Introduction to Mobile Communications TCOM 552, Lecture #9 Hung Nguyen, Ph.D. 06 November, 2006.

Introduction to Mobile Introduction to Mobile CommunicationsCommunications

TCOM 552, Lecture #9Hung Nguyen, Ph.D.06 November, 2006

11/06/2006Hung Nguyen, TCOM 552, Fall 20062

OutlineOutline

Wireless LAN Technology (Chapter 13) WLAN Standards (Chapter 14)


Wireless LAN ApplicationsWireless LAN Applications

LAN Extension Cross-building interconnect Nomadic Access Ad hoc networking


LAN ExtensionLAN Extension

Wireless LAN linked into a wired LAN on same premises– Wired LAN

Backbone Support servers and stationary workstations

– Wireless LAN Stations in large open areas Manufacturing plants, stock exchange trading floors,

and warehouses


Cross-Building InterconnectCross-Building Interconnect

Connect LANs in nearby buildings– Wired or wireless LANs

Point-to-point wireless link is used Devices connected are typically bridges or

routers


Nomadic AccessNomadic Access

Wireless link between LAN hub and mobile data terminal equipped with antenna– Laptop computer or notepad computer

Uses:– Transfer data from portable computer to office

server– Extended environment such as campus


Wireless LAN InfrastructureWireless LAN Infrastructure


Ad Hoc NetworkingAd Hoc Networking

Temporary peer-to-peer network set up to meet immediate need

Example:– Group of employees with laptops convene for a

meeting; employees link computers in a temporary network for duration of meeting


Ad Hoc LANAd Hoc LAN


Wireless LAN RequirementsWireless LAN Requirements

Throughput Number of nodes Connection to backbone LAN Service area Battery power consumption Transmission robustness and security Collocated network operation License-free operation Handoff/roaming Dynamic configuration


Wireless LAN CategoriesWireless LAN Categories

Infrared (IR) LANs Spread spectrum LANs Narrowband microwave


Strengths and Weaknesses of Infrared Strengths and Weaknesses of Infrared Over Microwave RadioOver Microwave Radio

Spectrum for infrared virtually unlimited– Possibility of high data rates

Infrared spectrum unregulated Equipment inexpensive and simple Reflected by light-colored objects

– Ceiling reflection for entire room coverage Doesn’t penetrate walls

– More easily secured against eavesdropping– Less interference between different rooms


Drawbacks of Infrared MediumDrawbacks of Infrared Medium

Indoor environments experience infrared background radiation– Sunlight and indoor lighting– Ambient radiation appears as noise in an

infrared receiver– Transmitters of higher power required

Limited by concerns of eye safety and excessive power consumption

– Limits range


IR Data Transmission TechniquesIR Data Transmission Techniques

Directed Beam Infrared Ominidirectional Diffused


Directed Beam InfraredDirected Beam Infrared

Used to create point-to-point links Range depends on emitted power and

degree of focusing Focused IR data link can have range of

kilometers– Cross-building interconnect between bridges or

routers


Omni-directionalOmni-directional

Single base station within line of sight of all other stations on LAN

Station typically mounted on ceiling Base station acts as a multiport repeater

– Ceiling transmitter broadcasts signal received by IR transceivers

– IR transceivers transmit with directional beam aimed at ceiling base unit


DiffusedDiffused

All IR transmitters focused and aimed at a point on diffusely reflecting ceiling

IR radiation strikes ceiling – Reradiated omnidirectionally – Picked up by all receivers


Spread Spectrum LAN ConfigurationSpread Spectrum LAN Configuration

Multiple-cell arrangement (Figure 13.2 next) Within a cell, either peer-to-peer or hub Peer-to-peer topology

– No hub– Access controlled with MAC algorithm

CSMA: Carrier Sense Multiple Access

– Appropriate for Ad Hoc LANs


Multiple-cell Wireless LANMultiple-cell Wireless LAN

CM: Control ModuleUM: User Module


Spread Spectrum LAN ConfigurationSpread Spectrum LAN Configuration

Hub topology– Mounted on the ceiling and connected to

backbone– May control access– May act as multiport repeater– Automatic handoff of mobile stations– Stations in cell either:

