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Spectrum Scarcity and Free Space Op1cal Communica1ons
Mohamed-‐Slim Alouini KAUST
January 2014
Agenda • Spectrum Scarcity
– RF spectrum – Mobile traffic growth and spectrum scarcity
• Cogni1ve Radio Networks (CRNs) – Categories of CRNs – Capacity results
• Free Space Op1cal (FSO) Communica1ons – Impact of scin1lla1ons and poin1ng errors – RF/FSO cascade systems
• Concluding Remarks
Challenges and Solu.ons Spectrum Scarcity
Radio Spectrum • RF spectrum typically refers to the full frequency range from 3 KHz to 300 GHz.
• RF spectrum is a na1onal resource that is typically considered as an exclusive property of the state.
• RF spectrum usage is regulated and op1mized • RF spectrum is allocated into different bands and is typically used for – Radio and TV broadcas1ng – Government (defense and public safety) and industry – Commercial services to the public (voice and data)
US Frequency Alloca1on Chart
Growth of Mobile Phone Subscribers
Mobile internet traffic is pushing the capacity limits of wireless networks !
RF Spectrum “Crunch”
• Smartphone usage tripled in 2011. • Between 2011 and 2016, global wireless data traffic is expected to increase 18 1mes more.
• Rapid increase in the use of wireless services has lead the problem of spectrum exhaus'on.
• FCC predicts that the US is going to start experiencing a spectrum deficit for wireless communica1ons in 2013.
Poten1al Solu1ons • More efficient usage of the available spectrum:
– Mul1ple antenna systems – Adap1ve modula1on and coding systems
• More aggressive temporal and spa1al reuse of the available spectrum: – Cogni1ve radio systems – Femto cells & Offloading solu1ons
• Use of unregulated bandwidth in the upper por1on of the spectrum: – Microwave and millimeter-‐wave such as 60 GHz & 90 GHz – THz carriers – Op1cal spectrum
Towards the Speeds of Wireline Networks
Free Space Op1cal (FSO) Communica1ons
FSO Basic Principle
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§ Connects using narrow beams two op1cal wireless transceivers in line-‐of-‐sight
§ Light is transmieed from an op1cal source (laser or LED) trough the atmosphere and received by a lens
§ Provides full-‐duplex (bi-‐direc1onal) capability § 3 “op1cal windows”: 850 nm, 1300 nm, & 1550 nm. § WDM can be used => 10 Gb/s (4x2.5 Gb/s) over 1 Km & 1.28 Tb/s (32x40 Gb/s) over 210 m
Why FSO ?
– License-‐free
– Cost-‐effec1ve
– Behind windows
– Fast turn-‐around 1me
– Suitable for brown-‐field
– Very high bandwidth (similar to fiber)
– Narrow beam-‐widths (point-‐to-‐point)
• Energy efficient
• Immune to interference
• High level of security
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fastlinks-‐wireless.com
FSO Applica1ons
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§ Ini1ally used for secure military as well as space applica1ons
§ Commercial use: Last mile solu1on, op1cal fiber back-‐up, high data rate temporary links, cellular
communica1on backhaul, etc …
FSO Challenges & Solu1ons
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§ Addi1ve noise (photo-‐detector) and background radia1on (direct, scaeered, and reflected sun light) => sensi1ve detectors + filters + heterodyne detec1on
§ Free space path loss => limited range § Atmospheric losses (rain, snow, fog, aerosol gases, smoke, low cloud, sand
storms, etc …) => power control + mesh architecture + hybrid RF/FSO § Atmospheric turbulences => space diversity § Buildings swaying, mo1on, and vibra1ons => tracking systems
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Vendor Wavelength Data Rate Range (@ 10 dB/km)
MIMO Hybrid RF/FSO
Price Range (USD)
fSONA (Canada)
1550nm Full Duplex with 2.5 Gbps
1 km No Yes RF: 150 Mbps (60–70 GHz)
8-‐12K
LightPointe (USA)
850nm 1550nm
Full Duplex with 1.25 Gbps
1.6 kms Yes (2 X 2) (4 X 4)
Yes RF: 250 Mbps (5.4–5.8 GHz)
11-‐19K
RedLine (South-‐Africa)
850nm Full Duplex with 1.25 Gbps
0.9 kms Yes (4 X 4)
Yes RF: 250 Mbps (4.9–5.8 GHz)
15-‐24K
Commercial Deployment
Types of Detec1on Techniques
• Intensity Modula/on/Direct Detec/on (IM/DD): IM/DD is the main
mode of detec1on in FSO systems but coherent communica1ons
have also been proposed as an alterna1ve detec1on mode.
• Coherent Modula/on/Heterodyne Detec/on (CM/HD): Among
coherent communica1ons, heterodyne detec1on is a more
complicated detec1on method but has the ability to beeer
overcome the thermal noise effects.
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Characteriza1on of the Scin1lla1ons
• Frequency flat fading channel • Channel coherence 1me: 10 μs and 100 ms • Turbulence strength depends on Rytov variance/number (i.e.
distance and index of refrac1on structure) • Turbulence regimes:
– Rytov number << 1 => Weak turbulence regime – Rytov number >> 1 => Strong turbulence regime
• Sta1s1cal models: – Weak turbulence: Lognormal or Gamma-‐Gamma (Generalized K) – Strong turbulence: Exponen1al or Gamma-‐Gamma (Generalized K)
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Unified PDF
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Reference: I. Ansari, F. Yilmaz, and M. -‐S. Alouini, “On the performance of mixed RF/FSO variable gain dual-‐hop transmission systems with poin1ng errors ”, (VTC Fall'2013), Las Vegas, Nevada, USA, September 2013.
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Wojnar Condi1onal BER for Binary Modula1ons
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RF/FSO Model
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Reference: I. Ansari, F. Yilmaz, and M. -‐S. Alouini, “On the performance of mixed RF/FSO dual-‐hop transmission systems”, (VTC Spring'2013), Dresden, Germany, June 2013.
Relaying and Channel Models
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CDF of RF/FSO
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Hybrid RF & RF/FSO Systems
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Reference: I. Ansari, F. Yilmaz, and M. -‐S. Alouini, “On the performance of hybrid RF and RF/FSO dual-‐hop transmission systems ”, (IWOW’2013), Newcastle, UK, October 2013.
Diversity Model
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BER for SC
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BER for MRC
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Numerical Result
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Summary and Next Steps ? Concluding Remarks
Conclusion and Current Work
• Spectrum scarcity is becoming a reality • This scarcity can be relieved through: – Cogni1ve radio networks – Extreme bandwidth communica1on systems
• Analy1cal results can be used to perform ini1al system level trade-‐offs
• On-‐going deployment and tes1ng the capabili1es of FSO systems in hot & humid desert climate condi1ons.
Thank You Ques.ons?
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