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Copyright © 2005 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
Mode Selection Criteria in MANETs using Heterogeneous Antenna Technologies
Vivek Jain, Nagesh Nandiraju, Dharma P. Agrawal
University of Cincinnati
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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 connectivityLack 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 antennaTransmits power equally in all directions
Directional antennaConcentrates power in a directed zone
Smart AntennaHas the in-built intelligence to change direction according to
requirement (steer the beam)
Multiple-Beam Smart AntennaSimultaneous 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 ProtocolsMAC Proposals differ based on
How RTS/CTS transmitted (omni, directional)Transmission range of directional antennasChannel access schemesOmni or directional NAVs
Antenna ModelTwo Operation modes
Omni & DirectionalOmni Mode:
Omni Gain = Go Idle node stays in Omni mode
Directional Mode:Capable of beamforming in specified directionDirectional Gain = Gd (Gd > Go) --> Range ExtensionDirectional Gain = Gd (Gd = Go) --> Spatial Reuse
Range Extension
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
ProsHigher gain (Reduced interference)
Spatial Reuse
ConsPotential 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 ValueData rate 2 MbpsData packet size 1500 bytesPackets Inter-arrival time Constant (0.005
seconds)Directional gain 0 dBi (main lobe)
-20 dBi (side lobes)Transmit Power 0.5 mWPacket reception-Power Threshold
-95 dBm
Buffer size 32 Kbytes (~21 Packets)Simulation Time 100 secondsPackets 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 scenarioReceivers 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 scenarioTwo 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 omni-directional 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 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 topologiesOnly the intended receiver or
transmitter in the communicating beams
Both the transmitters are deaf to each other communication
No other communicating node in those beams
Directional mode outperforms omni-directional mode of communication
Linear
ParallelX
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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 transmitterAnother node transmitting in same direction
All nodes in directional mode, in the remaining cases including:Another non-interfering transmitter or receiver in the communicating
beamsOnly 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 densityGame 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
IEEE 802.11 DCF – RTS/CTS access scheme
Physical Carrier Sense
Physical Carrier Sensing
Virtual Carrier Sensing
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Antenna System
Phased Array Antenna
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Direction of Arrival Estimation
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Beam Formation
Beam FormingTechnique 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
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