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

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

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.

Introduction



• Thesis roadmap








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.

Directional MAC Proposals-DMAC1/2

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

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


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


F

Transmission ☺☺Reception ☻☻

Extended RTSExtended RTS

A

Introduction



• Thesis roadmap








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



• Thesis roadmap








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)


20 CBR

30 CBR

Throughput

2627282930313233

1 2 3 4 5

Speed l evel

Thro

ughp

ut(k

bits

/s)


• 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


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)


End- to- End Del ay

05

101520253035

1 2 3 4 5

Speed l evel

End-

to-E

nd D

elay

(ms)


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)


• 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


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(%)



85

90

95

100

1 2 3 4 5

Speed l evel

Pack

et D

eliv

ery

Rati

o(%)



84

88

92

96

100

1 2 3 4 5

Speed l evel

Pack

et D

eliv

ery

Rati

o(%)


• 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


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



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



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


• 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



• Thesis roadmap








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

manner

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

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