Wireless Networks

Instructor: Hamid R. Rabiee

Spring 2012

2

Outlines

Wireless network components

Wireless technologies

Cellular Telephony (Wireless WANs)

Wireless WANs

Wireless MANs

Wireless LANs

Satellite Communication

Emerging Systems

WIRELESS NETWORK COMPONENTS

Basic Architecture consists of:

Radio Network components

Mobile Station (MS): Any Mobile Equipment

Base Station (BS): Responsible for relaying calls to and from mobile station.

Wire-line Transport Network

Mobile Switching Centre (MSC): A special switch configured for wireless

applications.

Databases

Home Location Register (HLR): A permanent record that contains entries of all

valid mobile stations

Visitor Location Register (VLR): A temporary record that is used to store and

retrieve information necessary to handle the calls of a visiting mobile user

3

Standardization of Wireless Networks

Wireless networks are standardized by IEEE.

Under 802 LAN MAN standards committee.

Application

Presentation

Session

Transport

Network

Data Link

Physical

ISO

OSI

7-layer

modelLogical Link Control

Medium Access (MAC)

Physical (PHY)

IEEE 802

standards

WIRELESS NETWORK COMPONENTS

5

Message (Frame) Types in a Wireless Network

RTS

CTS

ACK

PS-Poll

CF-End & CF-End

ACK

• Data

• Data+CF-ACK

• Data+CF-Poll

• Data+CF-ACK+CF-

Poll

• Null Function

• CF-ACK (nodata)

• CF-Poll (nodata)

• CF-ACK+CF+Poll

• Beacon

• Probe Request & Response

• Authentication

• De-authentication

• Association Request &

Response

• Re-association Request &

Response

• Disassociation

• Announcement Traffic

Indication Message (ATIM)

CONTROL DATA MANAGEMENT

Hidden terminals

A sends to B, C cannot receive A

C wants to send to B, C senses a “free” medium (Carrier Sense fails)

collision at B, A cannot receive the collision (Collision Detection fails)

A is “hidden” for C

Exposed terminals

B sends to A, C wants to send to another terminal (not A or B)

C senses carrier, finds medium in use and has to wait

A is outside the radio range of C, therefore waiting is not necessary

C is “exposed” to B

Hidden and Exposed Terminals

BA C

Multiple Access with Collision Avoidance (MACA)

MACA uses signaling packets for collision avoidance

RTS (request to send)

sender request the right to send from a receiver with a short RTS packet before it sends a data packet

CTS (clear to send)

receiver grants the right to send as soon as it is ready to receive

Signaling packets contain sender address

receiver address

packet size

Variants of this method are used in IEEE 802.11

MACA avoids the problem of hidden terminals

A and C want to

send to B

A sends RTS first

C waits after receiving

CTS from B

MACA avoids the problem of exposed terminals

B wants to send to A, C

to another terminal

now C does not have

to wait, as it cannot

receive CTS from A

MACA Solutions

A B C

RTS

CTSCTS

A B CRTS

CTS

RTS

Overview of Current Wireless Technologies

Cellular Telephony (Wireless

WANs)

GSM, GPRS, EDGE

3G: CDMA2000, EDVO

3G: UMTS

LTE (Long Term Evolution)

Wireless WANs

802.16e

802.20

Wireless MANs

802.16/WiMAX

Wireless LANs

Wi-Fi

Satellite Communication

Emerging Systems

Ad hoc wireless networks

Sensor networks

Distributed control networks

Cooperative networks

Cognitive radio

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Wireless Networks

A Wireless revolution is set to transform the world telecommunications

Industry.

Wireless networks are a class of networks that use infrared or radio

channels as the transmission medium.

Classification of growth of wireless networks:

First generation analog voice wireless networks.

Second generation digital voice/data networks are under development.

Third generation networks are designed to carry multimedia traffic.

