A MAC Protocol Using Directional Antennas in Ad Hoc Networks Issues and Solutions

1
A MAC Protocol Using Directional Antennas in Ad
Hoc Networks- Issues and Solutions -

• Masanori Takata Masaki Bandai Takashi
  Watanabe
• Graduate School of Science and Engineering,
  Shizuoka University, Japan
• Faculty of Informatics, Shizuoka University,
  Japan

2
Background and Motivation (1/2)

• Omni-directional Antennas
• Waste the network capacity
• Directional Antennas
• Increase spatial reuse of the wireless channel
• more simultaneous communications
• Extend the transmission range
• less routing hops

1.
2.
3
Background and Motivation (2/2)

• Directional MAC Protocols
• Issues of Directional MAC Protocols
• Location information staleness
• Deafness
• Directional hidden-terminal problem
• Directional exposed-terminal problem

In this paper
? Investigation of the issues of directional MAC
protocols ? Solutions of issues of directional
MAC protocols
4
Directional MAC Protocols

• DMAC(Directional MAC)Choudhury et al. MobiCom
  02
• All frames are exchanged directionally
• Directional Physical Carrier Sensing
• DNAV(Directional NAV)
• MMAC(Multihop RTS MAC)Choudhury et al. MobiCom
  02
• DVCS(Directional Virtual Carrier Sensing)Takai
  et al. MobiHoc 02
• Adaptive MAC Bandyopadhyay et al. Globecom 02
• Circular RTS MAC Korakis et al. MobiHoc 03
• Tone DMAC Choudhury et al. INCP 03
• SWAMP(Smart antennas based Wider-range Access MAC
  Protocol)
• Takata et al. ICC 04
• Dual access mode

1.RTS3.DATA
T
R
2.CTS4.ACK
5
SWAMP
Smart antennas based Wider-range Access MAC
Protocol
OC-mode (Omni-directional transmission range
Communication mode)
EC-mode (Extended transmission range
Communication mode)
OB
OB
B
C
A
D
B
C
A
D
DL
DL
DM
DH
RTS(OB)
RTS(OB)
RTS (DH)
CTS(OB)
CTS(OB)
CTS (DM)
Omni-NAV
DATA (DM)
SOF(OB)
SOF(OB)
Omni-NAV
ACK (DM)
d
DATA(DL)
Acquisition of NHDI (B)
Acquisition of NHDI (C)
ACK(DL)
NHDINext Hop Direction InformationSOF Start
of Frame
d
6
Issues of Directional MAC Protocols

• Location Information Staleness
• Deafness
• Directional Hidden-Terminal Problem
• Directional Exposed-Terminal Problem

7
Communication Failure Factors
()
D) Directional exposed-terminal problem
C) Directional hidden-terminal problem
B) Deafness
A) Location information staleness
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A) Location Information Staleness

• A gap between the cached location information and
  the actual location
• Due to the lapse of time and mobility of nodes
• Direction of transmission becomes inaccurate

Link break
Related Works
T1

• DVCS(Directional Virtual Carrier Sensing)M.
  Takai, J. Martin, A. Ren and R. Bagrodia, MobiHoc
  02
• Circular RTS MACT. Korakis, G. Jakllari and L.
  Tassiulas, MobiHoc 03
• DDSR(Directional DSR)R. R. Choudhury, N. H.
  Vaidya, PWC 03

R
T
R
T0
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A) Solutions of Location Information Staleness

• Optimization of the beamwidth and lifetime of the
  table information (TTL Time to Live)
• In low traffic load
• Frequency of update of the table information is
  low
• Gap between the table information and actual
  location becomes large
• Location information staleness is significant

Wide beamwidth can cover the addressed node and
fill the gap
Small TTL deletes the obsolete information and
table is kept fresh
Mitigation of Location Information Staleness
10
A) Solutions of Location Information Staleness

• Optimization of the beamwidth and lifetime of the
  table information (TTL Time to Live)
• In low traffic load
• Frequency of update of the table information is
  low
• Gap between the table information and actual
  location becomes large
• Location information staleness is significant

T1
R
T
R
T0
Wide beamwidth can cover the addressed node and
fill the gap
Small TTL deletes the obsolete information and
table is kept fresh
Mitigation of Location Information Staleness
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A) Solutions of Location Information Staleness

• Optimization of the beamwidth and lifetime of the
  table information (TTL Time to Live)
• In low traffic load
• Frequency of update of the table information is
  low
• Gap between the table information and actual
  location becomes large
• Location information staleness is significant

