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IT 2402 Mobile Communication ByDr Gnanasekaran Thangavel

UNIT II WIRELESS NETWORKS

Wireless LAN(WLAN) IEEE 802.11 Standards Architecture Services Mobile Ad hoc Networks-Wi Fi and WiMAX Wireless Local Loop(WLL)

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IEEE 802.11Wireless LAN TechnologyThe Institute of Electrical and Electronics Engineers developed the 802.11 standard to improve compatibility of products for Wireless Local Area Networks (WLANs). The standard has similarities with the 802.3 standard for ethernet wired LANs. The 802.11 series are the most well-known Wireless LAN standards. 3

Name, DescriptionIEEE 802.1, Bridging (networking) and Network ManagementIEEE 802.2, LLCIEEE 802.3, EthernetIEEE 802.4, Token busIEEE 802.5, Defines the MAC layer for a Token RingIEEE 802.6, MANs (DQDB)IEEE 802.7, Broadband LAN using Coaxial CableIEEE 802.8, Fiber Optic TAGIEEE 802.9, Integrated Services LAN (ISLAN or iso Ethernet)IEEE 802.10, Interoperable LAN SecurityIEEE 802.11 a/b/g/n, Wireless LAN (WLAN) & Mesh (Wi-Fi)IEEE 802.12, 100BaseVGIEEE 802.13, UnusedIEEE 802.14, Cable modemsIEEE 802.15, Wireless PANIEEE 802.15.1, Bluetooth certification4

IEEE 802.15.2, IEEE 802.15 and IEEE 802.11 coexistenceIEEE 802.15.3, High-Rate wireless PANIEEE 802.15.4, Low-Rate wireless PAN IEEE 802.15.5, Mesh networking for WPANIEEE 802.15.6, Body area networkIEEE 802.16, Broadband Wireless Access (WiMAX certification)IEEE 802.16.1, Local Multipoint Distribution ServiceIEEE 802.17, Resilient packet ringIEEE 802.18, Radio Regulatory TAGIEEE 802.19, Coexistence TAGIEEE 802.20, Mobile Broadband Wireless AccessIEEE 802.21, Media Independent HandoffIEEE 802.22, Wireless Regional Area NetworkIEEE 802.23, Emergency Services Working GroupIEEE 802.24, Smart Grid TAGIEEE 802.25, Omni-Range Area Network5

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Wireless LAN ApplicationsLAN ExtensionCross-building interconnectNomadic Access Ad hoc networking8

LAN ExtensionWireless LAN linked into a wired LAN on same premisesWired LAN BackboneSupport servers and stationary workstations Wireless LANStations in large open areasManufacturing plants, stock exchange trading floors, and warehouses9

Cross-Building InterconnectConnect LANs in nearby buildingsWired or wireless LANsPoint-to-point wireless link is usedDevices connected are typically bridges or routers10

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Nomadic AccessWireless link between LAN hub and mobile data terminal equipped with antennaLaptop computer or notepad computerUses:Transfer data from portable computer to office serverExtended environment such as campus12

WDS-Wireless Distribution System

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Ad Hoc NetworkingTemporary peer-to-peer network set up to meet immediate needExample:Group of employees with laptops convene for a meeting; employees link computers in a temporary network for duration of meeting14

Infrastructure-based wireless network15

Infrastructure-based wireless network16

Ad hoc network17

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Wireless LAN RequirementsThroughputNumber of nodesConnection to backbone LANService areaBattery power consumptionTransmission robustness and securityCollocated network operationLicense-free operationHandoff/roamingDynamic configuration19

Wireless LAN CategoriesInfrared (IR) LANsSpread spectrum LANsNarrowband microwave20

Strengths of Infrared Over Microwave RadioSpectrum for infrared virtually unlimitedPossibility of high data ratesInfrared spectrum unregulatedEquipment inexpensive and simpleReflected by light-colored objectsCeiling reflection for entire room coverageDoesnt penetrate wallsMore easily secured against eavesdroppingLess interference between different rooms21

