seminar report on wireless network

8/10/2019 Seminar Report on wireless network

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CHAPTER-1

OVERVIEW OF ZIGBEE WIRELESS SENSOR NETWORKS

1.1 INTRODUCTION

Wireless sensor networks (WSNs) have been utilized all over the world. Significant

development of smart sensors has been made in recent years. The responsibilities of those

sensors include sensing, measuring, gathering information from the environment, and

transmitting the sensed data to each other or to the user by some specific topology with

limited processing and computing resources, the sensors are built smaller and they are

cheaper than the traditional sensors. But there still is a project that wireless sensor network

technology now focuses on low-power and low-cost. Wireless sensor networks have been used

for many applications. The military applications, such as military target tracking and

battlefield surveillance, improved the technology of WSNs. Besides that, wireless sensor

networks can be used in many consumer and industrial applications, such as machine health

monitoring and control, environment and habitat monitoring, biomedical health monitoring,

home automation, traffic control, natural disaster relief, and seismic sensing.

1.2 SENSOR NODES

The WSN is built of sensor nodes, from a few to several thousands, where each node

is connected to one or several sensors. Sensor nodes have variable sizes and, with the

difference in size and cost, they can have some different constraints.

There are four sub-systems in a sensor node: a computing subsystem, a communication

subsystem, a sensing subsystem, and a power supply subsystem. Computing subsystem

consists of a microprocessor (MCU) which is used to control the sensors by some

specific communication protocols. Communication subsystem has a short range radio which is

used to communicate with other nodes in the sensor networks. Radios can operate under the


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Transmit (TX), Receive (RX), IDLE and SLEEP modes. A radio has to be in the transmit mode

for the sensor to send data, while it has to be in receive mode if the sensor wants to receive

data. With no packets to transmit or receive, the radio stays in IDLE mode. The radio goes to

SLEEP mode after a long time that it stays in IDLE mode, which can save the power of the

sensor. Sensing subsystem may consist of a number of sensors such as thermal, chemical,

optical, biological, and magnetic sensors to measure properties of the environment. Depending

on the application and the type of sensors used, actuators, which are applied to actuate the

sensing devices and adjust the parameters of the sensor nodes, may be incorporated. Battery is

the primary component in the power supply subsystem in most sensor nodes. Depending on

the environment where the sensor is deployed, secondary power supply may be added. Solar

panel is a common choice which harvests the energy from the sun and works for most of the

sensor nodes except the ones working underground.

1.3 WIRELESS SENSOR NETWORKS

A wireless sensor network usually contains tens to thousands of sensor nodes working

together to collect data about the environment and share the data they have. The WSNs can be

divided into structured WSNs and unstructured WSNs. In an unstructured WSN, sensor nodes

may be deployed in an ad-hoc manner. Ad-hoc deployment, which can have a large number of

sensor nodes, is for the region which has no infrastructure and usually implemented by tossing

the sensor nodes from an airplane or a missile. After deployed, the network is going to

perform sensing and reporting functions unattended. Howeverdue to the huge amount of

sensor nodes, network maintenance and management is difficult and may cost a lot. Different

with ad-hoc manner, sensor nodes are deployed in a pre-planned manner in a structured WSN.

With pre- planned manner, sensor nodes are placed at specific locations to provide

communication, resulting in lower network maintenance and management cost.

An unstructured WSN with ad-hoc deployment can be usually called wireless ad-hoc network.

The wireless ad-hoc network does not have a certain routing scheme because of no

infrastructure as mentioned before and the locations of the sensor nodes cannot be determined

until the ad-hoc deployment. So every sensor node participates in the routing in wireless ad-


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hoc network and normally flooding routing technique is applied. Emergent situations such as

natural disaster and military conflict are examples suitable for wireless ad-hoc network.

Current wireless sensor networks are deployed basically on land, underground, or underwater.

There are different challenges and constraints depending on the environment. According to

variable functions and structures, wireless sensor networks can have five types: terrestrial

WSN, underground WSN, underwater WSN, multi-media WSN, and mobile WSN.

Terrestrial WSNs are typically composed by hundreds to thousands of sensor nodes deployed

either in an ad-hoc or in a pre-planned manner. The sensor node in terrestrial WSN is

relatively inexpensive, for it does not need to fulfill the resistance to stress as in underground

WSNs or the waterproofness as in underwater WSNs. Only terrestrial WSN with pre-planned

deployment is concerned in this thesis.

1.4 ISSUES IN WIRELESS SENSOR NETWORKS

A WSN has its own design and resource constraints due to the limited size and cost of sensor

node such as limited energy and storage, short communication range, low bandwidth, and

limited processing, which is different with traditional sensor networks. Recent technology in

wireless communications and electronics have overcome some of the constraints and

enabled the development of sensor nodes which are low-power, low-cost, multifunctional,

and small in size. However, three primary problems such as energy efficiency, localization,

and routing still hold.

1.4.1 Energy Efficiency

The most important factor to determine the life of a sensor network is the energy consumption.

Driven by battery which is limited in power and may not be rechargeable, sensor node is

facing the big challenge of conserving energy.

This problem could be found in almost any part of a sensor node and the sensor network. In

computing subsystem, MCUs have various operating modes. The power of these modes


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should be carefully considered to prolong the lifetime of the network. In addition, another kind

of consumption of power which cannot be ignored is the changing between these modes.

Communication is a major consumer of energy, especially in RX and TX mode. However,

radio standing in IDLE mode still consumes as high power as in RX mode. And again, startup

in some cases and changing in the radios operation mode can consume a large amount of

power. So it could be a better way to turn the radio into SLEEP mode to minimize the energy

consumption than turn it to IDLE mode when it is not transmitting or receiving. And a fast

startup transmitter architecture may be applied. A sensor has three sources of power

consumption including signal sampling and conversion of physical signals to electrical ones,

signal conditioning, and analog- to-digital conversion. Energy can be reduced by using low

power sensor in the sensing subsystem. As a vital role in determining sensor node lifetime,

battery supplies the power of sensor node. By reducing the current or even turn it off often, the

lifetime of the sensor node can be increased effectively.

If energy awareness can be applied in every stage of wireless sensor, the lifetime of the

wireless sensor network can be maximized. Moreover, it will be more powerful for wireless

sensor networks to have the ability to make tradeoffs between energy consumption and system

performance gives a detailed design of energy-aware sensor network.

