mobile communications chapter 2: wireless transmission types of electromagnetic carriers ...

Mobile CommunicationsChapter 2: Wireless Transmission

Types of electromagnetic carriersAdvantages and disadvantages of wireless communicationBasics of Radio CommunicationThe Wireless Landscape

Mobile Communications: Wireless communications

Objectives

Explain how the major wireless technologies are used today

Describe various applications of wireless communications technology

Explain the advantages and disadvantages of wireless communications technology

List several different wireless technologies


What is Wireless Communication ?

Transmitting voice and data using electromagnetic waves in open space (atmosphere)

Electromagnetic waves Travel at speed of light (c = 3x108 m/s) Has a frequency (f) and wavelength (l)

c = f x l Higher frequency means higher energy photons

The higher the energy photon the more penetrating is the radiation


Types of wireless communication

celullar wireless computer network radio service


Electromagnetic radiation spectrum


Wavelength of Some Technologies

GSM Phones: frequency ~= 900 Mhz wavelength ~= 33cm

PCS Phones frequency ~= 1.8 Ghz wavelength ~= 17.5 cm

Bluetooth: frequency ~= 2.4Gz wavelength ~= 12.5cm


Types of electromagnetic carriers

when the distance between the sender and receiver is short (e.g. TV box and a remote control) infrared waves are used

for long range distances between sender and receiver (e.g. TV broadcasting and cellular service) both microwaves and radio waves are used radio waves are ideal when large areas need to be coverd

and obstacles exist in the transmission path microwaves are good when large areas need to be coverd

and no obstacles exist in the transmission path


Wireless applications (services)


Advantages and disadvantages of wireless communication

advantages: mobility a wireless communication network is a solution in areas

where cables are impossible to install (e.g. hazardous areas, long distances etc.)

easier to maintain disadvantages:

has security vulnerabilities high costs for setting the infrastructure unlike wired comm., wireless comm. is influenced by

physical obstructions, climatic conditions, interference from other wireless devices


Frequency Carries/Channels

The information from sender to receiver is carrier over a well defined frequency band.

This is called a channel Each channel has a fixed frequency

bandwidth (in KHz) and Capacity (bit-rate) Different frequency bands (channels) can be

used to transmit information in parallel and independently.


Example

Channel 1 (b - b+30)

Channel 2 (b+30 - b+60)

Channel 3 (b+60 - b+90)

Station A Station B

Assume a spectrum of 90KHz is allocated over a base frequency b for communication between stations A and B

Assume each channel occupies 30KHz.

There are 3 channels

Each channel is simplex (Transmission occurs in one way)

For full duplex communication:

Use two different channels (front and reverse channels)

Use time division in a channel


Radio waves generation when a high-frequency alternating current (AC) passes through a copper

conductor it generates radio waves which are propagated into the air using an antena

radio waves have frequencies between: 3 Hz – 300 KHz - low frequency 300 KHz – 30 MHz – high frequency 30 MHz – 300 MHz – very high frequency 300 MHz – 300 GHz – ultra high frequency

Basics of Radio Communication


Radio propagation

• radio waves are generated by an antenna and they propagate in all directions as a straight line

• radio waves travel at a velocity of 186.000 miles per second

• radio waves become weaker as they travel a long distance


there are 3 modes of propagation: surface mode – for low frequency waves direct mode – for high frequency waves ionospheric mode – long distance high frequency waves


Modulation modulation = adding information (e.g. voice) to a carrier

electromagnetic (radio) signal

Frequency Modulation (FM).Amplitude Modulation (AM)


Radio frequency interference

Radio signal attenuation (path loss)


How Wireless Technology is Used

• Wireless

– Describes devices and technologies that are not connected by a wire

• Wireless communications

– Transmission of user data without the use of wires• Wireless data communications technologies include:

– Bluetooth– Wireless LAN and WAN– Satellite– Cellular


A Wireless World

Wireless devices

– Distance: 300 feet (90 meters)– Bandwidth: 54 Mbps– Can also include Voice over IP (VoIP)

Wireless network interface card (Wireless NIC)

