Mode Selection Criteria in MANETs using
Heterogeneous Antenna Technologies
Vivek Jain, Nagesh Nandiraju, Dharma P. Agrawal
University of Cincinnati
Copyright © 2005 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
Outline
 Introduction
 Mobile Ad hoc Networks (MANETS)
 Antennas
 Multiple Access Protocols
 Mode Selection Criteria
 Motivations
 Assumptions
 Node Model
 Antenna Pattern
 Simulation Parameters
 Performance Evaluation
 Applicability of Mode Selection Criteria to Multiple Beam Antennas
 Conclusions
 Future Work
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Mobile Ad Hoc Networks (MANETs)
Peer-to-peer connectivity
Lack of fixed infrastructure
relays
Absence of centralized
authority
Multi-hop forwarding to
ensure network connectivity
Applications
 Military.. Combat Systems,
reconnaissance
 Rescue, medical emergency,
telemedicine
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Antenna Types
Omni-directional antenna
 Transmits power equally in all directions
Directional antenna
 Concentrates power in a directed zone
Smart Antenna
 Has the in-built intelligence to change direction according to
requirement (steer the beam)
Multiple-Beam Smart Antenna
 Simultaneous transmission/reception in more than one directions
Multiple Input Multiple Output (MIMO)
 Multiple streams of data in same channel.
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Smart Antenna System
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Antennas and MANETs
Omni-directional communication suffers from poor
spatial reuse
Directional communication leads to better spatial reuse,
reduces co-channel interference and provides range
extension
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Multiple Access Protocols
 MAC Proposals differ based on
 How RTS/CTS transmitted (omni, directional)
 Transmission range of directional antennas
 Channel access schemes
 Omni or directional NAVs
Range Extension
 Antenna Model
 Two Operation modes
 Omni & Directional
 Omni Mode:
 Omni Gain = Go
 Idle node stays in Omni mode
 Directional Mode:
Spatial Reuse
 Capable of beamforming in specified direction
 Directional Gain = Gd (Gd > Go) --> Range Extension
 Directional Gain = Gd (Gd = Go) --> Spatial Reuse
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Directional vs. Omni-directional
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
 Hidden Terminal
 Deafness
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Motivations
Which mode? Omni-directional or directional
Analyze various topologies involving neighboring
transmissions or receptions
Formulate mode selecting criteria for medium access
control (MAC) for MANETs with heterogeneous
technologies
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Assumptions
Two modes of operation: omni and directional
Directional transmission of RTS/CTS/DATA/ACK in
directional mode
Transmission range of directional antennas is same as
that of omni-directional ==> Spatial Reuse
4-Way CSMA for medium access control
The channel is symmetric
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Node Model
 The node model of
advance MANET
available in OPNET is
modified to facilitate
directional mode of
communication
 In directional mode, the
antenna (tx_rx_ant)
points in the desired
direction with the help of
antenna pointing
processor (tx_rx_point)
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Antenna Pattern
Conical directional antenna pattern of main lobe having beam-width of 45
degrees and a gain of 0 dBi. The gain in remaining spherical side-lobe is
confined to -20dBi
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Simulation Parameters
Parameter
Value
Data rate
Data packet size
Packets Inter-arrival time
Directional gain
2 Mbps
1500 bytes
Constant (0.005 seconds)
0 dBi (main lobe)
-20 dBi (side lobes)
0.5 mW
-95 dBm
32 Kbytes (~21 Packets)
100 seconds
Transmit Power
Packet reception-Power Threshold
Buffer size
Simulation Time
Packets generated = 200 packets/sec/transmitter
Maximum achievable throughput
~ 130 packets/sec/receiver (non-overlapping communication)
~ 65 packets/sec/receiver (two overlapping transmissions)
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Performance Evaluation – Deaf
Deaf communicating pair
scenario
 Receivers in same beam of the
transmitter
 Transmitters in same beam of
the receiver
 Both the transmitters are deaf to
each other communication
Omni-directional mode
performs better
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Performance Evaluation – Deaf
Degradation of throughput (~15%) in directional mode of
communication as compared to omni-directional mode
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Performance Evaluation – Deaf
Retransmission attempts are higher (~12 times) in directional
communication due increased collisions at the receiver. However,
average delay is nearly same in both cases
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Performance Evaluation – Common
Receiver
Common receiver scenario
 Two or more transmitters with
common receiver
 Usually both the transmitters
are deaf to each other
communication
Omni-directional mode
performs better
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Performance Evaluation – Common
Receiver
Degradation of throughput (~15%) in directional mode of
communication as compared to omni-directional mode
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Performance Evaluation – Common
Receiver
Retransmission attempts are higher (~12 times) in directional
communication due increased collisions at the receiver.