1.4.2 Localization

In some sensor networks, particularly in wireless ad-hoc network, sensor nodes are deployed

unplanned and the location of each sensor node cannot be predicted. So a problem about

determining the location of the nodes needs to be solved and this problem is called

localization. Since Global Positioning System (GPS), which comes to mind first, has some

strong factors that are not suitable for sensor networks such as the high cost and the limitation

of application in the presence of any obstruction like dense foliage, sensor nodes would need

to have other means of localization. Various localization techniques can be classified as fine-

grained and coarse-grained. Fine- grained includes Timing, Signal strength, Signal pattern

matching, and Directionality while Proximity based localization, basing on the technique of

recursive trilateration/multilateration, is an example of coarse-grained localization.


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1.4.3 Routing

Routing scheme is another factor that can influence the lifetime of wireless sensor networks.

Flooding routing techniques, as mentioned above, is an old technique that has some

deficiencies and is not suitable for the requirement of the wireless sensor networks.

Considering prolonging the lifetime of the wireless sensor network, routing scheme should be

designed with the requirement of constraints such as energy, memory, communication

bandwidth, and computation capabilities.

There are two types of routing protocols, proactive protocols and reactive protocols. Proactive

protocols try to maintain consistent routing between all the nodes while reactive protocols

create the routes only when they are needed. SPIN (Sensor Protocols for Information via

Negotiation) and Directed Diffusion are two primary routing protocols in wireless sensor

networks. SPIN protocols use information description for negotiation among all the sensor

nodes before transmission of the data. Directed diffusion is a reactive routing technique in

which a node sends out a sensing task for the data it needs throughout the network and then

the node which has the data sends it back to the former node.


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CHAPTER 2

FUNDAMENTALS OF ZIGBEE TECHNOLOGY

2.1 INTRODUCTION

In 21st century, wireless sensor networks are becoming necessary and seen as indispensable in

various medical and telecommunication equipment, smart energy resources, home automation

products etc., which require monitoring and control. Zigbee is a wireless technology, which

communicates on the principle of IEEE 802.15.4 standard. IEEE 802.15.4 is a standard that

states the details for the lower layers of the communication. This standard focuses on the low-

cost and low power communication. Because of Zigbees low cost, low power consumption

and ability to connect in a mesh network, it is becoming more optimum solution for

monitoring and control applications.

Ability to connect in mesh network allows Zigbee to provide more range compared to other

wireless technologies such as INFRARED, BLUETOOTH etc. In addition, it also

provides high reliability of the data reproduced at receiver. It also consumes less power in

communicating data between its transmitter and receiver, which means longer life withsmaller batteries. The primary reason for low power consumption in Zigbee devices is that

they work on very small duty cycle that helps them to have a longer life span. Variation in

duty cycle depends upon the application usage, for example, some applications need data more

frequently like in health centers compared to others such as home automation systems.

2.2 TYPES OF ZIGBEE DEVICES

2.2.1 Zigbee Coordinator

This acts as the building block of the Zigbee communication. Zigbee coordinator forms the

root of the various topologies like mesh, star, tree topology network etc. and communicates

from one device to other. There is only one Zigbee coordinator in the whole Zigbee

environment.


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Figure 2.1: Zigbee coordinator

2.2.2 Full Function Device

Full function devices support all IEEE 802.15.4 functions and features that are defined by the

standard. They can also function as a Zigbee coordinator. More memory and computing power

availability helps them to work as router also, which helps in transmitting data to longer

distances through different networks.

Figure 2.2: Full function device

2.2.3 Reduced Function Device

Reduced function devices just talk to the Zigbee coordinators or Full function devices. They

cannot perform the functions of a router or coordinator.

Zigbee CoordinatorZigbee

Devices

Full Function

Devices


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Figure 2.3: Reduced function device

2.3 ZIGBEE NETWORK

2.3.1 Network Setup

The Zigbee coordinator does Zigbee network initialization. As soon as the network is powered

up, the coordinator starts the network initialization sequence. After that, the coordinator starts

a search for the full function devices and reduced function devices to establish a network.

Joining Network as a New Device

Whenever a new device either Full Function Device (FFD) or Reduced Function Device

(RFD) wants to join a network, it sends a request to all other parent capability devices such asFFDs that it wants to join the network. Then all the parent devices send a packet, which gives

the information about their address and number of devices already connected to it. The child

device that can be either FFD or RFD collects all the data and then selects one of the devices

as a parent device, which is best suited for it. Then that parent device is responsible to provide

the child device a unique ID.

Joining Previous Network

Zigbee devices save the information in a table whenever they are connected to a network. This

table stores the information, which helps the device to reconnect to the same network again.

So next time whenever they are switched on, they first look into that table about the previous

information and try to connect to the old network. If the table is blank then they try to connect

into a network as a new device.

Reduced

Function

Devices


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2.3.2 Mechanism for Data Transfer

Whenever a device wants to send a data packet, it has to check for channel. If the channel is

idle, device can send a packet else it has to wait. If the receiver is FFD then transmitters can

send the packet any time because its transceiver always remains ON. However if the receiver

is RFD then there are chances that its transceiver is OFF to save power. So to avoid data loss

all RFDs send a packet to their corresponding parent device as soon as there transceiver comes

to ON position to get the data packet which was send to them when they were in sleeping

mode.

2.3.3 Zigbee Network Topology

Zigbee network topology can be divided into three types:

Star Topology

Star topology consists of one Zigbee coordinator and one or more RFDs or FFDs. All end

point devices directly communicate to coordinator. If the end point devices want to talk to

each other they have to send the information to coordinator first and then coordinator sends

that information to appropriate receiver.

Figure 2.4: Star topology

Mesh Topology

Mesh topology also consists of one Zigbee coordinator and one or more RFDs or FFDs, but in

this topology, FFDs can directly contact other FFDs to communicate the data packet.

Figure 2.5: Mesh topology

Zigbee Coordinator

Full Function Device

Reduced Function Device

Zigbee Coordinator




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Cluster Tree Topology

This type of topology is used when range from transmitter to receiver is large and Zigbee

coordinator has to join two or more networks.

