wireless lecture1

1Eng: Mohammed Hussein

Wireless Technology

Eng: Mohammed Hussein2

Wireless Technology can make the businesses more flexible and

cheaper for sending and receiving data in short time.

Increasing efficiency in the companies, and makes efficient and is

almost very economical.

Users have access easier at their offices.

Now at home, the users don't need to use cables to have internet

access.

Reduced the costs due to cheaper cost of install and maintains.

Mobility is very high for users, they can move inside the network

without sitting at one place. Avoiding LAN restrictions

Wireless Technology Classifications

1. The local area technologies as WLAN

(Wireless Local Area Network) with

moderate bandwidth. And WiMax

2. The large area technologies as GSM,

GPRS or UMTS, LTE which have

much higher bandwidth.


Data transmission


SMS

FAX

E-mail

Internet

Multimedia

114 kb/s

Voice +SMS +MM

IP

9.6 kb/s

Voice +SMS

Circuit-Switching

TimePacket-Switching

MB

IEEE 802.11 (WLAN) Architecture

ESS

BSS BSSIBSS

APAP

AP: Access point, BSS : Basic Set service, ESS : Extented Set Service, IBSS Independent BSS.

5 Eng: Mohammed Hussein

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GSM network ?

BSC

BSC

MSC

MS

MS

MSBTS

BTS

BTS

GMSC

PSTNISDNPSDN

EIRAUC

HLR

VLR


General Packet Radio Service (GPRS) ?


Scope

Enhanced algorithms

Fairness and QoSover wireless

to Satisfy Applications requirements


WLAN?

Access Port Switch

Ma

in C

orp

ora

te B

ac

kb

on

e

Server

Server

Server

iPaq

Notebook

PalmPilot

Mobile Phone

Notebook



IEEE 802.11

Frequency : band 2,4 GHz;

Infrastructure or Ad-hoc

IEEE 802.11 is Cellular


802.11 WLANs required centralized access points to mediate the wireless connection.

nodes are limited in power, computational capacities and memory.

IEEE 802.11

802.11

DSSS

FHSS

IR

802.11b 802.11g 802.11a

802.11 – 802.11e – 802.11i

802.11fMAC Layer

Physical Layer

LLC 802.2


WLAN

1990 : WLAN Project

IEEE (Institute of Electrical and Electronics

Engineers) :

IEEE 802.11 WiFi

IEEE 802.15

IEEE 802.16 WiMAX

Hiperlan (High Performance Local Area Network)

HiperLAN


3 Network

IP Routing Protocols

AODV , DSR , DSDV,…

2

Data Link

1 Physical (PHY)

LLC 802.2

MAC 802

4 Transport

5 Session

6 Presentation

7 Application

Figure :OSI layers with MAC and PHY details

802.3

CSMA/CD

802.4

Token Bus

802.5

Token Ring

802.11

Wireless

LAN

Logical Link Control

Network layers


SME/MLME = MAC Control / Management

Coordination Function

(DCF, PCF , HCF, ..) CSMA/CA

802.11 Media Access Control (MAC)

802.11 Physical Layer (PHY)

802.11a5

4 Mbps

/5

GHz

802.11b

11 Mbps

/2.4

GHz

PLME

Packet Transfer Function

802.11g

54 Mbps

/2.4

GHz

802.11e – Quality of Service

Sync, power

save, Beacon

Segmentation & Reassembly

802.11

legacy

2 Mbps

/2.4

GHz

FHSS

S-Band ISM

DSSS

S-Band ISM

OFDM

C-Band ISM

OFDM

S-Band ISM

802.11n

54-600

Mbps

/2.4 or

5 GHz

OFDM

MIMO14

Eng: Mohammed Hussein

Media Access Control (MAC)


The MAC is the way to transfer the data safely when there is more

than one node accessing a channel simultaneously .

The MAC have some techniques such as:

Distributed Coordination Function (DCF) used by both methods Ad-

Hoc mode or Infrastructure mode. With asynchronous transmission

data service.

Point Coordination Function (PCF) used only by Infrastructure mode.

With both asynchronous and time-bounded service

Access Method

MAC layer:

DCF (Distributed Coordination Function) :

based on CSMA/CA

PCF (Point Coordination Function) :

based on polling


The Medium Elements

Next FrameFrame

DIFS

PIFS

SIFS

DIFS

Time

Defer Access

Contention

Window

Backoff Slot time

Medium is available

17

DCF inter-frame spacing (DIFS) : between the end of one transmission and another next

round cycle transmission in Ad-Hoc mode

Short inter-frame spacing (SIFS) : has a high priority and comes after frames such as

(RTS, CTS, ACK).

