[PPT] - Wireless Networks and Protocols MAP-TELE Manuel P. Ricardo PowerPoint Presentation

SLIDE 1

Intro 1

Wireless Networks and Protocols

MAP-TELE Manuel P. Ricardo

Faculdade de Engenharia da Universidade do Porto

SLIDE 2

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

SLIDE 3

Intro 3

3

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

SLIDE 4

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

SLIDE 5

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

SLIDE 6

Intro 6

Bibliography



Slides



6

SLIDE 7

Intro 7

Grades

 Final Exam

50%

 Review of papers

20%

 Small project

30%

7

SLIDE 8

Intro 8

WNP – Wireless Networks

 About wireless communications systems  Addressed from a network and system perspectives

Common wireless communications systems

Cellular Apps Processor BT Media Processor

GPS

WLAN Wimax

DVB-H FM/XM

Mobile phone

SLIDE 9

Intro 9

 Wireless Networks characterised by

» wireless links » mobility of nodes » dynamic network topologies

Wired versus Wireless networks

T switch

AP

T

AP 1 2 1 2

Terminal Mobility

Computer Switch Computer AP

Wireless link

Wired link

Dynamic network topology

SLIDE 10

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

SLIDE 11

Intro 11

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

SLIDE 12

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 delivery

T switch

AP

T

AP 1 2 1 2

Terminal Mobility

SLIDE 13

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

T

AP 1 2 1 2

Terminal Mobility Channel 1 Channel 2

SLIDE 14

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

SLIDE 15

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

SLIDE 16

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

SLIDE 17

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

SLIDE 18

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

SLIDE 19

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

SLIDE 20

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

SLIDE 21

Intro 21

Evolution of Technologies

Rate

(bit/s)

Mobility

(km/s)

2G 3G 4G

802.11b WLAN 2G Cellular 802.11n Wimax/3G

SLIDE 22

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

SLIDE 23

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

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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

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Intro 25

Standards - Other

 ITU - Worldwide  ETSI - Europe  3GPP2 – American 3GPP

SLIDE 26

Intro 26

Homework

1.

Review slides

2.

Read from Schiller

»

Chap. 1

3.

Read from Goldsmith

»

Chap. 1

SLIDE 27

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?

SLIDE 28

Intro 28

Electromagnetic Wave

, / 10 * 3

8

s m c 

speed of light l - wavelength

d c t=t1 d=d1 t

T1/ f = Period

fc= 3 GHz  l  10 cm fc= 1 GHz  l  30 cm fc= 300 MHz  l  1m

SLIDE 29

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

SLIDE 30

Intro 30

Wireless Systems in Europe

In Portugal

ANACOM attributes the frequencies http://www.anacom.pt

FWA

Fixed Wireless Access

ISM

Industrial, Scientific and Medical

SLIDE 31

Intro 31

How does the power of a received signal depend on the distance and wavelength (l)?

SLIDE 32

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

SLIDE 33

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/4 l/2

SLIDE 34

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 lobe main

A P P G  

Ae – Antenna aperture depends on physical antenna characteristics

SLIDE 35

Intro 35

Received Power at Distance d - Pr(d)

 Power flow density Pd (W/m2)  Received Power at distance d, Pr(d)

Watt d G G P G d G P A P d P

r t t r t t e d r 2 2 2 2 2

) 4 ( 4 4 ) (  l  l    

2 2 2

4 4 m W d G P d EIRP P

t t d

   

SLIDE 36

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

SLIDE 37

Intro 37

Doppler Shift

 The received signal may have a Doppler shift of  Doppler frequency, fD

l   l   cos 2 2 t v d     

t fD     2

SLIDE 38

Intro 38

Suppose you are moving towards the transmitter. Will the perceived frequency of the carrier increase or decrease?