11Digital Media Lab - Sharif University of Technology

Wireless LANs (WLAN)

Wireless LANs connect local computers (100m)

Breaks data into packet

Channel access is shared (random access)

Backbone Internet provides best-effort service

Poor performance in some applications (e.g. video)

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Wireless LAN Standards

13

Wireless Standards

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Cellular Wireless

Single hop wireless connectivity to the wired world

Space divided into cells

A base station is responsible to communicate with hosts in its cell

Mobile hosts can change cells while communicating

Hand-off occurs when a mobile host starts communicating via a new base

station

Multi-Hop Wireless

May need to traverse multiple links to reach destination

Mobility causes route changes

3G Cellular

Data is bursty, whereas voice is continuous

Require different access and routing strategies

3G

384 Kbps to Mbps

Based on CDMA

Packet-based switching for both voice and data

4G starts to come up

Mostly based on OFDMA

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LTE-Beyond 3G

Evolutionary path beyond 3G

– Mobile class targets 100 Mbps with high mobility

– Local area class targets 1 Gbps with low mobility

3GPP is currently developing evolutionary/ revolutionary systems beyond 3G

– 3GPP Long Term Evolution (LTE)

IEEE 802.16-based WiMAX is also evolving towards 4G through 802.16m

LTE Enabling Technologies

Two main technologies

1. Orthogonal Frequency Division Multiplexing (OFDM)

2. Multiple-Input Multiple-Output (MIMO)

OFDM

Multi-carrier transmission offers various advantages over traditional single carrier approaches

Highly scalable

Simplified equalizer design in the frequency domain, also in cases of large delay spread

High spectrum density

Simplifies the usage of MIMO

Good granularity to control user data rates

Robustness against timing errors

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FDM vs. OFDM

Multiple-Input Multiple-Output (MIMO)

Future wireless services require high data rates and high signal quality

The wireless resources such as the bandwidth are scarce

Wireless channels have a lot of impairments such as fading, shadowing, and multiuser interference

One solution is the use of Diversity achieving schemes

Spatial diversity is of special interest!

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Evolution of LTE-Advanced

Asymmetric transmission bandwidth

Layered OFDMA

Advanced Multi-cell Transmission/Reception Techniques

Enhanced Multi-antenna Transmission Techniques

Support of Larger Bandwidth in LTE-Advanced

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Evolution of Radio Access Technologies

LTE (3.9G) :

3GPP

LTE-Advanced :

3GPP

802.16d/e

802.16m

Evolution of Mobile Communication

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26

0

32

64

9.6

128

144

384

1G 2G 3G

Voice

Text Messaging

Video Streaming

Still

ImagingAudio Streaming

Da

ta T

ran

sm

iss

ion

Sp

ee

d -

k b

ps

Electronic

Newspaper

Remote

Medical

Service

(Medical

image)

Video

Conference

(High quality)

Telephone

(Voice)

Voice

Mail

E-MailFax

Electronic

Publishing Karaoke

Video

Conference

(Lower quality)

JPEG

Still Photos

Mobile

Radio

Video Surveillance,

Video Mail, Travel

Image

Audio

Voice-driven Web Pages

Streaming Audio

Data

Weather, Traffic, News,

Sports, Stock updates

Mobile TV

E-Commerce

Video on

Demand:

Sports, News

Weather

Future Generations

27

WiMAX

WiMAX - Worldwide interoperability for Microwave

Access It is a forum of product certification for interoperability

Standard: IEEE 802.16-2004

Frequency Spectrum: 10 - 66 GHz (LOS)

2 – 11 GHz (NLOS) – both licensed and unlicensed

Last mile technology (MAN/WAN) Support point-to-point communication

Support Quality of Service (QoS)

Backhaul technology for wireless LANs (802.11)

Up to 30 miles of range with cell radius: 4-6 miles

Shared data rate up to 75 Mbps.

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WiMAX V.S. Wi Fi

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Scalability

Channel bandwidths can be chosen by operator (e.g. for sectorization)

1.5 MHz to 20 MHz width channels. MAC designed for scalabilityindependent of channel bandwidth

MAC designed to support thousands of users.

