Download 3.Introduction_on_Wireless_Communications

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Δρ. Χατζημίσιος Περικλής
Types of Networks

Coverage radius

(P) (L) (M) (W) Area Networks

Broadcast or Point-to-Point communication

Circuit or packet networks

Protocol (what is it?)

Protocol stack / Layers (OSI and TCP-IP)
Backbone and Access Networks
Terminal

Access
Network
Core
Network
Access Networks


Wired

PSTN, ISDN, xDSL,
Ethernet (ΙΕΕΕ 802.3),
CATV, Optics
Wireless

GSM/GPRS, UMTS, WLAN
(IEEE 802.11), WMANs
(IEEE 802.19), WPANs

Access
Network
Backbone networks




Optics
Internet
PDH/SONET/SDH
Microwave
Terminal
The wireless revolution

NO WIRES !
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Goals
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One Wireless standard for Home - Office - on the Move
Interoperability with wired networks
Security, QoS, roaming users
Usage:


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Entertainment (films, shows, gaming, music,..)
Information (Internet, ..)
E-commerce (secure home shopping,..)
Social contacts (email, voice, interest groups,..)
PC (documents, data, printing, scanner, server, ...)
Wireless Timeline

1991 - Specification of DECT (cordless phone)
 Digital European Cordless Telephone (today: Digital Enhanced Cordless
Telecommunications).
 1880-1900MHz, ~100-500m range, 120 duplex channels, 1.2Mbit/s data
transmission, voice encryption, authentication, up to several 10000
user/km2, used in more than 50 countries.

1992 - Start of GSM
 In Germany as D1 and D2, fully digital, 900MHz, 124 channels
 Automatic location, hand-over, cellular
 Roaming in Europe - now worldwide in more than 170 countries
 Services: data with 9.6kbit/s, FAX, voice, ...

1996 - HiperLAN (High Performance Radio Local Area Network)

ETSI, standardization of type 1: 5.15 - 5.30GHz, 23.5Mbit/s

Recommendations for type 2 and 3 (both 5GHz) and 4 (17GHz) as
wireless ATM-networks (up to 155Mbit/s)
…Wireless Timeline

1997 - Wireless LAN – IEEE 802.11:
 IEEE standard, 2.4 - 2.5GHz and infrared, 2Mbit/s
 Already many (proprietary) products available in the beginning

1998 - Specification of GSM successors:
 UMTS (Universal Mobile Telecommunication System) as European
proposals for IMT-2000
 Iridium: 66 satellites (+6 spare), 1.6GHz to the mobile phone

1999 - Standardization of additional wireless LANs:
 IEEE standard 802.11b, 2.4-2.5GHz, 11Mbit/s

Bluetooth for piconets, 2.4Ghz, <1Mbit/s
 Decision about IMT-2000
 Several “members” of a “family”: UMTS, cdma2000, DECT, …
 Start of WAP (Wireless Application Protocol) and i-mode
 Access to many (Internet) services via the mobile phone
…Wireless Timeline

2000 - GSM with higher data rates:
 HSCSD offers up to 57,6kbit/s
 First GPRS trials with up to 50 kbit/s (packet oriented!)
 GSM Enhancements for data transmission pick up (EDGE, GPRS,
HSCSD)
 UMTS auctions/beauty contests
 Hype followed by disillusionment (approx. 50 B$ payed in
Germany for 6 UMTS licenses!)

2001 - Start of 3G systems:
 Cdma2000 in Korea, UMTS in Europe, Foma (almost UMTS) in
Japan

2002 – Standardization of high-capacity wireless networks:
 IEEE 802.16 as Wireless MAN

2002 – today …… more wireless protocol standards are here!
… Why Not Wireless?

There are limitations and difficulties with
using wireless communications:

Wireless may be cheaper to deploy in some
cases, but it may have usage fees (cellular
service is still NOT cheap).

Issues of security (for example, WEP).

Incompatible standards that do not work well
with each other.
…Why Not Wireless?

Some mobile or wireless devices have hardware
or software limitations (small screen sizes, text
only displays, support for WML but not HTML,
etc.).

Wireless networks do not support the same data
rates as wired networks with the same reliability.
Wireless Link Characteristics
Differences from wired link ….


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Energy and computing-power limitations
Decreased signal strength
 Obstacles and hidden-terminal problem
 Collision detection hard or impossible
More noise
 Interference from other sources
 Multipath propagation  different delays
interferences between paths or (multipath)
fading
Lower signal/noise  Higher bit error rate
Wireless vs Mobile

Two aspects of mobility:
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

user mobility: users communicate (wireless) “anytime,
anywhere, with anyone”
device portability: devices can be connected anytime,
anywhere to the network
Wireless vs. mobile






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Examples
stationary computer
notebook in a hotel
wireless LANs in historic buildings
Personal Digital Assistant (PDA)
Applications ? Everywhere!

