communication engineering assignment final

7/31/2019 Communication Engineering Assignment Final

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Assignment on Wireless LAN

Course Code: CSE 411

Course Title: Communication Engineering

Submitted by:

A.K.M. Mohiuddin Ahammed

092-15-813

Mohammad Mahadi Hasan

092-15-791

Daffodil International University

Submitted to:

Md. Safiqul Islam

Senior Lecturer of the Department of CSE

Daffodil International University

Submission Date: 07/08/2012


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Introduction

What is a wireless network?

A technology that enables two or more entities to communicate without network

cabling

A wireless LAN or WLAN is a wireless local area network that uses radio waves as

its carrier.

The last link with the users is wireless, to give a network connection to all users in a

building or campus.

The backbone network usually uses cables

What is unique about wireless?

Interference and Noise

Full connectivity cannot be assumed

Hidden terminal problem

Battery Usage

Requires power management

Security

No physical boundaries

Overlapping LANs

Complete Wireless Networks

The physical size of the network is determined by the maximum reliable propagation range

of the radio signals.

Referred to as ad hoc networks

Are self-organizing networks without any centralized control

Suited for temporary situations such as meetings and conferences.


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Requirements of a wireless standard

Single MAC to support multiple PHY mediums

Robust to interference

Need to deal with the hidden terminal problem

Need provision for time bounded services

Support for power management to save battery power

Ability to operate world wide

Hence uses the 2.4GHz ISM band

System Architecture

Basically there are two types of wireless network services.

1. Basic Service Set.

2. Extended Service Set .

A Basic Service set can be two types based on the connection type.

1. Ad hoc network.

2. Infrastructure based network.

Ad hoc wireless LAN is a group of stations using the same radio frequency Basic Service Set.

There is no need of an APs to connect the devices in the network.

Fig:Ad-hoc network


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A peer-to-peer (P2P) network allows wireless devices to directly communicate with each other.

Wireless devices within range of each other can discover and communicate directly without

involving central access points. This method is typically used by two computers so that they can

connect to each other to form a network.

Infrastructure based Wireless LANs

In an infrastructure based network the devices are connented or communicate via an Access Point

(AP). AP acts as a distributed system connects cells to form a single network. A device from one

BSS can communicate with a device in another BSS via an AP. It has extends wireless area

coverage.

Access Points(APs)

Stations select an AP and associate with it. AP supports roaming of devices. It also provides other

functions, that is: time synchronization (beaconing), power management support, point coordination

function, Traffic typically (but not always) flows through AP, direct communication possible

Distribution system

Used to interconnect multiple wireless cells

Multiple BSS are connected to form an ESS Extended Service Set

Allows mobile stations to access fixed resources


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MAC layer

MAC layer controls medium access, distributed coordinated function.

Mandatory access mechanism CSMA/CA.

Optional RTS/CTS extension to deal with the hidden terminal problem

Point Coordinated function

Contention free polling method to support time bounded services.

MAC Sub layer

IEEE 802.11 defines two MAC sublayers: the distributed coordination function (DCF) and point

coordination function (PCF).Figure Shown above.

Distributed Coordination Function


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Problems of Distributed Coordination Function

1. Costly equipments

2. Hidden Station

3. Signal Fading distance

Addressing mechanism

Case 1: The frame is going from one station in a BSS to another without passing through the distribution

system. The ACK frame should be sent to the original sender. The address have how in above figure in

case1.


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Case 2: In case 2 the frame is coming from an AP and going to a station.The ACK should be sent to the

AP. The Addresses are as shown above figure under case 2.

Case 3: In case 3 the frame is going from a station to an AP. The ACK is sent to the original station. The

address are as shown in above figure under case 3.

Case 4: In case 3 the frame is going from one AP to another AP in a wireless distribution system. We do

not need to define addresses if the distribution system is a wired LAN because the frame in these cases

has the format of a wired LAN frame.

Hidden Station Problem

B and C are hidden each other with respect to A.

Hidden Station Solution

Exposed Station Problem

C is exposed to transmit from A and B


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Some examples of Wireless LAN

a. Bluetoothb. Wi-Fi

c. Wimax

d. Infrared

e. Radio web

Installation and Site Design IssuesBridging

Health Issues

a. Do not touch or move the antenna while the unit transmitting or receiving.

b. Do not hold a component containing radio, in such a way that the antenna is very close to or

touching any exposed part of the body, especially the face or eyes, while transmitting.

c. Do not operate the radio or attempt to transmit data unless the antenna is connected, otherwise the

radio may be damaged.

d. Use the following guidelines in specific environment:

-The use of wireless devices in hazardous locations is limited to the constraints posed by the

safety directors of such environment.

- The use of wireless devices in airplanes is governed by the U.S Fedaral Aviation

Administration(FAA).

- The use of wireless devices in hospitals is restricted to the limit sets forth by each hospital.

e. Use the following guidelines for antenna use

- In order to comply with FCC RF exposure limits, dipole antennas should be located at a

minimum distance of 20 cm(7.9 inc.) from all persons.


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References:

1. Book, Data Communication and Networking by Behrouz a Forouzan 4th Edition, Chapter-14.

2. Lecture Slide of Muhammad Safiqul Islam ,Senior Lecturer of Daffodil InternationalUniversity, Dhaka, Bangladesh.

3. http://en.wikipedia.org/wiki/Wireless_LAN

4. http://kb.iu.edu/data/aick.html
http://en.wikipedia.org/wiki/Wireless_LANhttp://kb.iu.edu/data/aick.htmlhttp://en.wikipedia.org/wiki/Wireless_LANhttp://kb.iu.edu/data/aick.html

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