performance evaluation of multiple access protocols for ad hoc networks using directional antenna

Performance Evaluation of MPerformance Evaluation of Multiple Access Protocols for Aultiple Access Protocols for Ad hoc Networks Using Directid hoc Networks Using Directi

onal Antennaonal AntennaTamer ElBatt, Timothy Anderson, Bo RyTamer ElBatt, Timothy Anderson, Bo Ry

uu

WCNC 2003, March 2003 WCNC 2003, March 2003

speakerspeaker：： Chen-Chi HsiehChen-Chi Hsieh

OutlineOutline

IntroductionIntroduction System ModelSystem Model Channel Reservation Based on Channel Reservation Based on

Directional Antennas InformationDirectional Antennas Information Results and DiscussionResults and Discussion

IntroductionIntroduction

The broadcast nature of omni-The broadcast nature of omni-directional antenna directional antenna causes multi-user interferencecauses multi-user interference thus limit the spatial reusethus limit the spatial reuse

Introduction – Introduction – Related WorkRelated Work

Three schemesThree schemes Omni-directional reservation (802.11)Omni-directional reservation (802.11) Directional reservation (DRTS/DCTS) Directional reservation (DRTS/DCTS) Hybrid reservation (DMAC using Hybrid reservation (DMAC using

DRTS/OCTS)DRTS/OCTS) Decide whether to proceed with a Decide whether to proceed with a

transmission in a specific direction or transmission in a specific direction or notnot

Rely on hearing/not hearing a reservation Rely on hearing/not hearing a reservation messagemessage

Introduction – Introduction – Related Work Related Work (cont.)(cont.)

NeighborNeighbor N(x) N(x) ：： Area covered by the radiation pattArea covered by the radiation patt

erns of all erns of all beams at node xbeams at node x Partition N(x) into Block-Neighbor BN(x) aPartition N(x) into Block-Neighbor BN(x) a

nd Unblock-Neighbor UBN(x)nd Unblock-Neighbor UBN(x) BN(x) BN(x) ：： at least one of its beams is blocked frat least one of its beams is blocked fr

om transmissionom transmission UBN(x) UBN(x) ：： not hear any reservation messagenot hear any reservation message

Cause collision to the ongoing transmissionCause collision to the ongoing transmission


Omni-directional Omni-directional Reservation(802.11)Reservation(802.11)

All neighbors become aware of the ongoing All neighbors become aware of the ongoing transmissiontransmission

N(S)=N(S)= ｛｛ 1,2,3,4,5,6,D1,2,3,4,5,6,D ｝｝ BN(S)=N(S) UNB(S)=ΦBN(S)=N(S) UNB(S)=Φ

N(D)=N(D)= ｛｛ 1,4,5,6,7,8,9,S1,4,5,6,7,8,9,S ｝｝ BN(D)=N(D) UNB(D)=ΦBN(D)=N(D) UNB(D)=Φ

•AdvantageAdvantage ：：•Minimize the possibility of coMinimize the possibility of collisionsllisions

•DrawbackDrawback ：：•Too conservativeToo conservative


Directional ReservationDirectional Reservation D-RTS/D-CTSD-RTS/D-CTS

•AdvantagesAdvantages ：：•Initiates more simultaneousInitiates more simultaneous reservation attemptsreservation attempts•Trade-off between collisions and Trade-off between collisions and spatial reusespatial reuse

•DrawbacksDrawbacks ：：•Unaware of each other Unaware of each other •Highly subject to collisionsHighly subject to collisions

N(S)=N(S)= ｛｛ 1,2,3,4,5,6,D1,2,3,4,5,6,D ｝｝ BN(S)= ｛ 4,5,6,D ｝ UBN(S)= ｛ 1,2,3｝

N(D)=N(D)= ｛｛ 1,4,5,6,7,8,9,S1,4,5,6,7,8,9,S ｝｝ BN(D)= ｛ 4,5,S ｝ UBN(D)= ｛ 1,6,7,8,9 ｝


Hybrid ReservationHybrid Reservation Use different combinations of omni-Use different combinations of omni-

directional and directional reservation directional and directional reservation messages (D-RTS/O-CTS)messages (D-RTS/O-CTS)

N(S)=N(S)= ｛｛ 1,2,3,4,5,6,D1,2,3,4,5,6,D ｝｝ BN(S)= ｛ 4,5,6,D ｝ UBN(S)= ｛ 1,2,3 ｝

N(D)=N(D)= ｛｛ 1,4,5,6,7,8,9,S1,4,5,6,7,8,9,S ｝｝ BN(D)= ｛ 1,4,5,6,7,8,9,S ｝ UBN(D)=ΦΦ

Introduction – Introduction – Related works (cont.)Related works (cont.)

