Wireless Communication Systems

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21 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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Background of Wireless Communication

Wireless Communication Technology

Wireless Networking and Mobile IP

Wireless Local Area Networks

Wireless Communication Systems

Wireless Communication Systems

Wireless Personal Area Networks

Wireless Metropolitan Area Networks

Wireless Wide Area Networks

Overview


Communication Systems


Wireless Communications


Current Wireless Systems



Wireless LANs


Paging Systems


Cellular systems


Satellite Systems


Bluetooth


Design challenges


4G Systems


Cognitive Radios


Communication Systems



Provide electronic exchange of multimedia Data, Voice, Video, Music,
Email, Web pages, etc.


Communication Systems of today are used for Radio, TV broadcasting,
Data and Public Switched Telephone Network (voice, fax, modem)


Cellular Phones


Computer networks (LANs, WANs, and the Internet)


Satellite systems (pagers, voice/data, movie broadcasts)


Bluetooth (Cable replacement)

Block diagram of a Communication Systems

Transmitter
Carrier
Information to
be transmitted
(Baseband signal)
Transmitted
signal
Channel
Received
signal
Receiver
Recovery of
information
Wireless Communications




Multimedia wireless Communications at any Time and
Anywhere


Brief history


Ancient Systems: Smoke Signals, Carrier Pigeons


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 more than 2 billion users worldwide today


Ignited the recent wireless revolution, 1980
-
2003

Current Wireless Systems


Cellular systems


Wireless LANs


Satellite Systems


Paging Systems


Bluetooth


Ultra Wide Band Systems


Zigbee


Cellular Systems:
Reuse channels to maximize capacity


Geographic region divided into cells


Frequencies/timeslots/codes reused at spatially
-
separated


locations.


Co
-
channel interference between same color cells.


Base stations/MTSOs coordinate handoff and control functions


Shrinking cell size increases capacity, as well as networking burden

BASE

STATION

MTSO

Type of Cells

Satellite

Macrocell

Microcell

Urban

In
-
Building

Picocell

Global

Suburban

Basic Terminal

PDA Terminal

Audio/Visual Terminal

Type of Cells


Cell radii can be vary from 10’s of meters in buildings to
100’s of meters in the cities, up to several km’s in the
countryside.


Macrocells, provide overall area coverage


Microcells, focus on slow moving subscribers moving
between buildings.


Picocells, focus on the halls of a theater, or exhibition
centre.








Cellular Phone Networks

BS

BS

MTSO

PSTN

MTSO

BS

Taxila

Lahore

Internet

The Wireless Revolution

Cellular is the fastest growing sector of communication

industry (exponential growth since 1982, with over 2 billion users worldwide
today)



Three generations of wireless



First Generation (1G): Analog 25 or 30 KHz FM, voice only, mostly
vehicular communication


Second Generation (2G): Narrowband TDMA and CDMA, voice and
low bit
-
rate data, portable units.


2.5G increased data transmission capabilities


Third Generation (3G): Wideband TDMA and CDMA, voice and high
bit
-
rate data, portable units



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

Access

Point

0101

1011

Wireless LAN Standards


802.11b
(Current Generation)


Standard for 2.4GHz ISM band (80 MHz)


Frequency hopped spread spectrum


1.6
-
10 Mbps, 500 ft range



802.11a
(Emerging Generation)


Standard for 5GHz NII band (300 MHz)


OFDM with time division


20
-
70 Mbps, variable range


Similar to HiperLAN in Europe


802.11g
(New Standard)


Standard in 2.4 GHz and 5 GHz bands


OFDM


Speeds up to 54 Mbps

Since 2008,

all WLAN

Cards have

all 3

standards

Satellite Systems


Cover very large areas


Different orbit heights


GEOs (39000 Km)


LEOs (2000 Km)



Optimized for one
-
way transmission


Radio (XM, DAB) and movie (SatTV)
broadcasting


Most two
-
way systems struggling or bankrupt


Expensive alternative to terrestrial system


A few ambitious systems on the horizon

Paging Systems


Broad coverage for short messaging


Message broadcast from all base stations


Simple terminals


Optimized for 1
-
way transmission


Answer
-
back hard


Overtaken by cellular

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


Wireless Comm. Design Challenges



Hardware Design


Precise components


Small, lightweight, low power


Cheap


High frequency operations


System Design


Converting and transferring information


High data rates


Robust to noise and interference


Supports many users


Network Design


Connectivity and high speed


Energy and delay constrains

4G Wireless Communication Systems


Evolution to 4G wireless communication systems


4G: New paradigm shift from technology centric to
user centric


4G: Integrated All
-
IP Architecture


Efficient spectrum sharing concept in 4G wireless
networks


Evolution towards to 4G

B. Walke, IEEE 802 System: Protocol, Multihop mesh/relaying, Performance and Spectrum Coexistence, John Wiley and
Sons, January 2007

The growth of number of mobile subscribers

M.A. Uusitalo, “ The Wireless World Research Forum
-

Global Vision of Wireless World,” IWCT2005, Oulu, Finland, June 2005.

