The Improvements in Ad Hoc Routing and Network Performances with Directional Antennas S-38.3310 Thesis Seminar on Networking Technology Supervisor: Prof Sven-Gustav Häggman Helsinki University of Technology Communications Laboratory 8.8.2006 Hao Zhou
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The Improvements in Ad Hoc Routing and Network Performances with Directional Antennas
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. Agenda. Introduction - PowerPoint PPT Presentation
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The Improvements in Ad Hoc Routing and
Network Performances with Directional Antennas
S-38.3310 Thesis Seminar on Networking Technology
Supervisor: Prof Sven-Gustav Häggman
Helsinki University of TechnologyCommunications Laboratory 8.8.2006
Hao Zhou
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
Agenda
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
Introduction
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
Research Problem
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
Thesis Roadmap
Chapter 2
Smart antennas
Chapter 4
Directional MAC proposals
Chapter 3
MAC protocols
Chapter 7
Case studies
Chapter 6
Directional routing proposals
Chapter 5
Routing protocols
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
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.
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
Agenda
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
IEEE 802.11 MAC Protocol
t
SIFS
DIFS
data
ACK
Access to medium deferred
NAV
DestinationNode
SourceNode
data
DIFS
backoff
RTS
CTS
SIFSSIFS
NAV (RTS)
NAV (CTS)
t
t
ACK: Acknowledgement CTS: Clear to Send DIFS: Distributed Inter-Frame Space NAV: Network Allocation Vector
RTS: Request to Send SIFS: Short Inter-Frame Space
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 => 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
Directional MAC Problems
Directional MAC Scheme 1/2
Each node knows about location of neighbor nodes and itself based on GPS devices.
(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
ORTS(DMAC2)
E A B C DDATA
ACK
OCTS
DRTS
OCTS
DRTS
OCTS
DATA
ACK
Multi-hop RTS MAC scheme
Each node is equipped with an omni-directional antenna together with a directional
antenna
Directional MAC Proposals-MMAC
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
G
B C
FD
Forward RTS
A
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
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
Directional MAC Proposals-DVCS
AB
C
DDNAVDNAV
DNAVDNAV
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.
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
Directional MAC Proposals-C-DRTS
X
A
B
C
A
B
C
Traditional Traditional Omni CTS Omni CTS
Traditional Traditional DRTS DRTS
Circular Circular DRTSDRTS
ReceptionReceptionAreaArea
CommunicationCommunication
Extended RTS/CTS scheme
Each node knows about the neighbor node location information
Directional MAC Proposals-E-R/CTS
A
Added LobeAdded Lobe
CommunicationCommunication
CB
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
B
E
CommunicationCommunication
F
Transmission ☺☺Reception ☻☻
Extended RTSExtended RTS
A
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
Agenda
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
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
Directional Routing Problems
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
Directional Routing Proposals for directional route discovery
• 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
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.
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
Agenda
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
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
The general simulation environment parameters
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
Simulation Analysis I-static communication distance case
Throughput
28
30
32
34
200 400 600 800 1000 1200 1400
Di stance between sender andrecei ver(m)
Thro
ughp
ut(k
bits
/s)
AODV (Omni )AODV (Di r . )OLSR (Omni )OLSR (Di r . )
End- to- End Del ay
01
23
45
6
200 400 600 800 1000 1200 1400
Di stance between sender andrecei ver(m)
End-
to-E
nd D
elay
(ms)
AODV (Omni )AODV (Di r . )OLSR (Omni )OLSR (Di r . )
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
• 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
Simulation Environment II-mobility speed case
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
• 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.
Simulation Analysis II-mobility speed case
Throughput
262728293031323334
1 2 3 4 5
Speed l evel
Thro
ughp
ut(k
bits
/s)
AODV(Omni )AODV(Di r)
10 CBR
Throughput
2627282930313233
1 2 3 4 5
Speed l evel
Thro
ughp
ut(k
bits
/s)
AODV(Omni )AODV(Di r)
20 CBR
30 CBR
Throughput
2627282930313233
1 2 3 4 5
Speed l evel
Thro
ughp
ut(k
bits
/s)
AODV(Omni )AODV(Di r)
• 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
Simulation Analysis II-mobility speed case
10 CBR
20 CBR
30 CBR
End- to- End Del ay
0
5
10
15
20
25
1 2 3 4 5
Speed l evel
End-
to-E
nd D
elay
(ms)
AODV(Omni )AODV(Di r)
End- to- End Del ay
05
101520253035
1 2 3 4 5
Speed l evel
End-
to-E
nd D
elay
(ms)
AODV(Omni )AODV(Di r)
End- to- End Del ay
0
10
20
30
40
50
1 2 3 4 5
Speed l evel
End-
to-E
nd D
elay
(ms)
AODV(Omni )AODV(Di r)
• 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
Simulation Analysis II-mobility speed case
10 CBR
20 CBR
30 CBR
Packet Del i very Rat i o
85
90
95
100
1 2 3 4 5
Speed l evel
Pack
et D
eliv
ery
Rati
o(%)
AODV(Omni )AODV(Di r)
Packet Del i very Rat i o
85
90
95
100
1 2 3 4 5
Speed l evel
Pack
et D
eliv
ery
Rati
o(%)
AODV(Omni )AODV(Di r)
Packet Del i very Rat i o
84
88
92
96
100
1 2 3 4 5
Speed l evel
Pack
et D
eliv
ery
Rati
o(%)
AODV(Omni )AODV(Di r)
• 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
Simulation Analysis II-mobility speed case
10 CBR
20 CBR
30 CBR
Average path l ength
1. 2
1. 4
1. 6
1. 8
2
2. 2
1 2 3 4 5
Speed l evel
numb
er o
f ho
ps
AODV(Omni )AODV(Di r)
Average path l ength
1. 2
1. 4
1. 6
1. 8
2
2. 2
1 2 3 4 5
Speed l evel
numb
er o
f ho
ps
AODV(Omni )AODV(Di r)
Average path l ength
1. 2
1. 4
1. 6
1. 8
2
2. 2
2. 4
1 2 3 4 5
Speed l evel
numb
er o
f ho
ps
AODV(Omni )AODV(Di r)
• 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.
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
Agenda
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
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