Hybrid ReservationHybrid Reservation ““Medium Access Control Protocols Using Medium Access Control Protocols Using

Directional Antennas in Ad Hoc Networks” IEEE Directional Antennas in Ad Hoc Networks” IEEE INFOCON 2000INFOCON 2000

A B C D E

DRTS(B)

OCTS(B,C)OCTS(B,C)

DATA

ACK

DRTS(D)

OCTS(D,E)

DATA

ACK

OCTS(D,E)

Exploit the spatial reuse but raise collision problem

Introduction – Introduction – Related works (cont.)Related works (cont.)

Hybrid Reservation (cont.)Hybrid Reservation (cont.)

DrawbacksDrawbacks Doesn’t strike a balance

minimizing control packet collisions May lead to further collisionsMay lead to further collisions

Introduction Introduction (cont.)(cont.)

New concepts in this paperNew concepts in this paper All neighbors of the source and the destinAll neighbors of the source and the destin

ation should ation should bebe aware of the intended traaware of the intended transmissionnsmission ，， if possibleif possible

Antenna blocking decisions should be basAntenna blocking decisions should be based on the information included ed on the information included in the RTSin the RTS/CTS packets/CTS packets

Introduction Introduction (cont.)(cont.)

The contributions of this paperThe contributions of this paper Balance the Balance the trade-offtrade-off

between omni-directional and directional between omni-directional and directional reservationsreservations

Resolve new type of Resolve new type of collisionscollisions ConceptConcept

Sending reservation packets carrying Sending reservation packets carrying ““directional antennas informationdirectional antennas information” to as ” to as many neighbors as possiblemany neighbors as possible

Knowing their locations relative to the Knowing their locations relative to the transmitter-receiver pairtransmitter-receiver pair

System Model - System Model - Antenna ModelAntenna Model

Antenna ModelAntenna Model Each nodeEach node

a fixed number (B)a fixed number (B) of switched beams of switched beams Each of width Each of width θθ ＝＝ 2π/B2π/B radians radians

Transmitted energyTransmitted energy uniformly in a beam of width θuniformly in a beam of width θ

Nodes receive Nodes receive omni-directionallyomni-directionally Beams are non-overlappingBeams are non-overlapping

System Model System Model – – Network Network Assumptions (cont.)Assumptions (cont.)

Each node obtains neighboring Each node obtains neighboring information by a information by a node-discovery schemenode-discovery scheme

Information of each nodeInformation of each node The identities of all neighborsThe identities of all neighbors The identities of neighbors that lie within The identities of neighbors that lie within

the coverage of each beamthe coverage of each beam Location of a nodeLocation of a node

RS

A

not allowed to engage in any communicationsnot allowed to engage in any communications

A

transmit on any directional beam transmit on any directional beam except the one pointing towards the transmitterexcept the one pointing towards the transmitter

Channel Reservation Based Channel Reservation Based on Directional Antennas on Directional Antennas

InformationInformation Balance the aforementioned trade-Balance the aforementioned trade-

offoff Send RTS/CTS packets over Send RTS/CTS packets over all all

unblockedunblocked beams beams Add two fields to the RTS/CTS Add two fields to the RTS/CTS

messagesmessages the index of the directional beam the index of the directional beam currently currently

being usedbeing used the index of the directional beam the index of the directional beam intended intended

to be usedto be used


Information Information (cont.)(cont.)

