Intro 1

Wireless Networks and Protocols

MAP-TELE

Manuel P. Ricardo

Faculdade de Engenharia da Universidade do Porto

Intro 2

WNP – Professors

Prof. Adriano Moreira

» Universidade do Minho

Prof. Manuel Ricardo

» Universidade do Porto

» mricardo@fe.up.pt

» http://www.fe.up.pt/~mricardo

Prof. Rui Aguiar

» Universidade de Aveiro

Intro 33

Syllabus

Introduction to Wireless Networks and Protocols

» What are Wireless networks

» History of wireless networks

» Standards and market issues

» Evolution and trends on wireless networking

Fundamentals of wireless communications

» Transmission

» Wireless data links and medium access control

» Networking

» Mobility concepts and management

Intro 4

Syllabus

Telecommunications systems

» GSM and GPRS

» UMTS

» TETRA

» Broadcast and satellite: DVB, DMB

IEEE wireless data networks

» WLAN: 802.11

» WMAN: 802.16

» WPAN: 802.15

Convergence and interoperability of wireless systems

» 4G wireless networks

» 3GPP and Mobile IPv6 approaches

» Integration of ad-hoc networks

4

Intro 5

Syllabus

Quality of service

» Characterization and models

» Case studies: 3GPP-QoS, IEEE-QoS, IP-QoS

Support for services and applications

» Web services components: XML and SOAP, UDDI and WSDL

» Services and applications platforms

5

Intro 6

Bibliography

Slides

Recommended papers

Chapters from multiple books» Wireless and Mobile Network Architectures, Yi-Bing Lin, Imrich Chlamtac Wiley, 2001

» Wireless IP and Building the Mobile Internet, Sudhir Dixit, Ramjee Prasad, Artech House, 2002.

» Andrea Goldsmith. Wireless communications. 2006. Cambridge University Press

» The 3G IP Multimedia Subsystem, Merging the Internet and the Cellular Worlds, Gonzalo Camarillo and Miguel a. Garcia-Martin,Wiley, Second Edition, 2005

» Ad-hoc Wireless Networks, Architectures and Protocols, C. Silva Murthy, B. Manoj, Prentice Hall, 2004

» Advanced Wireless Networks - 4G Technologies, S. Glisic, Wiley, 2006.

» Mobile Communications, Jochen Schiller, Second Edition, Addison-Wesley, 2003

» Wireless Communications - Principles and Practice, Theodore S. Rappaport, Second Edition, Prentice Hall, 2002

» Mobile IP Technology and Applications, Stefan Raab and Madhavi W. Chandra, Cisco Press, 2005

» GSM cellular radio telephony, Joachim Tisal, John Wiley & Sons, 1997

» Wireless Communications and Networks, William Stallings, Prentice Hall, 2002

» WCDMA for UMTS : radio acess for third generation mobile communications, Harri Holma, John Wiley & Sons, 2000

» UMTS networks : architecture, mobility and services, Heikki Kaaranen, et al, John Wiley & Sons, 2001

6

Intro 7

Grades

Final Exam - 50%

Review of papers - 20%

Small project - 30%

7

Intro 8

WNP – Wireless Networks

About wireless communications systems

Addressed from a network and system perspectives

Common wireless communications systems

Cellular

AppsProcessor

BT

MediaProcessor

GPS

WLAN

Wimax

DVB-H

FM/XM

Mobile phone

Intro 9

Wireless Networks characterised by

» wireless links

» mobility of nodes

» dynamic network topologies

Wired versus Wireless networks

T

switch

AP

TAP

1

2

1

2

Terminal

Mobility

Computer Switch

Computer AP

Wireless link

Wired link

Dynamic network topology

Intro 10

Wireless Link

Low powers received low SNR

large % of bits possibly received in error

SNR varies with time and positions

variable capacity (bit/s) or variable error ratio (BER)

Broadcast nature

» Information easily accessible by third parties security mechanisms

Pt

Pr

Intro 11

How to obtain low Bit Error Ratio in a Wireless Link?

