spectrum scarcity and optical wireless ... - ict...
TRANSCRIPT
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Spectrum Scarcity and Optical Wireless
Communications
Mohamed-Slim AlouiniKAUST
May 2016
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King Abdullah University of
Science & Technology (KAUST)
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Built on 36 million square meters on the
Red Sea in Thuwal 80 Km north of the city of Jeddah
Where is KAUST?
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What is KAUST?
• Graduate Level research university governed by an independent Board of Trustees
• Merit based, open to all from around the world
• Research Centers as primary organizational units
• Research funding and collaborative educational programs
• Collaborative research projects, linking industry R&D and economic development
• Environmentally responsible campus
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Electrical Engineering @ KAUST
Electro-Physics Systems
Hakan Bagci
(PhD-UIUC)
Ganesh
Sundaramoorthi
(PhD-GATECH)
Andrea Fratalocchi
(PhD-Roma Tre)
Atif Shamim
(PhD-Carleton)
- Faculty members: 18 (+ 2 Adjunct Faculty + 2 Visiting
Faculty)
- Postdoc Fellows & Research Scientists: 30
- PhD Students: 75 - MS/PhD: 30 - MS: 15
- Fall 2015: 55 students/933 applicants, 18 countries
- ee.kaust.edu.sa
Bernard
Ghanem
(PhD-UIUC)
MeriemLaleg-Kirati(PhD-INRIA)
Jurgen Kosel
(PhD-Vienna Univ)
Hossein Fariborzi
(PhD-MIT)
Boon Ooi Muhammad Hussain JR He Khaled Salama Slim Alouini Jeff Shamma Wolfgang Heidrich Basem Shihada
(PhD-Glasgow) (PhD-UT Austin) (PhD-NTCU) (PhD-Stanford) (PhD-Caltech) (PhD-MIT) (PhD- Erlangen) (PhD-Waterloo)
Tareq
Al-Naffouri
(PhD-Stanford)
Xiaohang Lii
(PhD-GATECH)
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Agenda
• Spectrum Scarcity
– Radio Frequency (RF) spectrum
– Mobile traffic growth and spectrum scarcity
– Potential solutions
• Optical Wireless Communications (OWC)
– Capacity of OWC systems
– Secrecy rate of OWC systems with friendly jammers
– Impact of turbulence and pointing errors
– Application to cost-effective wireless backhaul
• Concluding Remarks
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Challenges and Solutions
Spectrum Scarcity
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Spectrum Scarcity : Challenges and Solutions
RF Spectrum
• RF spectrum typically refers to the full frequency range from 3 KHzto 300 GHz.
• RF spectrum is a national resource that is typically considered as anexclusive property of the state.
• RF spectrum usage is regulated and optimized• RF spectrum is allocated into different bands and is typically used for
– Radio and TV broadcasting– Government (defense and public safety) and industry– Commercial services to the public (voice and data)
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Growth of Mobile Phone Subscribers
Mobile internet traffic is pushing the capacity limits of wireless networks ! => Spectrum exhaustion/deficit
Spectrum Scarcity : Challenges and Solutions
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Potential Solution
• More efficient usage of the available spectrum:
– Multiple antenna systems
– Adaptive modulation and coding systems
Spectrum Scarcity : Challenges and Solutions
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Other Potential Solutions
• More aggressive temporal and spatial reuse of the availablespectrum:
– Cognitive radio systems
– Femto cells & offloading solutions
• Use of unregulated bandwidth in the upper portion of thespectrum:
– Microwave and millimeter-wave such as 60 GHz & 90 GHz
– THz carriers
– Optical spectrum
Spectrum Scarcity : Challenges and Solutions
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Optical Wireless CommunicationsTowards the Speeds of Wireline Networks
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Optical Wireless Communications
• Point-to-point free space optical communications (FSO) usinglasers in the near IR band (750 nm -> 1600 nm)
• Visible light communications (know also as Li-Fi for Light-Fidelity) using LEDs in the 390 nm -> 750 nm band.
• NLOS UV communication in the 200 nm to 280 nm band.
Spectrum Scarcity : Challenges and Solutions
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FSO Basic Principle
Optical Wireless Communications: Towards the Speeds of Wireline Networks
• Connects using narrow beams two optical wireless transceiversin line-of-sight.
• Light is transmitted from an optical source (laser or LED) troughthe atmosphere and received by a lens.
