Scaling Mesh for Real Ed Knightly ECE Department Rice University http://www.ece.rice.edu/~knightly
Jan 01, 2016
Scaling Mesh for Real
Ed Knightly
ECE Department
Rice University
http://www.ece.rice.edu/~knightly
Ed Knightly
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
Ed Knightly
Research Challenges
1. Physical layer– 400 Mb/s
2. Media access– Target multi-hop and exploit PHY capabilities
3. Fairness and traffic control– Prevent starvation, remove spatial bias
4. Prototypes, Testbeds, and Measurement Studies– Platforms for experimentation and proof-of-concept
5. Architecture– Node placement, security, economics, etc.
Ed Knightly
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
Ed Knightly
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
Ed Knightly
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
Ed Knightly
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
Ed Knightly
TFA Research Issues
Architecture– Node/wire placement
Sustainable non-profit business model
Protocol deployment– traffic management
Security
Measurement studies
Ed Knightly
Two Tier Architecture
Access: connects homes to mesh nodes Backhaul: connects mesh nodes to wires
Ed Knightly
Parking Lot Scenario
One branch of the access tree is shown
Parking lot is dominant traffic matrix
Ed Knightly
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
Ed Knightly
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
Ed Knightly
Hidden Terminals in Access Networks
Ethernet
Ethernet
Ethernet
Ethernet
Internet
TAP1 TAP2 TAP3 TAP4
collision no collision
Ed Knightly
Information Asymmetry
Ethernet
Ethernet
Ethernet
Ethernet
Internet
TAP1 TAP2 TAP3 TAP4
RTS
TAP2 sets its NAVNo CTS
RTS
• Asymmetric view of channel state
• Node with more information knows when to contend; other attempts randomly
Ed Knightly
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
Ed Knightly
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, …