– Sends and receives data over radio waves Smartphone

– Combination mobile phone and personal digital assistant (PDA)


A Wireless World


Bluetooth and Ultra Wide Band

• Radio frequency identification device (RFID) tags

– Small chips containing radio transponders• Can be used to track inventory

• Bluetooth and Ultra Wide Band (UWB)

– Wireless standards designed for very short ranges

– Communicate using small, low-power transceivers

• Link manager

– Special software that helps identify other Bluetooth devices


Bluetooth and Ultra Wide Band (continued)

• Bluetooth

– Distance: up to 33 feet (10 meters)– Bandwidth: 1 Mbps

• Ultra Wide Band

– Distance: 150 feet (50 meters)– Bandwidth: 100 Mbps to 2 Gbps

• Piconet

– Wireless personal area network (WPAN)– Consists of two or more Bluetooth devices

that are exchanging data with each other


Bluetooth and Ultra Wide Band


Wireless Local Area Networks

Wireless Local Area Network (WLAN)

Extension of a wired LAN Connecting to it through a device called a wireless access point

Access point (AP)

Relays data signals between all of the devices in the network

Each computer on the WLAN has a wireless network interface card (NIC)

With an antenna built into it


The original version of the standard IEEE 802.11 was released in 1997 and clarified in 1999, but is today obsolete. It specified two net bit rates of 1 or 2 megabits per second (Mbit/s), plus forward error correction code. It specified three alternative physical layer technologies: diffuse infrared operating at 1 Mbit/s; frequency-hopping spread spectrum operating at 1 Mbit/s or 2 Mbit/s; and direct-sequence spread spectrum operating at 1 Mbit/s or 2 Mbit/s. The latter two radio technologies used microwave transmission over the Industrial Scientific Medical frequency band at 2.4 GHz.

IEEE 802.11


Some earlier WLAN technologies used lower frequencies, such as the U.S. 900 MHz ISM band.Legacy 802.11 with direct-sequence spread spectrum was rapidly supplanted and popularized by 802.11b.

802.11a

The 802.11a standard uses the same data link layer protocol and frame format as the original standard, but an OFDM based air interface (physical layer). It operates in the 5 GHz band with a maximum net data rate of 54 Mbit/s, plus error correction code, which yields realistic net achievable throughput in the mid-20 Mbit/s.

802.11a


Since the 2.4 GHz band is heavily used to the point of being crowded, using the relatively unused 5 GHz band gives 802.11a a significant advantage. However, this high carrier frequency also brings a disadvantage: the effective overall range of 802.11a is less than that of 802.11b/g. In theory, 802.11a signals are absorbed more readily by walls and other solid objects in their path due to their smaller wavelength and, as a result, cannot penetrate as far as those of 802.11b. In practice, 802.11b typically has a higher range at low speeds (802.11b will reduce speed to 5 Mbit/s or even 1 Mbit/s at low signal strengths). 802.11a also suffers from interference,[11] but locally there may be fewer signals to interfere with, resulting in less interference and better throughput.

.


`802.11b has a maximum raw data rate of 11 Mbit/s and uses the same media access method defined in the original standard. 802.11b products appeared on the market in early 2000, since 802.11b is a direct extension of the modulation technique defined in the original standard. The dramatic increase in throughput of 802.11b (compared to the original standard) along with simultaneous substantial price reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology.802.11b devices suffer interference from other products operating in the 2.4 GHz band. Devices operating in the 2.4 GHz range include microwave ovens, Bluetooth devices, baby monitors, cordless telephones and some amateur radio equipment

802.11b



Institute of Electrical and Electronic Engineers (IEEE) standards

802.11a, 802.11b, and 802.11g


Major WLAN Components

Distribution System (DS). A wired/wireless medium which connect the Access Points to one another. The backbone network used to relay frames between access points

Access Points (AP). APs form a bridge between wired and wireless medium. Coordinate the connection of wireless stations to the DS

Wireless Medium. The Radio Frequency spectrum used to transfer frames between the

wireless station and the AP or between wireless stations. Wireless Stations.

Computing devices with wireless network interfaces. Typically battery operated laptops or handheld computers.


