Communications Towards the Speeds of Wireline Networks Free Space - - PowerPoint PPT Presentation

▶
communications
SMART_READER_LITE
LIVE PREVIEW

Communications Towards the Speeds of Wireline Networks Free Space - - PowerPoint PPT Presentation

Jan 17, 2024 109 likes •392 views

Free Space Optical (FSO) Communications Towards the Speeds of Wireline Networks Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks FSO Basic Principle Connects using narrow beams two optical wireless

slide-1
SLIDE 1

Towards the Speeds of Wireline Networks

Free Space Optical (FSO) Communications

slide-2
SLIDE 2

FSO Basic Principle

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks

  • Connects using narrow beams two optical wireless transceivers

in line-of-sight.

  • Light is transmitted from an optical source (laser or LED) trough

the 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)
  • ver 1 Km & 1.28 Tb/s (32x40 Gb/s) over 210 m.
slide-3
SLIDE 3

Why FSO ?

Free Space Optical (FSO) 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
slide-4
SLIDE 4

FSO Applications

Free Space Optical (FSO) 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 …

slide-5
SLIDE 5

FSO Challenges & Solutions

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks

  • Additive noise (photo-detector) and background radiation (direct, scattered, and

reflected sun light) => sensitive detectors + filters + heterodyne detection

  • 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, motion, and vibrations => tracking systems
slide-6
SLIDE 6

Commercial Deployment

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks 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

slide-7
SLIDE 7

Deployment Example: Lasers for High-Speed Traders (CNN)

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks

slide-8
SLIDE 8

Characterization of the Scintillations

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks

  • Frequency flat fading channel
  • Channel coherence time: 10 μs and 100 ms
  • Turbulence strength depends on Rytov variance/number (i.e.

distance and index of refraction structure)

  • Turbulence regimes:

– Rytov number << 1 => Weak turbulence regime – Rytov number >> 1 => Strong turbulence regime

  • Statistical models:

– Weak turbulence: Rice-Lognormal or Gamma-Gamma (Generalized K) – Strong turbulence: Exponential or Gamma-Gamma (Generalized K) – More generalized models: Double Gamma-Gamma or Malaga

slide-9
SLIDE 9

Pointing Errors

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks

  • Definition: Thermal expansion, dynamic wind loads, and weak

earthquakes result in the building sway phenomenon that causes vibration of the transmitter and the receiver known as pointing error.

  • Effect on Communication (ξ): These pointing errors may lead to

an additional performance degradation and are a serious issue in urban areas, where the FSO equipments are placed on high-rise buildings.

  • Model: The pointing error model developed and parameterized

by ξ which is the ratio between the equivalent beam radius and the pointing error jitter can be:

  • With Pointing Error: ξ is any number between 0 through 7
  • Without Pointing Error: ξ→ ∞
slide-10
SLIDE 10

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks

  • The general model reduces to special cases as follows

Generalized Pointing Errors Model

No misalignment Rayleigh Single sided Gaussian Hoyt Rician

slide-11
SLIDE 11

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks

Generalized Pointing Errors Model

  • The fraction of collected power at the receiver can be

approximated by [Farid and Harilovic, IEEE/OSA JLT, 2007] with r = |r| = is random x2 +y2

slide-12
SLIDE 12

On-Going Research Directions

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks

  • Unified performance analysis accounting for type of detection,

weak/strong scintillations, and pointing errors.

  • Computation of ergodic capacity over generalized FSO fading channels

– High SNR and low SNR bounds and approximations – Bounds and exact results for the capacity of diversity systems – Accurate approximations

  • Average probability of error computations over generalized FSO fading

channels – Differentially coherent vs. coherent system performance – Asymptotic results (coding and diversity gains)

slide-13
SLIDE 13

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks On-Going Research Directions:

Ergodic Capacity Computation

  • High SNR and Low SNR Results over FSO channels.
  • Bounds on the Capacity of Selection Diversity Systems
  • Exact Capacity Results for MRC and EGC Diversity Systems
  • Approximate results using PDF approximation
slide-14
SLIDE 14

Free Space Optical (FSO) 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

slide-15
SLIDE 15

Free Space Optical (FSO) 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,

SPAWC2012]

  • We need to find the moments of Ia and then compute derivatives.

On-Going Research Directions: Ergodic Capacity Calculations under the Impact of Pointing Errors

slide-16
SLIDE 16

Free Space Optical (FSO) 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
slide-17
SLIDE 17

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks On-Going Research Directions: Asymptotic Analysis of Ergodic Capacity

Asymptotic Results

  • High SNR
  • Low SNR
slide-18
SLIDE 18

Free Space Optical (FSO) 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 varying k at high SNR regime for RLN turbulence

slide-19
SLIDE 19

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 Errors Model

  • The fraction of collected power at the receiver can be

approximated by [Farid and Harilovic, IEEE/OSA JLT, 2007]

  • Such that r = |r| = is Beckmann distributed RV

So x2 +y2

slide-20
SLIDE 20

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

Generalized Pointing Errors Model

No misalignment Rayleigh Single sided Gaussian Hoyt Rician

slide-21
SLIDE 21

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

slide-22
SLIDE 22

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks Figure: The ergodic capacity for composite log-normal channel (LN). (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”, Submitted to ICC’15.

On-Going Research Directions: Ergodic Capacity Calculations under the impact of pointing errors

Asymptotic Ergodic Capacity

slide-23
SLIDE 23

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks On-Going Research Directions: Average Probability of Error Computations

SER Performance of MPSK and MDPSK

  • Symbol error rate performance of MPSK and MDPSK over

AWGN are given by [Pawula, TCOM’1999] and with

slide-24
SLIDE 24

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 MPSK and MDPSK

  • Well known that MDPSK performs 3 dB worse than MPSK in the Rayleigh

fading channels when the SNR is asymptotically large [Ekanayake- TCOM’1990]

  • Asymptotic SER performance of MDPSK with respect to MPSK over a

fading channel with diversity order t+1 ℎ 𝑢 ≜ 𝑡𝑗𝑜2𝜄 𝑢+1 𝑒𝜄.

𝜃𝜌

with and ,

  • Asymptotic SER performance of MDPSK with respect to MPSK over

lognormal fading channel

slide-25
SLIDE 25

Free Space Optical (FSO) Communications: Towards the Speeds of Wireline Networks On-Going Research Directions: Average Probability of Error Computations

Comparison of SER for MPSK and MDPSK in Lognormal Fading

Figure: Average SER of FSO using MPSK and MDPSK over weak turbulence Lognormal fading channels.

Reference: X. Song, F. Yang, J. Chengand M. -S. Alouini, “Asymptotic SER performance comparison of MPSK and MDPSK in fading channels ”, IEEE Wireless Comm Letters, 2014.

slide-26
SLIDE 26

Summary and Next Steps ?

Concluding Remarks

slide-27
SLIDE 27

Conclusion and Current Work

  • Spectrum scarcity is becoming a reality
  • This scarcity can be relieved through:

– Cognitive radio networks – Extreme bandwidth communication systems

  • Analytical and fast simulation results can be used to perform

initial system level trade-offs

  • On-going deployment and testing the capabilities of FSO

systems in hot & humid desert climate conditions.

slide-28
SLIDE 28

Thank You Questions?