Drawbacks of Infrared MediumIndoor environments experience infrared background radiationSunlight and indoor lightingAmbient radiation appears as noise in an infrared receiverTransmitters of higher power requiredLimited by concerns of eye safety and excessive power consumptionLimits range22

IR Data Transmission TechniquesDirected Beam InfraredOminidirectionalDiffused23

Directed Beam InfraredUsed to create point-to-point linksRange depends on emitted power and degree of focusingFocused IR data link can have range of kilometersCross-building interconnect between bridges or routers24

Omini directionalSingle base station within line of sight of all other stations on LANStation typically mounted on ceilingBase station acts as a multiport repeaterCeiling transmitter broadcasts signal received by IR transceiversIR transceivers transmit with directional beam aimed at ceiling base unit25

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DiffusedAll IR transmitters focused and aimed at a point on diffusely reflecting ceilingIR radiation strikes ceiling Reradiated omnidirectionally Picked up by all receivers27

Spread Spectrum LAN ConfigurationMultiple-cell arrangement (Figure 13.2)Within a cell, either peer-to-peer or hubPeer-to-peer topologyNo hubAccess controlled with MAC algorithmCSMAAppropriate for ad hoc LANs28

Multiple-cell Wireless LAN

UM-User module CM- Control Module29

Spread Spectrum LAN ConfigurationHub topologyMounted on the ceiling and connected to backboneMay control accessMay act as multiport repeaterAutomatic handoff of mobile stationsStations in cell either:Transmit to / receive from hub onlyBroadcast using Omni directional antenna30

RF: Spread Spectrum, no licensing required. Resistance to interferenceBand: 915-Mhz, 2.4 GHz (worldwide ISM), 5.2 GHz

Direct sequence spread spectrum (DSSS)broaden the signaling band by artificially increasing the modulation rate using a spreading code. 2M or 10M.

Frequency hopping spread spectrum (FHSS)hop from narrow band to narrow band within a wide band, using each narrow band for a specific time period.31

Narrowband Microwave LANsUse of a microwave radio frequency band for signal transmissionRelatively narrow bandwidthLicensedUnlicensed32

Licensed Narrowband RFLicensed within specific geographic areas to avoid potential interferenceMotorola - 600 licenses in 18-GHz range Covers all metropolitan areasCan assure that independent LANs in nearby locations dont interfereEncrypted transmissions prevent eavesdropping33

Unlicensed Narrowband RFRadioLAN introduced narrowband wireless LAN in 1995Uses unlicensed ISM spectrumUsed at low power (0.5 watts or less)Operates at 10 Mbps in the 5.8-GHz bandRange = 50 m to 100 m34

MAC Layer: Hidden Terminal Problem Node B can communicate with A and C bothA and C cannot hear each otherWhen A transmits to B, C cannot detect the transmission using the carrier sense mechanismIf C transmits, collision will occur at node BABC

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MCAC (Multiple Access with Collision Avoidance)When node A wants to send a packet to node B, node A first sends a Request-to-Send (RTS) to BOn receiving RTS, node B responds by sending Clear-to-Send (CTS), provided node B is able to receive the packetWhen a node (such as C) overhears a CTS, it keeps quiet for the duration of the transferTransfer duration is included in RTS and CTS bothABC

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ReliabilityWireless links are prone to errors. High packet loss rate detrimental to transport-layer performance.

Mechanisms needed to reduce packet loss rate experienced by upper layers

When node B receives a data packet from node A, node B sends an Acknowledgement (Ack).