• Provides full-duplex (bi-directional) capability.• 3 “optical 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.
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Why FSO ?
Optical Wireless Communications: Towards the Speeds of Wireline Networks
• License-free
• Cost-effective
• Behind windows
• Fast turn-around time
• 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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FSO Applications
Optical Wireless Communications: Towards the Speeds of Wireline Networks
• Initially used for secure military as well as space applications• Commercial use: Last mile solution, optical fiber back-up, high data rate
temporary links, cellular communication backhaul, etc …
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FSO Challenges & Solutions
Optical Wireless Communications: Towards the Speeds of Wireline Networks
• Additive noise (photo-detector) and background radiation (direct, scattered, andreflected sun light) => sensitive detectors + filters + heterodyne detection
• Free space path loss => limited range• Atmospheric losses depends on relative size of air particles and transmission
wavelength (rain, snow, fog, aerosol gases, smoke, low cloud, sand storms, etc …) =>power control + mesh architecture + hybrid RF/FSO
• Atmospheric turbulences => space diversity• Buildings swaying, motion, and vibrations => tracking systems
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Deployment Example: FSO for High-Speed Traders (CNN)
Optical Wireless Communications: Towards the Speeds of Wireline Networks
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Future Applications: Facebook and Google Projects
Optical Wireless Communications: Towards the Speeds of Wireline Networks
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Facebook Aquila Project
Optical Wireless Communications: Towards the Speeds of Wireline Networks
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
Underwater Optical Wireless Communications (UOWC)
Developed a fast simulator to calculate accurately
the UWOC channel path loss.
Demonstrated 1 Gb/s transmission rates over 10 m.References:
1- H. Oubei, K. -H. Park, C. Li, T. K. Ng, J. Yao, M. -S. Alouini, and B. Ooi, “2.3 Gbit/s underwater wireless optical communications using directly modulated 520 nm laser diode", Optics Express, July 2015.
2- H. Oubei, B. Janjua, J. R. He, T. Lee, H. Kuo, M. -S. Alouini, and B. Ooi, "4.8 Gbit/s 16-QAMOFDM transmission based on compact 450-nm laser for underwater wireless optical communication", Optics Express , Sept 2015.
3- C. Li, K. -H. Park, and M. -S. Alouini, "A direct radiative transfer equation solver for path loss
calculation of underwater optical wireless channels", IEEE Wireless Commun. Letters , October 2015.
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On-Going Research Directions
Optical Wireless Communications: Towards the Speeds of Wireline Networks
• Capacity of OWC channels– Bounds and exact results (IM/DD vs. heterodyne detection)– Accurate approximations– High SNR and low SNR bounds and approximations for the ergodic
capacity of FSO turbulent channels subject to pointing error
• Physical layer security for OWC systems– Achievable secrecy rate of visible light communication– Effect of channel state information on the secrecy rate
• Average probability of error computations over FSO turbulent channels– Differentially coherent vs. coherent system performance– Asymptotic results (coding and diversity gains)
• Cost effective backhaul design using hybrid RF/FSO technology
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IM/DD Case
Capacity of OWC Channels
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
OWC IM/DD Channel Capacity
,
• IM/DD channel model
On-Going Research Directions: Capacity of OWC IM/DD Channels
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
Channel Capacity
,
On-Going Research Directions: Capacity of OWC IM/DD Channels
For M codewords of length n symbols:
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
Sphere Packing Perspective: Classical Case
,
On-Going Research Directions: Capacity of OWC IM/DD Channels
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
Sphere Packing Perspective: IM/DD Case
,
On-Going Research Directions: Capacity of OWC IM/DD Channels
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
Bounds on Capacity
,
• Bounds using the Steiner-Minkowski formula [Farid &Hranilovic, IEEE Trans. IT, Dec 2010]
• Obtained bounds are geometry-independent:Replacing the ball by any other object with the samevolume yields the same bound.
On-Going Research Directions: Capacity of OWC IM/DD Channels
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
Alternative Bounds on Capacity
,
• Use a geometry-dependent recursive approach.
• Obtained bounds are geometry-independent:
On-Going Research Directions: Capacity of OWC IM/DD Channels
Reference: A. Chaaban, J. –M. Morvan, and M. -S. Alouini, “On the capacity of IM/DD freespace optical communications: Capacity bounds and approximations”, International Workshopon Optical Wireless Communication (IWOW’2015), Istanbul, Turkey, September 2015. Journalversion to appear in IEEE Trans. on Communications.
