RF over Fiber

1
RF over Fiber

• Dr. Gerhard Franz
• A. G. Franz Associates, LLC
• www.agfranz.com
• June 6, 2003

2
Fiber Basics

• Property of glass fiber carrying a signal first
  demonstrated in 1870 by John Tyndall
• Total internal reflection keeps light in the core
• Different index of refraction between the core
  and the cladding glass
• Critical angle
• Multi-mode fiber 62.5um diameter
• Single-mode fiber 8um diameter
• Greatly reduces dispersion
• Increases bandwidth

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Fiber Cable
6-268 fibers in a single cable
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Technologies

• Modulation of laser by RF
• Directly modulated (DM)
• RF signal directly varies the bias of a
  semiconductor laser diode
• Less costly
• Externally modulated (EM)
• Constant wave (CW) laser (always on bright)
• Light is modulated by an external lithium-niobate
  electro-optic modulator
• Best performance
• Very expensive
• CWDM - Coarse Wave Division Multiplexing
• DWDM - Dense Wave Division Multiplexing
• Combining multiple wavelengths (colors) in one
  fiber

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RF Fiber-Optical Links
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RF over Fiber Applications
RF ON FIBER Applications Diagram
LNA Gain is set so that maximum RF input to fiber
optic transmitter is less than 0 dBm. Noise
Figure of system is also set by LNA. Fiber-Span
can integrate an LNA with the fiber optic link
for low noise figure. LNB is used in microwave
systems such as TVRO.
RF / Fiber Optic Links are available as
transmitters, receivers, integrated transceivers
for bidirectional communications or built-up
into 19 inch subracks as subsystems.
Antenna
Base Station, Radio Receiver or Off-Air
Interface
Band-pass Filter
Fiber Optic Transmitter
Fiber Optic Receiver
LNA
fibers
Fiber Optic Receiver
Fiber Optic Transmitter
PA
Duplexer or Switch
Low-pass Filter
Unity Gain across short (lt1km) fiber link not
considering LNA or PA. For every 1 dBo increase
in optical loss, RF gain drops 2 dBe. Once
optical loss is know, fiber optic link can
modeled as an RF gain stage with RF Gain, Noise
Figure and IP3 (distortion).
Output amplifier generates the RF power
required for downstream transmission
Optimal RF Input level from radio 10 to 5
dBm (absolute maximum 10 or 20 dBm depending on
model.)
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RF over Fiber Benefits

• Why Fiber? - Advantages
• Range, bandwidth and RF performance
• Low noise figure, high dynamic range
• No signal egress (security)
• EMI/RFI Immunity (interference)
• Isolation from lightening strikes
• Transports signals in native RF format, complex
  circuitry at remote location
• Thin cable size, very low cable weight
• High frequency, low signal loss
• Flexible system configurations

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RF over Fiber Performance
Stable RF Gain
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RF over Fiber Performance
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RF over Fiber Performance
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RF over Fiber Cost
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RF over Fiber Drivers

• Technology insertion opportunities
• RF Performance and Cost is critical
• Antenna proliferation
• Growing spectrum demands
• Communications
• Weapons
• IFF, navigation
• Surveillance and Reconnaissance

13
RF over Fiber Applications

• Low Frequency to Microwave Systems
• RF Antenna Remoting and Signal Routing
• CATV
• Wireless Repeaters and Tunnels
• In-Building Coverage
• Traditional IF and L/S-band transport
• RF Delay Lines
• WDM/DWDM Information Networks
• SETI and Radio Astronomy (NRAO)

14
RF over Fiber Applications
Wireless Networks
Radio
Satellite
GPS
Broadcast
Tunnels-Subways
In-Building Distribution
Highways
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RF over Fiber Products