102

3

1

5

46

7

8

9

11

S DO-RTSO-CTS

Node 5 ： not engage in any communications

Node 2 ： (1)block only the beam pointing towards node S (2)can initiate a transmission with node 10


Information Information (cont.)(cont.) New types of collisionsNew types of collisions

A neighbor may miss reservation A neighbor may miss reservation messages due to messages due to lying in the coverage lying in the coverage of a blocked beamof a blocked beam

A

RTSRTS

S DNode A ： it may be active or inactive ， May cause collision later


Information Information (cont.)(cont.) Solution of collisionSolution of collision

Use Use auxiliary channelauxiliary channel to transmit to transmit specialspecial reservation packets on reservation packets on blocked blocked beamsbeams

Suffering collisions from active Suffering collisions from active usersusers

Special reservation packetsRTS

S DA ： inactive


Information Information (cont.)(cont.) Two solutions for solving collision prTwo solutions for solving collision pr

oblemoblem Use Use auxiliary channel(s)auxiliary channel(s) to transmit to transmit specspec

ialial reservation packets on reservation packets on blocked blocked beam beamss

Suffering collisions from active usersSuffering collisions from active users Send “Send “pending” RTS/CTSpending” RTS/CTS packets once packets once

the blocked beam becomes unblockedthe blocked beam becomes unblocked Involves synchronization complexityInvolves synchronization complexity

D1

S2Special RTS/CTS

S1RTS

RTS

DATA

S1 ： unaware the ongoing transmission

DATA

D2

S2 D1

S1RTS

Pending RTS/CTS


Information Information (cont.)(cont.) Solution of collisionSolution of collision

Use Use auxiliary channel(s)auxiliary channel(s) to transmit to transmit specspecialial reservation packets on reservation packets on blocked blocked beams beams

Suffering collisions from active usersSuffering collisions from active users Send “Send “pending” RTS/CTSpending” RTS/CTS packets once packets once

the blocked beam becomes unblockedthe blocked beam becomes unblocked Involves synchronization complexityInvolves synchronization complexity

Transmit different packets on multiple bTransmit different packets on multiple beams at the same timeeams at the same time

Results and DiscussionResults and Discussion NS-2 simulatorNS-2 simulator Under a wide variety of network Under a wide variety of network

loadsloads SchemesSchemes

omni-directional reservationomni-directional reservation directional reservationdirectional reservation hybrid reservationhybrid reservation

Results and Discussion – Results and Discussion – Simulation SetupSimulation Setup

Small networksSmall networks ：： n = 50 nodesn = 50 nodes A rectangular areaA rectangular area ：： 500 meters x 500 500 meters x 500

metersmeters Data packet sizeData packet size ：： 500 bytes500 bytes No mobilityNo mobility B = 6 switched beams per node

Each of 600 width duration ： 900 sec.

Results and Discussion – Results and Discussion – Simulation ResultsSimulation Results

Packet arrival rate/node λ(packets/sec)

Ave

rage

num

ber

of d

ata

pack

ets

tran

smitt

ed/s

ec

Results and Discussion – Results and Discussion – Simulation Results Simulation Results (cont.)(cont.)


Ave

rage

num

ber

of d

ata

pack

ets

colli

sion

s/se

c



MA

C t

hrou

ghpu

t (K

bps)


MA

C t

hrou

ghpu

t (K

bps)

Number of beams/node (B)


DrawbacksDrawbacks Real switched beam antennas experience soReal switched beam antennas experience so

me overlappingme overlapping SolutionsSolutions

minimizes beam overlap minimizes beam overlap Physical layer algorithms “captures” the Physical layer algorithms “captures” the ss

trongest signaltrongest signal from interference in the ove from interference in the overlapped areasrlapped areas

Carrying out reservations in a Carrying out reservations in a round-robinround-robin f fashion over the course of K phasesashion over the course of K phases ，， where where K may take values between 2 and BK may take values between 2 and B

ConclusionsConclusions

Incorporating aggressiveness in the Incorporating aggressiveness in the reservation schemereservation scheme

Modifying the channel occupancy Modifying the channel occupancy criterion to depend on information criterion to depend on information carried by the RTS/CTS messagescarried by the RTS/CTS messages

Candidate solutions for combating Candidate solutions for combating new types of collisions inherent to new types of collisions inherent to directional antennasdirectional antennas

performance evaluation of multiple access protocols for ad hoc networks using directional antenna

Documents

hybrid reservation cont

directional reservationdrtsd

d ubns

collisionsintroduction

s ubnd

paperall neighbors

nd unbd

neighboring information