Figure 2.6: Cluster tree topology

Zigbee Coordinator




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2.4 ZIGBEE DEVICE COMMUNICATION FLOW CHART

Figure 2.7: Flow Chart showing working of Zigbee coordinator

Initialize the Device

Setup a New Network

Waiting for the RFD/FFD to join

RFD/FFD Join?

Receive the RFD/FFD Data

YES

NO


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Figure 2.8 Flow Chart showing working of Zigbee device

Initialize the Device

Send Signal to join

network

Join Network

Waiting for the data

from/to sensor/device

Send/Receive data to/fromCoordinator

Successfully

Transferred

YES

YES

NO

NO


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CHAPTER 3

IEEE 802.15.4 SPECIFICATION

3.1 IEEE 802.15.4

802.15.4 is a packet-based radio protocol. It addresses the communication needs of wireless

applications that have low data rates and low power consumption requirements. It is the

foundation on which ZigBee is built. Figure 3.1 shows a simplified ZigBee stack, which

includes the two layers specified by 802.15.4: the physical (PHY) and MAC layers.

Table 3-1. Comparison of IEEE 802.15.4 Frequency Bands

3.1.1 PHY Layers

The PHY layer defines the physical and electrical characteristics of the network. The basictask of the PHY layer is data transmission and reception. At the physical/electrical level, this

involves modulation and spreading techniques that map bits of information in such a way as to

allow them to travel through the air.

Specifications for receiver sensitivity and transmit output power are in the PHY layer.


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The PHY layer is also responsible for the following tasks:

Enable/Disable the radio transceiver

Link quality indication (LQI) for received packets

Energy detection (ED) within the current channel

Clear channel assessment (CCA)

3.1.2 MAC Layer

The MAC layer defines how multiple 802.15.4 radios operating in the same area will share the

airwaves. This includes coordinating transceiver access to the shared radio link and the

scheduling and routing of data frames.

There are network association and disassociation functions embedded in the MAC layer.

These functions support the self-configuration and peer-to-peer communication features of a

ZigBee network.

The MAC layer is responsible for the following tasks:

Beacon generation if device is a coordinator

Implementing carrier sense multiple access with collision avoidance (CSMA-CA)

Handling guaranteed time slot (GTS) mechanism

Data transfer services for upper layers

3.2 PROPERTIES OF 802.15.4

802.15.4 Defines operation in three license-free industrial scientific medical (ISM) frequency

bands. Below is a table that summarizes the properties of IEEE 802.15.4 in two of the ISM

frequency bands: 915 MHz and 2.4 GHz.

3.2.1 Transmitter and Receiver

The power output of the transmitter and the sensitivity of the receiver are determining factors

of the signal strength and its range. Other factors include any obstacles in the communication

path that cause interference with the signal. The higher the transmitters output power, the

longer the range of its signal. On the other side, the receivers sensitivity determines the

minimum power needed for the radio to reliably receive the signal. These values are described

using dBm (deciBels below 1 mill watt), a relative measurement that compares two signals


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with 1 mill watt used as the reference signal. A large negative dBm number means higher

receiver sensitivity.

3.2.2 Channels

It have the three ISM frequency bands only the 2.4 GHz band operates world-wide. The 868

MHz band onlyoperates in the EU and the 915 MHz band is only for North and South

America. However, if globalinteroperability is not a requirement, the relative emptiness of the

915 MHz band in non-European countries might be an advantage for some applications. For

the 2.4 GHz band, 802.15.4 specifies communication should occur in 5 MHz channels ranging

from 2.405 to 2.480 GHz.

3.3 NETWORK TOPOLOGIES

According to the IEEE 802.15.4 specification, the LR-WPAN may operate in one of two

network topologies: star or peer-to-peer. 802.15.4 is designed for networks with low data

rates, which is why the acronym LR (for low rate) is prepended to WPAN.

Figure 3.1 Network Topologies Supported by IEEE 802.15.4

As shown in Figure 3.1, the star topology has a central node with all other nodes

communicating only with the central one. The peer-to-peer topology allows peers to

communicate directly with one another. This feature is essential in supporting mesh networks.


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3.4 NETWORK DEVICES AND THEIR OPERATING MODES

Two types of devices can participate in a LR-WPAN: A full function device (FFD) and a

reduced function device (RFD).

An RFD does not have routing capabilities. RFDs can be configured as end nodes only. They

communicate with their parent, which is the node that allowed the RFD to join the network.

An FFD has routing capabilities and can be configured as the PAN coordinator. In a star

network all nodes communicate with the PAN coordinator only so it does not matter if they

are FFDs or RFDs. In a peer-to-peer network there is also one PAN coordinator, but there are

other FFDs which can communicate with not only the PAN coordinator, but also with other

FFDs and RFDs.

There are three operating modes supported by IEEE 802.15.4: PAN coordinator, coordinator,

and enddevice. FFDs can be configured for any of the operating modes. In ZigBee

terminology the PAN coordinatoris referred to as simply coordinator. The IEEE term

coordinator is the ZigBee term for router.

3.5 ADDRESSING MODES SUPPORTED BY 802.15.4

802.15.4 Supports both short (16-bit) and extended (64-bit) addressing. An extended address

(also called EUI-64) is assigned to every RF module that complies with the 802.15.4

specification. When a device associates with a WPAN it can receive a 16-bit address from its

parent node that is unique in that network.

3.5.1 PAN ID

Each WPAN has a 16-bit number that is used as a network identifier. It is called the PAN ID.

The PAN coordinator assigns the PAN ID when it creates the network. A device can try and

join any network or itcan limit itself to a network with a particular PAN ID.ZigBee PRO

defines an extended PAN ID. It is a 64-bit number that is used as a network identifier in

placeof its 16-bit predecessor.


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CHAPTER 4

ZIGBEE SPECIFICATION

Its specification and promotion, is a product of the ZigBee Alliance. The Alliance is an

association of companies working together to ensure the success of this open global standard.

ZigBee is built on top of the IEEE 802.15.4 standard. ZigBee provides routing and multi-hop

functions to the packet-based radio protocol.

Figure 4.1 ZigBee Stack


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4.1 LOGICAL DEVICE TYPES

The ZigBee stack resides on a ZigBee logical device. There are three logical device types:

Coordinator

Router

End device

It is at the network layer that the differences in functionality among the devices are

determined. Refer Table 4-1 for more information. It is expected that in a ZigBee network the

coordinator and the routers will be mains-powered and that the end devices can be battery-

powered.