Vehicles
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Transmission of news, road condition, weather, music
personal communication using GSM
position via GPS
local ad-hoc network with vehicles close-by to prevent
accidents, guidance system, redundancy

Emergencies
 Replacement of a fixed infrastructure in case of
earthquakes, hurricanes (Katrina in USA), fire, etc
 Crisis, war, etc

Entertainment, education, sensor …
Bandwidth of access networks
 Dialup
~ 64 Kbps
 DSL/Cable
Cable
ADSL
VDSL
1 ~ 40 Mbps
1~10 Mbps(shared)
1~10 Mbps(dedicated)
20~50 Mbps or more (dedicated)
 Ethernet
100 Mbps ~ 10 Gbps (dedicated)
Bandwidth of access networks (2)
 Wireless LAN
802.11b
11 Mbps (shared)
802.11a
802.11g
802.16
54 Mbps (shared)
54 Mbps (shared)
50 Mbps (shared)
 Mobile Phone
2.5~3G
4G
0.1~2 Mbps (dedicated)
20~50 Mbps (dedicated)
Access network evolution

Development of fixed access technologies


Developments in ADSL and VDSL technology
Deployment of FTTx networks (FTTU - Fiber to the user)
More user data
rates than
wireless
technology
Increase in
per user
data rates
Ability to
offer high
data rate
services
NGN and
triple play
offers
Access network evolution

Developments in mobile access technologies

Evolved HSPA/HSPA+ enhancement (MIMO and 64 QAM modulation
 42 Mbps on single 5 MHz carrier)

Evolved Packet System (EPS) – QoS concepts

OFDM based technology - Long Term Evolution (LTE), mobile WiMAX
Increase in
per user data
rates
Mobile
Broadband
Increase
consumption of
multimedia
services
Issues in Wireless and Mobile Communications

Wireless Environment
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Power consumption and energy efficiency

Loss of data
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Restrictive regulations of frequencies
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Network and service convergence
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Cross-layer design
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Quality of Service (QoS)
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Cognitive radio networks / Software defined radios
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Economics

Security
The today (already old) of Wireless Communications
Wireless Wide Area Network
(WWAN)
• Metro/Geographical area
• “Always On” Services
• Ubiquitous public
connectivity with private
virtual networks
Mobility
Outside
Campus
Walk
Fixed/
Desktop
DECT
Bluetooth
0.1
1
HiperLAN2
802.11a
Walk
>3G
802.11b
Within
Campus
Fixed
CDMA2000 1X
GSM/GPRS
Vehicle
Wireless Local Area Network
(WLAN)
• Public or Private Site or
Campus
• Enterprise / premises
application voice & data
network extension
• Nomadic / “pull” services
• Non-licensed spectrum
10
LAN
100
Mbps
Mobile Wireless Technologies
●
Mobile wireless (Cellular Phones)
●
Fixed wireless (satellites, cordless phones)
●
Local wireless networks WLAN 802.11 (WiFi)
●
Personal wireless networks WPAN 802.15 (Bluetooth,
ZigBee)
●
More standards (e.g. WMAN 802.16 (WiMAX))
Wireless Technologies Overview

Core technologies (IEEE 802.1x family)

IEEE 802.16 (Wireless M(etropolitan) AN) – Under
development
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IEEE 802.15 (Wireless PAN – Bluetooth)

IEEE 802.11 (Wireless LAN)
MAN
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Facilitating technologies
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RF-Id
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IrDA
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Home-RF
LAN
PAN
Standardization

What is a standard?

Many standardization organizations exist:
–
–
–
–
–
–
–
–
–
–
–
IETF - Internet Engineering Task Force
IEEE - Institute of Electrical and Electronics Engineers
ANSI - American National Standards Institute
ITU-T - International Telecommunication Union Telecommunication Section (previous CCITT)
ISO - International Organization for Standardization
TIA - Telecommunications Industry Association
EIA - Electronics Industries Association
ATMF – Asynchronous Tranfer Mode Forum
OIF – Optical Inteρnetworking Forum
W3C – World Wide Web Consortium
TMF – Telecommunications Management Forum
Generations in Mobile Wireless Service (Cellular Phones)
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First Generation (1G)
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Second Generation (2G)
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Higher data rates than 2G
A bridge (for GSM) to 3G
Third Generation (3G)
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Primarily voice, some low-speed data (circuit switched)
Generation 2½ (2.5G)

