The Improvements in Ad Hoc Routing and Network Performances with Directional Antennas

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S-38.3310 Thesis Seminar on Networking Technology
The Improvements in Ad Hoc Routing and Network
Performances with Directional Antennas
Hao Zhou
Supervisor Prof Sven-Gustav Häggman
Helsinki University of Technology Communications
Laboratory 8.8.2006
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Agenda

• Introduction
• Research problem
• Objective and methodology
• Thesis roadmap
• Basic of smart antennas
• MAC protocol issue
• IEEE 802.11 MAC protocol
• Directional MAC problems
• Directional MAC proposals
• Routing protocol issue
• Ad hoc routing protocols
• Directional routing problems
• Directional routing proposals
• Case study
• Conclusion and future work

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Introduction

• Ad Hoc Network can be deployed immediately on
  demand by surrounding
• nodes without any fixed infrastructure
  supporting
• Each node in the ad hoc network is not only a
  host taking charge of
• sending and receiving packets but also a
  router with responsibility for
• relaying packets for other nodes
• Demand scenarios for ad hoc networks
• Military environment
• Emergency situation
• Wireless sensor networks
• Low cost commercial communication networks

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Research Problem

• A tremendous amount of MAC and routing
  protocols have been developed
• for a hoc network where devices equipped
  with omni-directional antennas
• With fast development of smart antenna
  technology, directional antennas
• have been proposed to improve ad hoc routing
  and network performance
• Several challenges and design issues arise when
  applying directional
• antennas to ad hoc networks

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Objective and Methodology

• Objectives
• Introduce the smart antenna technology
• Discuss the MAC and routing problems of
  utilizing directional antennas
• in ad hoc networks
• Survey directional MAC and routing proposals
• Evaluate routing and network performance
  between omni-directional
• antennas and directional antennas in case
  studies
• Methodology
• Literature study based on research papers,
  lecture slides, standardized
• technical specifications
• Computer simulations with QualNet simulator
• Discussion with researchers working on ad hoc
  network studies

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Thesis Roadmap
Chapter 3 MAC protocols
Chapter 4 Directional MAC proposals

Chapter 2 Smart antennas
Chapter 7 Case studies
Chapter 6 Directional routing proposals
Chapter 5 Routing protocols
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Basics of Smart Antennas

• The smart antenna consists of multiple elements
  in a special configuration and
• connected through complex weights. Smart
  antennas enable transmit and receive
• with more energy in certain direction

• Switched beam antennas explore multiple fixed
  beams
• in predetermined directions at the antenna
  site

• Adaptive array antennas could steer the main
  lobe towards
• receiver in any direction dynamically

• Some advantages of directional antennas
  compared with omni-directional antennas
• They could reach large range with the same
  power due to higher gains
• They could increase the channel capacity by
  rejecting interference better
• They could alleviate multi-path effect by
  proving spatial diversity
• They utilize power more efficiently.

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Agenda

• Introduction
• Research problem
• Objective and methodology
• Thesis roadmap
• Basic of smart antennas
• MAC protocol issue
• IEEE 802.11 MAC protocol
• Directional MAC problems
• Directional MAC proposals
• Routing protocol issue
• Ad hoc routing protocols
• Directional routing problems
• Directional routing proposals
• Case study
• Conclusion and future work

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IEEE 802.11 MAC Protocol

• IEEE 802.11 Distributed Coordinate Function
  (DCF) is developed to
• provide communications between multiple
  independent mobile node pairs
• without using access point or base station
• It utilizes Virtual Carrier Sensing (VCS) to
  alleviating collision happens in
• channel

ACK Acknowledgement CTS Clear to Send
DIFS Distributed Inter-Frame Space NAV
Network Allocation Vector RTS Request to
Send SIFS Short Inter-Frame Space
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Directional MAC Problems

• Neighbor location information and main lobe
  direction
• The source node need to know the direction
  of destination node and neighbor
• nodes in order to adjust the main lobe of
  antenna gain pattern for transmitting
• Extended transmission range
• The directional data forwarding could reach
  beyond the reserved area with
• conversional MAC protocol due to its higher
  gain
• New hidden terminal problem gt Collisions
• Due to unheard RTS/CTS
• The active node could not hear RTS/CTS send by
  other nodes due to directional
• antennas has a larger gain in the desired
  destination than other directions
• Due to asymmetric gain
• Node could not sense channel correctly with
  omni-directional antennas and
• might interfere other on-going communications
  by directional forwarding packets
• Deafness problem
• The source node fails to communicate with
  destination which is beam-forming to
• another direction for on-going communication

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Directional MAC Proposals-DMAC1/2
Directional MAC Scheme 1/2 Each node knows about
location of neighbor nodes and itself based on
GPS devices.

