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CSpy : Finding the Best Quality Channel without Probing

CSpy : Finding the Best Quality Channel without Probing. Souvik Sen , Bozidar Radunovic , Jeongkeun Lee, Kyn -Han Kim MobiCom’13. Wireless Everywhere. Wireless Display. Wireless Input. Performance really matters. Mobile Wireless. Wireless Performance in Theory. Rx. Tx.

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CSpy : Finding the Best Quality Channel without Probing

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  1. CSpy: Finding the Best Quality Channel without Probing SouvikSen, BozidarRadunovic, Jeongkeun Lee, Kyn-Han Kim MobiCom’13

  2. Wireless Everywhere Wireless Display Wireless Input Performance really matters Mobile Wireless

  3. Wireless Performance in Theory Rx Tx Channel Measurement Textbook Algorithms Channel Quality Limits Wireless Performance Question: How to SelecttheBestChannel? Adaptions Scheduling …

  4. Premier: Propagations and Channel Rx Tx Single Path Rx Tx Q1: How to evaluate different channels? Multipath

  5. How to Determine Channel Quality • Goal: High Throughput • Metric: Effective SNR (SIGCOMM’10) Effective SNR Measurements of A Single Channel

  6. Which Channel to Select? • Goal: High Throughput • Metric: Channel with Strongest Effective SNR Measurements of Multiple Channels Q2: How to find the best channel?

  7. How to Find the Best Quality Channel • Method: Probing • Measure every channel and compare their qualities • Problem: • Time consuming • Large overhead if frequent probing is needed Goal: Can we find the strongest channel Without Probing?

  8. Predicting an Unseen Channel • Insight: • Probing does not leverage information about the underlying propagation • Channel State Information (CSI) contains information about the multipath propagation structure Determine the strongest from a set of channels while probing only one channel

  9. Review: Channels, CSI, CIR

  10. Review: Channels, CSI, CIR # channels << # paths: underdeterminedsystem CSI • Explore correlation between • CIR from one channel • Index of the strongest channel IDFT

  11. Hypotheses and Measurements • Hypothesis 1: Links with the same strongest channel shares similarity in their multipath structure

  12. Hypotheses and Measurements • Hypothesis 2: Links with different strongest channel index exhibits different multipath characteristics

  13. Why does Prediction Work • A Simple Theoretical Analysis (proof in the paper) • If: phase of 1sttap < phase of 2ndtap in channel c • Then :amplitude of 1st tap in c+1 > amplitude of 1st tap in c-1 • A High-level Intuition • The phases of different paths are uniformly random and independent • When constructing an estimator based on relative phases, we can recover a bias correlated with channel quality Intractable for multiple channels Solution?

  14. Learning a Predictor • Feature Representation: • The relative phases of all taps w.r.t. the 1st tap • Training and Classification: • Multi-class support-vector machine (SVM)

  15. Experiment Setup • 70 links in 2 buildings, and 1 parking lot • CSI Tool enabled laptops operating at 5GHz • 9 channels (#36-48, #149-165)

  16. Performance • SCI (Strongest Channel Index) Estimation Mean Accuracy: 83%

  17. Performance • Accuracy/FP across different observing channels Performance degrades on edge channels

  18. Performance • Accuracy/FP w.r.t. increasing frequency gap Reliably estimate the strongest channel within 4-5 adjacent channels

  19. Performance • Throughput Gain 250%, 100% and 85% gain w.r.t. weakest, average, and an optimal algorithm

  20. Performance • Comparison with Probing-based Scheme

  21. Thank You!

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