Transcript Wireless Communication Systems

Wireless Communication Systems
Background of Wireless Communication
Wireless Communication Technology
Wireless Networking and Mobile IP
Wireless Local Area Networks
Wireless Personal Area Networks
Wireless Metropolitan Area Networks
Wireless Wide Area Networks
Wireless Communication Systems
Overview
 Communication Systems
 Wireless Communications
 Current Wireless Systems
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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)
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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
Carrier
Transmitted
signal
Transmitter
Information to
be transm itted
(Baseband signal)
Received
signal
Channel
Receiver
Recovery of
inform ation
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
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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
Global
Satellite
Suburban
Macrocell
Urban
Microcell
Basic Terminal
PDA Terminal
Audio/Visual Terminal
In-Building
Picocell
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
Taxila
BS
BS
Internet
MTSO
PSTN
Lahore
MTSO
BS
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
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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)
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Access
Point
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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)
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)
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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
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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
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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
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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
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Interference avoidance is worst-case design
 In practice, this may be too “soft” and overly limit throughput of secondary
users.
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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:
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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
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TV Transmitter
WRAN
Base Station
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Typical ~33km
Max. 100km
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: WRAN Base Station
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: CPE
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
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Assignment #3
 Answer the questions given on Slide No. 7
 Send your assignments in Word Document Format to
[email protected] or [email protected]
 Last date of submission of assignment is 14th April
2009.