Table 4.1. Comparison of ZigBee Devices at the Network Layer

In a ZigBee network there is one and only one coordinator per network. The number of routers

and/or end devices depends on the application requirements and the conditions of the physical

site.

Within networks that support sleeping end devices, the coordinator or one of the routers must

be designated as a Primary Discovery Cache Device. These cache devices provide server


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services to upload and store discovery information, as well as respond to discovery requests,

on behalf of the sleeping end devices.

4.2 ZIGBEE STACK LAYERS

As shown in Figure 4.1, the stack layers defined by the ZigBee specification are the network

and application framework layers. The ZigBee stack is loosely based on the OSI 7-layer

model. It implements only the functionality that is required in the intended markets.

4.2.1 Network (NWK) Layer

The network layer ensures the proper operation of the underlying MAC layer and provides an

interface to the application layer. The network layer supports star, tree and mesh topologies.

Among other things, this is the layer where networks are started, joined, left and discovered.

When a coordinator attempts to establish a ZigBee network, it does an energy scan to find the

best RF channel for its new network. When a channel has been chosen, the coordinator assigns

the logical network identifier, also known as the PAN ID, which will be applied to all devices

that join the network.A node can join the network either directly or through association. To

join directly, the system designer must somehow add a nodes extended address into the

neighbor table of a device. The direct joining device will issue an orphan scan, and the node

with the matching extended address (in its neighbor table) will respond, allowing the device to

join.To join by association, a node sends out a beacon request on a channel, repeating the

beacon request on other channels until it finds an acceptable network to join. The network

layer provides security for the network, ensuring both authenticity and confidentiality of a

transmission.

4.2.2 Application (APL) Layer

The APL layer is made up of several sub-layers. The components of the APL layer are shown

in Figure 4.2.and discussed below. The ovals symbolize the interface, called service access

points (SAP), between different sub-layer entities.


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Figure 4.2 ZigBee-Defined Part of Stack

4.2.2.1 Application Support Sub-layer (APS)

The APS sub-layer is responsible for:

Binding tables

Message forwarding between bound devices

Group address definition and management

Address mapping from 64-bit extended addresses to 16-bit NWK addresses

Fragmentation and reassembly of packets

Reliable data transport

The key to interfacing devices at the need/service level is the concept of binding. Binding

tables are keptby the coordinator and all routers in the network. The binding table maps a

source address and source endpoint to one or more destination addresses and endpoints. The

cluster ID for a bound set of devices will be the same.


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4.2.2.2 Application Framework

The application framework is an execution environment for application objects to send and

receive data. Application objects are defined by the manufacturer of the ZigBee enabled

device. As defined by ZigBee, an application object is at the top of the application layer and is

determined by the device manufacturer. An application object actually implements the

application; it can be a light bulb, a light switch, an LED, an I/O line, etc. The application

profile is run by the application objects. Each application object is addressed through its

corresponding endpoint. Endpoint numbers range from 1 to 240. Endpoint 0 is the address of

the ZigBee Device Object (ZDO). Endpoint 255 is the broadcast address, i.e., messages are

sent to all of the endpoints on a particular node. Endpoints 241 through 254 are reserved for

future use. ZigBee defines function primitives, not an application programming interface

(API).

4.2.2.3 ZigBee Device Object (ZDO)

The ZDO is responsible for overall device management, specifically it is responsible for:

Initializing the APS sub-layer and the NWK layer

Defining the operating mode of the device (i.e., coordinator, router, or end device)

Device discovery and determination of which application services the device provides

Initiating and/or responding to binding requests

Security management

Device discovery can be initiated by any ZigBee device. In response to a device discovery

inquiry end devices send their own IEEE or NWK address (depending on the request). A

coordinator or router willsend their own IEEE or NWK address plus all of the NWK addresses

of the devices associated with it. (A device is associated with a coordinator or router if it is a

child node of the coordinator or router.) Device discovery allows for an ad-hoc network. It

also allows for a self-healing network. Service discovery is a process of finding out what

application services are available on each node. This information is then used in binding tables

to associate a device offering a service with a device that needs that service.


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4.3 ZIGBEE ADDRESSING

Before joining a ZigBee network (i.e., a LR-WPAN), a device with an IEEE 802.15.4

compliant radio has a 64-bit address. This is a globally unique number made up of an

Organizationally Unique Identifier (OUI) plus 40 bits assigned by the manufacturer of the

radio module. OUIs are obtained from IEEE to ensure global uniqueness. When the device

joins a Zigbee network, it receives a 16-bit address called the NWK address. Either of these

addresses, the 64-bit extended address or the NWK address, can be used within the PAN to

communicate with a device. The coordinator of a ZigBee network always has a NWK address

of 0. ZigBee provides a way to address the individual components on the device of a node

through the use of endpoint addresses. During the process of service discovery the node makes

available its endpoint numbers and the cluster IDs associated with the endpoint numbers. If a

cluster ID has more than one attribute, the command is used to pass the attribute identifier.

4.3.1 ZigBee Messaging

After a device has joined the ZigBee network, it can send commands to other devices on the

same network. There are two ways to address a device within the ZigBee network: direct

addressing and indirect addressing.

Direct addressing requires the sending device to know three kinds of information regarding the

receiving device:

1. Address

2. Endpoint Number

3. Cluster ID

Indirect addressing requires that the above three types of information be committed to a

binding table. The sending device only needs to know its own address, endpoint number and

cluster ID. The binding table entry supplies the destination addressbased on the information

about the source address. The binding table can specify more than one destination

address/endpoint for a given source address/endpoint combination. When an indirect

transmission occurs, the entire binding table is searched for any entries where the source

address/endpoint and cluster ID matches the values of the transmission. Once a matching entry


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is found, the packet is sent to the destination address/endpoint. This is repeated for each entry

where the source endpoint/address and clusterID match the transmission values.

4.3.2 Broadcast Addressing

There are two distinct levels of broadcast addresses used in a ZigBee network. One is a

broadcast packet with a MAC layer destination address of 0xFFFF. Any transceiver that is

awake will receive the packet. The packet is re-transmitted three times by each device, thus

these types of broadcasts should only be used when necessary. The other broadcast address is

the use of endpoint number 0xFF to send a message to all of the endpoints on the specified

device.

