S-38.3310 Thesis Seminar on Networking Technology
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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. Agenda. Introduction

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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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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.


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

DIFS

RTS

data

Source

Node

SIFS

SIFS

SIFS

t

CTS

ACK

Destination

Node

t

DIFS

NAV (RTS)

data

NAV (CTS)

NAV

t

Access to medium deferred

backoff

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


The improvements in ad hoc routing and network performances with directional antennas

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 => 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


The improvements in ad hoc routing and network performances with directional antennas

DRTS

DRTS

OCTS

OCTS

OCTS

ORTS

(DMAC2)

B

C

D

E

A

DATA

DATA

ACK

ACK

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


The improvements in ad hoc routing and network performances with directional antennas

A

Forward RTS

B

C

D

G

F

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


The improvements in ad hoc routing and network performances with directional antennas

D

DNAV

C

A

B

DNAV

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.


The improvements in ad hoc routing and network performances with directional antennas

Traditional

Omni CTS

B

B

Communication

Communication

A

Traditional

DRTS

A

Circular

DRTS

C

C

X

Reception

Area

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


The improvements in ad hoc routing and network performances with directional antennas

A

Added Lobe

C

B

Communication

Extended RTS

F

E

B

A

Transmission☺

Communication

Reception☻

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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.


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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

Element antenna pattern used in QualNet


The improvements in ad hoc routing and network performances with directional antennas

Simulation Environment I-static communication distance case

  • 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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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.


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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


The improvements in ad hoc routing and network performances with directional antennas

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

THANKS!!


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