SLIDE 39

Intro 39

W, dBW, dBm, dB, Gain

dBm dBm dBW dBW W W W W

s r s r s r s r dB

P P P P P P P P Gain





         log . 10 log . 10 log . 10

W W dBW

r r r

P W P P log . 10 1 log . 10          

 

mW P r

W r dBm

P

1

log . 10 

s J W Time Energy Power P

W

r

1 1 1 , ,        

dBm dBm dBW dBW

r s r s dB dB dB

P P P P Gain Atenuation Loss







SLIDE 40

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

reflection scattering diffraction shadowing refraction

SLIDE 41

Intro 41

Real World Examples

SLIDE 42

Intro 42

Signal Propagation and Wireless Channels

Received Power can be modelled by 3 factors

– Path loss

Dissipation of radiated power; depends on the sender-receiver distance

– Shadowing

– caused by the obstacles between the transmitter and the receiver – attenuates the signal

– Multipath

constructive and destructive addition of multiple signal components

d=vt Pr /Pt

Very slow Slow Fast

Pr Pt d=vt v

SLIDE 43

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

SLIDE 44

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( . 20 4 log . 20 d G PG

l dB



         l

PGdB (dB) log(d)

Path loss

r s l

G G G 

SLIDE 45

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 )

t

h d 

c

d d 

SLIDE 46

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

SLIDE 47

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

SLIDE 48

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

l 10

0 

d

8 2 ,          g

g

d d K P P

s r

dBm dBm

s r dB

P P K d d



 

SLIDE 49

Intro 49

Shadowing

 Models attenuation introduced by obstructions  Random due to random number and type of obstructions 

SLIDE 50

Intro 50

Combined Path Loss and Shadowing

) , ( ~ , log 10 log 10 ) (

2 10 10 

   g N d d K dB P P

dB dB s r



      



10logK

Pr/Pt (dB) log(d)

Path loss Shadowing + Path loss

0 (d=d0)

SLIDE 51

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

SLIDE 52

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



1



SLIDE 53

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)

SLIDE 54

Intro 54

Multipath – Narrowband Channel

 Under Uniform Angle of arrival in [0,2]

» Autocorrelation is zero for d=0.4 l

SLIDE 55

Intro 55

Multipath - 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

SLIDE 56

Intro 56

Suppose you are the receiver. What information does this exponential distribution provide to you?

SLIDE 57

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




B T T

m n n m

 

SLIDE 58

Intro 58

Multipath + Shadowing + Path Loss

SLIDE 59

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)

SLIDE 60

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

SLIDE 61

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?

SLIDE 62

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)

SLIDE 63

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

SLIDE 64

Intro 64

Amplitude/Phase Modulator/Demodulator

Coherent Amplitude/Phase Demodulator Amplitude/Phase Modulator Communication System Model (no path loss)

SLIDE 65

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

SLIDE 66

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 P BER P

s b 2

log  

5 5 2

10 * 58 . 1 2 10 * 17 . 3 log



  M P BER

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

SLIDE 67

Intro 67

How does Ps depend on the SNR?

0,0 1,0 1,1 0,1

Ps

SLIDE 68

Intro 68

Digital Modulation – BER and SNR

, 1 , B T BT N E BT N E B N P SNR

s b b s s r

   

, N E N E

b b s s

  g g

SLIDE 69

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

SLIDE 70

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

SLIDE 71

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(2f0t)

x

cos(2fNt)

S

R bit/s R/N bit/s R/N bit/s

QAM Modulator QAM Modulator Serial To Parallel Converter



1



SLIDE 72

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

SLIDE 73

Intro 73

Most of the recent wireless communications tecnologies are adopting OFDM (e.g. WLAN, WIMAX, LTE). Why?

SLIDE 74

Intro 74

OFDM uses Discrete Fourier Transforms

 Discrete Fourier transforms given by  Circular convolution

SLIDE 75

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(2fct)

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]

SLIDE 76

Intro 76

FFT Implementation of OFDM - RX

Reverse structure at RX

x

cos(2fct) R bit/s

QAM demod FFT

Y[0] Y[N-1] y[0] y[N-1]

Remove cyclic prefix and Serial to Parallel Convert A/D LPF Parallel To Serial Convert

RX

x

cos(2fct)

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]

SLIDE 77

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

SLIDE 78

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

SLIDE 79

Intro 79

Direct Sequence Spread Spectrum – Immunity to Interferences

P

riginal signal

P f spread signal interferences f P f P Received signal f P received signal signal wideband interference narrowband interference f Signal after de-spreading

SLIDE 80

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

SLIDE 81

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

SLIDE 82

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)