Why mobile subscribers are increasing ?


Movement from the
Personal Computing Age

(one computing
device per person) to
Ubiquitous Computing Age

(several
platforms at user’s disposal whenever and wherever needed)


The convergence of media


Numerous demands of multimedia applications arose from
huge number of personal wireless devices, which are small,
cheap, more convenient and more powerful.

Road map of wireless communication systems

L.M. Gavrilovska and V. M. Atanasovski, “Interoperability in future wireless communications system: A roadmap to 4G,”
Microwave Review, June 2007

Key Concept of 4G


Global wireless communication system


All
-
IP based seamless connectivity


4G is foreseen as an integrator of all existing and future
wireless and wired networks, both terrestrial and satellite.


4G is not a new system design from scratch but 4G is a
concept of
integration and convergence

4G systems will deliver


All digital all
-
IP communication


End
-
to
-
end QoS guarantees


Efficient spectrum sharing and dynamic spectrum allocation


Diversified radio access (e.g. cellular, WLAN, ad hoc
networks)


Adaptive multimode user terminals (cognitive approach)


Seamless and transparent user roaming with fully support of
various handovers.


4G systems will deliver


Support for huge multimedia traffic


Integration of navigation and communication system in order
to offer a variety of location/situation/context aware service


Increased level of security


Increased personalization


Quickly deployable user services (anytime, anywhere, and
from any device) in cost effective manner


All
-
IP based 4G network

L.M. Gavrilovska and V. M. Atanasovski, “Interoperability in future wireless communications system: A roadmap to 4G,”
Microwave Review, June 2007

Research Challenge in Future Wireless
Communication Systems

Crucial issues needed to be investigated are


User terminals issue


Mobile Services issue


Access network issue


Communication issue


Spectrum efficiency and channel capacity


Provisioning of ubiquitous coverage


Cost
-
effective solution for high data rates


Increased bandwidth usability


Efficient spectrum allocation by using cognitive
approach

The Spectrum and Its Management


Most governments consider the electromagnetic
spectrum to be a public resource.


It is usually allocated by a governmental organization
(FCC, CRTC, ETSI, ARIB, etc.) that defines the
spectrum management policy
.


Most of the spectrum is currently
licensed

to users to
further the public good, e.g., radio, television, etc.


Examples of licensing


TV channels, radio,


Cellular service,


Unlicensed “free for all”, subject to some constraints
(e.g., 900 Mhz cordless phones, 2.4 Ghz wireless
WiFi).


Common belief
: we are running out of usable radio
frequencies. Is that true?

Current Spectrum Management Policy


















Fixed allocation


Rigid requirements on how to use


Little sharing

Spectrum Usage in Space, Time, & Frequency

Actual measurements

by the FCC have shown that many licensed spectrum
bands are unused most of the time. In NYC, spectrum occupancy is only 13%
between 30 MHZ


3.0 GHz.

Spectrum Usage


Good quality spectrum is
under
-
utilized.


Hence the problem is more a
spectrum
management policy

issue than a physical scarcity.


The problem is begging for a solution based on
dynamic
spectrum management or access. There
are many possibilities.


Cognitive Radio is a synonym of dynamic spectrum
access.


Dynamic Spectrum Sharing


There are 3 ways to share the spectrum dynamically


Dynamic Exclusive Access
: extension to the current licensing
policy. Flexible licensing. An improvement but not “fast”
enough.


Open Sharing Model
: horizontal sharing, a generalization of
the unlicensed band policy. All users/nodes have equal
regulatory status. Based on the huge success of WiFi and other
technologies working in the ISM band.


Hierarchical Access Model
: vertical sharing. All users do not
have equal regulatory status (i.e.,
primary users

and
secondary users
). Secondary users can opportunistically access
the spectrum as long as it does not affect the primary users’
performance. Allows for prioritized spectrum sharing provided
no
harmful interference

caused to primary users.

Harmful Interference


What is harmful interference?


Ultimately depends on the application.