• DMAC 1 allows source node sends RTS
  directionally and receiver sends CTS
• omni-directionally after receiving this RTS
• (Node E is a potential interferer to
  on-going communication between Node A and B)
• DMAC 2 setting a condition before source node
  sending RTS
• If none of the directional antennas of source
  node are blocked by other on-going
• communications, source node send RTS
  omni-directionally
• Otherwise, it send a directional RTS to the
  other directions which are not blocked

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Directional MAC Proposals-MMAC
Multi-hop RTS MAC scheme Each node is equipped
with an omni-directional antenna together with a
directional antenna

• Neighbor nodes can be divided into two groups
• Directional-Omni (DO) neighbor
• It could receive a directional transmission
  packet
• even it is in idle mode with omni-directional
  antenna
• eg A and B
• Directional-Directional (DD) neighbor
• It is able to receive a directional
  transmission only
• when its directional antenna beam-forms the
  source
• node for reception
• eg A and F

The basic idea is that DO neighbors help to
establish an DD link by informing the location
of source and destination node with Forward RTS
packet Node A sends a Forward RTS to the DO
neighbors one by one until to Node F, then F will
send directional CTS to A to help establish the
directional communication link between DD
neighbors A and F
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Directional MAC Proposals-DVCS
Directional Virtual Carrier Sensing Scheme DVCS
selectively disables particular directions
including in which the node would interfere with
on-going communications and allows the node to
transmit to other directions, which increases the
capacity greatly

• New features
• AOA caching
• Every node estimates and caches the angle of
  
• arrival of any signal received from its
  neighbors.
• Beam locking and unlocking
• The node could lock its antenna pattern in
  the
• directions of source and destination and
  unlock
• after a successful packet transmission.
• DNAV setting
• DNAV defines which angle range of the
  directional
• antenna of that node should be disabled.

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Directional MAC Proposals-C-DRTS
Circular DRTS scheme Without using any
predetermined neighbor location information,
source node uses all directional antennas
circularly scanning the whole neighbor area to
inform the neighbor for intended communication
Each node has a location table which maintains
the identity of detected neighbor, the beam
index on which it can be reached, the
corresponding beam index used by the neighbor. It
is used for block beam directions that could
produce inferences to active communication
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Directional MAC Proposals-E-R/CTS
Extended RTS/CTS scheme Each node knows about the
neighbor node location information

• Three new features
• Two lobe antenna pattern for DATA transmission
• Source node sends a tone signal in the
  opposite direction of the active communication
  link
• Higher gain for RTS/CTS transmission
• To overcome new hidden terminal problem due
  to asymmetric gain, the transmission range
• of RTS/CTS is increased to cover the extra
  area caused by the DD link
• Transmission NAV and Receiving NAV setting
• Different setting for transmission and
  receiving NAV to increase channel capacity, like
  Node
• E and F could transmit in the directional of
  source node

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Agenda

• Introduction
• Research problem
• Objective and methodology
• Thesis roadmap
• Basic of smart antennas
• MAC protocol issue
• IEEE 802.11 MAC protocol
• Directional MAC problems
• Directional MAC proposals
• Routing protocol issue
• Ad hoc routing protocols
• Directional routing problems
• Directional routing proposals
• Case study
• Conclusion and future work

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Ad Hoc Routing Protocols

• Proactive routing protocol
• Maintain and update network topology knowledge
  for each node
• Utilize routing algorithm to exchange
  periodical link information
• High routing traffic and power consumption
• OLSR
• Reactive routing protocol
• Route discovery and route maintenance are
  on-demand
• Large delay but less routing traffic and less
  power consumption
• AODV
• Hybrid routing protocol
• Combine advantage of both proactive and
  reactive routing protocols
• High power consumption
• ZRP

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Directional Routing Problems

