Scaling Mesh for Real

1
Scaling Mesh for Real

• Ed Knightly
• ECE Department
• Rice University
• http//www.ece.rice.edu/knightly

2
Scalable Mesh

• High bandwidth
• 400 Mb/sec to residences and small businesses
• High availability
• Nomadicity
• Large-scale deployment
• High reliability and resilience
• Economic viability
• /square mile

3
Research Challenges

• Physical layer
• 400 Mb/s
• Media access
• Target multi-hop and exploit PHY capabilities
• Fairness and traffic control
• Prevent starvation, remove spatial bias
• Prototypes, Testbeds, and Measurement Studies
• Platforms for experimentation and
  proof-of-concept
• Architecture
• Node placement, security, economics, etc.

4
Rice Transit Access Point (TAP) Platform

• 400 Mb/sec via 4x4 MIMO custom design
• Single 20 MHz WiFi channel at 2.4 GHz and 20
  bits/sec/Hz efficiency
• Feedback-based algorithms for beam-forming MIMO
• Custom MAC design and FPGA implementation

5
Rice Transit Access Point (TAP) Platform

• 400 Mb/sec via 4x4 MIMO custom design
• Single 20 MHz WiFi channel at 2.4 GHz and 20
  bits/sec/Hz efficiency
• Feedback-based algorithms for beam-forming MIMO
• Custom MAC design and FPGA implementation

6
Technology For All Deployment

• Technology For All Houston, Texas (non-profit)
• Empower low income communities through technology
• Neighborhood income 1/3rd national average, 37
  of children below poverty
• Applications
• Education and work-at-home

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Technology For All Mesh Deployment

• Multi-hop IEEE 802.11 wireless network covering
  40,000 residents
• Single wireline Internet backhaul
• Long-haul directional links
• OTS programmable platform
• 25k/square mile

8
TFA Research Issues

• Architecture
• Node/wire placement
• Sustainable non-profit business model
• Protocol deployment
• traffic management
• Security
• Measurement studies

9
Two Tier Architecture

• Access connects homes to mesh nodes
• Backhaul connects mesh nodes to wires

10
Parking Lot Scenario

• One branch of the access tree is shown
• Parking lot is dominant traffic matrix

11
Parking Lot Measurements (FTP/TCP upload)

• Single flow scenario widely studied
• Concurrent flows
• Without RTS/CTS, hidden terminals ? starvation
• With RTS/CTS, multi-hop flows achieve 20 of
  1-hop flows

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Parking Lot Measurements (FTP/TCP bi-directional)

• Near starvation with 3 or more hops
• TCP unable to throttle short flows to leave
  capacity for long flows
• MAC hidden terminals and Information Asymmetry
  GSK05
• Ongoing work
• congestion control over an imperfect MAC
• MAC redesign

13
Hidden Terminals in Access Networks
14
Information Asymmetry

• Asymmetric view of channel state
• Node with more information knows when to
  contend other attempts randomly

15
Result on Information Asymmetry GSK05

• Analytical model to predict throughput
• If randomly place nodes
• IA scenario is the most probable resulting in
  severe throughput imbalance
• Previous studies in mobile settings missed by
  focusing on average throughput
• Information Asymmetry is a fundamental property
  of wireless state cannot be perfectly shared

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Conclusions

• Communications advances enabling 400 Mb/s links
• At 3-4 hops, TCP/WiFi utilizes 1 of this
• We can do better!
• Challenges
• MAC multi-hop protocols
• Fairness distributed fairness algorithms
• Prototypes testbeds and proof-of-concept
• Architecture placement, economics, security,