There are generally two broad approaches to avoid harmful
interference:


Interference avoidance (spectrum overlay)


Interference control (spectrum underlay)


Of course they can be combined



(overlay) (underlay)

Spectrum Overlay: Interference Avoidance


Spectrum overlay approach impose restrictions on when and where the secondary
users may transmit. Secondary users have to identify and exploit the spectrum
holes defined in space, time, and frequency.


Compatible with the existing spectrum allocation

legacy systems can continue to
operate without being affected by the secondary users.


Regulatory policies define basic etiquettes for secondary users to ensure
compatibility with legacy systems.


In principle, interference avoidance involves only two steps:


Look for holes in spectrum/time.


Transmit only in those bands at those times.


Sounds a lot easier than it is.


Detection of spectral holes is difficult due to the large range of
potential modulation/coding schemes: careful measurements
based on actual primary signal statistics and signatures is
needed.


Hidden terminal problem: we have to protect the primary
receivers (but where are they?).


Fast detection time needed.

How to Use frequency gaps?


Suppose that after some sophisticated signal processing, we determine that
spectrum occupancy is:








How do we use these (non
-
contiguous) holes?


OFDM based approach solves the problem naturally.


OFDM has the advantages that


It is low complexity (FFT and IFFT based)


Can be naturally adjusted to fit almost any configuration of
spectral holes.


Is growing in popularity (802.11a, 802.16, 802.22)

Spectrum Underlay: Interference Control


Interference avoidance is worst
-
case design


In practice, this may be too “soft” and overly limit throughput of secondary
users.


Spectrum underlay approach constraints the transmission power of secondary users so that
they operate below the interference temperature limit of primary users (i.e., the receivers).


Interference temperature introduces new opportunities at a cost:







Additional difficulties


Secondary user needs to measure/know temp. at primary
receivers
.


Secondary measurements


Feedback from primary


Treats interference as noise.

Spectrum Opportunity










Channel is available at A (tx) if no primary rx
nearby
.


Channel is available at B (rx) if no primary tx
nearby
.


Channel is an opportunity if available at both A and B.

A Definition of Cognitive Radio (CR)


A cognitive radio is an unlicensed communication system


that is aware of its environment


learns from its environment


adapts to the statistical variations of its environment


and uses these to


achieve reliable communication and spectral efficiency
by employing spectral holes or opportunities and does
not generate harmful interference to the incumbents.




Cognitive Radios will be complex devices.

Some Examples


Two examples of star networks with cognitive
features:




IEEE 802.16h (WiMAX) provides extensions to
support unlicensed co
-
existence


IEEE 802.22 is an explicit cognitive WRAN that
will exploit vacant TV broadcast bands







TV Transmitter

WRAN

Base Station


: CPE







: WRAN Base Station



Typical ~33km

Max. 100km











A little more about IEEE 802.22


IEEE 802.22 has the following interesting characteristics:




Has a complex architecture to detect primary users.




Follows the spectrum overlay approach (avoids
interfering with primary users altogether)







Is OFDM based

Spectrum sharing of cognitive radios

L.M. Gavrilovska and V. M. Atanasovski, “Interoperability in future wireless communications system: A roadmap to 4G,”
Microwave Review, June 2007

Emerging paradigm of cognitive network

L.M. Gavrilovska and V. M. Atanasovski, “Interoperability in future wireless communications system: A roadmap to 4G,”
Microwave Review, June 2007

IEEE 802.21 framework of Multimedia Independent
Handover
-

Network

Network controlled handover

L.M. Gavrilovska and V. M. Atanasovski, “Interoperability in future wireless communications system: A roadmap to 4G,”
Microwave Review, June 2007

IEEE 802.21 framework of Multimedia Independent
Handover
-

User

L.M. Gavrilovska and V. M. Atanasovski, “Interoperability in future wireless communications system: A roadmap to 4G,”
Microwave Review, June 2007

4G Summary


The 4G paradigm is already on the road.


4G wireless system provide high speed, high
capacity, low cost per bits.


4G is IP
-
based services for broadband multimedia.


Concept of 4G is all about an integrated, global
network based on open system approach.


4G wireless systems utilize spectrum efficiently
via cognitive approach, and optimize the choice of
radio access technology.


Cognitive radio and networking will become the
key in reconfigurable wireless system.

Network Simulation Platforms


NS
-
3


http://www.nsnam.org/tutorials/simutools08/ns
-
3
-
tutorial
-
slides.ppt



OMNeT++ 4.0


http://www.omnest.com/webdemo/ide/demo.html


Q&A


?

Assignment #3


Answer the questions given on Slide No. 7


Send your assignments in Word Document Format to
adeel@uettaxila.edu.pk

or
adeel.akram@gmail.com



Last date of submission of assignment is 14
th

April
2009.