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Performance Evaluation –
Linear_Pair_SameBeam
Another communicating pair in
the same beam of the transmitter
Throughput of C-D pair suffers
due to interference from A-B
ongoing communication in
directional mode
For optimal performance C
switches to omni mode while
other remains in directional
mode
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Performance Evaluation –
Linear_Pair_SameBeam
Switching C to omni-directional mode while remaining nodes in
directional mode gives optimal throughput
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Performance Evaluation –
Linear_Pair_SameBeam
Delay is less in directional mode as all newly generated packets are
transmitted while packets in queue are dropped after maximum
retransmission attempts
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Performance Evaluation –
Linear_Pair_SameBeam
Retransmission attempts by node C are much higher in directional
mode owing to higher BER (i.e. collisions) at node D
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Performance Evaluation – Tx_0
Another node transmitting
in same direction
Again switching the mode
of intermediate
transmitting node to omnidirectional mode while
remaining with directional
mode yields optimal
performance
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Performance Evaluation – Tx_0
Average throughput in directional mode is about 15% lower than
in omni-directional mode
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Performance Evaluation – Tx_0
BER is much higher in directional mode due to interference from
transmitters as they are deaf to each other
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Performance Evaluation – Tx_90 and
Rx_90
Another non-interfering transmitter or receiver in the
communicating beams
Omni-mode restricts simultaneous transmissions, hence
directional mode is recommended
Tx_90
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Rx_90
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Performance Evaluation – Tx_90 and
Rx_90
Directional communication achieves maximum possible throughput
in all cases owing to better spatial reuse
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Performance Evaluation – Tx_90 and
Rx_90
Delay is more in omni-directional communication due to increased
media access delay at the transmitters
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Performance Evaluation – Tx_90 and
Rx_90
Due to increased channel contention at the transmitters packet
retransmission attempts are more in omni-directional mode
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Performance Evaluation – Linear,
Parallel and X topologies
 Only the intended receiver or
transmitter in the
communicating beams
 Both the transmitters are deaf
to each other communication
Linear
 No other communicating node
in those beams
 Directional mode outperforms
omni-directional mode of
communication
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X
Parallel
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Performance Evaluation – Linear,
Parallel and X topologies
Traffic Received (packets/sec) vs. time
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Mode Selection Criteria
 All nodes in omni-directional mode in the following cases:
 Deaf communicating pair scenario
 Receivers in same beam of the transmitter
 Transmitters in same beam of the receiver
 Both the transmitters are deaf to each other communication
 Common receiver scenario
 Two or more transmitters with common receiver
 Intermediate transmitting node in omni-directional mode while
other nodes in directional mode for the following cases:
 Another communicating pair in the same beam of the transmitter
 Another node transmitting in same direction
 All nodes in directional mode, in the remaining cases including:
 Another non-interfering transmitter or receiver in the communicating
beams
 Only the intended receiver or transmitter in the communicating beams
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Applicability of Mode Selection
Criteria to Multiple Beam Antennas
Multiple beam antennas
 Can either transmit or receive multiple packets simultaneously.
This requires:
 Packet receptions in different beams at the node to commence at the same
time
 Packet transmissions by a node in multiple beams to begin simultaneously
 A node cannot both send and receive data at the same time
 Can simulate omni-directional mode by transmitting in all
possible beams simultaneously
Can multiple beam antennas achieve optimal performance by
transmitting control packets in beams having transmitters and
receivers only ???
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Conclusions
 Directional mode
 Better spatial reuse
 Enhances system capacity
 Deafness and hidden terminal problems
 However there are some cases where omni-directional mode
performs better
 Deaf communicating pair scenario
 Interference from side-lobes cannot be ruled out
 Common receiver scenario
 Mode Selection Criteria forms the basis of developing MAC
protocols for MANETs using heterogeneous antenna technologies
 Dynamically switching a node from directional to omni-directional or vice
versa depending on the neighboring nodes
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Future Work
Work needs to be extended for multi-hop topologies
Extensive study needs to be done with more
communicating pairs within the vicinity so that
performance varies with the node density
 Game Theoretic approach for mode selection criteria in such
scenarios
Performance of multiple beam antennas transmitting
control packets in beams having transmitters and
receivers only, need to be evaluated
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IEEE 802.11
Physical Carrier
Sensing
Sense
Virtual
Carrier
Sensing
IEEE 802.11 DCF – RTS/CTS access scheme
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Antenna System
Phased Array Antenna
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Direction of Arrival Estimation
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Beam Formation
Beam Forming
Technique in which the gain pattern of an
adaptive array is steered to a desired
direction through either beam steering or
null steering signal processing algorithms
Adaptive beam forming algorithms can
provide substantial gains (of the order of
10log(M) dB, where M is number of array
elements) as compared to omni directional
antenna system
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Antenna Pattern of
7-element uniform
equally spaced
circular array.
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Smart Antenna System
 Switched Beam
 Consists of a set of
predefined beams.
 Allows selection of signal
from desired user.
 Beams have narrow main
lobe and small side-lobes.
 Signals received from side-lobes can be significantly
attenuated.
 Uses a linear RF network, called a Fixed Beam-forming
Network (FBN) that combines M antenna elements to
form up to M directional beams.
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General Smart Antenna
Architecture
Source: Chris Loadman, Zhizhang Chen and Dylan Jorgensen, “An Overview of Adaptive Antenna Technologies For Wireless
Communications,” In Proc. o Communication Networks and Services Research Conference (CNSR), pp 15-19, 2003.
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Features and Benefits of Smart
Antenna Systems
Source: http://hosteddocs.ittoolbox.com/MI102204.pdf
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The global market for smart
antennas growth
Source: US analyst firm Visant Strategies
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A terminal with 16 antennas
mounted on a laptop
Source: Alexiou, A.and Haardt, M., “Smart antenna technologies for future wireless systems: trends and
challenges,” IEEE Communications Magazine, Vol. 42, pp. 90-07, Sept. 2004
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MIMO PC Card
Source: http://www.airgonetworks.com/pdf/Farpoint Group 2003-242.1 MIMO Comes of Age.pdf
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