Intro 12

Mobility

Mobility: characteristic of portable terminals and moving objects

Problems introduced by the mobile terminal

» determine its new location

» Find radio resources in new location

» determine the new path for data deliveryT

switch

AP

TAP

1

2

1

2

Terminal

Mobility

Intro 13

The terminal is receiving packets and, after moving to a new

location, the terminal is expected to continue receiving packets.

What procedure would you implement to manage the terminal

mobility?

T

switch

AP

TAP

1

2

1

2

Terminal

Mobility

Channel 1

Channel 2

Intro 14

Dynamic Network Topology

Nodes move

Capacity of a link (bit/s) varies along the time

Communication of a node interferes with a neighbor node

Shortest path between two nodes varies along the time

Capacity of the network becomes hard to characterize

Dynamic network topology

Intro 15

History – Past and Radio

Past

» Fire signals used to communicate the fall of Troy to Athens

» 2nd century B.C., sets of torches to transmit characters

» 1793, 3 part semaphores on top hills and towers

» 1837, electric telegraph

Radio transmission

» 1895, first radio transmission

» 1906, amplitude-modulated (AM) radio

» 1920, broadcast of radio news program

» 1928, TV broadcast trials

» 1933, frequency-modulated (FM) radio

» 1946, Swedish police had the first radio phones installed in cars

» 1950, mobile phone with direct dialling

Intro 16

History – Cell, 1st Generation

Cellular topology

» 1950´s, cellular network concept

power of transmitted signal falls with square of distance

2 users can operate on same frequency at separate locations

» 1971, Finland, ARP, first public commercial cellular, mobile network

1st Generation Analogue, Frequency Division Multiplexing

» 1982, NMT network covering Finland/Sweden/Norway/Denmark

» 1983, AMPS in America

» 1985, TACS, Total Access Communications Service, in Europe

Intro 17

History – Packet Radio

1971, ALOHANET packet radio

» computers communicate with central HUB

1980's ad-hoc, self-configurable packet networks

1985, Wireless LANs authorized to use ISM bands

1997, first WLAN standard

Intro 18

History – 2nd and 3rd Generation

2nd Generation

digital transmission and signalling; ISDN based

» 1982, specification GSM is started

» Early 1990´s

– Europe: GSM

– USA: D-AMPS, cdmaOne

– Japan: Personal Digital Cellular (PDC)

3G systems

aimed at multimedia communication

» 2001, Japan, first implementation of 3G systems

Intro 19

Type of Networks

WPAN - Wireless Personal Area Networks

» short distances among a private group of devices

WLAN - Wireless Local Area Networks

» areas such as an home, office or group of buildings

WMAN - Wireless Metropolitan Area Networks

» from several blocks of buildings to entire cities

PLMN - Public Land Mobile Networks

» regions and countries

Broadcast

» single direction, audio and video

Intro 20

Technologies Comparison

• U=bit/s/Hz/km2

– PLMN 10 to 40 U (based on UMTS)

– WMAN 25 to 50 U

– WLAN 100 to 500 U

Intro 21

Evolution of Technologies

Rate(bit/s)

Mobility(km/s)

2G

3G

4G

802.11b WLAN

2G Cellular

802.11n

Wimax/3G

Intro 22

Standard Organizations - IEEE

IEEE - Institute of Electrical and Electronics Engineers

802 Standards for Local /Metropolitan Area Network, wired and wireless

» Wireless LANs (802.11)

» Wireless Personal Area Networks (802.15),

» Broadband Wireless Metropolitan Area Networks (802.16)

» Mobile Broadband Wireless Access (802.20)

» Media Independent Handoff Working Group (802.21)

http://standards.ieee.org/getieee802/index.html

Layers 1 and 2 of the OSI communications model

Below the IP communications layer

Intro 23

Standards – 3GPP

Scope of 3GPP

» Specifications for the 3rd Generation mobile system

» Maintain GSM, GPRS and EDGE

» Specifications developed by Technical Specification Groups (TSG)

http://www.3gpp.org

Intro 24

Standards - IETF

http://www.ietf.org

Defines standards for the Internet, including

» TCP/IP

» key services

» routing protocols

» deployment of IP over technologies

Intro 25

Standards - Other

ITU - Worldwide

ETSI - Europe

3GPP2 – American 3GPP

Intro 26

Homework

1. Review slides

2. Read from Schiller

» Chap. 1

3. Read from Goldsmith

» Chap. 1

Intro 27

How does an EM wave propagate in a wireless channel?