If node A fails to receive an Ack, it will retransmit the packetABC

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Protocol Architecture38

IEEE 802 Protocol Layers

39Please Do Not forget To feed Steve's Pet Alligator

Protocol ArchitectureFunctions of physical layer:Encoding/decoding of signalsPreamble generation/removal (for synchronization)Bit transmission/receptionIncludes specification of the transmission mediumTwo sub layers physical layerPhysical layer convergence procedure(PLCP) Mapping MAC layer protocol data units(MPDU)Physical medium dependent sub layer(PMD)Defines methods of transmitting and receiving 40

Protocol ArchitectureFunctions of medium access control (MAC) layer:On transmission, assemble data into a frame with address and error detection fieldsOn reception, disassemble frame and perform address recognition and error detectionGovern access to the LAN transmission mediumFunctions of logical link control (LLC) Layer:Provide an interface to higher layers and perform flow and error control41

Separation of LLC and MACThe logic required to manage access to a shared-access medium not found in traditional layer 2 data link controlFor the same LLC, several MAC options may be provided42

MAC Frame FormatMAC controlContains Mac protocol informationDestination MAC addressDestination physical attachment pointSource MAC addressSource physical attachment pointCRCCyclic redundancy check43

MAC Frame Format

MAC Frame FieldsFrame Control frame type, control informationDuration/connection ID channel allocation timeAddresses context dependant, types include source and destinationSequence control numbering and reassemblyFrame body MSDU or fragment of MSDUFrame check sequence 32-bit CRC

Frame Control FieldsProtocol version 802.11 versionType control, management, or dataSubtype identifies function of frameTo DS 1 if destined for DSFrom DS 1 if leaving DSMore fragments 1 if fragments followRetry 1 if retransmission of previous frame

Frame Control FieldsPower management 1 if transmitting station is in sleep modeMore data Indicates that station has more data to sendWEP 1 if wired equivalent protocol is implementedOrder 1 if any data frame is sent using the Strictly Ordered service

Control Frame SubtypesPower save poll (PS-Poll)Request to send (RTS)Clear to send (CTS)AcknowledgmentContention-free (CF)-endCF-end + CF-ack

Data Frame SubtypesData-carrying framesDataData + CF-AckData + CF-PollData + CF-Ack + CF-PollOther subtypes (dont carry user data)Null FunctionCF-AckCF-PollCF-Ack + CF-Poll

Management Frame SubtypesAssociation requestAssociation responseReassociation requestReassociation responseProbe requestProbe responseBeacon

Logical Link ControlCharacteristics of LLC not shared by other control protocols:Must support multiaccess, shared-medium nature of the linkRelieved of some details of link access by MAC layer51

LLC ServicesUnacknowledged connectionless serviceNo flow- and error-control mechanismsData delivery not guaranteedConnection-mode serviceLogical connection set up between two usersFlow- and error-control providedAcknowledged connectionless serviceCross between previous twoDatagrams acknowledgedNo prior logical setup52

Differences between LLC and HDLCLLC uses asynchronous balanced mode of operation of HDLC (High-Level Data Link Control) (type 2 operation)LLC supports unacknowledged connectionless service (type 1 operation) LLC supports acknowledged connectionless service (type 3 operation)LLC permits multiplexing by the use of LLC service access points (LSAPs)53

IEEE 802.11 ArchitectureDistribution system (DS)Access point (AP)Basic service set (BSS) Stations competing for access to shared wireless mediumIsolated or connected to backbone DS through APExtended service set (ESS) Two or more basic service sets interconnected by DS54

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IEEE 802.11 Services

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Distribution of Messages Within a DSDistribution serviceUsed to exchange MAC frames from station in one BSS to station in another BSSIntegration serviceTransfer of data between station on IEEE 802.11 LAN and station on integrated IEEE 802.x LAN58

Transition Types Based On MobilityNo transitionStationary or moves only within BSSBSS transitionStation moving from one BSS to another BSS in same ESSESS transitionStation moving from BSS in one ESS to BSS within another ESS59

Association-Related ServicesAssociationEstablishes initial association between station and APReassociationEnables transfer of association from one AP to another, allowing station to move from one BSS to anotherDisassociationAssociation termination notice from station or AP60