Wide, fixed (20MHz) frequency channels

MAC designed to support 10’s of users

802.16802.11

Optimized for up to 50 Km

Designed to handle many users spread out over kilometres

Designed to tolerate greater multi-path delay spread (signal reflections) up to 10.0μ seconds

PHY and MAC designed with multi-mile range in mind

StandardMAC; Sectoring/MIMO/AMC for Rate/Range dynamic trade-off

Optimized for ~100 meters

No “near-far” compensation.

Designed to handle indoor multi-path(delay spread of 0.8μ seconds).

Optimization centersaround PHY and MAC layer for 100m range.

Range can be extended by cranking up the power – but MAC may be non-standard.

802.16802.11

Range

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Bit Rate: Relative Performance

802.16a ~5.0 bps/Hz

~2.7 bps/Hz54 Mbps20 MHz

63 Mbps10, 20 MHz;

1.75, 3.5, 7, 14 MHz;3, 6 MHz

802.11a

ChannelBandwidth

Maximumbps/Hz

MaximumData Rate

Optimized for outdoor NLOS performance

Standard supports mesh network topology

Standard supports advanced antenna techniques

Optimized for indoor performance

No mesh topology support within ratified standards

802.16802.11

Coverage

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Quality of Service (QoS)

Grant-request MAC

Designed to support Voice and Video from ground up

Supports differentiated service levels: e.g. T1 for business customers; best effort for residential.

TDD/FDD/HFDD – symmetric or asymmetric

Centrally-enforced QoS

Contention-based MAC (CSMA/CA) => no guaranteed QoS

Standard cannot currently guarantee latency for Voice, Video

Standard does not allow for differentiated levels of service on a per-user basis

TDD only – asymmetric

802.11e (proposed) QoS is prioritization only

802.16a802.11

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WiMAX vs Wi-Fi

Bluetooth

It is an always on, low power, short ranged radio link for communication

between mobile devices

Developed in 1994 by the Swedish company Ericsson to enable laptops

make calls over mobile phones

Also known as 802.15, it employs the 2.4 GHz unlicensed band, the same

as 802.11b wireless, but does not interfere with it

Provides data rates of up to 720 Kbps

Power output is around 1 milliwatt, compared to the average cell phone’s

500 milliwatt power output

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Bluetooth Applications

Major use in consumer electronics

Embedded in a whole slew of electronic products ranging from on PDAs,

cell phones and printers, to automobiles

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Widespread Communication Among People and

Devices

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Ad-Hoc Networks

Setting up of fixed access points and backbone infrastructure is not always

viable

Infrastructure may not be present in a disaster area or war zone

Infrastructure may not be practical for short-range radios; Bluetooth (range ~

10m)

Ad hoc networks:

Do not need backbone infrastructure support

Are easy to deploy

Useful when infrastructure is absent, destroyed or impractical

Ad-Hoc Networks

Peer to peer communications

No backbone architecture

Dynamic topology

useful when infrastructure not available, impractical, or

expensive

military applications, rescue, home networking

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Ad-Hoc Networks

Each node generates independent data.

Source-destination pairs are chosen at random.

Routing can be multi-hop.

Topology is dynamic

Can allocate resources dynamically (rate, power, BW, routes,…)

Design Issues (Ad-Hoc Networks)

Transmission, access and routing strategies for ad hoc

networks are generally ad hoc

Ad hoc networks provide a flexible network infrastructure

for many emerging applications

The capacity is unknown

Energy constraints impose interesting design tradeoffs for

communication and networking

40

Wireless Sensor Networks (WSN)

Wireless Sensor Networks are networks that consists of

sensors which are distributed in an ad hoc manner.

These sensors work with each other to sense some physical

phenomenon and then the information gathered is

processed to get relevant results.

Wireless sensor networks consists of protocols and

algorithms with self-organizing capabilities.

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Comparison (WSN) with Ad Hoc Networks

Wireless sensor networks mainly use broadcast

communication while ad hoc networks use point-to-point

communication.

Unlike ad hoc networks wireless sensor networks are

limited by sensors limited power, energy and

computational capability.

Sensor nodes may not have global ID because of the large

amount of overhead and large number of sensors.