What is an antenna and an antenna gain?

What is shadowing, reflection, refraction, scattering, and

diffraction?

What is path loss? How to model it?

What is the simple path loss model?

How to model shadowing?

What is multipath? How does it affect the power received? How

does it affect narrowband and wideband communications?

What is the maximum theoretical capacity of a wireless channel?

Intro 28

Electromagnetic Wave

,/10*3 8 smc speed of light

l - wavelength

d

c

t=t1

d=d1

t

T1/ f = Period

fc= 3 GHz l 10 cm

fc= 1 GHz l 30 cm

fc= 300 MHz l 1m

Intro 29

Frequencies for Radio Transmission

Frequency bands as defined by the ITU-R Radio Regulations

VLF Very Low Frequency

VLF Very Low Frequency

LF Low Frequency

MF Medium Frequency

HF High Frequency

VHF Very High Frequency

UHF Ultra High Frequency

SHF Super High Frequency

EHF Extremely High Frequency

fc= 3 GHz l 10 cm

fc= 1 GHz l 30 cm

fc= 300 MHz l 1m

Intro 30

Wireless Systems in Europe

• In PortugalANACOM attributes the frequencies

http://www.anacom.pt

• FWAFixed Wireless Access

• ISMIndustrial, Scientific and Medical

Intro 31

How does the power of a received signal depend on the

distance and wavelength (l)?

Intro 32

Antenna – The Isotropic Radiator

Antenna

couples wires to space, for electromagnetic (EM) wave transmission or reception

Radiation pattern

pattern of EM radiation around an antenna

Isotropic radiator

» equal radiation in 3 directions (x, y, z)

» theoretical reference antenna

Isotropic radiator

y

x

y

z

z

x

y

x

z

Intro 33

Antennas - Simple Dipoles

Real antennas are not isotropic radiators

Simple antenna dipoles

» Length l/2 Hertzian dipole

» Length l/4 on car roofs

Shape of antenna proportional to l

Radiation pattern of a simple Hertzian dipole

x

y

z

y

x

z

l/4l/2

Intro 34

Antenna Gain, EIRP

Antenna Gain

» maximum power in direction of the main lobe (Pmain_lobe), compared to

power of an isotropic radiator (Pt) transmitting the same average power

» baloon

Effective Isotropic Radiate Power (EIRP)

» EIRP= Pt Gt

» Maximum radiated power in the direction of maximum antenna gain

2

_ 4

l

e

t

lobemain A

P

PG

Ae – Antenna aperture

depends on physical antenna characteristics

Intro 35

Received Power at Distance d - Pr(d)

Power flow density Pd (W/m2)

Received Power at distance d, Pr(d)

Wattd

GGPG

d

GPAPdP rttrtt

edr 22

22

2 )4(44)(

l

l

222 44 mW

d

GP

d

EIRPP tt

d

Intro 36

Transmit and Receive Signal Models

Transmitted signal modeled as

The received signal

if s(t) is transmitted through a time-invariant channel c then

where

» c(t)=hl(t) is the equivalent lowpass impulse response of the channel

» Hl(f) is the equivalent lowpass frequency response of the channel

Intro 37

Doppler Shift

The received signal may have a Doppler shift of

Doppler frequency, fD

l

l

cos22

tvd

tfD 2

Intro 38

Suppose you are moving towards the transmitter.

Will the perceived frequency of the carrier increase or decrease?

