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Rui Zhao , Bernhard Walke, Guido R. Hiertz ComNets Chair of Communication Networks

Rui Zhao , Bernhard Walke, Guido R. Hiertz ComNets Chair of Communication Networks RWTH Aachen University Aachen Germany. W-CHAMB Wireless CHannel Oriented Ad-hoc Multi-hop Broadband A new MAC for better support of Mesh networks with QoS. Outline. Overview of W-CHAMB

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Rui Zhao , Bernhard Walke, Guido R. Hiertz ComNets Chair of Communication Networks

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  1. Rui Zhao, Bernhard Walke, Guido R. Hiertz ComNets Chair of Communication Networks RWTH Aachen University Aachen Germany W-CHAMBWireless CHannel Oriented Ad-hoc Multi-hop BroadbandA new MAC for better support of Mesh networks with QoS Rui Zhao, ComNets, RWTH Aachen University

  2. Outline • Overview of W-CHAMB • Better Multi-hop Support • QoS Support of W-CHAMB • Synchronization of W-CHAMB • Summary • Simulation Result Rui Zhao, ComNets, RWTH Aachen University

  3. TDMA based Channel-oriented Fully distributed MAC protocol Possible PHY IEEE 802.11a/g OFDMA MC-CDMA Full scale QoS guarantee Prioritized access (DiffServ) Multi-hop operation Energy (E) signals Access-E-Signal Prioritized access to wireless medium Busy-E-Signal Calm down hidden stations Control transmission direction Adaptive multi-slot option Control of capacity of Traffic Channel (TCH) Increase of channel utilization Large-scale ad-hoc Mesh networks Overview of W-CHAMB Rui Zhao, ComNets, RWTH Aachen University

  4. Radio Resource Control (RRC) Call Admission Control (CAC) Dynamic Frequency Selection (DFS) Power Control (PC) Link Adaptation (LA) Media Access Control (MAC) Multiple access to wireless medium TDMA channels with dynamic TDD mode Hidden station elimination (busy tone) TDMA Traffic Channel (TCH) to connect neighbored Mesh points Priority handling of packet data flows per Mesh point Multiplex packets to TCHs under DiffServ Radio Link Control (RLC) Un-/acknowledged data W-CHAMB Protocol Stack Rui Zhao, ComNets, RWTH Aachen University

  5. All PHY parameters are examples only All durations are example values No assumption on PHY to be used is made Here: “.11a” OFDM like realistic PHY assumed Important Notice! Rui Zhao, ComNets, RWTH Aachen University

  6. Access Channel (ACH) Traffic Channel (TCH) Energy signal Channel (ECH) Single Value Busy-E-Signal (SVB) Signal “TCH occupied” to hidden stations Double Value Busy-E-Signal (DVB) Signal “TCH occupied & Reverse (TDD) transmission requested” 6us 6us 1us 1us 2us 2us 2us 2us 1us 1us Tx On Tx On Signal Signal Tx Off Tx Off Guard Guard MAC Frame and Energy Signals ACH TCH1 … TCHn … ACH1-n 45us x n ECH 1-n 6us x n 6us 6us x (n +m) + 28us Priori-tization Phase Contention Phase Transmission Phase 1us 1us 2us 2us n m 28us Signal Tx Off Tx On Guard Single Value Busy-E-Signal (SVB) Double Value Busy-E-Signal (DVB) Access-E-signal Rui Zhao, ComNets, RWTH Aachen University

  7. ACH-Prioritization Phase QoS-related contention n binary Access-E-signals ACH-Contention Phase Contention with m binary Access-E-signals Higher success probability of an access packet m depends on network size ACH-Transmission Phase Transmission of request-packet Network control data 6us x (n +m) + 28us Prioritization Phase Contention Phase Transmission Phase n m 28us Access Channel (ACH) Rui Zhao, ComNets, RWTH Aachen University

  8. Mesh Points generatenumber ∈ [0;2n-1] According to QoS requirement Check number bit by bit If 1, send E-signal If 0, listen If Mesh point hears E-signal, it defers from contention Winners of prioritization phase contend again Draw random numberfrom [0;2m-1] Winner sends request packet (or other) via ACH Access Method(similar to HiperLAN/1) Prioritized Access Method Rui Zhao, ComNets, RWTH Aachen University