42

Distributed Control over Wireless Links

Packet loss and/or delay impacts controller performance

Controller design should be robust to network faults

43

Cooperative Networks

Increase coverage area

Reduce number of blind spots

Reduce transmit power per node

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Challenges of Cooperation

Increase in transceiver complexity

More complex synchronization problems

More interference to be handled properly

Higher end-to-end delays

Real applications to justify the additional costs

45

Future of Wireless Technology

Mobile networks have already begun the migration to IP-based

networks

IP as the routing protocol

4G, New spectrum, and Emerging wireless air interfaces (very high

bandwidth 10 Mbps+)

It may entirely be IP-based and packet-switched

Increasing usage of wireless spectrum

On average, the number of channels has doubled every 30 months since

1985 (Cooper’s law)

46

Design Challenges

Wireless Channels are a difficult and a capacity limited broadcast

communications medium

Two main problems in media

Fading

Interference

Traffic patterns , user locations and network conditions are constantly

changing

Energy and delay constraints

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MOBILITY MANAGEMENT

8C32810.131-Cimini-7/98

• Location Management – identification and authentication – home and visitor location data bases (cellular) – discovery and registration (Mobile IP)

• Routing – fixed data bases (connection-oriented) – Mobile IP (connectionless)

• Hand off – transmissions may be delayed or dropped

impacts higher layer protocols – multi-homing inefficient use of resources

overhead and delay impact throughput suboptimal routing delay inefficiency and higher congestion

QUALITY OF SERVICE (QoS)

• Traffic dependent performance metrics required for type of data

transmitted

– bandwidth – latency – likelihood of packet (message) loss

• Categories– guaranteed – predictive – best effort

• Implications for high speed wireless data

– QoS performance generally based on switched, fiber-optic,

wired networks

– wireless links have high loss probability and high latency due

to link layer retransmission and unpredictable link bandwidths

– QoS guarantees and predictions are difficult to

make for wireless networks it is not clear

that the best effort is good enough for most applications

• The desire for mobility coupled with the demand

for Internet and multimedia services indicate a

bright future for wireless data.

• Current products and services have unsatisfactory

performance for high-speed wireless data applications.

• The inherent limitations of the radio channel can be

significantly reduced using signal processing and

architectural techniques, at the expense of cost

and complexity.

• The network-level design must take into account

the physical layer limitations of the wireless channel,

as well as the impact of user mobility.

8C32810.65-Cimini-7/98

SUMMARY

References

T. Rappaport, “wireless Communications, Principles and Practice”, 2nd

Edition, Prentice Hall .

D. Tse, D. Vaswanath , “ Fundamentals of wireless communication”,

Cambridge university press, 2005.

A. Goldsmith, “wireless communications”, Cambridge university press,

2005.

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Next Session

Wireless Multimedia Networking

Sharif University of Technology, Department of Computer Engineering, Multimedia Systems Course52

Appendix A

53

Ch2:54

WirelessNet

Tseng

802.11a: Specification enabling up to 54 Mb/s to be achieved in the 5 GHz

unlicensed radio band by utilizing OFDM

802.11b: Specification enabling up to 22 Mb/s to be achieved in the 2.4

GHz unlicensed radio band by utilizing DSSS

802.11c: Provides required information to ensure proper bridge operations, which is required when developing access points

802.11d: Covers additional regulatory domains, which is especially important for operation in the 5 GHz bands because the use of these

frequencies differ widely from one country to another

Task groups of 802.11

Ch2:55

WirelessNet

Tseng

802.11e: Covers issues of MAC enhancements for QoS, such as EDCF service differentiation and HCF

802.11f: Provides interoperability for users roaming from one access point to another of different vendor

802.11g: Specification enabling up to 54 Mb/s to be achieved in the 2.4 GHz unlicensed radio band

802.11h: Dynamic channel selection and transmission power control

802.11i: Specification for WLAN security to replace the weak Wired Equivalent Privacy (WEP)

802.11k: Radio resource measurement for 802.11 specifications so that a wireless network can be used more efficiently

Task groups of 802.11