Copyright © 2005 OPNET Technologies, Inc. Confidential, not for distribution to third parties. Mode Selection Criteria in MANETs using Heterogeneous Antenna

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

Copyright © 2005 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 2

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


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


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.


Smart Antenna System


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


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


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


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


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


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)


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


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)


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



Degradation of throughput (~15%) in directional mode of communication as compared to omni-directional mode



Retransmission attempts are higher (~12 times) in directional communication due increased collisions at the receiver. However,

average delay is nearly same in both cases


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



Degradation of throughput (~15%) in directional mode of communication as compared to omni-directional mode



Retransmission attempts are higher (~12 times) in directional communication due increased collisions at the receiver.


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



Switching C to omni-directional mode while remaining nodes in directional mode gives optimal throughput



Delay is less in directional mode as all newly generated packets are transmitted while packets in queue are dropped after maximum

retransmission attempts



Retransmission attempts by node C are much higher in directional mode owing to higher BER (i.e. collisions) at node D


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



Average throughput in directional mode is about 15% lower than in omni-directional mode



BER is much higher in directional mode due to interference from transmitters as they are deaf to each other


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



Directional communication achieves maximum possible throughput in all cases owing to better spatial reuse



Delay is more in omni-directional communication due to increased media access delay at the transmitters



Due to increased channel contention at the transmitters packet retransmission attempts are more in omni-directional mode


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


Performance Evaluation – Linear, Parallel and X topologies

Traffic Received (packets/sec) vs. time


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


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 ???


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


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



IEEE 802.11

IEEE 802.11 DCF – RTS/CTS access scheme

Physical Carrier Sense

Physical Carrier Sensing

Virtual Carrier Sensing


Antenna System

Phased Array Antenna


Direction of Arrival Estimation


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.


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.


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.


Features and Benefits of Smart Antenna Systems

Source: http://hosteddocs.ittoolbox.com/MI102204.pdf


The global market for smart antennas growth

Source: US analyst firm Visant Strategies


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


MIMO PC Card

Source: http://www.airgonetworks.com/pdf/Farpoint Group 2003-242.1 MIMO Comes of Age.pdf

Documents

Copyright © 2005 OPNET Technologies, Inc. Confidential, not for distribution to third parties. Mode Selection Criteria in MANETs using Heterogeneous Antenna