4.3.3 Group Addressing

An application can assign multiple devices and specific endpoints on those devices to a single

group address. The source node would need to provide the cluster ID, profile ID and source

endpoint.

4.4 ZIGBEE APPLICATION PROFILES

Basically a profile is a message-handling agreementbetween applications on different devices.

A profile describes the logical components and their interfaces.Typically, no code is

associated with a profile.The main reason for using a profile is to provide interoperability

between different manufacturers.

Forexample, with the use of the Home Lighting profile, a consumer could use a wireless

switch from onemanufacturer to control the lighting fixture from another manufacturer.There

are three types of profiles: public (standard), private and published. Public profiles are

managed by the ZigBee Alliance. Private profiles are defined by ZigBee vendors for restricted

use. A private profilecan become a published profile if the owner of the profile decides to

publish it.All profiles must have a unique profile identifier. You must contact the ZigBee

Alliance if you have createda private profile in order to be allocated a unique profile

identifier.A profile uses a common language for data exchange and a defined set of processing

actions. An applicationprofile will specify the following:


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Set of devices required in the application area

Functional description for each device

Set of clusters to implement the functionality

Which clusters are required by which devices

A device description specifies how a device must behave in a given environment. Each piece

of data that can be transferred between devices is called an attribute. Attributes are grouped

into clusters. Figure 4.3 illustrates the relative relationships of these entities and the maximum

number that can exist theoretically per application profile.

Figure 4.3 Maximum Profile Implementation

All clusters and attributes are given unique identifiers. Interfaces are specified at the cluster

level. There are input cluster identifiers and output cluster identifiers. At time of this writing,

the following public profiles are available:

Commercial building automation

Home automation

Industrial plant monitoring

Wireless sensor applications

Smart energy

4.4.1 ZigBee Device Profile

The ZigBee Device Profile is a collection of device descriptions and clusters, just like an

application profile. The device profile is run by the ZDO and applies to all ZigBee devices.

The ZigBee Device Profile is defined in the ZigBee Application Level Specification. It serves

as an example of how to write an application profile.


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CHAPTER 5

ENERGY-EFFICIENT MAC LAYER PROTOCOLS IN WSN

5.1 INTRODUCTION

A mobile ad hoc network (MANET) is defined as an autonomous system of mobile routers

(and their associated hosts) connected by wireless links the union of which forms an arbitrary

graph. It is characterized by fast deployment, dynamic multi-hop topology, self-organization

without typical infrastructure support, etc. These properties are desirable in situations such as

battlefields, where network connectivity is temporarily needed, or fixed infrastructures are

unavailable, expensive, or infeasible to deploy.

However, wide deployment of MANET has not come yet due to many technical challenges,

among which energy issue is a fundamental one. Typical wireless devices are powered by

small-sized batteries, whose replacement is very difficult or even impossible in some

applications (e.g. disaster relief operation). Therefore, power conservation is one of the most

important design considerations for MANET. It has attracted a large number of researchers in

recent years.

Power conservation in an ad hoc network is the procedure of determining the transmit power

of each communication terminal such that a design objective (e.g. network lifetime,

throughput, etc.) can be satisfied. There are two major reasons for transmit power control.

First, transmitting at a high power may increase the interference to co-existing users and

therefore degrade network throughput. Power saving mechanisms has been shown to be able

to decrease multi-user interference, and hence increase spatial channel reuse and the number

of simultaneous single-hop transmissions. One direct benefit of this increase is the enlarged

overall traffic carrying capacity of the network. Second, energy efficient schemes can impact

battery life, consequently prolonging the lifetime of the network. Current power

controlmechanisms include low-power wireless access protocols, power-aware routing for ad

hoc and sensor networks, and node-level energy efficient information processing. In this

paper, we will focus on energy aware MAC (Media Access Control) layer protocols for ad hoc


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networks. MAC layer is the sub-layer of the data link layer that is responsible for coordinating

and scheduling of transmissions among competing nodes. As claimed by, MAC protocols

could significantly reduce the power consumption of mobile terminals in MANETs.

The energy-aware MAC protocols in a multi-hop self-organizing mobile ad hoc network must

simultaneously satisfy the following three objectives. First, MAC protocols should facilitate

the creation of the network infrastructure. Second, MAC protocols are in charge of fairly and

efficiently sharing the wireless channels among a number of mobile terminals. In MAC layer

channel scheduling, packet collision among different users should be reduced or even

completely avoided, and the bandwidth should be fully-utilized. These two goals are

conflicting with each other. Therefore MAC protocols should be carefully designed to balance

them based on network requirements. Third, MAC protocols should be energy-aware for

extending battery lifetime. Supporting power management to save energy is required for

battery-powered mobile nodes in MANETs. Actually, this is the motivation of our paper. The

power conservation mechanisms for MANETs also must support multi-hop forwarding. They

should be distributed, as there is no centralized controll to rely on.

5.2 SOURCES OF POWER WASTE IN MAC LAYER OF ZIGBEE

5.2.1 Major sources of energy waste

The major sources of power waste in mobile computing devices include radio communication

and data processing, with radio communication often being the dominate source of energy

consumption. Data processing involves the usage of CPU, memory, hard drive, etc. Its energy

consumption is relatively negligible compared with that of the radios. The energy expenditure

in radio communication includes the power consumed by transmitting and receiving devices of

all nodes along the path from source to destination, together with their neighbors that can

overhear the transmission. Actually, there is a tradeoff on energy consumption between data

processing and radio communication, the two energy consuming factors.

For example, data compression techniques are introduced in to reduce packet length and

therefore achieve energy saving in radio communication, but the cost of computation is

increased. Let's first take a look at the characteristics of energy consumption in a radio

interface so that we can easily understand the motivations of the energy efficient mechanisms

discussed in the following sections. In mobile ad hoc networks, communication related energy


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consumption includes the power consumed by the radios at the sender, receiver and

intermediate nodes in the route from the source to the destination. Actually, at any time a

mobile node in MANETs must be in one of the following four modes: transmit, receive, idle

listening, and sleep.