Wide beamwidth can cover the addressed node and
fill the gap
Small TTL deletes the obsolete information and
table is kept fresh
Mitigation of Location Information Staleness
12
A) Solutions of Location Information Staleness

• In high traffic load
• Frequency of update of the table information is
  high
• Gap between the table information and actual
  location is small
• Location information staleness is not significant
• Optimization of beamwidth and TTL based on the
  (local) traffic load
• Mitigation of location information staleness and
  improvement of spatial reuse

Narrow beamwidth can reduce the interference and
contention
Large TTL prevents deletion of sufficiently
accurate information
13
B) Deafness

• Node S is unaware of X-D communication
• S does not overhear the signals between X-D
• S attempts to communicate with X
• But it fails because X has its beam pointed
  towards D
• S backs off longer and repeatedly attempts to
  communicate

Wastage of the wireless channel Excessive packet
drops Large delay variances Channel access
unfairness
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C) Directional Hidden-Terminal Problem

• Hidden-terminal due to asymmetry in gain R. R.
  Choudhury, X. Yang, R. Ramanathan, N. H. Vaidya,
  MobiCom 02
• Directional gain (Gd) gt Omni-directional gain
  (Go)
• Pr ? Pt Gt Gr

Related Work
Pt Transmit power Gt Tx gain Pr Received
power Gr Rx gain
M. Sekido, M. Takata, M. Bandai and T. Watanabe,
Directional NAV Indicators and Orthogonal
Routing for Smart Antenna Based Ad Hoc Networks,
WWAN 2005
Go
Gd
A
C
A
B
Directional hidden-terminal
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C) Solutions of Directional Hidden-Terminal
Problem

• High gain CTS(HCTS)
• Backward RTS(BRTS)
• Relayed CTS(RCTS)

DNAV
C
A
B
1.RTS
2.High gain CTS
High gain CTS
DNAV
C
DNAV
A
B
C
A
B
1.Backward RTS
2.RTS
3.Relayed CTS
1.RTS
2.CTS
Backward RTS
Relayed CTS
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C) Solutions of Directional Hidden-Terminal
Problem

• Straight model

directional hidden terminal problem
Original SWAMPltECgt shows low performance as
sending rate becomes higher ? Due to the
directional hidden terminal problem HCTS, BRTS,
RCTS show higher performance than Original
SWAMPltECgt ? solve directional hidden terminal
problem
17
D) Directional Exposed-Terminal Problem

• Each node waits for signals with the
  omni-directional mode in an idle state
• During A-C communication, node B gets engaged in
  receiving signals between A-C
• If node D sends RTS to B,

D
Collision at B
B
A
C
Collision
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Evaluation Model

• Simulation Environment
• Number of nodes 100
• Area size 1500m ?1500m
• Random way point model
• Max speed 40km/h, Pause time 0s
• Omni-directional transmission range 250m
• Directional transmission range 500m
• Beamwidth 45?
• Packet arrival Poisson
• Payload size 512 Bytes
• Location information 4 Bytes
• Retry limit (OC/EC) 7/4
• Data rate 2Mbps
• Protocols
• SWAMP (OCEC) with DNAV
• SWAMP (OC)
• IEEE 802.11

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Throughput
20
RTS Failure Ratio
RTS Failure Ratio ( of not received CTS / of
transmitted RTS) 100
21
Communication Failure Factors
Directional hidden-terminal problem
Deafness
Directional exposed-terminal problem
Location information staleness
22
Effects of Beamwidth
(narrow)
(wide)
23
Effects of TTL


0
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Contents

• Background and Motivation
• Directional MAC Protocols
• Issues of Directional MAC Protocols
• Solution of Location Information Staleness
• Performance Evaluation
• Summary

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Summary

• Issues of Directional MAC Protocols
• Location information staleness
• Deafness
• Directional hidden-terminal problem
• Directional exposed-terminal problem
• A) Solution of Location Information Staleness
• Optimization of beamwidth and TTL
• C) Solution of Directional Hidden-Terminal
  Problem
• High gain CTS, Backward RTS and Relayed CTS
• Performance Evaluation
• Location information staleness is significant
  issue in low traffic load
• Optimization of beamwidth and TTL mitigate
  location information staleness and improve the
  overall performance

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Future Works

• A) Effects of the beamwidth and TTL
• Mobility, density, etc.
• B) Solution of deafness problem
• D) Effects of the solution of directional
  exposed-terminal problem(interference suppression
  mechanism)
• Routing protocol using directional antennas

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Thank you very much for your attention
!Masanori Takata Ph.D. StudentGraduate
School of Science and Engineering, Shizuoka
University, Japan takata_at_aurum.cs.inf.shizuoka.ac
.jp