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Wireless Communication Systems


2.5G increased data transmission ... (SatTV) broadcasting Most two-way systems struggling or bankrupt Expensive alternative to terrestrial system ... Flexible ... – PowerPoint PPT presentation

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Title: 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
  • 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
  • Bluetooth (Cable replacement)

Block diagram of a Communication Systems
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
  • Ignited the recent wireless revolution, 1980-2003

Current Wireless Systems
  • Cellular systems
  • Wireless LANs
  • Satellite Systems
  • Paging Systems
  • Bluetooth
  • Ultra Wide Band Systems
  • Zigbee

Wireless Systems Range Comparison
Cellular Systems Reuse channels to maximize
  • Geographic region divided into cells
  • Frequencies/timeslots/codes reused at
  • 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

Type of Cells
Type of Cells
  • Cell radii can be vary from 10s of meters in
    buildings to 100s of meters in the cities, up to
    several kms 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
The Wireless Revolution
  • Cellular is the fastest growing sector of
  • 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)
Access Point
  • 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)
  • 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

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

  • 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

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 users
    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

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
  • Diversified radio access (e.g. cellular, WLAN, ad
    hoc networks)
  • Adaptive multimode user terminals (cognitive
  • 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

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

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

Dynamic Spectrum Sharing
  • There are 3 ways to share the spectrum
  • 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)

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
  • 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
  • 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
  • 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
  • Channel is available at B (rx) if no primary tx
  • Channel is an opportunity if available at both A
    and B.

A Definition of Cognitive Radio (CR)
  • A cognitive radio is an unlicensed communication
  • that is aware of its environment
  • learns from its environment
  • adapts to the statistical variations of its
  • 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
  • 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

A little more about IEEE 802.22
  • IEEE 802.22 has the following interesting
  • Has a complex architecture to detect primary
  • 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-tu
  • OMNeT 4.0
  • http//www.omnest.com/webdemo/ide/demo.html

  • ?

Assignment 3
  • Answer the questions given on Slide No. 7
  • Send your assignments in Word Document Format to
    adeel_at_uettaxila.edu.pk or adeel.akram_at_gmail.com
  • Last date of submission of assignment is 14th
    April 2009.
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