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Access and Privacy ServicesAuthenticationEstablishes identity of stations to each otherDeauthenticationInvoked when existing authentication is terminatedPrivacyPrevents message contents from being read by unintended recipient61

IEEE 802.11 Medium Access ControlMAC layer covers three functional areas:Reliable data deliveryAccess controlSecurity62

Reliable Data DeliveryMore efficient to deal with errors at the MAC level than higher layer (such as TCP)Frame exchange protocolSource station transmits dataDestination responds with acknowledgment (ACK)If source doesnt receive ACK, it retransmits frameFour frame exchangeSource issues request to send (RTS)Destination responds with clear to send (CTS)Source transmits dataDestination responds with ACK63

Access Control

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Medium Access Control Logic

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Inter frame Space (IFS) ValuesShort IFS (SIFS)Shortest IFSUsed for immediate response actionsPoint coordination function IFS (PIFS)Midlength IFSUsed by centralized controller in PCF scheme when using pollsDistributed coordination function IFS (DIFS)Longest IFSUsed as minimum delay of asynchronous frames contending for access66

IFS UsageSIFSAcknowledgment (ACK)Clear to send (CTS)Poll responsePIFSUsed by centralized controller in issuing pollsTakes precedence over normal contention trafficDIFSUsed for all ordinary asynchronous traffic67

Management Frame SubtypesAnnouncement traffic indication messageDissociationAuthenticationDeauthentication68

Wired Equivalent Privacy

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AuthenticationOpen system authenticationExchange of identities, no security benefitsShared Key authenticationShared Key assures authentication70

Physical Media Defined by Original 802.11 StandardDirect-sequence spread spectrumOperating in 2.4 GHz ISM bandData rates of 1 and 2 MbpsFrequency-hopping spread spectrumOperating in 2.4 GHz ISM bandData rates of 1 and 2 MbpsInfrared1 and 2 MbpsWavelength between 850 and 950 nm71

IEEE 802.11a and IEEE 802.11bIEEE 802.11aMakes use of 5-GHz bandProvides rates of 6, 9 , 12, 18, 24, 36, 48, 54 MbpsUses orthogonal frequency division multiplexing (OFDM)Subcarrier modulated using BPSK, QPSK, 16-QAM or 64-QAMIEEE 802.11bProvides data rates of 5.5 and 11 MbpsComplementary code keying (CCK) modulation scheme72

Mobile Ad Hoc Networks

What is a MANET (Mobile Ad Hoc Networks)?Formed by wireless hosts which may be mobileNo pre-existing infrastructureRoutes between nodes may potentially contain multiple hopsNodes act as routers to forward packets for each otherNode mobility may cause the routes change

ABC D

ABC D

Advantages: low-cost, flexibilityEase & Speed of deploymentDecreased dependence on infrastructureApplicationsMilitary environmentssoldiers, tanks, planesCivilian environmentsvehicle networksconferences / stadiumsoutside activitiesEmergency operationssearch-and-rescue / policing and fire fightingWhy MANET?

CollaborationCollaborations are necessary to maintain a MANET and its functionality.How to collaborate effectively and efficiently?How to motivate/enforce nodes to collaborate?

Dynamic topologyNodes mobilityInterference in wireless communicationsChallenges

Proactive protocolsDetermine routes independent of traffic patternTraditional link-state and distance-vector routing protocols are proactiveExamples: DSDV (Dynamic sequenced distance-vector)OLSR (Optimized Link State Routing)

Reactive protocolsMaintain routes only if neededExamples: DSR (Dynamic source routing)AODV (on-demand distance vector)

Hybrid protocolsExample: Zone Routing Protocol (intra-zone: proactive; inter-zone: on-demand)Routing Protocols: Overview

Latency of route discoveryProactive protocols may have lower latency since routes are maintained at all timesReactive protocols may have higher latency because a route from X to Y may be found only when X attempts to send to Y

Overhead of route discovery/maintenanceReactive protocols may have lower overhead since routes are determined only if neededProactive protocols can (but not necessarily) result in higher overhead due to continuous route updating

Which approach achieves a better trade-off depends on the traffic and mobility patternsRouting Protocols: Tradeoff

J. Broch, D. Johnson, and D. Maltz, The dynamic source routing protocol for mobile ad hoc networks, Internet-Draft Version 03, IETF, October 1999.

