Background of Wireless Communication

Wireless Communication Technology

Wireless Networking and Mobile IP

Wireless Local Area Networks

Wireless Communication Systems

Wireless Communication SystemsWireless 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)

Transmittedsignal

Channel

Receivedsignal

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

BASESTATION

MTSO

Type of Cells

Satellite

MacrocellMicrocell

UrbanIn-Building

Picocell

Global

Suburban

Basic TerminalPDA 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

BSBS

MTSOPSTN

MTSO

BS

Taxila

LahoreInternet

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)

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AccessPoint

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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

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TV TransmitterWRAN

Base Station

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: WRAN Base Station

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Typical ~33kmMax. 100km

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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

adeel@uettaxila.edu.pk or adeel.akram@gmail.com Last date of submission of assignment is 14th April

2009.