moving cells lets cell pattern move together with passing train => train communicates on same RFs during whole connection without requiring hand-overs Moving cells implemented at central station Central station is able to track location of train based on received upstream RF signals

Radio-over-fiber networks RoF & rail track networks