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Distributed-Queue Access for Wireless Ad Hoc Networks
Authors: V. Baiamonte, C. Casetti, C.-F. ChiasseriniDipartimento di Elettronica, Politecnico di Torino, Torino, ItalyFrom: Energy-Efficient Wireless Communications and Networks (EWCN 2004)Yuhe-yi Wang Jan 3, 2006
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Outline 802.11 Wireless MAC 802.6 DQDB Proposed Method -DQDC Simulation Result Conclusion
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802.11 Wireless MAC-Overview Defines MAC and PHY layers for a LAN with
wireless connectivity
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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
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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
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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
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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 B hears the RTS, and it is not currently deferring, it immediately replies with a Clear-to-Send(CTS) packet to A
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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 transmissionRTS
CTS
Data
ACK
4-way handshake
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Introduction to Interframe Space Concept
DIFS: Distributed InterFrame Space SIFS: Short InterFrame Space
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Basic Transmission Algorithm
Sense the medium(perform physical channel
assessment)
MediumIdle?
NAV=0?
Transmit Frame
Collision?
RandomBackoff
Time
Yes
No
Yes
No
No
Yes
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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
slot source
slot sink
slot sink
slot sourceBus B
Bus A
1 2 3 4
5
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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
slot source
slot sink
slot sink
slot sourceBus B
Bus A
1 2 3 4
5
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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
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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
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DQDC scheme
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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
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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
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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.
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Data Channel Access Scheme
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Control Channel Access Scheme
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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
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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.
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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
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Simulation Results-Throughput
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Simulation Results-Packet Delay
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Simulation Results-Energy per Successful Packet
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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