Using Directional Antennas for Medium Access Control in Ad Hoc Networks MOBICOM 2002 R. Roy Choudhury et al. 2002.10.16 Prepared by Hyeeun Choi
Jan 15, 2016
Using Directional Antennas for Medium Access Control in Ad Hoc Networks
MOBICOM 2002R. Roy Choudhury et al.
2002.10.16Prepared by Hyeeun Choi
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Contents
Introduction Related Works Preliminaries Basic Directional MAC (DMAC) Protocol Multi-Hop RTS MAC (MMAC) Performance Evaluation Future Work Conclusion
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Introduction
The Problem of utilizing directional Antennas to improve the performance of ad hoc networks is non-trivial
Pros Higher gain (Reduced interference) Spatial Reuse
Cons Potential possibility to interfere with
communications taking place far away
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Omni-directional Antennas
S
D
A
B
Silenced Node
C
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Directional Antennas
S
D
A
B
C
Not possible
using Omni
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Related Works
MAC Proposals differ based on How RTS/CTS transmitted (omni, directional) Transmission range of directional antennas Channel access schemes Omni or directional NAVs
Gain of directional antennas is equal to the gain of omni-directional antennas
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Preliminaries (1/2)
Antenna Model Two Operation modes
: Omni & Directional
Omni Mode: Omni Gain = Go Idle node stays in Omni mode.
Directional Mode: Capable of beamforming in specified direction Directional Gain = Gd (Gd > Go)
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Preliminaries (2/2)
IEEE 802.11
IEEE 802.11 DCF – RTS/CTS access scheme
Physical Carrier Sense
Physical Carrier Sensing
Virtual Carrier Sensing
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Problem Formulation
Using directional antennas Spatial reuse
Possible to carry out multiple simultaneous transmissions in the same neighborhood
Higher gain Greater transmission range than omni-
directional Two distant nodes can communicate with a
single hop Routes with fewer hops
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Basic DMAC Protocol (1/2)
Channel Reservation A node listens omni-directionally when idle Sender transmits Directional-RTS (DRTS) using
specified transceiver profile Physical carrier sense Virtual carrier sense with Directional NAV
RTS received in Omni mode (only DO links used) Receiver sends Directional-CTS (DCTS)
DATA,ACK transmitted and received directionally
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Basic DMAC Protocol (2/2)
Directional NAV (DNAV) Table Tables that keeps track of the directions
towards which node must not initiate a transmission
E
H
B
2*ß ε θ
ε = 2ß + Θ
If Θ> 0 ,New transmission can be initiated
DNAV
CCTS
RTS
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Problems with Basic DMAC (1/4)
Hidden Terminal Problems due to asymmetry in gain A does not get RTS/CTS from C/B
C
A B
DataRTS
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Problems with Basic DMAC (2/4)
Hidden Terminal Problems due to unheard RTS/CTS
CB
D
A
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Problems with Basic DMAC (3/4)
Shape of Silence Regions
Region of interference for directional transmissionRegion of interference for
omnidirectional transmission
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Problems with Basic DMAC (4/4)
Deafness
RTS
RTS A B
X
Z
DATA
X does not know node A is busy. X keeps transmitting RTSs to
node A
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MMAC Protocol (1/3)
Attempts to exploit the extended transmission range Make Use of DD Links
Direction-Direction (DD) Neighbor
C
A
A and C can communication each other directly
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MMAC Protocol (2/3)
Protocol Description : Multi-Hop RTS Based on Basic DMAC protocol
D
R
G
S
T
B
A
C
F
DO neighbors
DD neighborsRTS
DATA
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MMAC Protocol (3/3)
Channel Reservation Send Forwarding RTS with Profile of node F
R
G
S
T
BC
Fowarding RTS
DATA
A FD
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Performance Evaluation (1/6)
Simulation Environment Qualnet simulator 2.6.1 Beamwidth :45 degrees Main-lobe Gain : 10 dBi 802.11 transmission range : 250meters DD transmission range : 900m approx Two way propagation model Mobility : none
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Performance Evaluation (2/6)
A
B C
D E F
A B CD E F
High Spatial Reuse
Aggregate Throughput (Kbps)
IEEE 802.11 : 1189.73Basic DMAC : 2704.18
High Directional Interference
Hidden terminal Problem
Aggregate Throughput (Kbps)
IEEE 802.11 : 1194.81Basic DMAC : 1419.51
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Performance Evaluation (3/6)
150m
Aligned Routes
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Performance Evaluation (4/6)
Less aligned Routes
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Performance Evaluation (5/6)
Randomly Chosen Routes
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Performance Evaluation (6/6)
Random Topology
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Future Work
Design of directional MAC protocols that incorporate transmit power control
New protocols that rely less on the upper layers for beamforming information
Impact of directional antennas on the performance of routing protocols
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Conclusion
Directional MAC protocols show improvement in aggregate throughput and delay But not always
Performance dependent on topology Random topology aids directional
communication
MMAC outperforms DMAC & 802.11 802.11 better in some scenarios
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Related Works
Nasipuri et al Assume that the gain is equal to the gain of
omni-directional antennas Ko et al
A node may transmit in directions that do not interfere with ongoing transmission
Bandyopahyay et al Present another MAC which uses additional
messages to inform neighborhood nodes about ongoing communications
Takai et al Directional virtual Carrier Sensing (DVCS)
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Extra Slides
Gain of Antenna Used to quantify the directionality of an
antenna Relative power in one direction compared to
an omni-directional antenna