1 / 24

Capacity and Fairness in Multihop Wireless Backhaul Networks

Capacity and Fairness in Multihop Wireless Backhaul Networks. Ashu Sabharwal ECE, 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

tanek
Download Presentation

Capacity and Fairness in Multihop Wireless Backhaul Networks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Capacity and Fairness in Multihop Wireless Backhaul Networks Ashu Sabharwal ECE, Rice University Rice University

  2. 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 Rice University

  3. 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 Rice University

  4. 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 Rice University

  5. Characteristics of TAP Networks • No mobility in backbone • TAPs don’t move  static topology • Slow variability can be used at all time-scales • Physical layer can use fast feedback • Medium accesscould be topology aware • Qos routingcan be reliably done Opportunity for optimization based on topology via feedback at multiple time-scales Rice University

  6. 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 Rice University

  7. Multi-hop Networks 0 • 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 2 3 1 Rice University

  8. Cooperative PHY • Why use only one route every time ? • Carrier sense will shut off many TAPs • Use their power and antenna resources 0 2 3 1 Rice University

  9. Cooperative PHY • Send packet(s) to other TAPs 0 2 3 1 Rice University

  10. 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 2 3 1 Rice University

  11. Throughput Gains • Rule: Choose best “k-out-of-m” routes leading to minimum total delay • Substantial gains for moderate network size ~70% ~60% Throughput (Mbits/s) Maximum Available Routes Rice University

  12. 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 ? Rice University

  13. 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 Rice University

  14. Throughput Performance • Throughput gains (20-30%) outweigh spatial reuse loss • 2-4 routes give max gain due to handshake overhead 2-route OCR 3-routeOCR d 4-route OCR 2 Throughput (Mbits/s) 0 200 m 1 2-hop 802.11 3 Distance from source (d) Rice University

  15. 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 Rice University

  16. 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 Rice University

  17. 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 Rice University

  18. TA (1) TA (2) TA (3) Internet TAP4 TAP1 TAP2 TAP3 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 10Mbps 5Mbps Rice University

  19. 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 Rice University

  20. Throughput Comparisons Example 20Mbps 10Mbps 5Mbps Rice University

  21. 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 Rice University

  22. TAP Hardware Design • Platform for new PHY + Protocol Design • Generous compute resources • High-end FPGAs with fast interconnects • Simulink GUI environment for development • 2.4 GHz ISM band radios • 4x4 MIMO system • Open-source design • Both hardware and software Rice University

  23. TAP Testbed Goals • Prototype network on and around Rice campus • Measurement studies from channel conditions to traffic patterns Rice University

  24. Summary • Transit Access Points • WiFi “footprint” is dismal • 3G too slow and too expensive • Removing wires is the key for economic viability • Challenges • Enabling high capacity backbone • Multi-hop fairness Rice University

More Related