Intro 39

W, dBW, dBm, dB, Gain

dBmdBmdBWdBWWW

W

W

srsrsr

s

r

dB PPPPPPP

PGain ---

log.10log.10log.10

W

W

dBW r

r

r PW

PP log.10

1log.10

mW

P

rWr

dBmP

1log.10

s

JW

Time

EnergyPowerP

Wr 1

11,,

dBmdBmdBWdBW rsrsdBdBdB PPPPGainAtenuationLoss ---

Intro 40

Signal Propagation – Key Concepts

Propagation often modeled as rays (light)

Line-of-Sight (LOS) – direct ray receiver gets from transmitter

Relevant concepts

» Shadowing, Reflection caused by objects much larger than the wavelength

» Refraction caused by different media densities

» Scattering caused by surfaces in the order of wavelengths

» Diffraction similar to scattering; deflection at the edges

reflectionscattering diffractionshadowing refraction

Intro 41

Real World Examples

Intro 42

Signal Propagation and Wireless Channels

Received Power can be modelled by 3 factors

– Path lossDissipation of radiated power; depends on the sender-receiver distance

– Shadowing– caused by the obstacles between the transmitter and the receiver

– attenuates the signal

– Multipathconstructive and destructive addition of multiple signal components

d=vt

Pr /PtVery slow

Slow

Fast

PrPt

d=vt

v

Intro 43

Path Loss Models

Free space path loss model

Too simple

Ray tracing models

Demand site-specific information

Empirical models

Do not generalize to other environments

Simplified model

Good for high-level analysis

Intro 44

Path Loss - Free Space (LOS) Model

Path loss (PL) for unobstructed LOS path

Power falls off

» Proportional to 1/d2

» Proportional to l2 (inversely proportional to f 2)

d=vt

)log(.204

log.20 dG

PG l

dB -

l

PGdB

(dB)

log(d)

Path lossrsl GGG

Intro 45

Path Loss – Two-Ray Model

One LOS ray + one ray reflected by ground

Ground ray cancels LOS path above critical distance dc=4hthr/l

Power falls off

» Proportional to d2 ( ht< d < dc )

» Proportional to d4 ( d>dc )

thd

cdd

Intro 46

Path – Loss Empirical Models

Okumura model

» Empirically based (site/freq specific); 150-1500 MHz, Tokyo

» Empirical plots

Hata model

Analytical approximation to Okumura model

Cost 231 Model

Extension Hata model to higher frequency (1.5 GHz < fc < 2 GHz )

Walfish/Bertoni

Extends Cost 231 to include diffraction from rooftops

Intro 47

Path Loss – Indoor Factors

Walls, floors, layout of rooms, location and type of objects

» Impact on the path loss

» The losses introduced must be added to the free space losses

Intro 48

Path Loss - Simplified Model

Used when path loss is dominated by reflections

K

» determined by measurement at

» or,

Path loss exponent g is determined empirically

l100 d

82,0

g

g

d

dKPP sr

dBmdBm srdB PPKdd - 0

Intro 49

Shadowing

Models attenuation introduced by obstructions

Random due to random number and type of obstructions

Intro 50

Combined Path Loss and Shadowing

),0(~

,log10log10)(

2

0

1010

g

N

d

dKdB

P

P

dB

dB

s

r -

-

10logK

Pr/Pt

(dB)

log(d)

Path loss

Shadowing + Path loss

0 (d=d0)

Intro 51

Outage Probability and Cell Coverage Area

Path loss model circular cells

Path loss + shadowing amoeba cells

tradeoff between coverage and interference

Outage probability

Probability received power below given minimum

Cell coverage area % of cell locations at desired power

» Increases as shadowing variance () decreases

» Large % indicates interference to other cells

Intro 52

Statistical Multipath Model

Multipath multiple rays

» multiple delays from transmitter to receiver

» time delay spread

Multipath channel has a time-varying gain

» caused by the transmitter / receiver movements

» location of reflectors which originate the multipaths

0

1

Intro 53

Multipath – Narrowband Channel

In a narrowband channel

low B low symbol rate (symbol/s) large time/symbol (1/B)

multipath components arrive in the time period of their symbol

Assume also u(t-i) u(t)

No spreading in time (no distortion)

Intro 54

Multipath – Narrowband Channel

Under Uniform Angle of arrival in [0,2]

» Autocorrelation is zero for d=0.4 l

Intro 55Multipath - Narrowband Channel –

Rayleigh Fading

If there is no Line-of-Sight (LOS) component

» Power received may be modeled by

» an exponential probability density function

» Pr – average received power (path loss + shadowing)

If there is LOS Power received given by a Ricean distribution

Intro 56

Suppose you are the receiver.

