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QoS-based Admission Control for Multihop Wireless Backhauls

QoS-based Admission Control for Multihop Wireless Backhauls. Girija Narlikar Bell Labs Joint work with Seungjoon Lee, Martin Pal, Gordon Wilfong, Lisa Zhang. Multihop Wireless Backhaul. Gateway. fiber to Internet. backhaul links. access links. access links.

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QoS-based Admission Control for Multihop Wireless Backhauls

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  1. QoS-based Admission Control for Multihop Wireless Backhauls Girija Narlikar Bell Labs Joint work with Seungjoon Lee, Martin Pal, Gordon Wilfong, Lisa Zhang

  2. Multihop Wireless Backhaul Gateway fiber to Internet backhaul links access links access links • Provides connectivity to hot-spots, small businesses, residences, base stations using wireless links (e.g., WiMAX)

  3. Wireless Backhaul: why now? • Wireless access speeds (802.11x/3G) have increased: • T1/DSL backhauls no longer sufficient • T3/Fiber can be costly to install or lease • Longhaul, NLOS wireless technologies have improved • 802.16d (WiMAX) now standardized • Equipment cost likely to reduce • Ability to bypass incumbent wireline carrier’s network

  4. Multihop (Mesh) Backhauls • More than one hop to get to wired “gateway” • Can provide ubiquitous coverage in areas with no wired infrastructure • Can be deployed incrementally • Can adjust to failures or changing traffic load • Shorter links allow for higher link rates and greater spatial reuse Several start-ups as well as large vendors now offer wireless mesh products

  5. Single Vs Multiple hops 71Mbps 14Mbps 48Mbps 7Mbps 16Mbps 45Mbps G 63Mbps 42Mbps 67Mpbs G 17Mbps 69Mbps 6Mbps 51Mbps 30Mbps 69Mbps 15Mbps 32Mbps (a) f = 1552 Kbps • Each node sends a total of f Kbps (uplink + downlink) • Standard pathloss model • Spatial reuse: each node transmits or receives on one link at a time (b) f = 6692 Kbps

  6. Multihop Backhaul Challenges • Layout • Routing • Admission Control/QoS A Gateway B E C D • Scheduling • Challenges in Wireless Networks • Interference • Self-interference • Cross-interference • Different link capacities User Connections

  7. Network Model & Assumptions • Multiple nodes including a single gateway • Layout is given • We construct a tree topology rooted at the gateway • TDM physical layer with subchannels (e.g., 16) • Simultaneous transmission to (or reception from) multiple nodes • A node cannot simultaneously transmit and receive • How to assign time slots and subchannels? • Weighted Fair Queueing (WFQ) at each node • Delay and bandwidth guarantee in wireline networks • Worst-case delay  (# hops)/(bandwidth)

  8. Even-Odd Link Activation • Nodes alternately in transmitting ( ) or receiving ( ) modes; edges are alternately uplink and downlink • All nodes at same level in same mode • Approximately twice the delay of wireline case (e.g., WFQ) r r different subchannels v v odd timeslots even timeslots

  9. Delay Bounds For WFQ (Weighted Fair Queuing) and CEDF (Coordinated Earliest Deadline First) we can show that For each connection j : : worst case delay for connection jin real wireless network : worst case delay for connection jin imaginary wireline network with no propagation delays : number of hops for connection j

  10. QoS-based Admission Control • Objective • Choose a subset of connections such that we can satisfy • Both delay and bandwidth • Maximize total reward of admitted connections • All-in-One Approach Find a tree and a set of connections at the same time • Optimal Integer Linear Program (ILP) Formulation • Finding an optimal solution is NP-hard. • Use AMPL/CPLEX to solve small instances • Within reasonable error bound: identify upper bound

  11. Dynamic Program Based Approach • Assume a tree is given. Tree Construction Heuristics: • Star • Minimum Spanning Tree • Delay-aware scheme • Bottom-up Dynamic Program (DP) • “Optimal” subject to discretization of rates • Running time = O(n Fm4 M2) • Fm = maximum number of unique discretized rates • M =total number of subchannels

  12. Experimental Setup • 5km-by-5km square with a gateway in the middle • Random placement for other nodes • Fixed Path-loss model • No fast fading • Self-interference only: no cross-edge interference • QoS requirements and rewards

  13. Comparison between ILP and DP • Up to 10 nodes in each randomly generated scenario

  14. Effect of Network Size

  15. Conclusions and Future Work • First bandwidth and delay-based QoS using the Even-Odd framework • Optimal, ILP-based formulation • Tree construction + optimal connection selection • Admit all connections but degrade QoS as less as possible • Dynamic admission of new connections • Future work • Generalization for multiple gateways • Other topologies (e.g., multiple trees, DAGs) • Placement of gateways and nodes

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