WLAN Types

Independent Basic Service Set (IBSS). No Access Point An ad-hoc group of wireless nodes. Peer-to-peer transmission One node is elected to act as a proxy to perform the

functions of the AP.


Basic Service Set (BSS). A single Access Point The AP acts as a bridge between clients and the wireline. Roaming is limited to the single radio cell All clients operate on the same channel. A BSS connected to a wired network is called an Infrastructure BSS. The clients must request to join and be accepted to associate with the

AP before they can send data. A BSS is identified by a 48 bit hex value called the BSS identifier –

BSSID. This is the MAC address of the AP

Access Point

Network

Wireline Network

WLAN Types


Access Point Access Point Wireline Network

Extended Service Set (ESS). Multiple Access Points that communicate through the DS. The APs share the same Service Set Identifier (SSID) – an Extended SSID or

ESSID. The AP acts as a bridge between clients and the wireline. Each AP forms a radio cell that overlap. Each AP is assigned a different

channel All clients operate on the same channel in the same cell but can communicate

through the DS. The APs interconnected through the Wireline constitute a Distributed System.

WLAN Types


Access Point Access Point Wireline Network

Extended Service Set (ESS) Contd.

The SSID is used to control APs with which the stations can associate.

Clients may also associate with an AP using a special "null" SSID value which indicates they would like to associate with any AP within range regardless of the assigned APs SSID.

AP can be configured to reject this "null" value.

The BSSID identifies a single BS.

The ESSID denotes a group of APs sharing a common SSID within which a client can roam.

WLAN Types


Station Services Authentication - The client identifies itself to the AP

in order to form an Association. This can be done by: Service Set Identifier (SSID) MAC Filtering.

De-authentication - Destroys a previously known station identity- terminates the current Association.

The device shuts down. Out of AP range

802.11 Network Services


Distribution Services. Association - establish a logical connection between the client

and the AP, i.e., A station registers with an AP. Determines the location of the client for the DS. Determines the path to reach the DS needs to reach the client. A client can be authenticated to multiple APs but Associated

with only one AP.

Reassociation - Retains network session information when the wireless client passes from one AP to another AP.

This information tells the new AP the identify of the last AP.

This allows the old AP to forward any remaining frames to the new AP for delivery via the DS.

802.11 Architecture


Distribution ServicesDisassociation - Tear down the association between the AP

and the wireless device. The device leaves the AP area. The AP is shutting down.

Distribution - Determines the location to which the frame should be forwarded by the AP - An AP uses the DS to deliver frames.

Another AP. A Wireless client. The Wired Network.

Integration - Provides a MAC framing service to the AP. Translates the 802.11 format to the Wired LAN format. Translates the Wired LAN format to the 802.11 format.

802.11 Architecture


Fragmentation. Spatial Density results in interference which requires data retransmission. 802.11 can be configured to send smaller packets.

Power Management. Mobile clients can enter the sleep mode to conserve power but still remain

connected. A 20 byte Power Save Poll (PS-Poll) is sent to the AP. The AP buffers all packets destined for he device until it comes back on line.

Multicell Roaming. Roaming is based upon determining the S/N ratio. AP sends out beacon messages containing link measurement data The client listens and determines which AP has the stronger signal

802.11 - Other Operations


Locating a WLAN

The wireless client locates the Access Point by scanning the airways for its RF signal.

It locates the AP by identifying its Service Set Identifier (SSID) through:

Passive Scanning Active Scanning Beacons


Service Set Identifier (SSID)

The SSID is used by WLAN as a network name. Unique Case sensitive Alphanumeric value 2-32 characters

The SSID is used for Segmenting networks Rudimentary security measure Joining a network.

The SSID is used in: Beacons Probe Requests Probe Responses, etc.


Passive Scanning Passive Scanning is the process of listening for Beacons on each

channel for a specific period after the station has initialized. The beacons are sent by: Access Points in the Independent Basic Service Set (BSS) or Extended Basic Service

Set (EBSS) mode. Client stations in the Ad Hoc mode.

