Radio over Fibre for In-Building Distributed Antenna Systems

Transcription

1 Radio over Fibre for In-Building Distributed Antenna Systems David Wake University of Kent

2 Outline Distributed Antenna Systems (DAS) What are they and what are their advantages? Application areas and business models Transmission technologies Radio over Fibre Advantages over competing transmission options Technologies and typical performance Fibre DAS (F-DAS) Design Parameters Commercial products and architectures Outlook

3 Distributed Antenna Systems Enhanced coverage and capacity for in-building wireless communications Uniform coverage with low radiated power per antenna Reduced CapEx and OpEx through centralisation of radio resources Application areas include office blocks, shopping malls, transport hubs etc. Can be owned by building landlord, network operator or third party Traditionally use copper (coaxial) transmission cables for distribution of RF signals mobile device antenna transmission cable base station backhaul

4 Radio over Fibre (RoF) RF signal transmission over analogue optical fibre links Low loss transmission using small, lightweight cables compared to copper (RG-214, 11mm dia., 200kg/km) Provides alternative to copper transmission cables to give F-DAS Typical RoF link consists of 2 uncooled DFB laser, optical fibre, pin photodiode and RF amplifiers 1.5 Intensity modulation with direct detection 1 External modulation not used for F- DAS due to high cost and complexity 0.5 Allows possibility of inter-building links 0 attenuation, db/km fibre attenuation, db/km RG-142 RG frequency, MHz wavelength, nm

5 Typical F-DAS Architecture

6 F-DAS Link Types 1. RF over SMF simple, wideband double star topology passive antenna units BTS RF CENTRAL HUB L SMF REMOTE HUB PD coax ANTENNA UNIT RF 2. RF over MMF as RF over SMF, but special launch conditions required for transmission over MMF BTS RF CENTRAL HUB L MMF REMOTE HUB PD coax ANTENNA UNIT RF 3. IF over SMF / MMF complex, narrowband double star topology active antenna units BTS RF CENTRAL HUB IF IF L LO SMF / MMF REMOTE HUB PD UTP ANTENNA UNIT IF RF LO 4. Digitised IF over SMF / MMF complex, narrowband single star topology active antenna units BTS RF CENTRAL HUB IF IF A/D L LO SMF / MMF ANTENNA UNIT IF PD D/A LO RF

7 RF over low-quality MMF Coax SMF MMF A B x x Laser Photodetector Signal Generator 32QAM 2Ms/s 2.5GHz C D x x 300m MMF 300m MMF x x Signal Analyser A B C D Short Coaxial Cable Short SMF Patchcord MMF Link FRIDAY MMF Link

8 RoF optical components CENTRAL UNIT REMOTE UNIT RF input RF output Attn Laser PD Fibre PD Laser RF output RF input Laser frequency response efficiency P1dB relative intensity noise maximum operating current Fibre frequency response attenuation delay Photodiode frequency response responsivity P1dB

9 RoF link performance parameters Parameter Gain Input Noise IIP3 Typical Value at 2.5GHz -20 db -140 dbm 28 dbm SFDR 112 db.hz 2/3 P1dB CDR 10 dbm 150 db.hz Output Power (dbm) Gain = -20dB SFDR = 112dB.Hz 2/ N in (-140 dbm) Input Power (dbm) IIP3 (28 dbm) f 1 f 2 2f 1 f 2 2f 2 f 1

10 Radio Design Parameters Parameter Number of channels Channel bandwidth Channel frequencies Modulation scheme Duplex method Max. transmit noise and spurious emissions Transmit power Min. received power at antenna Max. received power at antenna (receiver blocking requirement) Impact on RoF design Power per channel is reduced as more channels are added Noise scales with bandwidth Component selection Complex schemes require high CNR FDD allows higher amplifier gains Limits gain of downlink amplifier Sets downlink CNR requirement Sets uplink noise figure requirement Limits gain of uplink amplifier

11 F-DAS vendors

12 Example F-DAS Products Type Product Features RF over fibre IF over fibre Digitised IF over fibre ION-B (Andrew) Unison (LGC Wireless) Digivance ICS (ADC) - Uses single mode fiber (3km reach) - Star topology using uncooled 1310nm DFB lasers - 1 fibre pair for 2 antennas (coax connected) - 4 way optical splitter in central unit - Wideband ( MHz) - Able to use multimode fibre (1km reach) - Double star topology (fibre + UTP) - 1 fibre pair for 8 antennas (UTP connected) - Remote units do not require local power supply - 4 way optical splitter in central unit - Narrowband (35MHz bandwidth) - Able to use established digital transmission technologies - Able to use multimode fibre - Reach limited only by protocol timing issues - 1 fibre pair per antenna - Star, double star or daisy chain topologies - Narrowband (25MHz bandwidth)

13 Outlook for F-DAS F-DAS market share is predicted to increase due to: reducing cost of active systems trend towards high data rate services and larger installations Europe and North America are expected to see a continued migration away from passive systems, with active systems... growing to roughly two thirds of all systems by 2009 (ABI Research, 2004) Long term future less certain due to emergence of digital base stations and remote radio heads specifications such as CPRI and OBSAI for UMTS and WiMAX will digital base stations become the dominant type in future? from CPRI specification v3.0

14 Summary and Conclusion Distributed antenna systems are being used increasingly to enhance coverage and capacity of in-building wireless The next 5 years will see dramatic growth of the in-building wireless systems industry (ABI Research, 2006) Radio over Fibre is predicted to become the dominant transmission technology for these systems Component options, link types, link performance parameters and radio design parameters described Commercial products compared Radio over fibre technology has very promising outlook for in-building wireless networks