Transmit to / receive from hub only Broadcast using omnidirectional antenna


Narrowband Microwave LANsNarrowband Microwave LANs

Use of a microwave radio frequency band for signal transmission

Relatively narrow bandwidth Licensed Unlicensed


Licensed Narrowband RFLicensed Narrowband RF

Licensed within specific geographic areas to avoid potential interference

Motorola holds 600 licenses (1,200 frequencies) in 18-GHz range – Covers all metropolitan areas– Can assure that independent LANs in nearby

locations don’t interfere– Encrypted transmissions prevent eavesdropping


Unlicensed Narrowband RFUnlicensed Narrowband RF

RadioLAN introduced narrowband wireless LAN in 1995– Uses unlicensed ISM spectrum– Used at low power (0.5 watts or less)– Operates at 10 Mbps in the 5.8-GHz band– Range = 50 m to 100 m

IEEE 802.11 Wireless LAN IEEE 802.11 Wireless LAN StandardStandard


IEEE 802 Protocol LayersIEEE 802 Protocol Layers


802.11 Physical Layer Standard802.11 Physical Layer Standard


Pulse Position ModulationPulse Position Modulation

The location of the pulse within the specified pulse frame indicates what was sent

Example


Gaussian Frequency Shift KeyingGaussian Frequency Shift Keying

GFSK is a type of Frequency Shift Keying modulation that utilizes a Gaussian filter to smooth positive/negative frequency deviations, which represent a binary 1 or 0.

It is used by DECT and Bluetooth. For Bluetooth the minimum deviation is 115 kHz.


Protocol ArchitectureProtocol Architecture

Functions of physical layer:– Encoding/decoding of signals (PSK, QAM, etc…)– Preamble generation/removal (for

synchronization)– Bit transmission/reception– Includes specification of the transmission

medium


IEEE 802.11 ServicesIEEE 802.11 Services


Protocol ArchitectureProtocol Architecture

Functions of medium access control (MAC) layer:– On transmission, assemble data into a frame

with address and error detection fields– On reception, disassemble frame and perform

address recognition and error detection– Govern access to the LAN transmission medium

Functions of logical link control (LLC) Layer:– Provide an interface to higher layers and perform

flow and error control


Separation of LLC and MACSeparation of LLC and MAC

The logic required to manage access to a shared-access medium not found in traditional layer 2 data link control

For the same LLC, several MAC options may be provided


MAC Frame FormatMAC Frame Format

MAC control– Contains Mac protocol information

Destination MAC address– Destination physical attachment point

Source MAC address– Source physical attachment point

CRC– Cyclic redundancy check


Logical Link ControlLogical Link Control

Characteristics of LLC not shared by other control protocols:– Must support multi-access, shared-medium

nature of the link– Relieved of some details of link access by MAC

layer


LLC ServicesLLC Services

Unacknowledged connectionless service– No flow- and error-control mechanisms– Data delivery not guaranteed

Connection-mode service– Logical connection set up between two users– Flow- and error-control provided

Acknowledged connectionless service– Cross between previous two– Datagrams acknowledged– No prior logical setup


Differences between LLC and HDLCDifferences between LLC and HDLC

LLC uses asynchronous balanced mode of operation of HDLC (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)


IEEE 802.11 ArchitectureIEEE 802.11 Architecture

Distribution system (DS) Access point (AP) Basic service set (BSS)

– Stations competing for access to shared wireless medium

– Isolated or connected to backbone DS through AP

Extended service set (ESS) – Two or more basic service sets interconnected

by DS


Distribution of Messages Within a DSDistribution of Messages Within a DS

Distribution service– Used to exchange MAC frames from station in

one BSS to station in another BSS Integration service

– Transfer of data between station on IEEE 802.11 LAN and station on integrated IEEE 802.x LAN


Transition Types Based On MobilityTransition Types Based On Mobility

No transition– Stationary or moves only within BSS

BSS transition– Station moving from one BSS to another BSS in

same ESS ESS transition

– Station moving from BSS in one ESS to BSS within another ESS


Association-Related ServicesAssociation-Related Services

Association– Establishes initial association between station

and AP Re-association

– Enables transfer of association from one AP to another, allowing station to move from one BSS to another

Disassociation– Association termination notice from station or AP


Access and Privacy ServicesAccess and Privacy Services

Authentication– Establishes identity of stations to each other

De-authentication– Invoked when existing authentication is

terminated Privacy

– Prevents message contents from being read by unintended recipient


IEEE 802.11 Medium Access ControlIEEE 802.11 Medium Access Control

MAC layer covers three functional areas:– Reliable data delivery– Access control– Security