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
Analytical Results
,
On-Going Research Directions: Capacity of OWC IM/DD Channels
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
Numerical Results
,
On-Going Research Directions: Capacity of OWC IM/DD Channels
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
FSO Capacity Fitting
,
On-Going Research Directions: Capacity of OWC IM/DD Channels
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
FSO Capacity HD vs. IM/DD
,
On-Going Research Directions: Capacity of OWC IM/DD Channels
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Extensions• Capacity region of the IM/DD optical broadcast channel• Capacity bounds for parallel IM/DD optical wireless channels• Capacity bounds for the Gaussian IM/DD optical multiple-access channel• Asymptotic ergodic capacity of IM/DD optical over turbulent channels
References:1- A. Chaaban, Z. Rezki, and M.-S. Alouini, “On the capacity of the 2-User IM-DD opticalbroadcast channel”, in Proc. of the 6th Globecom Workshop on Optical Wireless Communications, San Diego, USA, Dec. 2015. Journal version to appear in IEEE Trans. on Wireless Communications2- A. Chaaban, Z. Rezki, and M.-S. Alouini, “Capacity bounds for parallel IM-DD optical wireless channels”, To appear in IEEE International Conference on Communications (ICC), Kuala Lumpur, Malaysia, May 2016.3- O. M. S. Al-Ebraheemy, A. Chaaban, T. Y. Al-Naffouri, and M.-S. Alouini, “Capacity bounds for the 2-user Gaussian IM-DD optical multiple-access channel”, in Proc. of IEEE International Conference on Circuits and Systems (ISCAS), Montreal, Canada, May 2016.4- I. Ansari, M. -S. Alouini, and J. Cheng, “On the capacity of FSO links under log-normalturbulence", in Proc. IEEE Vehicular Technology Conference (VTC), Vancouver, BC, Canada,September 2014. Journal version in IEEE Transationson Wireless Communications, August 2015.
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Asymptotic Results
Ergodic Capacity of OWC Channels
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Asymptotic Analysis of Ergodic Capacity
Unified SNR Statistics
• Heterodyne Detection
• IM/DD
• Unified
with irradiance I = Ia Ip
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
Asymptotic Ergodic Capacity
,
• Recall that the irradiance I = Ia Ip and SNR g is proportional to Ir
• The asymptotic ergodic capacity can be obtained as [Yilmaz and Alouini,SPAWC’2012]
• We need to find the moments of Ia then compute derivatives.
On-Going Research Directions: Asymptotic Analysis of Ergodic Capacity
Reference: I. Ansari, M. -S. Alouini, and J. Cheng, “On the capacity of FSO links under log-normal turbulence", Proceedings IEEE Vehicular Technology Conference (VTC Fall'2014), Vancouver, BC, Canada, September 2014. Journal version to appear in IEEE Transations on Wireless Communications, August 2015.
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Asymptotic Analysis of Ergodic Capacity
Exact Closed-Form Moments
• I= Ia Ip = IR IL Ip where IR, IL, and IP are independent random processes
• Unified Rician Moments
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Asymptotic Analysis of Ergodic Capacity
Asymptotic Results
• High SNR
• Low SNR
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Optical Wireless Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Asymptotic Analysis of Ergodic Capacity
Asymptotic Results
Figure: Ergodic capacity results for IM/DD technique and varyingk at high SNR regime for RLN turbulence
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The Beckman Distribution
Impact of the Pointing Errors
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Impact of Pointing Errors
Optical Wireless Communications: Towards the Speeds of Wireline Networks
• Effect on Communication: These pointing errors maylead to an additional performance degradation and are aserious issue in urban areas, where the FSO equipmentsare placed on high-rise buildings.
