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

Outline

802.11 Wireless MAC 802.6 DQDB Proposed Method -DQDC Simulation Result Conclusion

802.11 Wireless MAC-Overview

Defines MAC and PHY layers for a LAN with wireless connectivity

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

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

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

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

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

RTS

CTS

Data

ACK

4-way handshake

Introduction to Interframe Space Concept

DIFS: Distributed InterFrame Space SIFS: Short InterFrame Space

Basic Transmission Algorithm

Sense the medium(perform physical channel

assessment)

MediumIdle?

NAV=0?

Transmit Frame

Collision?

RandomBackoff

Time

Yes

No

Yes

No

No

Yes

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

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

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

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

DQDC scheme

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

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

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.

Data Channel Access Scheme

Control Channel Access Scheme

Low-traffic Contention

AC counting down to 0 Original counter mechanism doesn’t work for con

tention Solution:

post-backoff phase backoff counter to down count if NO transmission on DAT

A decrease to 0 allows to transmit

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.

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

Simulation Results-Throughput

Simulation Results-Packet Delay

Simulation Results-Energy per Successful Packet

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