When a node is in transmitting or receive mode, it is transmitting or receiving a packet. Idle

listening mode means the node is neither transmitting nor receiving a packet, but is doing

channel monitoring. This mode consumes power because the node has to listen to the wireless

medium continuously in order to detect the arrival of the packet thatit should receive, so that

the node can switch to receive mode. When in the sleep mode, nodes do not communicate at

all. Receive and idle mode consume similar amount of power, while transmit mode requires

slightly larger amount. Nodes in sleep mode consume extremely low power.

Asan example, we illustrate the energy consumption of different modes for the 2.4GHz DSSS

Lucent IEEE 802.11WaveLAN PC \Bronze" (2Mbps) wireless network interface card in Table

1. Note that mobile ad hoc nodes must keep on monitoring the media for possible data

transmission. Thus most of the time nodes must be in idle listening mode instead of sleeping.

Actually, a network interface operating in ad hoc status has a constant idle power

consumption, which reflects the cost of listening to the wireless channel. Many measured

results have shown that the energy spent by idle listening is 50s100% of that by receiving. In

other words, idle listening consumes only slightly less energy than actually receiving traffic.

Thus, significant energy isconsumed even when there is no traffic in the MANETs. Further,

the energy expenditure for the radio interface to transit from one mode to anther is not

negligible because the transition time cannot be infinitesimally short.

For example, the transition between transmit and receive modes typically takes

6 to 30s, while the transition from sleep to transmit or receive generally takes even more time

(250s). Mode transitions have significant impact on energy consumption of wireless nodes.

Besides the power consumption in transmit, receive and idle listening, there exists other

significant energy expenditure in packet retransmission, node overhearing and protocol

overhead. Retransmission is caused by collision. When a packet is corrupted, it must be

discarded and transmitted again. Retransmission increases energy consumption. In fact, due to

the lack of a centralized authority in mobile ad hoc networks, transmissions of packets from

distinct mobile terminals are more prone to overlap, resulting in more serious packet collisions


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and energy loss. Overhearing means a node picks up packets that are destined for other nodes.

Wireless nodes will consume power unnecessarily due to overhearing transmissions of

theirneighboring nodes. Protocol overhead is generated by packets dedicated for network

control and header bits of data packets. It should be reduced as much as possible because

transmitting data packet headers or control packets also consumes energy, which results in the

transmission of less amount of useful data packets.

5.2.2 Low-power mac design guidelines

The major energy waste comes from idle listening, retransmission, overhearing and protocol

overhead. Thus there is no wonder why all power-aware MAC protocols try hard to reduce

energy waste from one or all of the above sources. To make a MAC protocol energy efficient,

at least one of the following design guidelines must be obeyed:

5.2.2.1 Minimize random access collision and the consequent retransmission

Collisions should be avoided as far as possible since otherwise the followed retransmission

will lead to unnecessary energy consumption and longer time delay. Actually, one of the

fundamental tasks of any MAC protocol is to avoid collisions so that two interfering nodes do

not transmit at the same time. The simplest ways for collision avoidance in a general network

include code division multiple access (CDMA), time division multiple access (TDMA), and

frequency division multiple access (FDMA). However, for mobile ad hoc networks there exist

many special issues that need to be addressed for a MAC protocol design. For example,

because of the nonexistence of fixed base stations in MANETs, mechanisms to avoid collision

among mobile nodes must be distributed. Since collision avoidance may result in substantial

overhead, which will burn more energy, tradeoffs must be explored to achieve reasonable

solution. Further analysis on channel reuse mechanisms based on scheduling will be given in

Section 3. Such schemes are designed to increase the channel utility and at the same time to

avoid collisions.

5.2.2.2 Minimize idle listening

In typical MANET systems, receivers have to be powered on all the time. This results in

serious energy waste. Since the power consumed in idle listening is significant, we should pay

attention to the energy conservation in nodes other than the source and destination. Ideally the


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radio should be powered on only when it needs to transmit orreceive packets, thus remove the

unnecessary monitoring of the media. Recently, energy-aware MAC protocols that require

nodes be in sleep mode periodically for energy conservation have been proposed. When in

sleep mode, nodes neither transmit nor receive packets; but they must be woken up to idle

mode first for attending traffic relay. Sleep mode requires more than an order of magnitude

less power than idle mode. Hence, intelligently switching to sleep mode whenever possible

will generally lead to significant energy saving.

5.2.2.3Minimize overhearing

Wireless nodes consume power unnecessarily due to overhearing the transmissions of their

neighbors. This is often the case in a typical broadcast environment. For example, as the

IEEE 802.11 wireless protocol defines, receivers remain on and monitor the common channel

all the time. Thus the mobile nodes receive all packets that hit their receiver antennae. Such

scheme results in significant power consumption because only a small number of the received

packets are destined to the receiver or needed to be forwarded by the receiver. One solution to

this problem is the introduction of a control channel for the transmission of control signals that

will wake up the nodes only when needed.

5.2.2.4 Minimize control overhead

Protocol overhead should be reduced as much as possible, especially for transmitting short

packets. Due to the large channel acquisition overhead, small packets have disproportionately

high energy costs. Header compression can be used to reduce packet length, thus achieving

energy savings. Since significant energy is consumed by the mobile radio when switching

between transmit and receive modes, packet aggregation for header overhead reduction will be

useful. When mobile nodes request multiple transmission slots with a single reservation

packet, the control overhead for reservation can be reduced. Allocating contiguous slots for

transmission or reception to reduce the turnaround also helps to achieve low power

consumption.


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CHAPTER 6

POWER SAVING SMAC PROTOCOLS FOR ZIGBEE WSNS

6.1 INTRODUCTION AND NEED OF POWER SAVING

Wireless Sensor Networks have become one of the flourishing research fields in recent years,

as they are intended to have wide applications in military, environmental, and many other

fields. Normally, the throughput, latency and the energy efficiency are unpredictable, and

there exists a tradeoff among these measures. The objective of this work is to explore the

maximum achievable throughput under certain network configurations and receiver structures,

as well as optimum network designs that achieve the desired throughput, latency with minimal

energy consumption.

Wireless Sensor Networks establish a special class of wireless data communication networks.

