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Chapter 1

INTRODUCTION

Based on the slides of Dr. Andrea Goldsmith, Stanford University and Dr. Dharma P. Agrawal, University of Cincinnati

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Course Objectives:

This course will cover the fundamental aspects of wireless networks, with emphasis on current and next-generation wireless networks. Various aspects of wireless networking will be covered including: fundamentals of cellular communication, mobile radio propagation, multiple access techniques, mobility support, channel allocation, Wireless PAN/LAN/MAN standards, mobile ad-hoc networks, wireless sensor networks, and routing in wireless and mobile networks. The goal of this course is to introduce the students to state-of-the-art wireless network protocols and architectures. We will introduce the students to wireless networking research and guide them to investigate novel ideas in the area via semester-long research projects. We will also look at industry trends and discuss some innovative ideas that have recently been developed. Some of the course material will be drawn from research papers, industry white papers and Internet RFCs.

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Wireless History

Radio invented in the 1880s by Marconi

Many sophisticated military radio systems were developed during and after WW2

Cellular has enjoyed exponential growth since 1988, with almost 1 billion users worldwide today

Ignited the recent wireless revolution3G roll-out disappointing in Europe, nascent in USAsia way ahead of the rest of the world

Much hype in 1990s, great failures around 20001G Wireless LANs/Iridium/Metricom

Ancient Systems: Smoke Signals, Carrier Pigeons, …

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Exciting Developments

Internet and laptop use exploding

2G/3G wireless LANs growing rapidly

Huge cell phone popularity worldwide

Emerging systems such as Bluetooth, UWB, Zigbee, and WiMAX opening new doors

Military and security wireless needs

Important interdisciplinary applications

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Future Wireless Networks

Wireless Internet accessNth generation CellularWireless Ad Hoc NetworksSensor Networks Wireless EntertainmentSmart Homes/SpacesAutomated HighwaysAll this and more…

Ubiquitous Communication Among People and Devices

•Hard Delay Constraints•Hard Energy Constraints

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Design Challenges

Wireless channels are a difficult and capacity-limited broadcast communications medium

Traffic patterns, user locations, and network conditions are constantly changing

Applications are heterogeneous with hard constraints that must be met by the network

Energy and delay constraints change design principles across all layers of the protocol stack

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Evolution of Current Systems

Wireless systems today2G Cellular: ~30-70 Kbps.WLANs: ~10 Mbps.

Next Generation3G Cellular: ~300 Kbps.WLANs: ~70 Mbps.

Technology Enhancements Hardware: Better batteries. Better circuits/processors.Link: Antennas, modulation, coding, adaptivity, DSP, BW.Network: Dynamic resource allocation. Mobility support.Application: Soft and adaptive QoS.

“Current Systems on Steroids”

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Future Generations

Rate

Mobility

2G

3G

4G802.11b WLAN

2G Cellular

Other Tradeoffs:Rate vs. CoverageRate vs. DelayRate vs. CostRate vs. Energy

Fundamental Design Breakthroughs Needed

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Multimedia Requirements

Voice VideoData

Delay

Packet Loss

BER

Data Rate

Traffic

<100ms - <100ms

<1% 0 <1%

10-3 10-6 10-6

8-32 Kbps 1-100 Mbps 1-20 Mbps

Continuous Bursty Continuous

One-size-fits-all protocols and design do not work well

Wired networks use this approach, with poor results

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Wireless Performance Gap

WIDE AREA CIRCUIT SWITCHING

User Bit-Rate (kbps)

14.4digitalcellular

28.8 modem

ISDN

ATM

9.6 modem

2.4 modem2.4 cellular

32 kbps PCS

9.6 cellular

wired- wireless bit-rate "gap"

1970 200019901980YEAR

LOCAL AREA PACKET SWITCHING

User Bit-Rate (kbps)

Ethernet

FDDI

ATM100 M Ethernet

Polling

Packet Radio

1st genWLAN

2nd genWLAN

wired- wirelessbit-rate "gap"

1970 200019901980.01

.1

1

10

100

1000

10,000

100,000

YEAR

.01

.1

1

10

100

1000

10,000

100,000

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Quality-of-Service (QoS)

QoS refers to the requirements associated with a given application, typically rate and delay requirements.

