1. Radio-over-fiber networks

2. 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

3. 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

4. Radio-over-fiber networks
Fiber-optic microcellular radio

5. 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

6. 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

7. Radio-over-fiber networks
Remote
modulation

8. 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 WLAN
PHS
GSM
Electroabsorption modulator (EAM) based method used to combine various radio signals onto common single-mode fiber (SMF) => radio-over-SMF networks

9. Radio-over-fiber networks
Radio-over-SMF networks

10. 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 WLAN
DECT PRS

11. 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

12. 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

13. 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

14. 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

15. Radio-over-fiber networks
RoF & rail track networks