Opportunistic Cooperation for FSO Links Aided by Decode and Forward - PowerPoint PPT Presentation

Opportunistic Cooperation for FSO Links Aided by Decode and Forward Relay Michael (Qunfeng) He * , Zhengyuan Xu + * Department of Electrical Engineering University of California, Riverside + Department of Electronic Engineering Tsinghua University, China

Outline  Motivations and Setup  Problem Formulation and Signal Model  Channel Model  Link Outage Analysis: DT, dDF and oDF Numerical Results  2 2

Motivations and Setup  Motivations  FSO link in IR wavelength is challenged by turbulence  Traditional approaches: time and spatial diversity  Recent advances: user cooperation i n Poisson domain [Karimi 09], [Abou-Rjeily 11]  Our work: Gaussian noise assumption, opportunistic relay [Safari 08]  System setup  DT phase: S-R & S-D  DF phase: S-D or R-D (conditional)  R-S: CSI feedback link  Categories  Non-cooperation (Direct transmission)  Deterministic cooperation  Opportunistic cooperation A three-way FSO network for opportunistic cooperation. 3

Problem Formulation and Signal Model  Problem formulation: outage probability of a FSO link  Characterize the outage over fading channel 𝑆 = 𝑚𝑝𝑕 2 (1 + 𝑇𝑂𝑆)  Given SNR, the instantaneous rate  Probabilistic event s.t. R meets required R 0 𝑄 𝑝𝑣𝑢 𝑆 0 = 𝑄 𝑠 𝑚𝑝𝑕 2 1 + Γ < 𝑆 0 = 𝑄 𝑠 Γ < Γ 𝑢ℎ (1)  SNR model  Consider binary PPM, 𝑠 𝑇 𝑂𝐷 𝑄 𝑡 𝑕 𝑡𝑒 + 𝑆𝑈𝑡𝑄𝑐 + 𝑜𝑡𝑒 𝑠 𝑂𝐷 = = 𝑠 𝑜 𝑂𝐷 (2) 𝑆𝑈 𝑡 𝑄 𝑐 + 𝑜𝑜𝑒  Electrical SNR 𝜈 𝑡 −𝜈 𝑜 2 2 𝑄 𝑡 𝑕 𝑡𝑒 Γ = Γ 𝑂𝐷 = (3) 𝜏 2 𝜏 2 𝑜 𝑜 4

Channel Model 𝒉 = 𝜷 𝟑 𝑴(𝒆)  Channel coefficient, described by [Safari 08] (4) 𝐵 𝑠 𝑀 𝑒 = Ω𝑒 2 exp (−𝜊𝑒)  Path loss: (5)  Turbulence model, weak turbulence: log-normal distribution 1 (− 𝑚𝑜𝛽 − 𝜈 𝑦 𝑔(𝛽) = exp ) 7 11 2 𝑒 = 0.124𝑙 𝜏 𝑦 6 𝐷 𝑜 2 𝑒 (6) 6 2𝜏 𝑦 2 2𝜌𝜏 𝑦 2 𝛽  Outage probability of a DT FSO link  Plugging SNR and fading models Γ 𝑢ℎ 𝜏 𝑜 2 2 < 𝑄 𝑝𝑣𝑢, 𝐸𝑈 = 𝑄 𝑠 Γ < Γ 𝑢ℎ = Pr 𝛽 𝑡𝑒 (𝑀𝑡𝑒𝑄 𝑡 ) 2 (7) 2 (𝑒𝑡𝑒) ln 𝐿 𝑡𝑒,𝑢ℎ,𝐸𝑈 −2𝜏 𝑦 = Q 2𝜏 𝑦 (𝑒𝑡𝑒) 5