It is hard to make a one-size-fits all network that supports requirements of different applications.

Wired networks often use this approach with poor results, and they have much higher data rates and better reliability than wireless.

QoS for all applications requires a cross-layer design approach.

Crosslayer Design

Application

Network

Access

Link

Hardware

Delay ConstraintsRate Constraints

Energy ConstraintsChannel-State

Adapt across design layersReduce uncertainty through scheduling

Provide robustness via diversity

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Current Wireless Systems

Cellular Systems

Wireless LANs

Satellite Systems

Bluetooth

Ultrawideband radios

Zigbee radios

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Fundamentals of Cellular Systems

Illustration of a cell with a mobile station and a base station

BS

MS

Cell

Hexagonal cell area used in most models

Ideal cell area (2-10 km radius)

Alternative shape of a cell

MS

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FDMA (Frequency Division Multiple Access)

User 1

User 2

User n

…

Time

Frequency

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FDMA Bandwidth Structure

1 2 3 … nFrequency

Total bandwidth

4

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FDMA Channel Allocation

Frequency 1 User 1

Frequency 2 User 2

Frequency n User n

Base Station

… …

Mobile Stations

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TDMA (Time Division Multiple Access)

Use

r 1

Use

r 2

Use

r n

…

Time

Frequency

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TDMA Frame Structure

1 2 3 … nTime

Frame

4

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TDMA Frame Illustration for Multiple Users

Time 1

Time 2

Time n……

Base Station

User 1

User 2

User n

…

Mobile Stations

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CDMA (Code Division Multiple Access)

Use

r 1

Time

Frequency

Use

r 2

Use

r n

Code

...

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Transmitted and Received Signals in a CDMA System

Information bits

Code at transmitting end

Transmitted signal

Received signal

Code at receiving end

Decoded signal at the receiver

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Frequency Hopping

Frequency

f5

f4

f3

f2

f1

Frame Slot

Time

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Cellular System Infrastructure

BS

Service area (Zone)

Early wireless system: Large zone

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Cellular System: Small Zone

BS BS

BS BS BS

BS BS

Service area

Cellular Systems:Reuse channels to maximize capacity

Geographic region divided into cellsFrequencies/timeslots/codes reused at spatially-separated locations.Co-channel interference between same color cells.Base stations/MSCs coordinate handoff and control functionsShrinking cell size increases capacity, as well as networking burden

BASESTATION

MSC

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Home phone

PSTN

MSC

BSC …

BS

…

…

MS

…

BS MS

BSC

BS MS

…

BS MS

BSC

BS MS

…

BS MS

BSC

BS MS

…

BS MS

MSC

MS, BS, BSC, MSC, and PSTN

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Control and Traffic Channels

Base Station

Forward

(downlin

k) contro

l channel

Mobile Station

Reverse (

uplink) c

ontrol c

hannel

Forward

(downlin

k) traff

ic channel

Reverse (

uplink) tr

affic

channel

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Steps for a Call Setup from MS to BS

BS MS

1. Need to establish path

2. Frequency/time slot/code assigned

(FDMA/TDMA/CDMA)

3. Control Information Acknowledgement

4. Start communication

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Steps for a Call Setup from BS to MS

BS MS

2. Ready to establish a path

3. Use frequency/time slot/code

(FDMA/TDMA/CDMA)

4. Ready for communication

5. Start communication

1. Call for MS # pending

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A Simplified Wireless Communication System Representation

Information to be transmitted (Voice/Data)

Coding Modulator Transmitter

Information received

(Voice/Data)

Decoding Demodulator Receiver

Antenna

AntennaCarrier

Carrier

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Signaling

before, during, after connection/call

call setup and teardown (state)

call maintenance (state)

measurement, billing (state)

between:

end-user <-> network

end-user <-> end-user

network element <-> network element

signaling: exchange of messages among network entities to enable (provide service) to connection/call