When node S wants to send a packet to node D, but does not know a route to D, node S initiates a routing processRuns in three phasesRoute Discovery Route Reply Path EstablishmentRoute DiscoverySource node S floods Route Request (RREQ) Each node appends own identifier when forwarding RREQDynamic Source Routing

Route Discovery in DSRBASEFHJDCGIK

ZY

Represents a node that has received RREQ for D from SM

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BASEFHJDCGIK

Represents transmission of RREQZY

Broadcast transmission

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[S][X,Y] Represents list of identifiers appended to RREQRoute Discovery in DSR

BASEFHJDCGIK

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[S,E][S,C]Route Discovery in DSR

BASEFHJDCGIK

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[S,C,G,K][S,E,F,J]Route Discovery in DSR

Route Reply in DSRDestination D on receiving the first RREQ, sends a Route Reply (RREP)

RREP is sent on a route obtained by reversing the route appended to received RREQ

RREP includes the route from S to D on which RREQ was received by node D

BASEFHJDCGIK

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RREP [S,E,F,J,D]

Represents RREP control messageRoute Reply in DSR

Node S on receiving RREP, caches the route included in the RREP

When node S sends a data packet to D, the entire route is included in the packet headerHence the name source routing

Intermediate nodes use the source route included in a packet to determine to whom a packet should be forwardedRoute Reply in DSR

BASEFHJDCGIK

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DATA [S,E,F,J,D]Packet header size grows with route lengthData Delivery in DSR

Some Other Routing ProtocolsLocation information aided protocolsPower-aware protocolsOthers e.g., considering the stability of topology

Location-Aided Routing (LAR)Y. Ko and N. Vaidya, Location-aided routing (LAR) in mobile ad hoc networks, MobiCom'98.

Exploits location information to limit scope of route request floodLocation information may be obtained using GPSExpected Zone is determined as a region that is expected to hold the current location of the destinationExpected region determined based on potentially old location information, and knowledge of the destinations speedRoute requests limited to a Request Zone that contains the Expected Zone and location of the sender node

B. Karp, and H. Kung, Greedy Perimeter Stateless Routing for Wireless Networks, MobiCom 2000.

Power-Aware RoutingModification to DSR to make it power aware (for simplicity, assume no route caching):Route Requests aggregate the weights of all traversed linksDestination responds with a Route Reply to a Route Request ifit is the first RREQ with a given (current) sequence number, orits weight is smaller than all other RREQs received with the current sequence number

Geography Adaptive FidelityEach node associates itself with a square in a virtual gridNode in each grid square coordinate to determine who will sleep and how long[Y. Xu, et al. Geography Adaptive Fidelity in Routing, Mobicom2001]

Grid head

Research in Other LayersTransport layerA survey: A. Hanbali, E. Altman, P. Nain, A Survey of TCP over Mobile Ad Hoc Networks (2004).Application layerData managemente.g., B. Xu, A. Ouksel, and O. Wolfson, "Opportunistic Resource Exchange in Inter-vehicle Ad Hoc Networks," MDM, 2004. Distributed algorithmsclock synchronizationmutual exclusionleader electionByzantine agreement

Security in Mobile Ad Hoc Networks

ProblemsHosts may misbehave or try to compromise security at all layers of the protocol stack

Transport layer: securing end-to-end communicationNeed to know keys to be used for secure communicationMay want to anonymize the communication