• Transceivers Transmitters Receivers

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Remote Antenna Configuration
Fiber Optic Remote Antenna
Typical System Configurations
Antenna
LNA
RF out
To Base Station or
AC 231
AC 231
off-air antenna
RF in
LPA
Fiber Optic
Fiber Optic
Duplexer
Transceiver
Transceiver
Fiber
or switch
Two Fiber Bidirectional System
Antenna
LNA
RF out
AC231W
To Base Station or
AC231W
-1.3
off-air antenna
-1.5
Single Fiber
RF in
Fiber Optic
LPA
Fiber Optic
Duplexer
Transceiver
Transceiver
with internal WDM
with internal WDM
or switch
Single Fiber Bidirectional WDM System
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Distributed Antenna
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HFC System

• Low loss fiber improves end-of-line performance
• 54 - 870 MHz bandwidth
• Fiber deep design
• Fiber-to-the-curb FTTC
• Fiber-to-the-building FTTB
• Fiber-to-the-home FTTH
• Fiber-to-the-desk FTTD
• Bidirectional systems
• 1550nm in one direction
• 1310nm in opposite direction

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HFC Outdoor Optical Node
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FTTH Optical Node
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RF over Fiber Systems Today

• Satcom IF example
• 70 MHz
• Malaysia Installation
• Hughes outfitted satellite ground station
• lightning problems

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RF over Fiber Systems Today

• Direct Satellite Systems
• L-Band 950 - 2100 MHz
• Complete transponder BW (dual polarization)
• IBM Internal distribution
• Roof-top to network rooms
• TX to 110 splitter to 10 remote locations
• Cable size and run lengths, 2 GHz freq.

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RF over Fiber Systems Today

• LMDS Systems
• Base station roof top systems
• IF lt 2 GHz
• IF to Microwave conversion _at_ antenna
• Cable size and weight

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RF over Fiber Systems Today

• Airports
• Denver, SF, Newark
• PCS, Cellular, Emerg/fire/ems
• SFDR 102 dB/Hz
• Cable size, run lengths

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RF over Fiber Systems Today

• Delay Lines
• Raytheon Altimeter production testing
• compact size
• low RF loss
• 1.5 to 6 us delay

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RF over Fiber Systems Today

• Radio Astronomy
• Smithsonian Project
• 5 GHz IF (200 GHz RF band)
• WDM Fiber links for timing signal
• NRAO, Allen (SETI)

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RF over Fiber Systems Today

• ISM Band
• Philadelphia Airport
• Two remotes per one base unit
• Simple wavelength management
• Temp. cooled remotes

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RF over Fiber Systems Today

• Airborne Repeater
• Tethered balloons
• Cellular repeater
• South America
• 3000 foot height
• Covers entire city

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RF over Fiber Systems Today

• PCS Repeater
• LG Telecom
• Over 6K deployed in one network
• Star Architecture

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RF over Fiber Systems Today

• Multi-band, Multi-Carrier Tunnel System
• Tunnel Application
• Brooklyn Battery Tunnel
• 4 service providers
• Cellular, PCS, SMR
• AC power problem averted

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RF over Fiber Systems Today

• In-Building
• PCS, cellular
• Multi-band, multi-operator
• Risers but horizontal spans too
• 95 to 100 dB/Hz
• 10 to 23 dBm output power
• 8 to 12 dB Noise figure
• 2K per antenna link

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RF over Fiber Systems Today

• In-Building Backhaul
• BTS to In-door space
• up to 20 km
• leased fiber
• 1.3 and 1.5 WDM

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RF over Fiber Systems Today

• GPS on Fiber
• Commercial for base station timing needs
• Military - Spawar
• Retro-fit all Navy ships
• Cable size
• Interference
• Zero Field Failures!

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RF over Fiber Applications

• Next-Generation Networks
• Software Defined Radios (SDR)
• High Capacity point-to-point links
• Multi-band, multi-beam phased-array antenna
  operations
• Shared apertures / Active arrays
• True-time-delay (TTD) beamforming

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Summary

• RF can be transported directly over fiber
• Fiber has technical and economic benefits over
  coaxial cable
• Wireless, cable and satellite systems are
  increasingly using this technology