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Telephone network: circuit-switched voice trunks (data plane)

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Telephone network: data and control planes

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SS7: telephone signaling network

Note: redundancy in SS7 elements

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Signaling System 7: telephone network signaling

out-of-band signaling: telephony signaling carried over separate network from telephone calls (data)

allows for signaling between any switches (not just directly-connected )

allows for signaling during call (not just before/after)

allows for higher-than-voice-data-rate signaling

security: in-band tone signaling helps phone phreaks; out of band signaling more secure

SS7 network: packet-switched

calls circuit-switched

lots of redundancy (for reliability) in signaling network links, elements

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Signaling System 7: telephone network

signaling between telephone network elements:

signaling switching point (SSP):

attach directly to end user

endpoints of SS7 network

signaling control point (SCP):“services” go heree.g., database functions

signaling transfer point (STP):packet-switches of SS7 networksend/receive/route signaling messages

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Example: signaling a POTS call

1. caller goes offhook, dials callee. SSP A decides to route call via SSP B. Assigns idle trunk A-B

A B

W

X

Y

2. SSP A formulates Initial Address Message (IAM), forwards to STP W

3. STP W forwards IAM to STP X

4. STP X forwards IAM SSP B

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Example: signaling a POTS call5. B determines it serves callee,

creates address completion message (ACM[A,B,trunk]), rings callee phone, sends ringing sound on trunk to A

A B

W

XY

Z7. SSP A receives ACM, connects subscriber line to allocated A-B trunk (caller hears ringing)

6. ACM routed to Z to Y to A

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Example: signaling a POTS call8. Callee goes off hook,

B creates, sends answer message to A (ANM[A,B,trunk])

A B

W

XY

Z

10. SSP A receives ANM, checks caller is connected in both directions to trunk. Call is connected!

9. ANM routed to A

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Example: signaling a 800 ca11

A B

WM

1. Caller dials 800 number, A recognizes 800 number, formulates translation query, send to STP W

800 number: logical phone numbertranslation to physical phone number needed, e.g., 1-800-CALL_ATT translates to 162-962-1943

2. STP W forwards request to M

3. M performs lookup, sends reply to A

A

Y

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Example: signaling a 800 call

A B

W

X

MZ

1. A begins signaling to set up call to number associated with 800 number

800 number: logical phone number

translation to physical phone number needed

A

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3G Cellular Design: Voice and DataData is bursty, whereas voice is continuous

Typically require different access and routing strategies

3G “widens the data pipe”:384 Kbps.Standard based on wideband CDMAPacket-based switching for both voice and data

3G cellular struggling in Europe and Asia

Evolution of existing systems (2.5G,2.6798G):GSM+EDGEIS-95(CDMA)+HDR100 Kbps may be enough

What is beyond 3G? The trillion dollar question

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Third Generation Cellular Systems and Services

IMT-2000 (International Mobile Telecommunications-2000):

- Fulfill one's dream of anywhere, anytime communications a reality.

Key Features of IMT-2000 include:

- High degree of commonality of design worldwide;

- Compatibility of services within IMT-2000 and with the fixed networks;

- High quality;

- Small terminal for worldwide use;

- Worldwide roaming capability;

- Capability for multimedia applications, and a wide range of services and terminals.

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Third Generation Cellular Systems and Services

Important Component of IMT-2000 is ability to provide high bearer rate capabilities:

- 2 Mbps for fixed environment;- 384 Kbps for indoor/outdoor and pedestrian environments;- 144 kbps for vehicular environment.