If there are multiple APs in the area then the client attempts to join the strongest signal strength and lowest bit rate.

Passive Scanning continues after association to allow the Client to create a list of available access points should the current connection be broken.


Active Scanning Active Scanning is the process of sending a Probe Request frame

from a wireless client. The station is actively seeking a network to join. The probe contains either the network Service Set Identifier (SSID) or

a broadcast SSID. Only Access Points servicing that SSID will respond with a Probe

Response frame. This frame is identical to the Beacon frame with the exception that

it does not contain a Traffic Indication Map (TIM) All APs respond to the Broadcast SSID.

The wireless station then initiates the Authentication and Association steps.


Probe Request

Frame Control

Duration

ID

DA SA BSSID Sequenc

e Control

FCS

2 2 6 6 6 2 0-2,312 4 Frame Body

SSID

Var Var

Supported Rates

Probe Requests are used by stations to scan an area for 802.11 networks. The station sends our Probe Requests sequentially on all channels with its SSID

and listens for Probe Responses All Access Points must respond with a Probe Response.

Some APs are configured to ONLY send a Probe Request to a matching SSID.

The Probe Response contains: Service Set Identity (SSID) - The identity of the service set. Supported Rates - Data rates supported by the 802.11 network.


Probe Request

Indicates a Probe Request is contained within the MAC header


Probe Request


Probe Response

Frame Control

Duration

ID

DA SA BSSID Sequenc

e Control

FCS

2 2 6 6 6 2 0-2,312 4 Frame Body

Timestamp Beacon

Interval Capabilit

y Info SSI

D

FH Param

Set

8 2 2 Var 7 2 8 4 DS

Param Set

CF Param

Set

IBSS Param

Set

The Probe Response is sent by the AP in response to the Probe Request.

The Probe Response format is the same as the Beacon with the exception that it does not include the TIM Element.

The station is not yet associated with the AP therefore it does not need to now the TIM parameter.


Probe Response Contd

Frame Control

Duration

ID

DA SA BSSID Sequenc

e Control

FCS

2 2 6 6 6 2 0-2,312 4 Frame Body

Timestamp Beacon

Interval Capabilit

y Info SSI

D

FH Param

Set

8 2 2 Var 7 2 8 4 DS

Param Set

CF Param

Set

IBSS Param

Set Timestamp - Synchronization between stations. Beacon Interval - Announce existence of 802.11 network. Capability Info - Advertisement of network's capabilities. Service Set Identity (SSID) - The identity of the service set. FH Parameter Set - Specifies such things a Dwell time, Hop Set and Hop Pattern. DS Parameter Set - Specifies the DSSS channel number. CF Parameter Set – Specifies the parameters relating to the duration of the Contention

Free period. It is only sent by APs supporting the Point Coordination Function (PCF). Very few APs support this function.

IBSS Parameter Set - Specifies the number of Time Units between Announcement Traffic Indication Map (ATIM) windows



Indicates a Probe Response


BEACON

The Beacon Management frame serves the following major purposes. Time Synchronization.

The Beacon time stamp synchronize the client to the transmitter. This ensures all time sensitive functions, (FHSS, etc) are properly

timed. FH/DS (FHSS/DSSS) Parameter Sets.

FHSS hop sequence, hop time and dwell time. DSSS channel information

SSID Information The beacon contains the SSID the client wishes to join and sends

an authentication request to the MAC address contained in the Beacon.

Conversely, the client can be set to join ANY network that: (1) sends a beacon or (2) the strongest signal if there are multiple APs.


BEACON

Beacon frame is one of the management frames in IEEE 802.11 based WLANs. It contains all the information about the network. Beacon frames are transmitted periodically to announce the presence of a Wireless LAN network. Beacon frames are transmitted by the Access Point (AP) in an infrastructure BSS. In IBSS network beacon generation is distributed among the stations.

Traffic Indication Map (TIM) The TIM indicates which sleeping stations have traffic

queued by the Access point. The time synchronized stations power up, listen to the

Beacon, and check the TIM to see if they have traffic queued.