A Deterministic Cooperative FSO Link  Deterministic cooperation: dDF  Parallel links in nature: S-D and S-R-D  Outage happens when both paths fail  Outage of dDF:  Assume the same signal expressions 𝑄 𝑝𝑣𝑢, 𝑒𝐸𝐺 = 𝑄𝑝𝑣 𝑢, 𝑡𝑒, 𝐸𝑈 𝑄 𝑝𝑣𝑢, 𝑡𝑠𝑒, 𝐸𝐺 (8) where, 𝑄 𝑝𝑣𝑢, 𝑡𝑠𝑒, 𝐸𝐺 = 1 − (1 − 𝑄𝑝𝑣𝑢 , 𝑡𝑠 )(1 − 𝑄𝑝𝑣𝑢 , 𝑠𝑒 ) (9) 2 (𝑒𝑡𝑒) 𝑄 𝑝𝑣𝑢, 𝑒𝐸𝐺 = Q ln 𝐿 𝑡𝑒, 𝑢ℎ, 𝑒𝐸𝐺 − 2𝜏 𝑦 2𝜏 𝑦 (𝑒𝑡𝑒) 2 (𝑒𝑡𝑠) 2 (𝑒𝑠𝑒) . 1 − 1 − Q ln 𝐿 𝑡𝑠, 𝑢ℎ, 𝑒𝐸𝐺 − 2𝜏 𝑦 1 − Q ln 𝐿 𝑠𝑒, 𝑢ℎ, 𝑒𝐸𝐺 − 2𝜏 𝑦 2𝜏 𝑦 (𝑒𝑡𝑠) 2𝜏 𝑦 (𝑒𝑠𝑒) (10) 6

An Opportunistic Cooperative FSO Link  Outage probability for opportunistic cooperation of FSO links 𝑄 𝑝𝑣𝑢, 𝑝𝐸𝐺 = 𝑄𝑝𝑣 𝑢, 𝑡𝑠𝑄𝑝𝑣𝑢, 𝑝𝐸𝐺 − 𝐸𝑈 + 1 − 𝑄𝑝𝑣𝑢 , 𝑡𝑠 𝑄 𝑝𝑣𝑢, 𝑝𝐸𝐺 − 𝐸𝐺 (11)  Each component can be retrieved from prev. analysis  Obtaining the signal representation  Developing the SNR  Applying the outage probability expression  Numerical study  Direct computation on analytical outage probability equations  Monte-Carlo simulation on SNR and numerical outage probability  Compare above results to validate the analysis 7

Numerical Results (1)  A special case where relay lies on the middle point of S-D  To verify cooperation does improve the link  Contrast the analytical form against Monte-Carlo simulation 0 10 -2 10 -4 10 -6 10 -8 10 NC, Analytical NC, Numerical -10 10 dDF Coop, Analytical dDF Coop, Numerical -12 oDF Coop, Analytical 10 oDF Coop, Numerical -14 10 -16 10 -160 -155 -150 -145 -140 -135 P tot T b , dBJ Outage performance of opportunistic FSO system aided by DF relay, dsr= drd= 500m,dsd= 1000m. 8

Numerical Results (2)  Increasing the S-R separation, equivalent to downgrading the S-R quality  Opportunistic cooperation excels deterministic version in high power regime  Opportunistic cooperation has wider adaptability  There exists an range within which cooperation is applicable 0 10 -5 10 -10 10 NC, Analytical NC, Numerical dDF Coop, Analytical dDF Coop, Numerical oDF Coop, Analytical oDF Coop, Numerical -15 10 -150 -148 -146 -144 -142 -140 -138 -136 -134 -132 -130 P tot T b , dBJ Outage performance of opportunistic FSO system aided by DF relay, dsr= drd= dsd= 1000m. 9

Numerical Results (3)  Checking the outage performance on multiple separations of S-R -2 10 dDF Coop, MC oDF Coop, MC -3 10 -4 10 -5 10 -6 10 500 600 700 800 900 1000 1100 1200 1300 1400 1500 r sr , meters Outage performance of opportunistic cooperation vs. S-R link distance, drd= dsd= 1000m. 10

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