Standardization Work:- Release 1999 specifications- In processing

Scheduled Service:- Started in October 2001 in Japan (W-CDMA)

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Subscriber Growth

3G Subscribers

2G Digital only Subscribers

1G Analogue only Subscribers

Sub

scri

bers

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

Year

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Wireless Local Area Networks (WLANs)

WLANs connect “local” computers (100m range)

Breaks data into packets

Channel access is shared (random access)

Backbone Internet provides best-effort service

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

01011011

InternetAccessPoint

0101 1011

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Wireless LAN Standards

802.11b (Current Generation)Standard for 2.4GHz ISM band (80 MHz)Frequency hopped spread spectrum1.6-10 Mbps, 500 ft range

802.11a (Emerging Generation)Standard for 5GHz NII band (300 MHz)OFDM with time division20-70 Mbps, variable rangeSimilar to HiperLAN in Europe

802.11g (New Standard)Standard in 2.4 GHz and 5 GHz bandsOFDM Speeds up to 54 Mbps

In 200?,all WLAN cards will have all 3 standards

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Satellite Systems

Cover very large areas

Different orbit heightsGEOs (39000 Km) versus LEOs (2000 Km)

Optimized for one-way transmissionRadio (XM, DAB) and movie (SatTV) broadcasting

Most two-way systems struggling or bankruptExpensive alternative to terrestrial system

8C32810.61-Cimini-7/98

Bluetooth

Cable replacement RF technology (low cost)

Short range (10m, extendable to 100m)

2.4 GHz band (crowded)

1 Data (700 Kbps) and 3 voice channels

Widely supported by telecommunications, PC, and consumer electronics companies

Few applications beyond cable replacement

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Ultrawideband Radio (UWB)

UWB is an impulse radio: sends pulses of tens of picoseconds(10-12) to nanoseconds (10-9)

Duty cycle of only a fraction of a percent

A carrier is not necessarily needed

Uses a lot of bandwidth (GHz)

Low probability of detection

Excellent ranging capability

Multipath highly resolvable: good and badCan use OFDM to get around multipath problem.

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IEEE 802.15.4 / ZigBee Radios

Low-Rate Low-Cost WPAN

Data rates of 20, 40, 250 kbps

Star clusters or peer-to-peer operation

Support for low latency devices

CSMA-CA channel access

Very low power consumption

Frequency of operation in ISM bands

Focus is primarily on radio and access techniques

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Data rate

10 kbits/sec

100 kbits/sec1 Mbit/sec

10 Mbit/sec

100 Mbit/sec

0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz

802.11a

UWBZigBee

Bluetooth

ZigBee

802.11b

802.11g

3G

UWB

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Range

1 m

10 m

100 m

1 km

10 km

0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz

802.11a

UWB

ZigBee BluetoothZigBee

802.11b,g

3G

UWB

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Power Dissipation

1 mW

10 mW

100 mW

1 W

10 W

0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz

802.11a

UWB

UWBZigBee

Bluetooth

ZigBee

802.11bg3G

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Emerging Systems

Ad hoc wireless networks

Sensor networks

Distributed control networks

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Ad-Hoc Networks

Peer-to-peer communications.No backbone infrastructure.Routing can be multihop.

Topology is dynamic.

Fully connected with different link SIRs

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Design Issues

Ad-hoc networks provide a flexible network infrastructure for many emerging applications.

The capacity of such networks is generally unknown.

Transmission, access, and routing strategies for ad-hoc networks are generally ad-hoc.

Crosslayer design critical and very challenging.

Energy constraints impose interesting design tradeoffs for communication and networking.

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Sensor NetworksEnergy is the driving constraint

Nodes powered by nonrechargeable batteriesData flows to centralized location.Low per-node rates but up to 100,000 nodes.Data highly correlated in time and space.Nodes can cooperate in transmission, reception, compression, and signal processing.

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Spectrum Regulation

Spectral Allocation in US controlled by FCC (commercial) or OSM (defense)

FCC auctions spectral blocks for set

applications.

Some spectrum set aside for universal use

Worldwide spectrum controlled by ITU-RRegulation can stunt innovation, cause economic

disasters, and delay system rollout

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Standards

Interacting systems require standardization

Companies want their systems adopted as standard

Alternatively try for de-facto standards

Standards determined by TIA/CTIA in US

IEEE standards often adopted

Process fraught with inefficiencies and conflicts

Worldwide standards determined by ITU-TIn Europe, ETSI is equivalent of IEEE

Protocols are standardized by IETF as RFCs