What information does this exponential distribution provide to you?

Intro 57

Multipath – Wideband Channel

Multipath components

» may arrive at the receiver within the time period of the next symbol

» causing Inter-Symbol Interference (ISI).

Techniques used to mitigate ISI

» multicarrier modulation

» spread spectrum

transmitted signal received signal

1

0 |,|max -- BTT mnnm

Intro 58

Multipath + Shadowing + Path Loss

Intro 59

Capacity of an Wireless Channel

Assuming Additive White Gaussion Noise (AWGN)

» Given by Shannon´s law

N0 – Noise power spectral density

Capacity in a fading channel (shadowing + multipath)

usually smaller than the capacity of an AWGN channel

(bit/s)

Intro 60

Homework

1. Review slides

» use them to guide you through the recommended books

2. Read from Goldsmith

» Chap. 2, Chap. 3 (sections 3.1, 3.2, 3.3), Chap. 4 (section 4.1)

3. Read from Schiller

» Chap. 2 (sections 2.1, 2.2, 2.3, 2,4)

4. Rappaport also provides an excellent description of these topics

» See Chap. 3 and Chap. 4

Intro 61

How to transmit bits in a carrier? What are the modulations

commonly used in wireless networks?

How does the BER depend on the modulation and SNR?

What is a code? What are its benefits for wireless

communications? Why is interleaving combined with codes?

What is multicarrier modulation? What is OFDM? Why is it so

important? How to implement it with DFTs?

What is spread spectrum? How does the RAKE receive work?

What is Software Defined Radio?

What are the main purposes of Cognitive Radio?

Intro 62

Digital Modulation/Demodulation

Modulation: maps information bits into an analogue signal (carrier)

Demodulation: determines the bit sequence based on received signal

Two categories of digital modulation

» Amplitude modulation - α(t) / Phase modulation - θ(t)

» Frequency modulation - f(t)

Modulated signal s(t)

Signal trasmited over time symbol i si(t)

Intro 63

Amplitude and Phase Modulation

sent over a time symbol interval

Amplitude/phase modulation can be:

» Pulse Amplitude Modulation (MPAM)

information coded in amplitude

» Phase Shift Keying (MPSK)

information coded in phase

» Quadrature Amplitude Modulation (MQAM)

information coded both in amplitude and phase

Intro 64

Amplitude/Phase Modulator/Demodulator

Coherent Amplitude/Phase DemodulatorAmplitude/Phase Modulator

Communication System Model (no path loss)

Intro 65

Differential Modulation

Bits associated to a symbol

depend on the bits transmitted over a previous symbol

Differential BPSK (DPSK)

» 0 no change phase

» 1 change phase by

Diferential 4PSK (DQPSK)

» 00 change phase by 0

» 01 change phase by /2

» 10 change phase by -/2

» 11 change phase by Differential PSK Demodulator

Intro 66

Ps

Estimating BER –

Nearest Neighbor Approximation

dmin – minimum distance between constellation points

Mdmin – number of constellation points at distance dmin

Example

Mdmin =2

M

PBERP s

b

2log

55

2

10*58.12

10*17.3

log

--

M

PBER s

A symbol error associated with

an adjacent decision region

corresponds to only one bit error

Ps – probability of a symbol being received in error

Ps

0,0

1,0

1,1

Ps

0,1

Intro 67

How does Ps depend on the SNR?