Supported Rates Informs the clients the speed capability of the

Access PointMobile Communications: Wireless communications

Beacon Frame

Frame Control

Duration

ID

DA SA BSSID Sequenc

e Control

FCS

2 2 6 6 6 2 0-2,312 4 Frame Body

Timestamp Beacon

Interval Capabilit

y Info SSI

D

FH Param

Set

TIM

8 2 2 Var 7 2 8 4 Var DS

Param Set

CF Param

Set

IBSS Param

Set

Timestamp - Synchronization between stations.

Beacon Interval - Announce existence of 802.11 network.

Capability Info - Advertisement of network's capabilities.

Service Set Identity (SSID) - The identity of the service set.

FH Parameter Set - Specifies such things a Dwell time, Hop Set and Hop Pattern.

DS Parameter Set - Specifies the DS channel number.


Beacon Frame

Frame Control

Duration

ID

DA SA BSSID Sequenc

e Control

FCS

2 2 6 6 6 2 0-2,312 4 Frame Body

Timestamp Beacon

Interval Capabilit

y Info SSI

D

FH Param

Set

TIM

8 2 2 Var 7 2 8 4 Var DS

Param Set

CF Param

Set

IBSS Param

Set

CF Parameter Set – Specifies parameters relating to the duration of the Contention Free period. It is only sent by APs supporting the Point Coordination Function (PCF).

Very few APs support this function.

IBSS Parameter Set - Specifies the number of Time Units between Announcement Traffic Indication Map (ATIM) windows

Traffic Indication Map (TIM) - Traffic Indication map to indicate which stations have buffered traffic.

Mandatory Optional


Beacon Frame

The Basic Service Set identifier (BSSID) is a 6 byte hex number identifying the Access Point.It is not the same as the SSID

This is the MAC Header

Indicates the Beacon is contained within the MAC header


Beacon Frame

This is the Beacon frame


Beacon FrameThis is the SSID

Supported Rates

DSS Element

TIM Element


802.11Authentication and Association

- Joining a Wireless LAN-


Authentication & Association

There are two separate sub-processes for connecting a client to a WLAN. These are:

Authentication: The process by which a node's identity is verified. Authentication must occur before Association

Association: A state in which a node is allowed to pass traffic through an access point

There are three distinct states.

Unauthenticated and Unassociated Authenticated and Unassociated. Authenticated and Associated.


States of Authentication & Association

Unauthenticated and Unassociated The initial state. The client is not connected to the WLAN and is unable to

pass data. Authenticated and Unassociated.

The Client has passed the Authentication state but is not yet associated with an Access Point.

The Client cannot send or receive packets. Authenticated and Associated.

The client is completely connected and is able to send and receive packets.

A client can be authenticated with multiple Access Points but only associated with one .

Pre-authentication makes for faster roaming Mobile Communications: Wireless communications

Fixed Broadband Wireless

Integrated Services Digital Networks (ISDN)

Transmit at 256 Kbps over regular phone lines T1 lines

Transmit at 1.544 Mbps Cable modems and digital subscriber lines (DSL)

Generally only available in residential areasMaximum transmission speed is only about 8

Mbps



Wireless metropolitan area network (WMAN)

Covers a distance of up to 35 milesBased on the IEEE 802.16 Fixed Broadband

Wireless standardUses small custom antennas on the roof of

each buildingTransmission speeds

75 Mbps at distances of up to 4 miles (6.4 km) 17 to 50 Mbps at distances over 6 miles (10 km)


Wireless Wide Area Network

• Hypertext Markup Language (HTML)

– Standard language for displaying content from the Internet

• Microbrowser

– Miniaturized version of a Web browser• Wireless Application Protocol version 2.0 (WAP2)

– Provides a standard way to transmit, format, and display Internet data

• For small wireless devices such as cell phones



Programming languages

BREW (Binary Run-Time Environment for Wireless)

J2ME (Java 2 Micro Edition) Wireless Wide Area Network (WWAN)

Enables employees to access corporate data and applications from virtually anywhere


The Wireless Landscape


Digital Convergence

Digital convergence

Refers to the power of digital devices to combine voice, video, and text processing capabilities

