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Ashu Sabharwal,才智在线淘宝Rice University,Capacity and Fairness in Multihop Wireless Backhaul Networks,Ashu Sabharwal ECE, Rice University,Ashu Sabharwal,才智在线淘宝Rice University,Wireless Utopia: Mobile Broadband,WiFi Hot-spots Reasonable speeds Expensive + poor coverage low subscriber rates, failing companies, 3G Ubiquitous, allows mobility but low data rates Expensive to deploy slow deployments Major costs Wired connection to backbone Spectral fees Uneasy “on-demand” growth,Ashu Sabharwal,才智在线淘宝Rice University,Transit Access Points: Multi-hop Backbone,Few wires Most TAPs multi-hop to wired gateways Add wires to TAPs as demand grows Use both licensed and unlicensed spectrum Licensed spectrum: protected, allows guarantees Unlicensed spectrum: free, more, less interference outdoors,Multiple radios & MIMO,Ashu Sabharwal,才智在线淘宝Rice University,Major Challenges,High information density around wires Capacity per gateway log(n) Service quality transparent to user location Users close to wire can win big TCP on RTT time-scale, too slow,Ashu Sabharwal,才智在线淘宝Rice University,Characteristics of TAP Networks,No mobility in backbone TAPs dont move static topology Slow variability can be used at all time-scales Physical layer can use fast feedback Medium access could be topology aware Qos routing can be reliably done Opportunity for optimization based on topology via feedback at multiple time-scales,Ashu Sabharwal,Outline,Opportunistic Cooperative Relaying Sadeghi,Chawathe,Khoshnevis,Sabharwal Route diversity Cooperative PHY OCR TAP Fairness Gambiroza,Sadeghi,Knightly Performance of current protocols Inter-TAP fairness model Rice TAP Testbed,Ashu Sabharwal,才智在线淘宝Rice University,Multi-hop Networks,Multiple routes to destination Many routes exist to destination Route quality function of time Coherence time Time for which channel SNR remains constant For low mobility channels, several packets long Route diversity,0,1,2,3,Ashu Sabharwal,才智在线淘宝Rice University,Cooperative PHY,Why use only one route every time ? Carrier sense will shut off many TAPs Use their power and antenna resources,0,1,2,3,Ashu Sabharwal,才智在线淘宝Rice University,Cooperative PHY,Send packet(s) to other TAPs,0,1,2,3,Ashu Sabharwal,才智在线淘宝Rice University,Cooperative PHY,Send packet(s) to other TAPs All TAPs together “forward” the packet Acts like a 3M x M antenna system (in above picture) Simplest form of network coding,0,1,2,3,Ashu Sabharwal,才智在线淘宝Rice University,Throughput Gains,Rule: Choose best “k-out-of-m” routes leading to minimum total delay Substantial gains for moderate network size,Maximum Available Routes,Throughput (Mbits/s),60%,70%,Ashu Sabharwal,才智在线淘宝Rice University,Challenges in Realizing Route Diversity,Quality of routes unknown Use of a route depends on its current condition Thus, routes have to measured before every use Multiple TAP coordination Medium access has to coordinate multiple TAPs Knowledge of routes Many routes exist Which subset to actively monitor ?,Ashu Sabharwal,才智在线淘宝Rice University,Opportunistic Cooperative Relaying,4-way multi-node handshake Allows source (TAP 0) to know all channel qualities AND coordinate participating TAPs TAP 0 chooses the smallest delay route Multi-hop MAC Forwarded packets do not contend again Slot reservation ensures safe passage to destination,Ashu Sabharwal,才智在线淘宝Rice University,Throughput Performance,Throughput gains (20-30%) outweigh spatial reuse loss 2-4 routes give max gain due to handshake overhead,Distance from source (d),Throughput (Mbits/s),0,1,2,3,200 m,d,2-hop 802.11,2-route OCR,3-route OCR,4-route OCR,Ashu Sabharwal,才智在线淘宝Rice University,Outline,Opportunistic Cooperative Relaying Sadeghi,Chawathe,Khoshnevis,Sabharwal Route diversity Cooperative PHY OCR TAP Fairness Gambiroza,Sadeghi,Knightly Performance of current protocols Inter-TAP fairness model Rice TAP Testbed,Ashu Sabharwal,才智在线淘宝Rice University,Unfairness in Current Protocol,IEEE 802.11, 5 MUs/TAP TAP1 completely starved Same for TCP Caused mainly by information assymetry In general, closest to the wire TAP wins,Ashu Sabharwal,才智在线淘宝Rice University,Inter-TAP Fairness,Ingress Aggregation Flows originating from a TAP treated as one TAPs implement inter-flow fairness Temporal fairness Different links have different throughputs Throughput fairness hurts good links Removal of Spatial Bias Equal temporal share not sufficient More hop flows get lesser bandwidth,Ashu Sabharwal,才智在线淘宝Rice University,Throughput with Temporal Fairness,Temporal Fairness Equal time shares to all flows Flow receives 1/F of the throughput of the case it was the only flow Shares: 18%, 21%, 61% Increase in number of hops decrease in throughput,20Mbps,5Mbps,10Mbps,Ashu Sabharwal,才智在线淘宝Rice University,Removing Spatial Bias,Spatial Bias Removal (SBR) Find the bottleneck link of each flow Share of all flows traversing bottleneck equal SBR+Temporal Fair = Equal temporal share in bottleneck links SBR + Throughput Fair = Equal throughput for all flows regardless of their paths,Ashu Sabharwal,才智在线淘宝Rice University,Throughput Comparisons,20Mbps,5Mbps,10Mbps,Example,Ashu Sabharwal,才智在线淘宝Rice University,Outline,Opportunistic Cooperative Relaying Sadeghi,Chawathe,Khoshnevis,Sabharwal Route diversity Cooperative PHY OCR TAP Fairness Gambiroza,Sadeghi,Knightly Performance of current protocols Inter-TAP fairness model Rice TAP Testbed,Ashu Sabharwal,才智在线淘宝Rice University,TAP Hardware Design,Platform for new PHY + Pro