0,0

1,0

1,1

0,1

Ps

Intro 68

Digital Modulation – BER and SNR

,1

,000 B

TBTN

E

BTN

E

BN

PSNR s

b

b

s

sr

00

,N

E

N

E bb

ss gg

Intro 69

Coding

Coding enables bit errors to be either

detected or corrected by receiver

Coding gain, Cg

the amount of SNR that can be reduced for a given Pb

Coding rate, k/n

» Code generates n coded bits for every k uncoded bits

» If channel+modulation enable the transmission of R bit/s

» Information rate = R * k/n bit/s

Intro 70

Coding in Wireless Channels

Codes designed for AWGN channels » do not work well on fading channels

» cannot correct the long error bursts that may occur in fading

Codes for fading channels are usually » based on an AWGN channel code

» combined with interleaving

» objective spread error bursts over multiple codewords

Interleaving

Rayleigh

Intro 71

Multicarrier Modulation

Divides a bitstream into N low rate substreams

Sends substreams simultaneously over narrowband subchannels

Subchannel» has bandwidth BN = B/N

» provides a data rate RN R/N

» For N large, BN = B/N << 1/Tm

flat fading (narrowband like effects) on each sub-channel, no ISI

x

cos(2f0t)

x

cos(2fNt)

SR bit/s

R/N bit/s

R/N bit/s

QAM

Modulator

QAM

Modulator

Serial

To

Parallel

Converter

0

1

Intro 72

Overlapping Substreams

Separate subchannels could be used, but

» required passband bandwidth is N*BN= B

OFDM uses overlaps substreams

» Substream separation is B/N

» Total required bandwidth is B/2, for TN=1/BN

f0 fN-1

B/N

Intro 73

Most of the recent wireless communications tecnologies are

adopting OFDM (e.g. WLAN, WIMAX, LTE).

Why?

Intro 74

OFDM uses Discrete Fourier Transforms

Discrete Fourier transforms given by

Circular convolution

Intro 75

FFT Implementation of OFDM - TX

Use IFFT at TX to modulate symbols on each subcarrier

Cyclic prefix makes circular channel convolution

no interference between FFT blocks in RX processing

x

cos(2fct)

R bit/s QAM

Modulator

Serial

To

Parallel

Converter

IFFT

X[0] x[0]

x[N-1]

Add cyclic

prefix and

Parallel

To Serial

Convert

D/A

TX

X[N-1]

Intro 76

FFT Implementation of OFDM - RX

Reverse structure at RX

x

cos(2fct)

R bit/sQAM

demodFFT

Y[0]

Y[N-1]

y[0]

y[N-1]

Remove

cyclic

prefix and

Serial to

Parallel

Convert

A/DLPFParallel

To Serial

Convert

RX

x

cos(2fct)

R bit/sQAM

Modulator

Serial

To

Parallel

Converter

IFFT

X[0] x[0]

x[N-1]

Add cyclic

prefix and

Parallel

To Serial

Convert

D/A

TX

X[N-1]

Intro 77

Spread Spectrum

Spread spectrum techniques

» hide the information signal below the noise floor

» mitigate inter-symbol interferences

» combine multipath components

The spread spectrum techniques

» multiply the information signal by a spreading code

Intro 78

Spread Spectrum – Direct Sequence

Modulator

Information signal

(Rb bit/s)

Spread signal

(Rc = N Rb chip/s)

Pseudo-random sequence (Rc = N Rb chip/s)

De-modulador

Pseudo-random sequence

Spread signal Information signal

Intro 79Direct Sequence Spread Spectrum –

Immunity to Interferences

P

original signal

P

fspread signal

interferencesf

P

f

P

Received signalf

Preceived

signal

signal

wideband interference

narrowband interferencef

Signal after de-spreading

Intro 80

Software Defined Radio

Software Defined Radio

aims at implementing the radio functions in software

Digital Signal Processors being integrated with microcontroller

better integration of radio and communications functions

Intro 81

Cognitive Radio

Cognitive radio

» fills unused bands

» avoids interferences

» increases spectral efficiency

Paves the way to

» dynamic spectrum licensing

» secondary markets in spectrum usage

Intro 82

Homework

1. Review slides

1. Detailed information about these topics can found at the

Goldsmith’s book

» Chap. 5 (sections 5.1, 5.2, 5.3, 5.5)

» Chap. 6 (sections 6.1, 6.3)

» Chap. 7 (sections 7.1, 7.2)

» Chap. 8 (section 8.1)

» Chap. 9 (section 9.1)

» Chap. 12 (sections 12.1, 12.2, 12.4)

» Chap. 13 (sections 13.1, 13.2, 13.3)