As well as to be connected to business and home networks and to the Internet


Wireless Applications

• Main areas

– Education– Home entertainment– Health Care– Government and Military– Office environments– Event management– Travel– Construction and warehouse management– Environmental research– Industrial control


Education

Ideal application for colleges and schools It frees students from having to go to a specific computer lab or the

library

To get on the school’s computer network Wireless technology translates into a cost savings for colleges as

well


Home Entertainment

Wireless communication

Enables movie and audio enthusiasts to download, distribute, and control all forms of digital entertainment from anywhere in the house


Health Care

Administering medication in a hospital setting

A major problem area for the health care industry

Wireless point-of-care computer systems

Allow medical staff to access and update patient records immediately

Even telephones are now being connected to hospital IEEE 802.11 WLANs

Employing VoIP technology


Government

Wireless communication

Lets city employees and contractors at remote sites access data stored in a central database

Delivers broadband connectivity to schools, libraries, and government buildings

Provides free Internet access to residents and attracts visitors and businesspeople


Military

Universal Handset

A 1.5-pound deviceAllows military personnel in the field to

communicate through a variety of methods Using wireless technologies

Military is currently working on preventing enemies from eavesdropping on or jamming the signal


Office Environments

Employees in all lines of work no longer have to be away from the data they need

To help them make decisions Wireless technologies allow businesses to create an office

Where the traditional infrastructure doesn’t already exist


Event Management

Wireless networks

Help identify a stolen or counterfeit ticketCan also give a real-time look at traffic flow In-progress game statistics are available to

any fan in the stadium with a wireless device


Travel

Wireless global positioning systems (GPS)

Tie into emergency roadside assistance services

Satellite radio

Transmits over 150 music and talk stations Airport terminals are likewise turning to wireless technologies Airplanes themselves are being equipped with wireless data access


Construction

Wireless communications

Send information from the job site to the main office

Alert when maintenance operations need to be performed on equipment


Warehouse Management

• Implementing wireless technology is key for many warehouse operations

• Warehouse management system (WMS) software

– Used to manage all of the activities from receiving through shipping

• In the near future

– Most of the bar code functions, including inventory counting, will be replaced by RFID tags


Environmental Research

Scientists are now using small, battery- or solar-cell-powered WLAN sensors

In places that were previously difficult to access and monitor


Industrial Control

Motes

Remote sensorsCan connect to a WLAN

Then collect data and transmit it to a central location


Wireless Advantages and Disadvantages

As with any new technology, wireless communications offers both advantages and disadvantages

• Mobility

– Freedom to move about without being tethered by wires– Permits many industries to shift toward an increasingly

mobile workforce– Gives team-based workers the ability to access the

network resources• Easier and less expensive installation

– Installing network cabling in older buildings can be a difficult, slow, and costly task

– Makes it easier for any office to be modified with new cubicles or furniture

Advantages of Wireless Networking


Advantages of Wireless Networking (continued)

Increased reliability

Network cable failures may be the most common source of network problems

Disaster recovery

In the event of a disaster, managers can quickly relocate the office


Disadvantages of Wireless Networking Radio signal interference

The potential for two types of signal interference exists Security

It is possible for an intruder to be lurking outdoors with a notebook computer and wireless NIC

With the intent of intercepting the signals from a nearby wireless network

Some wireless technologies can provide added levels of security

Health risks High levels of RF can produce biological damage through

heating effectsWireless devices emit low levels of RF while being used


Summary

Wireless communications have become commonplace Wireless networks and devices are found in all circles of life

today Wireless wide area networks will enable companies of all

sizes to interconnect their offices Without the high cost charged by telephone carriers for

their landline connections WLAN applications are found in a wide variety of industries

and organizations Remote sensors

Capable of communicating using wireless technologies Used in large manufacturing facilities

To monitor equipment and for scientific research


• Wireless communication advantages

– Mobility– Easier and less expensive installation– Increased network reliability– Support for disaster recovery

• Wireless communication disadvantages

– Radio signal interference– Security issues– Health risks


mobile communications chapter 2: wireless transmission types of electromagnetic carriers ...

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base frequency b

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