Radio-over-fiber networks. RoF networks –Optical fiber is medium of choice in...

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Transcript of Radio-over-fiber networks. RoF networks –Optical fiber is medium of choice in...

  • Radio-over-fiber networks

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

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

  • Radio-over-fiber networksFiber-optic microcellular radio

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

  • Radio-over-fiber networksRemote modulationRemote modulation avoids equipping each radio port with a laser & associated circuit to control laser parameters such as temperature, output power, and linearityRemote 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 networksRemote modulation

  • Radio-over-fiber networksRadio-over-SMF networksApart from microcellular radio signals, optical fibers can be used to support wide variety of other radio signalsRoF networks provide transparency against modulation techniques & support various digital formats and wireless standards in cost-effective mannerExperimental demonstration of RoF network able to simultaneously transmit following four wireless standards in downstream direction using a single antennaWCDMAIEEE 802.11 WLANPHSGSMElectroabsorption modulator (EAM) based method used to combine various radio signals onto common single-mode fiber (SMF) => radio-over-SMF networks

  • Radio-over-fiber networksRadio-over-SMF networks

  • Radio-over-fiber networksRadio-over-MMF networksMany buildings have preinstalled multimode fiber (MMF) cables rather than SMF links => radio-over-MMF networksCost-effective MMF-based networks can be realized by deploying low-cost vertical-cavity surface-emitting lasers (VCSELs) operating in 850-nm transmission windowExperimental 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 standardsGSMUMTSIEEE 802.11 WLANDECT PRS

  • Radio-over-fiber networksWDM RoF networksIntroduction of wavelength dimension not only increases capacity of WDM RoF networks but also increases number of base stations serviced by a single central stationExperimental demonstration of WDM RoF ring network based on ROADMsWDM fiber loop connects multiple remote nodes with central officeEach remote node deploys array of tunable FBGsA remote node is able to locally drop one or more wavelengths by tuning its FBGs accordinglySeveral so-called radio access units (RAUs) are attached to each remote nodeEach RAU may serve one or more mobile usersROADMs 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 networksRoF & FTTH networksFuture 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 networksRoF & WDM PON networksGiven that WDM PONs become rapidly mature, it is desirable to integrate WDM PONs with RoF systemsExperimental demonstration of seamless integration of eight 2.5 Gb/s WDM signals with RoF systemSimultaneous frequency upconversion of the eight WDM signals was done all-optically by means of FWMFWM is independent of signal bit rate & modulation format => FWM can be used for simultaneous frequency upconversion of different optical WDM signals

  • Radio-over-fiber networksRoF & rail track networksFast-moving users (e.g., train passengers) suffer from frequent hand-overs in cellular networks => numerous packet losses & significantly decreased network throughputSo-called moving cell concept solves this problemRoF network is installed along rail tracksHigh-capacity wireless services provided to high-speed-train passengers by using hierarchical approachWireless link between railway & train using RoF networkSeparate wireless link between train & users deploying one or more WLAN access points in each train carriageConcept of moving cells lets cell pattern move together with passing train => train communicates on same RFs during whole connection without requiring hand-oversMoving cells implemented at central stationCentral station is able to track location of train based on received upstream RF signals

  • Radio-over-fiber networksRoF & rail track networks