Network layer: misbehaving hosts may create many hazardsMay disrupt route discovery and maintenance:Force use of poor routes (e.g., long routes)Delay, drop, corrupt, misroute packetsMay degrade performance by making good routeslook bad

MAC layer: misbehaving nodes may not cooperateDisobey protocol specifications for selfish gainsDenial-of-service attacks

Security in MANET: AgendaKey managementSecuring communicationsDealing with MAC and Network layer misbehaviors

Key ManagementChallengesIn pure ad hoc networks, access to infrastructure cannot be assumedNetwork may also become partitioned

SolutionsDistributed public key infrastructureSelf-organized key management Distributed key certificationTESLAOthers

Self-Organized Public Key Management [Capkun03]Nodes form a Certificate Grapheach vertex represents a public keyan edge from Ku to Kw exists if there is a certificate signed by the private key of node u that binds Kw to the identity of some node w.

KuKw

(w,Kw)Pr Ku

Four steps of the management scheme

Step 1: Each node creates its own private/public keys.Each node acts independentlySelf-Organized Public Key Management [Capkun03]

Step 2: When a node u believes that key Kw belongs to node w, node u issues a public-key certificate in which Kw is bound to w by the signature of u

u may believe this because u and w may have talked on a dedicated channel previouslyEach node also issues a self-signed certificate for its own key

Step 3: Nodes periodically exchange certificates with other nodes they encounterMobility allows faster dissemination of certificates through the networkSelf-Organized Public Key Management [Capkun03]

Step 4: Each node forms a certificate graph using the certificates known to that node

Authentication: When a node u wants to verify the authenticity of the public key Kv of node v, u tries to find a directed graph from Ku to Kv in the certificate graph. If such a path is found, the key is authentic.

Self-Organized Public Key Management [Capkun03]

Misbehaving hosts may issue incorrect certificates

If there are mismatching certificates, indicates presence of a misbehaving host (unless one of the mismatching certificate has expired)Mismatching certificates may bind same public key for two different nodes, or same node to two different keys

To resolve the mismatch, a confidence level may be calculated for each certificate chain that verifies each of the mismatching certificatesChoose the certificate that can be verified with high confidence else ignore both certificatesSelf-Organized Public Key Management [Capkun03]

With the previously discussed mechanisms for key distribution, it is possible to authenticate the assignment of a public key to a node

This key can then be used for secure communicationThe public key can be used to set up a symmetric key between a given node pair as wellTESLA provides a mechanism for broadcast authentication when a single source must broadcast packets to multiple receiversSecure Communication

Sometimes security requirement may include anonymity

Availability of an authentic key is not enough to prevent traffic analysis

We may want to hide the source or the destination of a packet, or simply the amount of traffic between a given pair of nodesSecure Communication

Wireless channel

Access PointAB

Nodes are required to follow Medium Access Control (MAC) rulesMisbehaving nodes may violate MAC rulesWireless channel

Access PointCD

MAC Layer Misbehavior

Causing collisions with other hosts RTS or CTSImpatient transmitterSmaller backoff intervalsShorter Inter-frame SpacingsSome Possible Misbehavior

Diagnose node misbehaviorCatch misbehaving nodes

Discourage misbehaviorPunish misbehaving nodes

Details will be discussed later in this courseSolutions

A node agrees to join a route(for instance, by forwarding route request in DSR) but fails to forward packets correctly

A node may do so to conserve energy, or to launch a denial-of-service attack, due to failure of some sort, or because of overload

SolutionsOpt I: Detect the attacks tolerate themOpt II: Avoid some attacksNetwork Layer Misbehavior: Drop/Corrupt/Misroute

Wireless Local LoopWired technologies responding to need for reliable, high-speed access by residential, business, and government subscribersISDN, xDSL, cable modemsIncreasing interest shown in competing wireless technologies for subscriber accessWireless local loop (WLL)Narrowband offers a replacement for existing telephony servicesBroadband provides high-speed two-way voice and data service108