• Model: The pointing error model developed andparameterized by ξ which is the ratio between theequivalent beam radius and the pointing error jitter canbe:
- With pointing error: ξ is between 0 and 7- Without pointing error: ξ→ ∞
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
Original Pointing Error Model
- The fraction of collected power at the receiver can be approximated by [Farid and Hranilovic, IEEE/OSA JLT 2007]
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
• The general model reduces to special cases as follows
On-Going Research Directions: Ergodic Capacity Calculations under the Impact of Pointing Errors
Other Pointing Errors Models
No misalignment
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Ergodic Capacity Calculations under the Impact of Pointing Errors
Generalized Pointing Error Model
• The fraction of collected power at the receiver can be approximated by [Farid and Hranilovic, IEEE/OSA JLT, 2007]
The random variable r follows a Beckman distribution
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Ergodic Capacity Calculations under the Impact of Pointing Errors
Moments of the Irradiance
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
Asymptotic Ergodic Capacity
,
• The asymptotic ergodic capacity can be obtained as
• The moments of Ia are known for both lognormal (LN) and Gamma-Gamma (ΓΓ). Then, the asymptotic capacity can be written as
On-Going Research Directions: Ergodic Capacity Calculations under the Impact of Pointing Errors
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
Figure: The ergodic capacity for:(a) ξx = 6.7 and ξy = 5.1(b) ξx = 6.7 and ξy = 0.9(c) ξx = 0.8 and ξy = 0.9
Reference: H. Al-Quwaiee, H.-C. Yang, and M. -S. Alouini, “On the asymptotic ergodic capacity of FSO Links with Generalized pointing error model”, Proceedings IEEE ICC’15, London, UK, June 2015.
On-Going Research Directions: Ergodic Capacity Calculations under the impact of pointing errors
Asymptotic Ergodic Capacity
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Outage Capacity
Optical Wireless Communications: Towards the Speeds of Wireline Networks
• FSO channels are typically viewed as slowly varyingchannels => Coherence time is greater than the latencyrequirement
• Outage capacity is considered to be a more realisticmetric of channel capacity for FSO systems
• Closed-form expressions are not possible => Importancesampling-based Monte Carlo simulations
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Importance Sampling (IS)
P=P(g<gth) = P(I=Ia Ip <Ith) = P(ya + yp < )
where ya=log(Ia), yp=log(Ip), and 𝜀 = log Ith
• IS estimator:
𝐼∗ =1
𝑁∗
𝑛=1
𝑁∗
1 𝑦𝑎,𝑛∗ +𝑦𝑝,𝑛∗ <𝜀 𝑤𝑦𝑎(𝑦𝑎,𝑛∗ )𝑤𝑦𝑝(𝑦𝑝,𝑛
∗ )
where 𝑦𝑘∗ (.) 𝑓𝑦𝑘
∗ (. ) =𝑓𝑦𝑘(.)𝑤𝑦𝑘(.), 𝑘 = 𝑎, 𝑝
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IS Exponential Twisting
• Weighting Choice: 𝑤𝑦𝑘(𝑥) = 𝑒−𝜃𝑥𝑀𝑦𝑘(𝜃)
where 𝑀𝑦𝑘(.) is the MGF of 𝑦𝑘• IS Estimator:
𝐼∗ =1
𝑁∗
𝑛=1
𝑁∗
1 𝑦𝑎,𝑛∗ +𝑦𝑝,𝑛∗ <𝜀 𝑒−𝜃(𝑦𝑎,𝑛
∗ +𝑦𝑝,𝑛∗ ) 𝑀𝑦𝑎(𝜃)𝑀𝑦𝑝(𝜃)
𝑀𝑦𝑎 𝜃 = 𝐸 ℎ𝑎𝜃 = exp(
1
2𝜃(𝜃 − 1) 𝜎𝑅
2) (LN fading)
𝑀𝑦𝑎 𝜃 = 𝐸 ℎ𝑎𝜃 =
(𝛼𝛽)−𝜃 𝛼+𝜃 (𝛽+𝜃) 𝛼 (𝛽)
(G-G fading)
𝑀𝑦𝑝 𝜃 = 𝐸 ℎ𝑝𝜃 =
𝑥𝑦𝐴0𝜃exp −
2𝜃
𝑤𝑧𝑒𝑞2𝜇𝑥2𝑥2
𝑥2+𝜃+𝜇𝑦2𝑦2
𝑦2+𝜃
𝑥2+𝜃 𝑦2+𝜃
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Optimal
• Minimization problem:
min𝜃𝐸 1 𝑦𝑎+𝑦𝑝<𝜖 𝑤𝑦𝑎
2 (𝑦𝑎, 𝜃)𝑤𝑦𝑝2 (𝑦𝑎, 𝜃)
Stochastic optimization problem: Not feasible analytically except for a few simple cases.
