Scaling Mesh for Real Ed Knightly ECE Department Rice University

Ed Knightly Scalable Mesh l High bandwidth –400 Mb/sec to residences and small businesses l High availability –Nomadicity –Large-scale deployment –High reliability and resilience l 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 l 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 l Custom MAC design and FPGA implementation

Ed Knightly Rice Transit Access Point (TAP) Platform l 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 l Custom MAC design and FPGA implementation

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

Ed Knightly Technology For All Mesh Deployment l Multi-hop IEEE 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 l Architecture –Node/wire placement l Sustainable non-profit business model l Protocol deployment –traffic management l Security l Measurement studies

Ed Knightly Two Tier Architecture l Access: connects homes to mesh nodes l Backhaul: connects mesh nodes to wires

Ed Knightly Parking Lot Scenario l One branch of the access tree is shown l Parking lot is dominant traffic matrix

Ed Knightly Parking Lot Measurements (FTP/TCP upload) l Single flow scenario widely studied l 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) l 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] l Ongoing work: –congestion control over an imperfect MAC –MAC redesign

Ed Knightly Hidden Terminals in Access Networks Internet TAP1 TAP2 TAP3 TAP4 collisionno collision

Ed Knightly Information Asymmetry Internet TAP1 TAP2 TAP3 TAP4 RTS TAP2 sets its NAV No 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] l Analytical model to predict throughput l 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 l Information Asymmetry is a fundamental property of wireless: state cannot be perfectly shared

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