• Directional route discovery problem
• Current route discovery algorithms are
  carried out using an omni-
• directional broadcast scheme, so DO and DD
  neighbor nodes which
• could be reached by directional antennas are
  ignored
• Routing overhead problem
• One reason is that route discovery scheme
  broadcast route finding
• packet omni-directionally
• Another reason is that some directional routing
  scheme produces
• route redundant packets in route discovery
  procedure, like sweeping
• scheme which sweeps the beam sequentially
  across all directions to
• find the route

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Directional Routing Proposals for directional
route discovery

• Sweeping scheme
• Through sequentially sweeping the antenna
  beam in omni-directional, DO
• neighbors are easily detected, which leads
  to large routing traffic
• Heartbeat scheme
• It could find the DO and DD neighbors by
  periodical broadcasting and
• scoring of the heartbeat packets

• Informed discovery
• After exchanging neighbor node information,
  each node
• tries to directional transmit heartbeat
  packet to the two-
• hop neighbors to establish DO link
• Blind discovery
• With a synchronized time based on GPS
  devices, all nodes
• performs discovery by a common direction
  which is
• chosen by system. Each node alternates
  randomly between
• sending heartbeat packets in that direction
  and listening in
• the opposite direction to try to establish DD
  link

Blind discovery
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Directional Routing Proposals for mitigating
routing overhead

• Selective forwarding scheme
• It prevent the same broadcast packet from
  transmitting
• back to the node from which the packet is
  received
• The intermediate node receiving the control
  packet will
• forward it using half of its antenna beams
  in the opposite
• direction of incoming angle of arrival

• Relay-node-based scheme
• It innovates a manner to decide the relay
  node which could forward the control packet
• efficiently and there is only one relay
  node in each of antenna element direction.
• The node which is the farthest from the
  control packet sender is selected as relay node
  

• Location-based scheme
• Each node obtain its location from a GPS
  device and attaches it in
• the header of control packets. The
  receiving nodes will calculate the
• additional coverage ratio and determine the
  forwarding delay, which
• is inversely proportional to the additional
  coverage, for each
• direction. The node must wait for the
  forwarding delay before
• forwarding this packet. If same packet
  arrives within this forwarding
• delay, the node will not forward in that
  direction.

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Agenda

• Introduction
• Research problem
• Objective and methodology
• Thesis roadmap
• Basic of smart antennas
• MAC protocol issue
• IEEE 802.11 MAC protocol
• Directional MAC problems
• Directional MAC proposals
• Routing protocol issue
• Ad hoc routing protocols
• Directional routing problems
• Directional routing proposals
• Case study
• Conclusion and future work

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Simulation environment parameters

• Routing and network performance comparison of
  directional antennas
• with omni-directional antennas
• Simulation environment
• QualNet simulator
• Simulation results
• Throughput
• End to end Delay
• Packet delivery ratio
• Path length

The general simulation environment parameters
Parameter Value
Propagation channel frequency 5 GHz
Path loss model Two Ray
Directional antenna model Switched beam
Directional antenna gain 15 dBi / 0 dBi
MAC protocol IEEE 802.11 with DVCS
Directional NAV delta Angel 37 degree
AOA cache expiration time 2 s
Element antenna pattern used in QualNet
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Simulation Environment I-static communication
distance case
Parameter Value
Number of nodes 49
Node placement Grid
Grid size 200 m
Terrain size 2000x2000 m
Simulation time 600 s
Bandwidth 24 Mbps
Transmission power 18 dBm
Receiver sensitivity -83 dBm
Mobility model None
Traffic type Constant Bit Rate
Packet rate 8 packets/s
Packet size 512 byte
Number of flows 1

• The sender and receiver node place
• between 7 different distance from 200 m
• to 1400 m to see the network and routing
• performance in static scenario in different
• communication distance

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Simulation Analysis I-static communication
distance case