Alternative: Find a sub-optimal 𝜃:
– Cumulant generating function:
𝜇 𝜃 = log 𝐸 𝑒𝜃 𝑦𝑎+𝑦𝑝 = log 𝑀𝑎(𝜃) + log 𝑀𝑝(𝜃)
– Sub-optimal 𝜃:
𝜇′ 𝜃 = 𝜖
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Sub-Optimal 𝜃
• Weak turbulence:
log 𝐴0 +𝜎𝑅2
22𝜃 − 1 −
𝑥2 + 𝑦
2 + 2𝜃
2 𝑥2 + 𝜃 𝑦
2 + 𝜃−2𝜃
𝑤𝑧𝑒𝑞2
𝜇𝑥2𝑥4
(𝑥2+𝜃)2
+𝜇𝑦2𝑦4
(𝑦2+𝜃)2
= 𝜖
• Strong turbulence:
log𝐴0𝛼𝛽−
𝑥2 + 𝑦
2 + 2𝜃
2 𝑥2 + 𝜃 𝑦
2 + 𝜃−2𝜃
𝑤𝑧𝑒𝑞2
𝜇𝑥2𝑥4
(𝑥2+𝜃)2
+𝜇𝑦2𝑦4
(𝑦2+𝜃)2
+ 𝛼 + 𝜃 + (𝛽
+ 𝜃) = 𝜖
where 𝑥 =′(𝑥)(𝑥)
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Outage Probability
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Efficiency Indicator
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Impact of Jitter Unbalance on Outage Probability
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Friendly Jammers
Secrecy Rate of VLC Systems
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Visible Light Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions:
Improved Achievable Secrecy Rate of Visible Light Communication with Cooperative Jammers
• Physical layer security (PLS) is a paradigm that aims at securingcommunications leveraging randomness in fading channels.
• PLS achieves its goal via a sophisticated combination of both coding andsignaling techniques.
• PLS has been recognized as a complementary technique to existingcryptographic systems.
• There exists a large body of work on PLS over RF communications.• Recently, there has been several attempts to extend the previous studies to
VLC e.g., [Mostafa & Lampe, JSAC’2015 and Zaid & al., GlobalSIP’2015].
ReferenceH. Zaid, Z. Rezki, A. Chaaban, and M.-S. Alouini, “Improved achievable secrecy rate of visible light communication with cooperative jamming”, in Proc. of the IEEE Global Conference on Signal and Information Processing (GlobalSIP), Orlando, FL, Dec. 2015.
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Visible Light Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions:System Model
• Consider a VLC network with a transmitter (Alice), a legitimate receiver (Bob),an eavesdropper (Eve) and a (friendly) jammer equipped with Nj light fixtures.
• Alice transmits her data via a single fixture.• The jammer has no access to data transmitted by Alice.• Bob and Eve are equipped each with a single photodetector
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Visible Light Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions:
System Model (Continued)
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Visible Light Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions:
Friendly Jamming Scheme
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Visible Light Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions:
Achievable Secrecy Rate
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Visible Light Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions:
Comparison
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Visible Light Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions:
Eve’s CSI Known Perfectly to the Jammer:Optimal Beamforming
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Visible Light Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions:
Eve’s CSI Not Known Perfectly to the Jammer:Robust Beamforming
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Visible Light Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions:
Eve’s CSI Known Perfectly
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Visible Light Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions:
Eve’s CSI Not Known Perfectly
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Comparison M-PSK vs. M-DPSK
Probability of Error Computation
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions:
Average Probability of Error Computations
• Generic Exact and Asymptotic Results over Gamma-Gamma Channels
• Average Performance of Differentially Coherent & Coherent MPSK
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Average Probability of Error Computations
SER Performance of M-PSK and M-DPSK
• Symbol error rate performance of M-PSK and M-DPSK over AWGN are given by [Pawula, TCOM, Sept 1999]
and
with
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Average Probability of Error Computations
Asymptotic SER Performance Comparison of M-PSK and M-DPSK
• Well known that MDPSK performs 3 dB worse than MPSK in the Rayleighfading channels when the SNR is asymptotically large [Ekanayake, TCOM,October 1990]
• Asymptotic SER performance of MDPSK with respect to MPSK over afading channel with diversity order t+1
ℎ 𝑡 ≜ 0
𝜂𝜋
𝑠𝑖𝑛2𝜃 𝑡+1 𝑑𝜃.with
and
,
• Asymptotic SER performance of MDPSK with respect to MPSK overlognormal turbulence channel
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Average Probability of Error Computations
Comparison of SER for M-PSK and M-DPSK in Lognormal Fading
Figure: Average SER of FSO using MPSK and MDPSK over weak turbulence Lognormal fading channels.