  9. Guarantee single winner In almost every contention Even in high density mesh Failed Mesh Points Initiate new contention in next frame Use bigger contention number Increase chance to win Achieve fairness among Mesh points With control algorithms of TCH Support bottle-neck Mesh Points (Mesh AP, portal) Get bigger contention number Win more access trials More transmission chances 6us x (n +m) + 28us Prioritization Phase Contention Phase Transmission Phase n m 28us Contention Sub-phase in ACH Rui Zhao, ComNets, RWTH Aachen University

  10. Send a request packet on ACH containing proposed TCHs and QoS description Connection Setup Check available channels Accept the request by signaling SVB on ECH(s) corresponding to the selected TCH(s) Send packet data via the reserved TCH(s). (Data might be station`s own or relay data) Forward Transmission Signal SVB on the corresponding ECH(s) Send packet data via the reserved TCH(s) Reverse Transmission (On Demand TDD) Signal DVB on the ECHs to request reverse TDD transmission Send packet data via the reserved TCH(s) in alternate direction Signal SVB(DVB) on the corresponding ECH(s) Transmission Sender Receiver Check available channels A TCH is defined on a per hop basis only. Rui Zhao, ComNets, RWTH Aachen University

  11. Busy-E-Signal (6μs) Does not containuser related information Preamble notneeded TCHs definedon disjointtime slots TCH4 ECH4 ECH3 TCH3 Busy-E-Signal to Calm DownHidden Stations STA5 STA4 STA6 STA8 STA3 STA7 STA1 STA2 Rui Zhao, ComNets, RWTH Aachen University

  12. TCH freed by a Mesh Point No packet in TCH buffer Hang-on time expired Dependent on type of service Higher service level = longer hang-on time Longer value → lower transmission delay Packet-oriented behavior Example for hang-on time equal to 2 MAC frames Capacity Increase: Release of a TCH After Specified Hang-on Time Rui Zhao, ComNets, RWTH Aachen University

  13. Dynamic Adjustment of Number of TCH for a Connection • Mesh points contend for more TCHs if QoS cannot be satisfied • Release TCH after hang-on time • Service specific • Here • Hang-on time = 1 MAC frame • Max TCHs = 3 TCHs • Efficient resource use even for rt-VBR Rui Zhao, ComNets, RWTH Aachen University

  14. 45µs 90µs PDU PDU AGC SYN PDU PDU AGC SYN Tx power on Tx power off Tx power on Tx power off 27µs 4.7µs 4.3µs 4.7µs 36µs 4.3µs 81µs 135µs AGC SYN PDU PDU PDU PDU Tx power on Tx power off 31.5µs 4.7µs 4.3µs 126µs PDU Trains for better Efficiency ACH ECHs ACH • PDU trains • Achieve higher efficiency • >2 adjacent TCHs used from source to same destination TCH TCHs ECHs ACH TCHs ECHs Rui Zhao, ComNets, RWTH Aachen University

  15. No central control Mesh Points connect to neighbor pico-nets Any Mesh point is centre of a pico-net Power control/save mode depend on Mesh point Routing modes: Bridge/routerbased MANET Mesh points care for TCHs to neighbors Medium Access Fully Decentralized Rui Zhao, ComNets, RWTH Aachen University

  16. Bottle-necks (BNs), Mesh APs or portals More in & out traffic than average Powerful computational ability & plenty power supply & large memory In “right” location Schemes for transmission between BNs Several continuous TCHs reserved According to load Longer hang-on time values Multiplexing of different traffic streams into reserved TCHs Expedited forwarding (EF) PHB (Per-Hop Behaviors) (DiffServ) [6] ACH TCHs ECHs Hang-on times (unit: MAC frames) 10 8 4 Traffic Schemes for Bottle-necks Prrmium TCHs Gold Silver Bronze BN STA Rui Zhao, ComNets, RWTH Aachen University

