A Performance Study of Deployment Factors in Wireless Mesh Networks - - PowerPoint PPT Presentation

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A Performance Study of Deployment Factors in Wireless Mesh Networks - - PowerPoint PPT Presentation

May 25, 2023 193 likes •439 views

Background Methodology Results Conclusion A Performance Study of Deployment Factors in Wireless Mesh Networks Joshua Robinson and Edward Knightly Rice University Rice Networks Group networks.rice.edu Joshua Robinson and Edward Knightly

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Background Methodology Results Conclusion

A Performance Study of Deployment Factors in Wireless Mesh Networks

Joshua Robinson and Edward Knightly Rice University Rice Networks Group networks.rice.edu

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

City-wide Wireless Deployments

Many new city-wide wireless mesh networks being planned or deployed: Two-tier mesh networks

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Houston-wide Wireless Network

  • 620 square miles of

coverage:

  • 95% Outside
  • 90% Inside (window)
  • Earthlink
  • $50 million estimated cost
  • 15k mesh nodes and 3k

gateways

  • Operational by 2009
  • Miami-Dade Co. wants 2k
  • sq. miles coverage

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Deployment Strategies

State of the art deployment strategies

  • Exhaustive survey (WLAN, cellular) costly
  • Community networks do not cover efficiently
  • Rules of thumb in practice

Problem: what deployment factors are important to mesh performance and why?

  • For general network environments, not specific

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Deployment Factors and Mesh Performance

We identify critical deployment factors and explore how they affect mesh performance Topology and Architecture

  • Mesh topology structures
  • Multiple radios for access

and backhaul

  • Number of wired gateways

Real-world limitations

  • Placement perturbations
  • Unplanned deployments

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Three Mesh Performance Criteria

Goals for a high-performance mesh network? Focus on each part of the mesh: access tier, backhaul tier, and gateway nodes

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Three Mesh Performance Criteria

Goals for a high-performance mesh network?

  • Ubiquitous coverage

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Three Mesh Performance Criteria

Goals for a high-performance mesh network?

  • Ubiquitous coverage
  • High quality routes to a gateway

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Three Mesh Performance Criteria

Goals for a high-performance mesh network?

  • Ubiquitous coverage
  • High quality routes to a gateway
  • Fairly support many simultaneous flows

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Evaluating Mesh Performance

Three mesh performance metrics

  • 1. Coverage Area
  • Does the access tier provide all-over coverage?
  • 2. Connectivity
  • Are all mesh nodes connected to a gateway?
  • 3. Fair Mesh Capacity
  • What fair rates can users in the network expect?

Identify and study the deployment factors that control each metric

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Evaluation Methodology

Calculating each performance metric

  • Compute performance of each mesh node and client location
  • Use measurement data to drive study
  • Monte Carlo simulations for topologies
  • Infinite plane topology, no edge results reported
  • Performance of single-link fundamental

Well-known pathloss model PdBm(d) = PdBm(d0) − 10αlog10( d d0 ) + ǫ

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Technology-For-All (TFA) Mesh Testbed

Operational mesh in pilot neighborhood in Houston’s East End (Pecan Park)

  • Status: 18 nodes with

approximately 3 km2 of coverage and 2,000 users

  • Operational since May 2005
  • More info at tfa.rice.edu
  • Results presented use TFA

measurements for pathloss*

* “Measurement Driven Deployment of a Two-Tier Urban Mesh Access Network” In Proceedings of MobiSys 2006. Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Coverage Area

Coverage area is the expected fraction

  • f client locations which connect to a

mesh node above a threshold signal strength

  • Threshold value is 2 Mbps
  • Connect to at least one mesh node
  • Uniform user distribution

Controlling topology factors: Mesh node density and configuration

Figure: Two access nodes with poor coverage.

Coverage = 1 −

  • ∀i

(1 − Probdi[X > Tmin])

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Coverage Area, Regular and Random

10 20 30 40 50 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Mesh Node Density (per km2) Coverage Area Square Triangular Hexagonal Random

  • Ideal grid placement and 2-d Poisson point process
  • Compare mesh node densities, equivalent resources
  • 95% coverage: random requires twice the density!

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Perturbations from Ideal Grid Placement

Regular Perturbed

  • Not usually possible to deploy a perfect grid
  • Random angle and distance chosen from uniform distribution
  • Results from averaging 100 trials

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Mesh Node Perturbations

Fix average node density at 20 nodes per km2

  • Inter-node spacing for

square grid is 225 meters

  • Coverage declines only 3%

up to 1

5 of the inter-node

spacing

  • High perturbation better

than coverage of random networks

50 100 150 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 Average Perturbation (meters) Fraction of Client Locations Covered Square Random

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Deploying with Perturbations

50 100 150 10 20 30 40 50 60 70 Average Perturbation Distance (meters) Required Mesh Density (nodes per km2)

  • Coverages declines because of increasing dead spots
  • Resource demands for 95% coverage grow rapidly with

perturbations above 40 meters

  • Perturbations of 1

5 inter-node distance correspond to 25%

  • ver-provisioning

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Fair Mesh Capacity

Model a gateway node as alternating between:

  • Rx/Tx to one-hop neighbors
  • Deferring to other neighbors within interference range

Capacity is then found by the percentage of time doing Rx/Tx

  • All flows receive fair time shares
  • Depends on gateway placement and routing

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Calculating Fair Mesh Capacity

Find routes first, then Tx/Rx and Defer times

  • Uniform distribution of clients
  • Two-hop neighbors interfere
  • Single-radio system
  • Assume fair scheduling exists
  • Longer routes add more defer time

Figure: Square grid network with wire ratio of

1 16

δ = Tx/Rx Time Tx/Rx Time + Defer Time = 16

46 = 35%

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Second Radio for the Access Tier

Architectural Feature: dedicated radios for access and backhaul links

  • Client to Mesh transmissions

do not interfere on wireless backhaul

Figure: With two radios, fair share is 1

2.

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Calculating Capacity for Two Radios

δ = 16

33 = 48%

  • Backhaul tier is 39% more efficient
  • Expect fair mesh capacity to increase proportionally
  • Spatial reuse decreases benefits

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Fair Mesh Capacity Results

10 20 30 40 50 60 500 1000 1500 2000 2500 3000 3500 Mesh Node Density (nodes per km2) Adjusted Fair Mesh Capacity (kbps) Separate Access Unified Access

  • Backhaul tier has more time available for useful transmissions
  • Fair mesh capacity increases by factor of almost 2
  • Adjusted capacity does not include the clients at a wired

gateway

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Summary and Contributions

Measurement-driven methodology for evaluating mesh network performance

  • Coverage, connectivity, and capacity metrics
  • Topology, architecture, deployment factors

Identified critical deployment factors and how they impact mesh performance, including

  • Coverage Area: studies regular grids, random networks, and

the impact of perturbations

  • Connectivity: studied asymmetric links, redundant paths, and

multiple backhaul radios

  • Fair Mesh Capacity: studied regular grid topologies, random

networks, and two-radio mesh architectures

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh

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Background Methodology Results Conclusion

Ongoing and Future Work

Continued Expansion of the TFA network

  • Doubling the number of mesh nodes and gateways

Deployment issues

  • Selecting gateway placements
  • Optimal deployment strategies
  • Increasing capacity with additional radios

Joshua Robinson and Edward Knightly Rice University A Performance Study of Deployment Factors in Wireless Mesh