Hai-Heng Ng, Wee-Seng Soh, Mehul MotaniNational University of Singapore

IEEE GLOBECOM 2008

OutlineIntroductionMACA overviewProposed MACA-U Adaptation For Multi-hop

Underwater NetworkSimulationConclusion

IntroductionTerrestrial wireless communication uses radio waves

LatencyBandwidth

MAC schemes such asFrequency Division Multiple Access (FDMA)Time Division Multiple Access (TDMA)

IntroductionUnderwater communication relies on acoustic waves

Long latencylimited bandwidth

However, terrestrial MAC schemes such asFrequency Division Multiple Access (FDMA)

Narrow bandwidth

Time Division Multiple Access (TDMA) Time synchronization and long guard time

IntroductionExisting underwater contention based MAC solutions

Aloha based.Handshaking based.

IntroductionPure Aloha based.

PacketS→D

DataS → D

DS

DataS → D

S

D

O

PacketS→D

PacketS→D

PacketS→D

ACKD→S

IntroductionPure Aloha based.

PacketS→D

DataS → D

DS

DataS → D

S

D

A

PacketS→D

PacketS→D

PacketS→D

ACKD→S

DataD → A

DataD → A

A

IntroductionWe examine how an existing asynchronous handshaking

based protocol

GoalsImprovement lower throughput

P. Karn, “MACA-A new channel access method for packet radio,” in Proc. ARRL/CRRL Amateur Radio Ninth Computer Networking Conf.,September 1990.

H. Matsuno, H. Ishinaka and A. Hamanaga, “A simple modification for the drastic improvement of MACA in large propagation delay situation,” in Proc. Wireless Communications and Networking Conference, September 2000.

Original MACA overview

RTSS→D

DataS → D

DS

CTSD→S

DataS → D

QUIET

S

D

O

defer its transmissionand

transit to QUIET state

IDLE

IDLE

IDLE

CONTEND

RTSS→D

CTSD→S

MACA-State Transition RulesEvent Type \State

ReceivesRTS

Receives CTS

Overhears xRTS

Overhears xCTS

Timer Expired

IDLETransmit: CTS

WFDATA

Disregard packet

QUIET QUIET -

CONTENDTransmit: CTS

WFDATA

Disregardpacket

QUIET QUIETTransmit: RTS

WFCTS

WFCTSDisregard

packet

Transmit: DATASend Data→IDLE

QUIET QUIET IDLE

WFDATADisregard

packetDisregard

packetQUIET QUIET IDLE

QUIETDisregard

packetDisregard

packetQUIET QUIET IDLE

Improvement original MACAThe state transition rulesThe backoff algorithm

MACA-UFive distinct states, IDLE, CONTEND (CTD), WFCTS,

WFDATA and QUIET.WFCTS ： 2τmax + Tcts

τmax ： maximum propagation delay

Tcts ： CTS duration

WFDATA ： 2τmax + Tdata

Tdata ： Data packet duration

QUIET QUIET_RTS QUIET_CTS

MACA-U-Timing diagram

RTSB→C

DataB → C

CB

CTSC→B

WFDATAData

B → C

QUIET_CTS2τmax + Tdata

B

C

D

A

D

RTSB→CA

RTSB→C

WFCTSCTS

C→B

CTSC→B

QUIET_RTS2τmax + Tcts

MACA-U-State Transition RulesEvent Type \State

ReceivesRTS

Receives CTS

Overhears xRTS

Overhears xCTS

Timer Expired

IDLETransmit: CTS

WFDATA

Disregard packet

Set Timer :QUIET_RTS

QUIET

Set Timer :QUIET_CTS

QUIET-

CONTENDTransmit: CTS

WFDATA

Disregardpacket

Set Timer :QUIET_RTS

QUIET

Set Timer :QUIET_CTS

QUIET

Transmit: RTSSet Timer:

QUIET RTSWFCTS

WFCTSDisregard

packet

Decrement BEBTransmit: DATASend Data→IDLE

Disregardpacket

Set Timer :QUIET_CTS

QUIET

Increment BEBBackoff for Retransmit

IDLE

WFDATADisregard

packetDisregard

packetDisregard

packetDisregard

packetIDLE

QUIETDisregard

packetDisregard

packetQUIET QUIET IDLE

MACA-U-State Transition Rules

WFCTS

RTSB→A

DataB → A

CB

WFDATAData

C → D

B

C

D

A

D

RTSB→AA

RTSB→A

WFCTSCTS

A→B

CTSA→B

WFDATA

RTSC→D

RTSC→D

RTSC→D

CTSD→C

CTSD→C

DataB → A

DataC → D

In WFCTS Overhears xRTS↓

Disregard packet

The system throughput can be improved

MACA-U-State Transition Rules

WFCTS

RTSA→B

WFDATACTS

B→AData

B → A

CB

WFDATAData

C → D

B

C

D

A

D

AWFCTS

RTSC→D

RTSA→B

RTSC→D

CTSD→C

CTSD→C

DataC → D

CTSB→A

DataB → A

In WFCTS Overhears xCTS↓

QUIET

RTSC→D

CTSB→A

PotentialData Collision

MACA-U-Backoff AlgorithmBackoff algorithm is a collision resolution methodology

to

minimize packet collision probability.Each node doubles its backoff counter in the event of

RTS failure

The retransmission or contention slot duration is defined by Trts+τmax., the backoff interval, Tbk

SimulationParameter Value

Grid spacing 700m

Maximum transmission range 1.75 times the grid spacing, or 1225m

Equipped Half duplex omni-directional antenna

Bit rate 2400 bps

Acoustic propagation speed 1500 m/s

Control packets lengths 100 bits

Data packet lengths 1200, 2400, 4800 bits

Backoff parameters Bmin = 1, and Bmax = 64

Other No ACK

Simulation

Simulation

Simulation

Simulation

Simulation

ConclusionTwo areas of improvement are investigated, namely, the

state transition rules, and the backoff algorithm.

The simplicity and throughput stability of MACA-U

More advanced underwater MAC may benchmark its performance against.