Reference: X. Song, F. Yang, J. Cheng and M. -S. Alouini, “Asymptotic SERperformance comparison of MPSK and MDPSK in fading channels ”, IEEEWireless Communication Letters, Feb 2015.
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Cost Effective Backhaul DesignCombining Optical Fibers and RF/FSO Systems
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
Backhaul Design
,
On-Going Research Directions: Cost Effective Backhaul Design
• An enormous demand for mobile data services is expected in next generation mobile networks (5G).
• Need to significantly increase:• Data capacity, • Coverage performance, • Energy efficiency.
• Move from the traditional single base-station to heterogeneous networks (HetNets).
• Backhaul congestion should be addressed.
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
Backhaul Technologies
,
On-Going Research Directions: Cost Effective Backhaul Design
• Various technologies are available for the backhaul:• Copper links: Low capacity and thus not suitable for 5G.• Optical fiber (OF) links: High data rates over long distances
however very expensive.• Radio-frequency (RF) links: Limited capacity but cost-effective and
scalable solution.• Free-space optics (FSO) links: High data rates, free to use, and
immune to electromagnetic interference but sensitive to weather conditions.
• In order to combine the advantages of RF links (reliability) and FSO links (capacity), the usage of hybrid RF/FSO technology has been proposed.
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
Optimization Problem
,
On-Going Research Directions: Cost Effective Backhaul Design
• Minimizing network deployment cost under the constraints:• Connections between nodes
can be either OF or hybrid RF/FSO.
• Each node has a data rate that exceeds the target data rate.
• Each node can communicate with any other node through single or multiple hop links (i.e. the graph is connected).
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
System Parameters
,
On-Going Research Directions: Cost Effective Backhaul Design
• d(.,.): Distance operator.• π(o)(x) and π(h)(x): Cost of an OF link and a hybrid
RF/FSO over a distance x.• R(o)(x) and R(h)(x): Normalized data rates of an OF
and a hybrid RF/FSO links over a distance x.• λ2 : Second smallest eigenvalue of the Laplacian
matrix known as the algebraic connectivity.• X and Y: Existence of an OF or a hybrid RF/FSO
link.
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
Backhaul Design Problem Formulation
,
On-Going Research Directions: Cost Effective Backhaul Design
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
Close to Optimal Heuristic Solution
,
On-Going Research Directions: Cost Effective Backhaul Design
Reference: A. Douik, H. Dahrouj, T. Al-Naouri, and M. -S. Alouini, "Cost-effective backhaul design using hybrid radio/free-space optical technology", in Proc. of IEEE International Workshop on Next Generation Backhaul/Fronthaul Networks (BackNets 2015) in conjunction with IEEE ICC'2015, London, UK, June 2015. Journal version revised for IEEE Trans. Communications.
• Optimization problem is NP-hard.• Difficult to solve because:
• Simultaneous optimization over X and Y.• Connectivity condition λ2.
• Adopted sub-optimal strategy:• Solve the optical fiber only problem.• Use the solution to replace the condition on λ2.• Reformulate the problem as a maximum weight clique problem.
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Cost Effective Backhaul Design
Total Cost vs. Number of Base Stations
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Cost Effective Backhaul Design
Total Cost vs. Cost of Hybrid RF/FSO
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Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks
On-Going Research Directions: Cost Effective Backhaul Design
Percentage of OF Usage vs. Cost of Hybrid RF/FSO
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Summary and Next Steps ?
Concluding Remarks
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Conclusion and Current Work
• Spectrum scarcity is becoming a reality
• This scarcity can be relieved through:
– Heterogeneous networks
– Extreme bandwidth communication systems
• Need to develop new information theoretical results specificto OWC channels
• Analytical and fast simulation results can be used to performinitial system level trade-offs
• On-going deployment and testing the capabilities of OWCsystems in hot & humid desert climate conditions.
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Thank You ctl.kaust.edu.sa