• The throughtput of AODV and OLSR have no
• big diffence in short communication distance
• the performance of AODV with omni-diectional
• antenna decrease significently when the
  distance
• is more than 1000 m directional antennas are
  not
• affected by increasing the communication
  distance
• The end to end delay of AOVD with omni-
• directional antennas increase more than OLSR
• with the same antenna model directiona
  antennas
• have much better performance than
  omni-direcitonal
• antennas the increase of end to end delay
  much
• depends on the increase of path leangth

path length
Distance (m) 200 400 600 800 1000 1200 1400
AODV (Omni) 1 2 3 3 4 5 6
AODV (Dir) 1 1 2 2 2 3 3
OLSR (Omni) 1 2 3 3 4 5 6
OLSR (Dir) 1 2 2 2 2 3 3
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Simulation Environment II-mobility speed case

• The Random Waypoint mobility model defines
• three parameters pause time minimum speed
• and maximum speed.
• Each node randomly selects a destination
  location
• within the physical terrain, and then it moves
  in
• that direction in a speed uniformly chosen
  between
• minimum and maximum speed. After it reaches
  the
• destination, the node stays there for a pause
  time
• period.

Parameter Value
Number of nodes 50
Node placement Random
Terrain size 1000x1000 m
Simulation time 900 s
Initial time 200 s
Bandwidth 24 Mbps
Transmission power 18 dBm
Receiver sensitivity -83 dBm
Mobility model Random Waypoint
Pause time 1 s
Traffic type Constant Bit Rate
Packet rate 4 packets/s
Packet size 512 bytes
Mobility level 1 2 3 4 5
Minimum speed (m/s) 0 5 10 15 20
Maximum speed (m/s) 5 10 15 20 25
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Simulation Analysis II-mobility speed case
10 CBR
30 CBR

• The throughputs of both antenna models decrease
  with
• the increase of mobility level, but the
  throughput of
• directional antennas decreases slower than
  omni-
• directional antennas
• With the increase of traffic load, the
  throughput of
• directional antennas doesnot have big changes,
  while
• the one of omni-directional antennas decreases
  
• accordingly

20 CBR
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Simulation Analysis II-mobility speed case
10 CBR
30 CBR

• When the mobility level increases, the end to
  end delay
• rises for both antenna models. In the heavy
  traffic load
• scenario, the end to end delay increases
  slower than in
• the other two light traffic load scenarios
• The more traffic flows in the network, the
  larger is the
• end to end delay
• The end to end delay of omni-directional
  antennas is
• about four times of the one of directional
  antennas

20 CBR
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Simulation Analysis II-mobility speed case
10 CBR
30 CBR

• The behavior of the packet delivery ratio is
  almost
• the same as the one of the throughput
• The directional antennas gain more than 7
  packet
• delivery ratio when comparing with
  omni-directional
• antennas

20 CBR
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Simulation Analysis II-mobility speed case
10 CBR
30 CBR

• The path length does have noticeable change
  when the
• mobility increases or the traffic flow rises
• This suggests that path length slightly depends
  on the
• mobility speed level and traffic flows. The
  directional
• antennas always save 25 of the hops when
• comparing with omni-directional antennas.

20 CBR
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Agenda

• Introduction
• Research problem
• Objective and methodology
• Thesis roadmap
• Basic of smart antennas
• MAC protocol issue
• IEEE 802.11 MAC protocol
• Directional MAC problems
• Directional MAC proposals
• Routing protocol issue
• Ad hoc routing protocols
• Directional routing problems
• Directional routing proposals
• Case study
• Conclusion and future work

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Conclusion

• The network performance of directional antennas
  is not affected by increasing the
• communication distance in static scenario
• The routing performance of OLSR outperforms
  AODV when devices equipped with
• omni-directional antennas in long
  communication distance in static scenario
• The network performance deteriorates with
  increase of mobility level, but directional
• antennas show significant advantage compared
  with omni-directional antennas.
• The important finding is that the network
  performance of directional antennas always
• outperform omni-directional antennas both in
  static and mobility scenarios, and the
• advantage of directional antennas is more
  obviously when channel condition
• become worse or mobility level is large or
  traffic load is heavy

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Future work

• This thesis concentrates on unicast routing
  protocol. The multicast routing protocol
• is also an interesting issue that needs to
  be considered
• There is a need to implement a new directional
  route discovery algorithm for direction
• antennas in the QualNet simulator to replace
  omni-directional route finding scheme in
• order to mitigating broadcast storm problem
• The security is a very important issue in ad
  hoc networks. Since the ad hoc network
• does not have any centralized control, the
  security must be processed in a distributed
• manner

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• THANKS!!