WIRELESS ACCESS USING MICROWAVE PHOTONICS Alwyn Seeds Dept. of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, U. K., Tel. +44 20 7679 7928, Fax. +44 20 7388 9325, a.seeds@ee.ucl.ac.uk
Outline Introduction; commercial systems. Broadband access. Millimetre-wave systems; architecture options. Local oscillator signal generation; Optical Injection Phase Lock Loop (OIPLL). Future systems; Wavelength Division Multiplex (WDM).
Commercial Fibre-Radio Systems 1.3µm PIN Photodiode PA 16 Channels Transmit/ Receive PIN Photodiode CENTRAL SITE 1.3µm LNA BASE STATION Circ. Antenna Electrical Optical
Application Example Sydney Olympic Games Tekmar BriteCell In-building and external pico-cell Multi-operator system (3 GSM operators) Multi-standard radio (900/1800 MHz GSM) > 500 Remote Antenna Units 0.8 x 1.8 km Low RF power distributed antenna system Dynamic allocation of network capacity 500 000 wireless calls on the opening day
Distributed Antenna Systems Unreliable coverage from outdoor cells Dedicated indoor capacity Fewer access points (APs) needed compared to distributed radios Centralised management and hand-over remote antenna unit fibre optic cable optical transceiver hub APs and switch
Evolution to Broadband Traffic Studio Quality Digital HDTV Medical Imaging Quality Digital Video 1080 650 Studio Quality Digital Video 216 Compressed Digital Video (MPEG) 8 Professional Quality Stereo Audio CD Quality Stereo Audio 1.4 2.3 Voice 0.064 0.01 0.1 1 10 100 1000 10000 Data Rate (Mb/s)
Future Broadband Access Connections to mobile and portable terminals. Reduced cost final drop in areas of medium population density. Date rates evolving from 64 kb/s to 100 Mb/s+. Carrier frequencies evolving from UHF to millimetre-wave UK allocations in 5.3, 28, 42, 48 and 60 GHz bands.
Millimetre-Wave over Fibre: : Systems Concept Millimetre-wave radio provides high bandwidth capacity. Limited propagation distance allows well defined microcells and frequency re-use. Inexpensive mm-wave equipment is essential. Base stations and central station are connected by low-loss optical fibre. Possible applications are: High resolution mobile multimedia services Wireless Video Distribution Systems Wireless Local Area Networks (WLANs) Central Station (Optical transmitter and receiver) OPTICAL FIBRE Remote Base Station, Mobile communication (Optic/RF and RF/Optic converter) Remote Base Station, Video distribution
Modulation Frequency Limits Direct Modulation (1,550 nm): > 25 GHz [Morton et al, Electron Lett., 1994, 30, pp. 2,044-2,046] External Modulation: > 75 GHz Detectors: > 300 GHz [Noguchi et al, J. Lightwave Technol., 1998, 16, pp. 615-619] [Ito et al, Electron Lett., 2000, 36, pp. 1,809-1,810]
Cell Site Transceiver mm-wave Fibre-Radio System 1.5µm PIN Photodiode Multi-channel Mod.and TX Baseband IN/OUT WDM PIN Photodiode WDM 1.3µm Multi-channel RX and Demod. Circ. Antenna Central Site Site Micro-Cell Site Site Electrical Optical Disadvantage: Cell Site Complexity.
Cell Site LO mm-wave Fibre-Radio System 1.5µm PIN Photodiode PA IF IN/OUT WDM PIN Photodiode WDM 1.3µm LO LNA Circ. Antenna Central Site Site Micro-Cell Site Site Electrical Optical DRO temp. coeff. 10-6 /K 7.5 MHz drift at 60 GHz over -40 C to +85 C Disadvantage: Limited frequency agility.
Central Site LO mm-wave Fibre-Radio System LO 1.5µm PIN Photodiode Diplexer PA IF IN/OUT WDM PIN Photodiode WDM 1.3µm LO RF LNA Circ. Antenna Central Site Site Micro-Cell Site Site Electrical Optical
Optical Heterodyning vs.. Modulators Advantages: High generated frequency possible, limited only by photodetector bandwidth. High detected power, all optical power contributes to generated mm-wave carrier. Single sideband modulation, low sensitivity to chromatic dispersion. Disadvantage: Need for control for phase noise reduction, can result in a complex system λ2 Photodetector λ1 ƒ mm =ƒ λ1 -ƒ λ2
OIL - OPTICAL INJECTION LOCKING Advantages: Wide linewidth lasers usable. Good phase noise suppression. Disadvantages: Limited locking range. Optimum phase noise suppression at only one point of slave laser detuning relative to the free-running frequency. Master Sub-harmonic Reference f ref Slave ML f mm-wave Optical output SL Optical Frequency
Optical Phase Lock Loop (OPLL) Master Slave Loop filter Photo/ Phase det. Optical output Reference linewidth (MHz) Requirement for 0.01 rad 2 phase error variance 10 1 0.1 0.01 0.1 1 10 100 Loop delay (ns) Electrical Optical Advantages: Wide locking range Good tracking capabilities Disadvantages: Narrow linewidth lasers or low delay electronics and short optical path needed.
