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Distributed-Queue Access for Wireless Ad Hoc Networks

This paper presents a novel MAC protocol designed for wireless ad hoc networks, termed the Distributed Queue Dual Channel (DQDC). By leveraging the existing Distributed Coordination Function (DCF) scheme alongside principles from the Distributed Queue Dual Bus (DQDB) protocol, the proposed method aims to optimize data channel utilization and reduce collision probabilities. The implementation relies on two separate channels for control and data, enhancing communication efficiency among stations in an ad hoc configuration. Simulation results demonstrate the effectiveness of the DQDC protocol in real-world scenarios.

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Distributed-Queue Access for Wireless Ad Hoc Networks

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  1. Distributed-Queue Access for Wireless Ad Hoc Networks Authors: V. Baiamonte, C. Casetti, C.-F. Chiasserini Dipartimento di Elettronica, Politecnico di Torino, Torino, Italy From: Energy-Efficient Wireless Communications and Networks (EWCN 2004) Yuhe-yi Wang Jan 3, 2006

  2. Outline • 802.11 Wireless MAC • 802.6 DQDB • Proposed Method -DQDC • Simulation Result • Conclusion

  3. Defines MAC and PHY layers for a LAN with wireless connectivity 802.11 Wireless MAC-Overview

  4. 802.11 Architecture • Can be with/without infrastructure support • With • A centralized controller for each cell, AP • Without • Each node is a Station. • Each communicates directly with each other. • Mobile ad-hoc configuration mode

  5. 802.11- Two access control services • contention-based • DCF –Distributed Coordination Function • contention-free access control services • PCF -- Point Coordination Function • polling principle • Centralized MAC algorithm

  6. DCF • Basic access method of IEEE 802.11 • Specifies the use of CSMA with CA • CSMA/CA • Carrier Senses: • Every node senses the carries before transmitting • If the node detects carrier then defers transmitting • Multiple Access • Transmissions by one node are generally “received” by all other nodes using the medium

  7. CSMA/Collision Avoidance • Each node must inform other nodes of an intent to transmit • CSMA/CA With RTS/CTS • When station A wishes to transmit to station B, it sends a Request-to-Send (RTS) packet to B; • Destination + Length of Message • If station Bhears the RTS, and it is not currently deferring, it immediately replies with a Clear-to-Send(CTS) packet to A

  8. RTS CTS Data ACK CSMA/CA with RTS/CTS • Any station overhearing an RTS defers all transmissions until some time after the associated CTS packet world have finished • random backoff period • NAV (Network Allocation Vector) • alerts all others to back off for a duration of the transmission 4-way handshake

  9. Introduction to Interframe Space Concept • DIFS: Distributed InterFrame Space • SIFS: Short InterFrame Space

  10. No NAV=0? Yes Sense the medium (perform physical channel assessment) Random Backoff Time No Medium Idle? Yes Transmit Frame Yes Collision? No Basic Transmission Algorithm

  11. slot source Bus A slot sink â â â â â 1 4 3 5 2 á á á á ß slot sink Bus B slot source DQDB (Distributed Queue Dual Bus) • MAC layer specified in IEEE 802.6 standard used in wired MANs. • Can be 30 miles long with 34~155 Mbps • Composed of 2 bus lines with stations attached to both

  12. slot source Bus A slot sink â â â â â 1 4 3 5 2 á á á á ß slot sink Bus B slot source Function of DQDB • Transmitting Data • Node acquires slot • Sets header • Copies data into slot • Cells propagate to end of bus • (absorbed by sink) • Copied by intended destination on way

  13. Proposed Method-DQDC • Distributed Queue Dual Channel • Propose a MAC protocol for wireless ad hoc networks • Key idea • relies on DCF scheme with DQDB protocol • 2 separate channels: a control and a data • Objective: • to achieve 100% utilization of the data channel, • minimizing the collision probability on it. • Simulation result by ns-2

  14. DQDC Overview • Data channel • Data frames, and ACKs • Control channel • STA contend for future access to data channel • Successful STA stored into a virtual distributed queue system • only switch to data channel when at the top of the queue

  15. DQDC scheme

  16. DQDC in Detail • each STA maintains 2 counters • Access Counter (AC) • Countdown Counter (CC) • Access Counter (AC) • a global counter that • ++ every time a successful contention on control channel • -- each transmission on data channel

  17. DQDC in Detail (contd.) • Countdown Counter (CC) • associated with a single data frame waiting to be transmitted • reset to current AC value while winning a control-channel contention. • -- when start of a transmission on data channel • 1: the station is up next for transmits

  18. More Than one Frame to Send • How about STA with several frames to send? • Allowed to occupy more entries at once in the virtual queue. • local vector to store each pending AC. • CC will be reset to 0 or set to the value for the next entry.

  19. Data Channel Access Scheme

  20. Control Channel Access Scheme

  21. Low-traffic Contention • AC counting down to 0 • Original counter mechanism doesn’t work for contention • Solution: • post-backoff phase • backoff counter to down count if NO transmission on DATA • decrease to 0 allows to transmit

  22. Missed Transmission Opportunities • What if STA that won the contention is turned off? • Can be detected when • idle channel more than SIFS+SIFS following the ACK • AC is > 0 • Solution: • Decrement AC, CC as if the transmission had occurred.

  23. Simulation Results-Scenario • Simple Network Scenario: • 4 stations, which communicate in pairs. • Ad Hoc Mode • All within radio proximity • Trans. Rate: • Data: 11 Mbps • Control: 1 Mbps • No multihop trans

  24. Simulation Results-Throughput

  25. Simulation Results-Packet Delay

  26. Simulation Results-Energy per Successful Packet

  27. Conclusions • Proposed DQDC: • bases DCF + DQDB (two buses) key idea • Goal: • achieving 100% utilization of the data channel, minimizing the collision probability on it. • DQDC Performance in throughput, delay, energy better than standard DCF • Issue: • Simulation needs to consider more complex scenarios

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