Post on 01-Jan-2016
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…