  17. Interference range Sensing range ACH-Req ECHs Transmitting in parallel in different TCHs TCHs Better Multi-hop Support • Ongoing transmission between Mesh point 4 & 5 • Mesh point 1 attempts to initiate a transmission to 2 (Instability, see [4]) Transmission range RTS 1 2 3 4 5 IEEE802.11 CTS TCHs 1 2 3 4 5 W-CHAMB has knowledge about existing transmission Rui Zhao, ComNets, RWTH Aachen University

  18. Efficient prioritized access Up to 16 levels TCH Valid transmission time (VTT) Associated with QoS type Higher Qos level=higher value Statistical interruption of lower level transmission TCH Hangon time Depends on priority Controls traffic performance (longer value → lower transmission delay) Multi-slots capability for higher throughput QoS guarantee under heavy load Due to channel-oriented structure No probing packets for CAC (Call Admission Control) Observe TCHs & ECHs QoS Support Rui Zhao, ComNets, RWTH Aachen University

  19. Periodic Beacons Every Mesh Point participates in generation Analysis by recipients In full ad-hoc operations mode Able to support large scale networks Support multi-hop operation Support Mesh Point mobility Clock shift compensation algorithm Combat clockdrifts Accuracy forone-hopnetwork = 0.4±0.1 µs Synchronization of W-CHAMB [5] Rui Zhao, ComNets, RWTH Aachen University

  20. Channel-Oriented On top of any existent or future PHY layer Decentral Control Scheme Flexible Multi-Hop (Mesh) Support Perfect Ad-Hoc Mesh Networking Sophisticated QoS Guarantee Support of large number of Mesh points in ad-hoc Mesh W-CHAMB Summary Rui Zhao, ComNets, RWTH Aachen University

  21. References • [1]. B. Xu, B. Walke, W-CHAMB: A Wireless Channel-oriented Ad-hoc Multihop Broadband Network – Comparison with IEEE 802.11. In Proc. European Wireless’99, Munich, Germany, October 1999. pp. 79-84 • [2]. B. Xu, B. Walke, Protocols and Algorithms supporting QoS in an Ad-hoc Wireless ATM Multihop Network, in Proc. EPMCC’99, pp. 79-84, Paris, France, Mar. 1999. • [3]. M. Lott and B. Walke, Performance of theWireless Ad hoc Network W-CHAMB, in Proc. European Wireless (EW’99), (Munich, Germany), Oct. 1999. • [4]. S. Xu and T. Saadawi – “Does the IEEE 802.11 MAC Protocol Work Well in Multihop Wireless Ad Hoc Networks?” IEEE Communications Magazine, June 2001, pp 130-137. • [5]. R. Zhao, and B. Walke: A Synchronization Scheme for the Wireless Channel-oriented Ad-hoc Multi-hop Broadband System (W-CHAMB). In Wireless World Research Forum, Zurich, Switzerland, July 2003 • [6]. RFC 2598, An Expedited Forwarding PHB, June 1999 Rui Zhao, ComNets, RWTH Aachen University

  22. Comparing maximum through-put, 802.11 & W-CHAMB PHY: 802.11a (OFDM) Packet size = 9 symbols W-CHAMB 81B @ QPSK¾,162B @ 16QAM¾,243B @ 64QAM¾ 802.11 115B @ QPSK¾ ,192B @ 16QAM¾,277B @ 64QAM¾ W-CHAMB MAC Number of TCH & ECH 16 TCH 45µs Energy signal 6µs ACH (6*4+8*4+28)µs = 100µs Simulation STA2 STA1 2 hop2 MAP1 MAP2 1 hop STA3 MAP3 MAP6 STA6 MAP MAP5 MAP4 STA4 STA5 A two hop scenario MAP: Mesh AP STA: Station Rui Zhao, ComNets, RWTH Aachen University

  23. Maximum Throughput Rui Zhao, ComNets, RWTH Aachen University

  24. Thanks for your attention rui@comnets.rwth-aachen.de hiertz@ieee.org walke@comnets.rwth-aachen.de http://www.comnets.rwth-aachen.de Rui Zhao, ComNets, RWTH Aachen University

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