LO Generation by Optical Injection Phase Lock Loop (OIPLL) Master DFB 36 GHz modulated optical output Slave DFB Loop filter PIN Subharmonically pumped double balanced mixer Electrical Optical 12 GHz reference source
Spectral Purity of Generated Carrier L. Johansson (UCL) Detected spectra around 36 GHz, res. B/w: 1 MHz Detected spectra around 36 GHz, res. B/w: 300 Hz Signal power (dbm) Signal power (dbm) Frequency offset from carrier (MHz) Frequency offset from carrier (khz)
Spectral Purity of Generated Carrier [L. Johansson (UCL)] -70 Phase noise of generated carrier, relative to reference source Phase noise (dbc/hz) -80-90 -100 OIPLL Reference -110 1000 10 4 10 5 10 6 10 7 10 8 Frequency offset from the 36 GHz carrier (Hz)
68 Mb/s DPSK Transmission Experiment [L. Johansson (UCL)] 68 Mbit/s 2 23-1 PRBS TX Differential Encoding 12 GHz OIPLL 36 GHz, 68 Mbit/s 3π/2-DPSK modulated optical output 65.0 km SSM fibre PIN 36 GHz 1.8 GHz BER detector RX 37.8 GHz Spectrum analyser τ d Oscilloscope
Detected Eye and Spectra 1m of fibre, BER < 10-10. 0 8 16 24 32 40 48 50 Time (ns) 65 km of fibre, BER ~10-9 0 8 16 24 32 40 48 50 Time (ns) Detected power (dbm) 0km 25 km -10 40 km -20 65 km -30-40 -50-60 -70-204-136-68 0 68 136 204 Frequency offset (MHz)
BER Versus Received Optical Power [L. Johansson (UCL)] Transmission over up to 65 km of fibre. No optical amplification required. Log (BER) -2-4 -6-8 No fibre dispersion compensation required -10 0 0km 25 km 65 km -24-22 -20-18 -16 Received optical power (dbm)
Emerging Technologies: WDM Efficient usage of metropolitan fibre base for BTS hotel concept Neutral host, multi-operator Typically 8 x 200GHz Full RF bandwidth per wavelength Flexible service provision Dual ring architecture using OADM being trialled by Tekmar Sistemi BTS 1 BTS 2 BTS 3 BTS n BTS 1 BTS 2 BTS 3 BTS n RF COMBINER RF SWITCH POWER SPLITTER E/O E/O E/O E/O E/O E/O E/O E/O OPTICAL MUX O/E O/E O/E O/E O/E O/E O/E O/E
Remote Up- and Down-Conversion Up and downconversion mm-wavemodulated optical source 1.8 GHz transceiver Control station WDM MUX Antenna unit WDM DEMUX mm-wave Optical receiver 155 Mbit/s data 1.8 GHz transceiver Electrical Optical
WDM mm-wave Fibre-Radio DistributionSystem IF1T IF2T IF1R IF2R Heterodyne Optical Source (OIPLL) LIN. LASER LIN. LASER RX RX λ0 λ1 λ2 λ3 λ4 MUX / DEMUX Electrical Optical BIDIRECTIONAL OPTICAL AMPLIFIER ANTENNA SITE OADM λ0 λ1 λ3
CII Wireless over Fibre: Objectives Study technologies for achieving Gb/s transfer rates using millimetrewave over fibre infrastructure. Investigate low-cost wavelength division multiplex (WDM) technology to place wireless overlay on single mode fibre infrastructure. Study seamless wireless hand-over in multiple antenna systems. Study implications of wireless over fibre networks for wireless protocols.
Conclusion Fibre-radio is established as a technique for improving cellular radio coverage, particularly for in-building and multi-operator applications. Expanding demand for broadband services such as IEEE 802.11x requires microwave and millimetre-wave radio systems, with consequent small cell sizes. Fibre-radio simplifies antenna units, with most equipment remoted to the central site, allowing centralised management, security and resource sharing. Fibre-radio distribution networks are signal format transparent enabling future-proof multi-operator and multi-service usage. The wide transmission bandwidth is attractive for UWB and other future wireless systems. The main future challenges are to provide high volume, low-cost optoelectronics technology and to develop wireless protocols which allow optimally for hand-over and antenna remoting.
Acknowledgements EPSRC OSI Broadband Radio Over Fibre project: (Leif Johansson), University of Kent (Dr. N. J. Gomes), Nortel, BT. EPSRC OSI Passive Integrated Picocells project: (Chin-Pang Liu); Imperial College (Professor G. Parry), Bookham, Corning. EPSRC OSI Wavelength Multiplexed Bilateral Linearised Optically Fed Wireless Systems project: (Chin-Pang Liu); University of Cambridge (Professor R. V. Penty/Professor I. H. White), Agilent. EPSRC/DTI LINK Fibre Radio for In-Building Distributed Antenna Systems project: (Chin-Pang Liu); University of Cambridge (Professor R. V. Penty/Professor I. H. White), Agilent, Remec, ZinWave. EU FP6 GANDALF project.