Spectrum Scarcity and Free Space Op1cal Communica1ons. Mohamed- Slim Alouini KAUST January 2014

Transcription

1 Spectrum Scarcity and Free Space Op1cal Communica1ons Mohamed- Slim Alouini KAUST January 2014

2 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

3 Spectrum Scarcity Challenges and Solu.ons

4 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)

5 US Frequency Alloca1on Chart

6 Growth of Mobile Phone Subscribers Mobile internet traffic is pushing the capacity limits of wireless networks!

7 RF Spectrum Crunch Smartphone usage tripled in 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.

8 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

9 Free Space Op1cal (FSO) Communica1ons Towards the Speeds of Wireline Networks

10 FSO Basic Principle 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 10

11 Why FSO? License- free Cost- effec1ve Behind windows Fast turn- around 1me Suitable for brown- field fastlinks- wireless.com Very high bandwidth (similar to fiber) Narrow beam- widths (point- to- point) Energy efficient Immune to interference High level of security 11

12 FSO Applica1ons 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 12

13 FSO Challenges & Solu1ons 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 13

14 Commercial Deployment 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 ( GHz) 11-19K RedLine (South- Africa) 850nm Full Duplex with 1.25 Gbps 0.9 kms Yes (4 X 4) Yes RF: 250 Mbps ( GHz) 15-24K 14

15 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. 15

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17 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) 17

18 Unified PDF 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

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27 Wojnar Condi1onal BER for Binary Modula1ons 27

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32 RF/FSO Model 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

33 Relaying and Channel Models 33

34 CDF of RF/FSO 34

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37 Hybrid RF & RF/FSO Systems 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

38 Diversity Model 38

39 BER for SC 39

40 BER for MRC 40

41 Numerical Result 41

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45 Concluding Remarks Summary and Next Steps?

46 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.

47 Thank You Ques.ons?