WLL Configuration

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Advantages of WLL over Wired ApproachCost wireless systems are less expensive due to cost of cable installation thats avoidedInstallation time WLL systems can be installed in a small fraction of the time required for a new wired systemSelective installation radio units installed for subscribers who want service at a given timeWith a wired system, cable is laid out in anticipation of serving every subscriber in a given area110

Propagation Considerations for WLLMost high-speed WLL schemes use millimeter wave frequencies (10 GHz to about 300 GHz)There are wide unused frequency bands available above 25 GHzAt these high frequencies, wide channel bandwidths can be used, providing high data ratesSmall size transceivers and adaptive antenna arrays can be used111

Propagation Considerations for WLLMillimeter wave systems have some undesirable propagation characteristicsFree space loss increases with the square of the frequency; losses are much higher in millimeter wave rangeAbove 10 GHz, attenuation effects due to rainfall and atmospheric or gaseous absorption are largeMultipath losses can be quite high112

Fresnel ZoneHow much space around direct path between transmitter and receiver should be clear of obstacles?Objects within a series of concentric circles around the line of sight between transceivers have constructive/destructive effects on communicationFor point along the direct path, radius of first Fresnel zone:

S = distance from transmitterD = distance from receiver

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Atmospheric AbsorptionRadio waves at frequencies above 10 GHz are subject to molecular absorptionPeak of water vapor absorption at 22 GHzPeak of oxygen absorption near 60 GHzFavorable windows for communication:From 28 GHz to 42 GHzFrom 75 GHz to 95 GHz114

Effect of RainAttenuation due to rainPresence of raindrops can severely degrade the reliability and performance of communication linksThe effect of rain depends on drop shape, drop size, rain rate, and frequencyEstimated attenuation due to rain:

A = attenuation (dB/km)R = rain rate (mm/hr)a and b depend on drop sizes and frequency

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Effects of VegetationTrees near subscriber sites can lead to multipath fadingMultipath effects from the tree canopy are diffraction and scatteringMeasurements in orchards found considerable attenuation values when the foliage is within 60% of the first Fresnel zoneMultipath effects highly variable due to wind116

Multipoint Distribution Service (MDS)Multichannel multipoint distribution service (MMDS)Also referred to as wireless cableUsed mainly by residential subscribers and small businessesLocal multipoint distribution service (LMDS)Appeals to larger companies with greater bandwidth demands117

Advantages of MMDSMMDS signals have larger wavelengths and can travel farther without losing significant powerEquipment at lower frequencies is less expensiveMMDS signals don't get blocked as easily by objects and are less susceptible to rain absorption118

Advantages of LMDSRelatively high data ratesCapable of providing video, telephony, and dataRelatively low cost in comparison with cable alternatives119

WiMax Worldwide Interoperability for Microwave Access120

WiMAX IntroductionWorldwide Interoperability for Microwave Access The Institute of Electrical and Electronics Engineers (IEEE) 802 committee (802.16 ).Orthogonal Frequency Division Multiplexing (OFDM) (carriers of width of 5MHz or greater can be used )connectivity at speeds up to 70 Mbps provide high speed access to about 60 businesses at T1 speeds.can serve up to a thousand homes in term of DSL speed.

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How it works??WiMAX system consists of two parts: WiMAX Base Station: Typically, a base station can cover up to 10 km radius.WiMAX receiver: could be a stand-alone box or a PC card.