A classic node in the WSN consists of a sensor, embedded processor, adequate amount of

memory and transmitter/receiver circuitry. These sensor nodes are normally battery powered

and they cooperate among themselves to perform a common task. Sensor Networks are the

key to gathering the information needed by smart environments, whether in buildings, utilities,

industrial, home, shipboard, transportation systems automation, or elsewhere. A SensorNetwork is required that is fast and easy to connect and maintain. More and more wireless

sensor networks are being used to gather information in real life applications. Looking toward

to the future, the technology seems even more auspicious in two directions. First, a few years

from now more powerful wireless sensor devices will be accessible, and wireless sensor

networks will have applicability in an endless number of scenarios, as they will be able to

handle traffic loads not possible today, make more calculations, store more data, and live

longer because of better energy sources. Second, a few years from now, the opposite scenario

might also be possible. The availability of very forced, nanotechnology made wireless sensor

devices will bring a whole new world of applications, as they will be able to operate in

environments and places unimaginable today. These twoscenarios, at the same time, will both

bring new research challenges that are always welcome to researchers. The main goal of a

WSN is to collect data from the environment and send it to a reporting site where the data can


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be observed and analyzed. Recent advances in sensor and wireless communication

technologies in aggregation with developments in microelectronics have made available a new

type of communication network made of batterypowered integrated wireless sensor devices.

At present time, due to economic and technological reasons, most available Wireless Sensor

devices are very selfconscious in terms of computational, memory, power, and

communication capabilities. This is the main reason why most of the research on WSNs has

focused on the design of energy and computationally efficient algorithms and protocols, and

the application domain has been restricted to simple dataoriented monitoring and reporting

applications. Medium Access Control (MAC) is an important technique that permits the

successful operation of the network. Medium Access Control for wireless sensor networks has

been a very active research area in recent years. The old

style wireless medium access controlprotocol such as IEEE 802.11 is not suitable for the sensor network application because these

are battery powered. The recharging of these sensors nodes is expensive and also not normally

possible.

6. 2. ENERGY RELATED ISSUES

MAC sublayer protocols for WSNs must address the following energyrelated issues:

6.2.1 Collisions:The collisions occur when two nodes transmit at the same time. The packets

can get corrupted and it may be required to be retransmitted. So a lot of time and energy gets

wasted during this transmission and reception. Collisions should be avoided because of the

extra energy wasted in frame retransmission.

6.2.2 Overhead: The other major problem is the Control Packet Overhead. These Control

Packets do not contain any application data but are essential for the communication. The

transmission and reception of these packets is overhead on the sensor network. Control

messages and long headers in frames need to be avoided as much as possible, as theyimply

extra expensive communication costs.

6.2.3 Overhearing: The other problem is overhearing in which a sensor node may receive

packets that are not intended for it. This node could have turned off its radio to save its energy.

Overhearing is the energy consumed by the nodes by being constantly listening and decoding


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frames that are not meant for them. This is a consequence of using a shared media in which

nodes do not know a priori whether the transmissions are for them or not.

6.2.4 Idle listening:Idle listening refers to the energy expended by the nodes by having their

circuits ON and ready to receive while there is no activity in the network.

This is particularly important in WSNs, as nodes use the channel sporadically. Strategies to

turn nodes ON and OFF are very important in WSNs. The idle listening problem in wireless

networks can be minimized by putting the radio into sleep mode.

6.2.5 Complexity: Complexity refers to the energy expended as a result of having to run

computationally expensive algorithms and protocols. One of the most importantdesign goals in

WSNs is therefore simplicity. The other important characteristics of the Wireless Sensor

Network are fairness, latency, throughput and bandwidth.

6. 3. WSN MEDIUM ACCESS CONTROL PROTOCOLS

Many medium access control (MAC) protocols for wireless sensor networks have been

planned in the recent years. Most of these protocols have energy safeguarding as an objective.

The pattern of energy use in the sensor nodes, however, depends on the nature of the

application. The MAC techniques proposed for WSNs can be divided into two categories

namely Contentionbased and Schedule based. Schedule based protocol can avoid collisions,

overhearing and idle listening by scheduling transmit and listen periods but have strict

timesynchronization requirements.The contention based protocol on the other hand relax time

synchronization requirements and easily adjust to the topology changes as some new nodes

may join and other may die few years after deployment. These protocols are based on Carrier

Sense Multiple Access (CSMA) technique and have higher costs for message collisions,

overhearing, and idle listening.


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Figure 6.1. The SMAC and TMAC Protocols

IEEE 802.11 DCF (Distributed Coordination Function) is a contention based MAC protocol

that is mainly built on the MACAW and widely employed in early WSN applications. This

section describes a number of energyefficient MAC protocols for WSNs and states their

contributions toward addressing their main issues such as overhearing, idle listening, control

packet head and collision avoidance. Medium Access Control for wireless sensor networks has

been a very energetic research area in recent years.

6.3.1 Power Aware MultiAccess with Signaling (PAMAS) Protocol

The Power Aware MultiAccess with Signaling (PAMAS) protocol is based on the MACA

protocol but includes a separate signaling channel to avoid the collisions and overhearing

problems. All nodes utilize the signaling channel to exchange RTSCTS frames and therefore

gain access to the media. All nodes know who has gained the media and for how long,

information that nodes use to turn themselves off. The other channel is used exclusively to

transmit data frames, which is collisionfree. The main disadvantage of PAMAS is that it


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needs an additional radio for the signaling channel, which adds to the cost of sensor network

devices.

6.3.2 Sensor MAC (SMAC) Protocol

The Sensor MAC (SMAC) protocol was introduced in to solve the energy consumption

related problems of idle listening, collisions, and overhearing in WSNs using only one

transceiver. SMAC considers that nodes do not need to be awake all the time given the low

sensing event and transmission rates. A contention based SMAC protocol is based on

CSMA/CA, energy conservation and self-configuration are primary goals, while pernode

fairness and latency are less important. To provide energy conservation, the SMAC protocol

tries to reduce undesirable energy depletion due to collision, overhearing, packet overhead and

idle listening as well as it turns the radio on and off based on the fixed duty cycles. The maindrawback of SMAC is that the use of fixed duty cycles can waste considerable amounts of

energy since the communication subsystem is activated even though no communication will

take place.