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Mobile voice services
Seamless integration of voice and data
High data rates, full support for packet switched data
Fourth Generation (4G)
Evolution of Mobile Wireless (1)
Advance Mobile Phone Service (AMPS)
• FDMA
• 824-849 MHz (UL), 869-894 MHz (DL)
• U.S. (1983), So. America, Australia, China
European Total Access Communication System (E-TACS)
• FDMA
• 872-905 MHz (UL), 917-950 MHz (DL)
• Deployed throughout Europe
Evolution of Mobile Wireless (2)
Global System for Mobile communications (GSM)
• TDMA
• Different frequency bands for cellular and PCS
• Developed in 1990, expected >1B subscriber by end of 2003
IS-95
• CDMA
• 800/1900 MHz – Cellular/PCS
• U.S., Europe, Asia
Evolution of Mobile Wireless (3)
General Packet Radio Services (GPRS)
• Introduces packet switched data services for GSM
• Transmission rate up to 170 kbps
• Some support for QoS
Enhanced Data rates for GSM Evolution (EDGE)
• Circuit-switched voice (at up to 43.5 kbps/slot)
• Packet-switched data (at up to 59.2 kbps/slot)
• Can achieve on the order of 475 kbps on the downlink, by
combining multiple slots
Evolution of Mobile Wireless (4)
Universal Mobile Telecommunication Systems (UMTS)
• Wideband DS-CDMA
• Bandwidth-on-demand, up to 2 Mbps
• Supports handoff from GSM/GPRS
IS2000
• CDMA2000: Multicarrier DS-CDMA
• Bandwidth on demand (different flavors, up to a few Mbps)
• Supports handoff from/to IS-95
Some more IEEE standards for mobile communications

IEEE 802.16: Broadband Wireless Access: WMAN, WiMax
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IEEE 802.20: Mobile Broadband Wireless Access (MBWA)

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Licensed bands < 3.5 GHz, optimized for IP traffic
Peak rate > 1 Mbit/s per user
Different mobility classes up to 250 km/h and ranges up to 15 km
IEEE 802.21: Media Independent Handover Interoperability


Wireless distribution system for the last mile, alternative to DSL
75 Mbit/s up to 50 km LOS, up to 10 km NLOS; 2-66 GHz band
Initial standards without roaming or mobility support
802.16e adds mobility support, allows for roaming at 150 km/h
Standardize handover between different 802.x and/or non 802 networks
IEEE 802.22: Wireless Regional Area Networks (WRAN)

Radio-based PHY/MAC for use by license-exempt devices on a non-interfering basis
in spectrum that is allocated to the TV Broadcast Service
Elements of a wireless network
network
infrastructure
wireless hosts

laptop, PDA, IP phone

run applications

may be stationary (nonmobile) or mobile

wireless does not
always mean mobility
Elements of a wireless network
network
infrastructure
base station

typically connected to
wired network

relay - responsible for
sending packets
between wired
network and wireless
host(s) in its “area”
 e.g., cell towers
802.11 access points
Elements of a wireless network
network
infrastructure
wireless link

typically used to
connect mobile(s) to
base station

also used as backbone
link

multiple access
protocol coordinates
link access

various data rates,
transmission distance
Elements of a wireless network
network
infrastructure
infrastructure mode

base station connects
mobiles into wired
network

handoff: mobile
changes base station
providing connection
into wired network
Elements of a wireless network
Ad hoc mode

no base stations

nodes can only
transmit to other nodes
within link coverage

nodes organize
themselves into a
network: route among
themselves
Mobility issues …
Location dependent issues

Location dependent carrier sensing

Hidden nodes. A hidden node is one that is within the
range of the intended destination but out of range of the
sender

Exposed nodes. An exposed node is one that is within the
range of the sender but out of range of the destination

Capture. This event occurs when a receiver can correctly
receive a transmission from one of two (or more)
simultaneous transmissions, all within its range, because
the signal strength of the correctly received signal is much
higher than strength of the other signals
Hidden and Exposed Node Problems
Hidden node
• A is transmitting to B
• C is out of range of A and is unaware of the transmission
• If C transmits to B it will cause a collision at B
• B is transmitting to A
Exposed node
• C wants to transmit to D
• C senses transmission & declines even if its transmission will not cause
any collision at A
Capture Problem
A
dA
B
B
dCB
C
D
If A and C transmit
simultaneously to B then
the signal power of C,
received at B, is higher than
the one from A and there is
a good probability that C’s
signal can be correctly
decoded in the presence of
A’s transmission
This capture of C’s signal can improve protocol performance, but it results
in unfair sharing of the channel with preference given to nodes closer to
the receiver.
RTS-CTS Handshake*
RTS-CTS handshake used to resolve hidden terminal problem

RTS = Ready to send; transmitted by sender to inform receiver of available data

CTS = Clear to send; broadcasted by receiver to inform all neighbors that channel will be occupied

ACK = Acknowledgement; broadcasted by receiver to inform all neighbors that channel is free
again.
WLAN Standards
Wireless
LAN
2.4 GHz
5 GHz
802.11
802.11b
802.11g
HiSWANa
802.11a
HiperLAN2
(2 Mbps)
(11 Mbps)
(22-54 Mbps)
(54 Mbps)
(54 Mbps)
(54 Mbps)
HomeRF 2.0
Bluetooth
HomeRF 1.0
(10 Mbps)
(1 Mbps)
(2 Mbps)
802.11e
802.11f
802.11h
802.11i
(QoS)
(IAPP)
(TPC-DFS)
(Security)
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