Reliable Data DeliveryReliable Data Delivery

More efficient to deal with errors at the MAC level than higher layer (such as TCP)

Frame exchange protocol– Source station transmits data– Destination responds with acknowledgment (ACK)– If source doesn’t receive ACK, it retransmits frame

Four frame exchange– Source issues request to send (RTS)– Destination responds with clear to send (CTS)– Source transmits data– Destination responds with ACK


Access ControlAccess Control


Medium Access Control LogicMedium Access Control Logic


Interframe Space (IFS) ValuesInterframe Space (IFS) Values

Short IFS (SIFS)– Shortest IFS– Used for immediate response actions

Point coordination function IFS (PIFS)– Mid-length IFS– Used by centralized controller in PCF scheme

when using polls Distributed coordination function IFS (DIFS)

– Longest IFS– Used as minimum delay of asynchronous frames

contending for access


IFS UsageIFS Usage

SIFS– Acknowledgment (ACK)– Clear to send (CTS)– Poll response

PIFS– Used by centralized controller in issuing polls– Takes precedence over normal contention traffic

DIFS– Used for all ordinary asynchronous traffic


MAC Frame FormatMAC Frame Format


MAC Frame FieldsMAC Frame Fields

Frame Control – frame type, control information

Duration/connection ID – channel allocation time

Addresses – context dependant, types include source and destination

Sequence control – numbering and reassembly

Frame body – MSDU or fragment of MSDU Frame check sequence – 32-bit CRC


Frame Control FieldsFrame Control Fields

Protocol version – 802.11 version Type – control, management, or data Subtype – identifies function of frame To DS – 1 if destined for DS From DS – 1 if leaving DS More fragments – 1 if fragments follow Retry – 1 if retransmission of previous frame


Frame Control FieldsFrame Control Fields

Power management – 1 if transmitting station is in sleep mode

More data – Indicates that station has more data to send

WEP – 1 if wired equivalent protocol is implemented

Order – 1 if any data frame is sent using the Strictly Ordered service


Control Frame SubtypesControl Frame Subtypes

Power save – poll (PS-Poll) Request to send (RTS) Clear to send (CTS) Acknowledgment Contention-free (CF)-end CF-end + CF-ack


Data Frame SubtypesData Frame Subtypes

Data-carrying frames– Data– Data + CF-Ack– Data + CF-Poll– Data + CF-Ack + CF-Poll

Other subtypes (don’t carry user data)– Null Function– CF-Ack– CF-Poll– CF-Ack + CF-Poll


Management Frame SubtypesManagement Frame Subtypes

Association request Association response Re-association request Re-association response Probe request Probe response Beacon


Management Frame SubtypesManagement Frame Subtypes

Announcement traffic indication message Dissociation Authentication De-authentication


Wired Equivalent PrivacyWired Equivalent Privacy


AuthenticationAuthentication

Open system authentication– Exchange of identities, no security benefits

Shared Key authentication– Shared Key assures authentication


Physical Media Defined by Original Physical Media Defined by Original 802.11 Standard802.11 Standard

Direct-sequence spread spectrum– Operating in 2.4 GHz ISM band– Data rates of 1 and 2 Mbps

Frequency-hopping spread spectrum– Operating in 2.4 GHz ISM band– Data rates of 1 and 2 Mbps

Infrared– 1 and 2 Mbps– Wavelength between 850 and 950 nm


IEEE 802.11a, 802.11b and 801.11gIEEE 802.11a, 802.11b and 801.11g

IEEE 802.11a– Makes use of 5-GHz band. Provides rates of 6, 9, 12, 18,

24, 36, 48, 54 Mbps– Uses orthogonal frequency division multiplexing (OFDM).

Sub-carrier modulated using BPSK, QPSK, 16-QAM or 64-QAM

IEEE 802.11b– Provides data rates of 5.5 and 11 Mbps– Complementary code keying (CCK) modulation scheme

IEEE 802.11g– Uses 2.4 GHz band with DSSS & OFDM. Data rates from

1 to 54 Mbps. Compatible with WiFi at 11 Mbps

Introduction to Mobile Communications TCOM 552, Lecture #9 Hung Nguyen, Ph.D. 06 November, 2006.

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Transcript of Introduction to Mobile Communications TCOM 552, Lecture #9 Hung Nguyen, Ph.D. 06 November, 2006.