6.3.3 Timeout MAC (TMAC) Protocol

Timeout TMAC is the protocol based on the SMAC protocol in which the active period is

preempted and the sensor goes to the sleep period if no activation event has occurred for a

time. The event can be reception of data, start of listen/sleep frame time etc. The

TimeoutMAC (TMAC) protocol introduces the idea of having an adaptive active/inactive

(listening/sleeping) duty cycle tominimize the idle listening problem and improve the energy

savings over the classic CSMA and SMAC fixed duty cyclebased protocols. The TMAC

protocol, however, suffers from the known early sleep problem, which can reduce throughput.

6.3.4 Wise MAC Protocol

The Wise MAC protocol which combines TDMA and CSMA techniques determines the

length of the preamble dynamically to reduce the power consumption and thus it results better

performance under especially variable traffic conditions as shown in figure 6. 2.


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Figure 6.2. The preamble sampling technique used in wise MAC

Wise MAC performs better than one of the SMAC variants. Besides, its dynamic preamble

length adjustment results in better performance under variable traffic conditions. Main

drawback of Wise MAC is that decentralized sleep listenscheduling results in different sleep

and wakeup times for each neighbor of a node. This is especially an important problem for

broadcast type of communication, since broadcasted packet will be buffered for neighbors in

sleep mode and delivered many times as each neighbor wakes up. However, this redundant

transmission will result inhigher latency andpower consumption. In addition, the hidden

terminal problem comes along with Wise MAC model as in theSpatial TDMA and CSMA

with Preamble Sampling algorithm. That is because Wise MAC is also based on no persistent

CSMA. This problem will result in collisions when one node starts to transmit the preamble to

a node that is already receiving another nodes transmission where the preamble sender is not

within the range.


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CHAPTER 7

CONCLUSION AND FUTURE WORK

The Sensor MAC (SMAC) protocol was introduced in to solve the energy consumption

related problems of idle listening, collisions, and overhearing in WSNs using only one

transceiver. SMAC considers that nodes do not need to be awake all the time given the low

sensing event and transmission rates. SMAC reduces the idle listening problem by turning the

radio OFF and ON periodically. Nodes are synchronized to go to sleep and wake up at the

same time. In order to address the issue of synchronization over multi-hopnetworks, nodes

broadcast their schedules to all its neighbors. This is performed sending a small SYNC frame

with the node schedule periodically. SMAC divides time in two parts: the active (listening)

part and the inactive (sleeping) part. The active part is divided at the same time in two time

slots. During the first time slot, nodes are expected to send their SYNC frames to synchronize

their schedules. The second time slot is for data transmission in which the SMAC protocol

transmits all frames that were queued up during the inactive part. In order to send SYNC

frames over the first time slot or RTSCTSDATAACK frames over the second time slot,

nodes obtain access to the media utilizing the same contention mechanism included in IEEE802.11, which avoids the hidden terminal problem and does a very good job avoiding

collisions too. However, nodes using the

IEEE 802.11 protocol waste a considerable amount of energy listening and decoding frames

not intended for them. In order to address this problem, SMAC allows nodes to go to sleep

after they hear RTS or CTS frames. During the sleeping time, a node turns off its radio to

preserve energy.

Advantages:The energy wastage caused by idle listening is reduced by sleep schedules. In

addition to its implementation simplicity, time synchronization overhead may be prevented

with sleep schedule announcements.

Disadvantages: Broadcast data packets do not use RTS/CTS which increases collision

probability. Adaptive listening incurs overhearing or idle listening if the packet is notdestined


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to the listening node. Sleep and listen periods are predefined and constant, which decreases the

efficiency of the algorithm under variable traffic load.

FUTURE WORK

Different Wireless Sensor Network MAC protocols such as Power Aware Multi Access with

Signaling (PAMAS) protocol, Sensor MAC (SMAC) protocol, Timeout TMAC protocol,

WiseMAC protocol, have been discussed. We have drawn the conclusion that the MAC

protocol influences network lifetime. However, different MAC protocols can be efficient

depending on the given environment and applications. During this work, we realized that the

MAC protocols for the wireless sensor networks are a hard and extensive area. Although

modification in S

MAC protocol has been proposed, there is possible future work for systemperformance optimization. Therefore, some of the planned work has to be streamlined away

for future work. We see clear paths for future work:

Verification through employment and wideranging simulations.

Formal descriptions to address other type of MAC protocols and addition of

components.

Cross layer optimization is an area that needs to be explored more extensively.

Extension of components and formal descriptions to address the other type of WSN

MAC Protocols.


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REFERENCES

1. Ye, W.; Heidemann, J.; Estrin, D., Medium AccessControl With Coordinated

Adaptive Sleeping forWireless Sensor Networks, IEEE/ACM Transactionson

Networking, Volume: 12, Issue: 3, June 2004,pp:493506.

2. Akyildiz, Ian F; Weilian Su ; Yogesh W.;Sankarasubramaniam ; Cayirci, E ; A survey

on sensornetworks, IEEE Communications Magazine :2002,pp.102114.

3. Labrador, M. A.; Wightman, P. M., Topology Controlin Wireless Sensor Networks

Springer, USA.

4. Rugin, R., Mazzini, G., A simple and efficient MACroutingintegrated algorithm for

sensor network,IEEE International Conference on Communications,Volume: 6, 2024

June 2004, pp: 3499 3503.

5. Zorzi, M., A new contentionbased MAC protocol forgeographic forwarding in ad hoc

and sensornetworks, IEEE International Conference oncommunications, Vol.6, June

2004, pp: 34813485.

6. Brenner, Pablo, A Technical Tutorial on the IEEE 802.11 Protocol, BreezeCom

WirelessCommunications, July 1996.

7. Ghosh, S.; Veeraraghavan, P.; Singh, S.; Zhang, L.;Performance of a Wireless Sensor

Network MACProtocol with a Global Sleep Schedule InternationalJournal of

Multimedia and Ubiquitous Engineering,Vol. 4, No. 2, April, 2009, pp 99114.

8. Ye, W.; Heidemann, J. ;Estrin, D., An EnergyEfficient MAC Protocol for Wireless

SensorNetworks, TwentyFirst Annual Joint Conference ofthe IEEE Computer and

Communications Societies(INFOCOM) 3 2002, pp15671576.


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9. IEEE Standard 802.11., Wireless LAN Medium AccessControl (MAC) and Physical

Layer (PHY)Specifications, 1999.

seminar report on wireless network

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