A QoS MAC Protocol for A QoS MAC Protocol for Differentiated Service in Mobile Differentiated Service in Mobile

Ad Hoc NetworksAd Hoc Networks

Chi-Hsiang Yeh, Tiantong You

Queen’s University

ICPP 2003’

Outline Introduction PICK PIC Negative/Implicit ACK Performance Conclusion

Introduction 802.11 and 802.11e are design for

WLANs, rather then ad hoc networks. 802.11e are base on

Persistent factors(PFs) for backoff Arbitrary interframe space(AIFS) for the idle

detection time These mechanisms will work well in

single-hop WLANs

Introduction 802.11e can’t provide small and bounded delay to

high-priority packet in a multihop environment Block by nearby transmissions/receptions of low

priority packets RTS/CTS messages collision (30%) Data packets collision (10%)

The delay can’t be bounded due to Repeated RTS/CTS dialogues Data packet retransmissions

Introduction Periodical reservation-based MAC

protocols are not collision-free due to the mobility of ad hoc networks

PICK Priority ID Countdown with negative/implicit

ACK Goals

Priority Short/long-term fairness Low collision rate Smaller control channel overhead Distributed MAC protocol

Priority ID Countdown(PIC) Wireless stations(WS) select an competition

number to join a new round of binary countdown competition

Wireless station with the biggest competition number is winner that can transmit its RTS, CTS or other control messages

Priority ID Countdown(PIC) An example of competition number (CN)

1 0 0 1 1 0 0 1Device a

Binary countdown slot

The Competition The binary countdown competition

The frame formation for the control channel of PICK

1.Synchronization2.Start competition with the same bit-slot

The Competition If bit-slot i is 1 then transmits a “pulse signal” to

all the WSs with in a distance of 2R

1 0 0 1 1 0 0 1Device a

a R

2R

R: Transmission range

Pulse Signal

The Competition If bit-slot i is 0 then keeps silent and senses

whether there is any pulse signal

1 0 0 1 1 0 0 1Device a

a R

2R

R: Transmission range

Sensing…

The Competition If WS’s bit-slot i is 0 and senses pulse signal,

then this WS is kicked out the competition Such surviving WS per bit slot whose

CN=1 CN=0 but don’t sense any Pulse Signal

Final Survivor is the winner that can transmit its RTS, CTS or other control messages

The Competition Example

Competition Number Generation CN with unique ID

CN compose of priority number,random number and unique ID

Must be only one winner 100% Collision-Free Control channel overhead

1 0 0 1 1 0 0 1Device a

Priority Number Random Number Unique ID

Competition Number Generation CN without unique ID

CN compose of priority number and random number

Lower control overhead Low control message rate collision 0% data packet collision

1 0 0 1 1 0 0 1Device a

Priority Number Random Number

Competition Number Generation

11 The Highest Priority

10 High Priority

01 Medium Priority

00 Low Priority

Priority Level

Negative/Implicit ACK NI-ACK

If receiver fails to receive the scheduled data packet, it will reply a negative ACK, otherwise it remain silent(implicit ACK).

When transmitter receives a NAK, it will send an RTS to schedule for a retransmission.

TransmitterReceiver

RT SucceededSilent

RT failedNAKRTS

Negative/Implicit ACK Reason

Smaller overhead in control channel Less ACK will compete for the control

channel of PICK under heavy traffic load No expose terminal problem

A BC D

Performance 80 WSs in 400X400-unit grid area Transmission Radius R=100 grid unit Mobility Model

1 unit/s moving speed 4 seconds pause time Exponential distribution

PICK with packet arrival rate is 80 MT/s

Dual-channel 802.11e with packet arrival rate is 80 MT/s

Conclusion Collision-free in date channel and low

collision rate in control channel does not rely on busy tone and additional transceiver

Support prioritization and DiffServ in multihop ad hoc network

Short/long-term fairness

Thank you…