wireless networks 03

8/8/2019 Wireless Networks 03

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Prachi Raut

1st Generation (Analog CellularSystem)

Analog cellular, cordless phones, paging systemsUse of analog modulation (FM modulation)Multiple access techniques used are FDMA/FDDIncludes systems like AMPS, TACS, JTACS, NMT, MCSand CNET


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2nd Generation (Digital CellularSystem)

Digital Cellular phones, PCS, WLANUse digital modulation techniquesTDMA/FDD and CDMA/FDD multiple access techniqueslike GFSK,GMSK,QPSK

digital cellular systems include GSM, IS-136 TDMA andCDMA

Generation 2.5: Packet Based DigitalCellular

Improved digital radio technology to increase datatransmission ratesNew packet based technology to increase the systemefficiency for data users

Digital cellular systems of Generation 2.5 include GPRS,EDGE, and CDMA2000, 1xRTT.


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AcronymsGSM : G lobal System for M obileGPRS : G lobal Packet R adio ServicesEDGE : E nhanced Data Rate for G SM E volutionCDMA : C ode Division M ultiple Access

3 rd Generation (Wideband DigitalCellular)

Increased voice quality, capacity of network and data rateof mobile data servicesUses wideband digital radio technologyWCDMA and OFDM


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4 th GenerationUltra Wideband Technology (UWB)data rates up to 100 MbpsIP based


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Infrastructure Topology

Ad-Hoc Topology


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Infrastructure Ad-Hoc

Scalability Easily scalable Difficult to scale

Flexibility Deployment is timeconsuming and expensive

Inherently flexible

Controllability Controlling implemented inBS or AP

Controlling is difficult

Routing Complexity Routing is easy Multi-hop peer-to-peernetworks implementation of

routing is difficult

Coverage More Limited

Reliability Less reliable since SinglePoint failure is possible

More

Store & forward delayand Media UsageEfficiency

Delay occurs since datatransmitted twice

No delay in single hop, moredelay in multi-hop networks


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Handoff Algorithms

Handoff AlgorithmsRSSRSS with ThresholdRSS with HysteresisRSS with Threshold and Hysteresis


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Bluetooth Technology


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Bluetooth TechnologyWireless LAN technologyConnects devices such as telephones, notebooks,computers, cameras, printers etc.Ad-hoc network

Types of network : Piconet and Scatternet

Piconet


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Scatternet

Bluetooth Stack


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Radio LayerEquivalent to physical layerBluetooth uses 2.4 GHz ISM band divided into 79 channels

of 1 MHz eachFHSS method in the physical layer to avoid interference

from other devices or other networksGFSK (FSK with Gaussian bandwidth filtering)

modulation

Baseband LayerEquivalent to MAC sub-layer in the LANsAccess method is TDD-TDMA

Single Secondary CommunicationMultiple Secondary Communication

Two link types are supportedSynchronous Connection-Oriented (SCO)Asynchronous Connectionless (ACL)

Frame format


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Frame Format


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Access code : 72-bit field contains synchronization bits and theidentifier of the primary to distinguish the frame of one piconet

from otherHeader : 54-bit field is a repeated 18-bit pattern. Each patternhas following subfields:

Address : 3-bit. Can define up to seven secondaries. If the addressis zero, it is used for broadcast communication from primary toall secondaries.Type : 4-bit. Defines the type of data coming from the upperlayers.F: This 1 bit subfield is for flow control. When set(1), it indicatesthat the device is unable to receive more frames. (Buffer is full).A: 1 bit. Used for acknowledgement in Stop-and-Wait ARQS: 1 bit .Holds a sequence number in Stop-and-Wait ARQHEC : 8 bit. Header error correction subfield is a checksum todetect errors in each 18-bit header section.

Payload : Can be 0 to 2740 bits long. Contains data or controlinformation coming from upper layers.

L2CAPLogical Link Control and Adaptation Protocol (L2CAP) isequivalent to the LLC sub-layer in LANsUsed for data exchange on a ACL link

L2CAP data packet format:16-bit length field defines the size of the data, in bytes,coming from the upper layersChannel ID (CID) defines a unique identifier for the virtualchannel created at this level


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Duties of L2CAP layer

Concepts that distinguish Bluetooth fromother wireless technologies


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AdvantagesReliable and Secure Transmissions

Functions even in noisy radio environments, ensuringaudible voice transmissions in severe conditionsProtects data by using error-correction methodsProvides a high transmission rateEncrypts and authenticates for privacy

Low-power architectureUnits move into lower-power modes when not activelyparticipating on the network Units consume less power during operation. For example,the Bluetooth radio consumes less than 3 percent of thepower that a mobile phone consumes

Global compatibility

DisadvantagesRangeSlower compared to other technologiesLimited no. of devices can be connectedInterference with wireless LANs


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Infrared TechnologyWireless technology where data is conveyed through IRradiationsIR is electromagnetic energy whose frequency is less thanred color of the visible light spectrumIR wireless is used for short and medium rangecommunications and controlLine-of-sight requiredIR wireless cannot pass through walls

IR is more private than RF. Hence more secure.

IR Technology StandardsIrDA-SIR (slow speed) infrared supporting data rates upto 115 KbpsIrDA-MIR (medium speed) infrared supporting data ratesup to 1.15 Mbps

IrDA-FIR (fast speed) infrared supporting data rates up to4 Mbps


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Advantages of IR TechnologyLow power requirements. Ideal for laptops, telephones,personal digital assistantsLow circuitry costsSimple circuitry

Higher securityPortable

Few international regulatory constraintsHigh noise immunity

Disadvantages of IRTechnology

Line of sightBlocked by common materialsShort rangeLight, weather sensitiveSpeed


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wireless networks 03

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