Several base stations can be connected with one another by backhaul microwave links. wireline backhauling microwave Point-to-Point connectionwhat would happen if you got WiMAX ??Internet service providerWiMAX base station 10 miles from your home WiMAX-enabled computer receive a special encryption code base station beam data from the Internet to your computer 122

WiMax vs. WLAN WiMAX provides a media access control (MAC) layer.the support of real-time and voice applications is simpleWiMAX proposes the full range of security Terminal authentication by exchanging certificates to prevent rogue devices User authentication using the Extensible Authentication Protocol (EAP) Data encryption using the Data Encryption Standard (DES) or Advanced Encryption Standard (AES) , both much more secure than the Wireless Equivalent Privacy (WEP) used by WLAN

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WiMax VS. WiFi WiFi connection can transmit up to 54Mbps (under optimal conditions)WiMAX should be able to handle up to 70MbpsThe biggest difference isn't speed!! WiFi's range is about 100 feet (30 m) WiMAX will blanket a radius of 30 miles (50 km) with wireless accessdue to the frequencies used and the power of the transmitter.WiMAX(10-66 GHz frequency)WiFi(5GHz frequency maximum)

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Where can be applied??large area public (airports, university campuses,)Large numbers of small and medium sized businesses (for lower costs)High speed internet for areas where wired connectivity is not viable.

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802.16 Standards DevelopmentUse wireless links with microwave or millimeter wave radiosUse licensed spectrumAre metropolitan in scaleProvide public network service to fee-paying customersUse point-to-multipoint architecture with stationary rooftop or tower-mounted antennas126

802.16 Standards DevelopmentProvide efficient transport of heterogeneous traffic supporting quality of service (QoS)Use wireless links with microwave or millimeter wave radiosAre capable of broadband transmissions (>2 Mbps)127

IEEE 802.16 Protocol Architecture

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Protocol ArchitecturePhysical and transmission layer functions:Encoding/decoding of signalsPreamble generation/removalBit transmission/receptionMedium access control layer functions:On transmission, assemble data into a frame with address and error detection fieldsOn reception, disassemble frame, and perform address recognition and error detectionGovern access to the wireless transmission mediumConvergence layer functions:Encapsulate PDU framing of upper layers into native 802.16 MAC/PHY framesMap upper layers addresses into 802.16 addressesTranslate upper layer QoS parameters into native 802.16 MAC formatAdapt time dependencies of upper layer traffic into equivalent MAC service

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IEEE 802.16.1 ServicesDigital audio/video multicastDigital telephonyATMInternet protocolBridged LANBack-haulFrame relay130

IEEE 802.16.3 ServicesVoice transportData transportBridged LAN131

IEEE 802.16.1 Frame Format

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IEEE 802.16.1 Frame FormatHeader - protocol control informationDownlink header used by the base stationUplink header used by the subscriber to convey bandwidth management needs to base stationBandwidth request header used by subscriber to request additional bandwidthPayload either higher-level data or a MAC control messageCRC error-detecting code133

MAC Management MessagesUplink and downlink channel descriptorUplink and downlink access definitionRanging request and responseRegistration request, response and acknowledgePrivacy key management request and responseDynamic service addition request, response and acknowledge134

MAC Management MessagesDynamic service change request, response, and acknowledgeDynamic service deletion request and responseMulticast polling assignment request and responseDownlink data grant type requestARQ acknowledgment135

Physical Layer Upstream TransmissionUses a DAMA-TDMA techniqueError correction uses Reed-Solomon codeModulation scheme based on QPSK136

Physical Layer Downstream TransmissionContinuous downstream mode For continuous transmission stream (audio, video)Simple TDM scheme is used for channel accessDuplexing technique is frequency division duplex (FDD)Burst downstream modeTargets burst transmission stream (IP-based traffic)DAMA-TDMA scheme is used for channel accessDuplexing techniques are FDD with adaptive modulation, frequency shift division duplexing (FSDD), time division duplexing (TDD)137

ReferencesBook: Wireless Communications and Networks by William Stallings PPT: WilliamStalling.com/StudentsSupport.html.http://www.doc.ic.ac.uk/~nd/surprise_95/journal/vol2/mjf/article2.htmlhttp://www.wildpackets.com/resources/compendium/wireless_lan/overviewhttp://www.wirelesscommunication.nl/reference/chaptr01/dtmmsyst/80211early.htm

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THANK YOU139