PCF inter-frame spacing (PIFS) : between the end of one transmission and another next round

cycle transmission in Infrastructure mode

Medium is Busy


Wireless Problems


Hidden Terminal Problem


BA C

The transmissions from node A and node C collide at the

receiver node B . (in the same time)

Exposed Terminal Problem


BA C D

Wait the

medium is busy

The node C senses the medium is busy, therefore node C waits unnecessarily

time before it begins transmitting to node D.

So the waiting here is not required and node C is exposed to node B.

CSMA/CA PROTOCOL


The nodes throughputs are measured in the CSMA/CA by a collisions and idle slots resulting from Backoff algorithm for each CW period.

The CSMA/CA is algorithm for IEEE 802.11 DCF, simply listen-before-talk scheme.

N+1-th Packet

TransmissionCollision

DIFSSIFS DIFS

N-th Packet

Transmission ACK ACKCollision

Idle Backoff Slots

(at each contention period)

Virtual Transmission Time

SIFS DIFSCollision

Node 1

Node 2

Node 3

Node 4

Time

DIFS

DCF (NAV , RTS, CTS, ACK )DIFS

Node 5

Data

Data General data frameBackoff slot time

ACK

RTS

CTSSIFS

SIFS

SIFS

Defer Access

Node 4 increase

2 slot more

SIFS

Data

ACK

CTS

RTS ACKRequest To Send Frame

NAV (RTS)

NAV (CTS)

NAV (data)

Remaining Backoff

Clear To Send FrameClear To Send Frame

Backoff

NAV NAV timer

NAV

updates


(PCF) infrastructure mode

The idea of this access method is that the access point pools

its mobile nodes corresponding to a list.

For avoiding problems with the two DCF access methods

the PCF-IFS (PIFS) are used.

They grant an access point priority access to the medium


Beacon in infrastructure mode

Synchronization in infrastructure mode is very easy.

The Access Point (AP) regularly sends out a synchronization packet

(beacon).

If the medium is busy the AP just waits for a free PIFS frame


Server(internet)

802.11 frame

2Bytes 2 6 6 6 2 6 0-2312 4

Frame

Control

Duration / ID

Address 1

Address 2

Address 3

Sequence

Control

Payload

(Frame Body)

CRC

Address 4

MAC Header


frame

controlduration

address

1

address

2

address

4

address

3payload CRC

2 2 6 6 6 2 6 0 - 2312 4

seq

control

802.11 frame: addressing

Address 2: MAC addressof wireless host or AP transmitting this frame

Address 1: MAC addressof wireless host or AP to receive this frame

Address 3: MAC addressof router interface to which AP is attached

Address 3: used only in ad hoc mode


BSS1

BSS2

DS ( Distribution System)

STA 2

SS STA 3

DSS

DSS

802.X LAN

internet

DSS

ESS

STA 1

STA 4

802.11 MAC/PHY

802.11 MAC/PHY

SS :Station services

SS

STA :Station

DSS: Distribution System services

ESS: Extended Service Set

BSS: Basic Service Set

Portal


Infrastructure network


Handover between APs


Ad-Hoc Network

IBSS (Independent Basic Service Set)


Ad-Hoc Network


Ad Hoc classification


Sensor node

Internet

Manager Nodeuser

Sink Node

The environment Sensors field

Target

Wireless Sensor Network


Sensor Node


WiMax Scenario


Scenarios for integrated

WiFi and WiMAX networks


Summary of QoS


COMNET III

COMNET III is a commercial off-the-shelf

application whose function is to allow users to

estimate the performance characteristics of

computer based networks.

A network description is created graphically using a

window interface, and no actual programming is

required of the user.

The application was formulated primarily for the

modeling of both Wide Area Networks (WANs) and

Local Area Networks (LANs). 39


COMNET III

The COMNET III application was written in the

programming language MODSIM II using an

object-oriented design.

1. RUNNING A SIMULATION

2. STATISTICAL DISTRIBUTIONS AND TABLES

3. REPORTS

4. PLOTS AND PERCENTILES

COMNET III uses a discrete event simulation

methodology when running the simulation of a

network model.


References


Some Books : Second Generation Mobile And Wireless Technologies; Black, Uyless Prentice Hall; 09/1998; Wireless Personal Communications; A Systems Approach; Goodman,

David J. Addison Wesley; 09/1997; Principles of Mobile

Communication; Stuber, Gordon L. Kluwer Academic Publishing; 6/96.

http://www1.fatbrain.com/asp/bookinfo/bookinfo.asp?theisbn=0136212778






wireless lecture1

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