Lec 2-Wireless Technology Generations

7/24/2019 Lec 2-Wireless Technology Generations

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Introduction: Challenges in wireless networks

Efficient allocation and use of spectrumEfficient modulationEfficient data coding and compressionResistance against interference, multipath, bursts,

absorption, etc. Power consumption (mobile devices)Spatial separation of transmitters

Cellular network

Reuse of frequenciesHandoff

Social aspects


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Multiplexing - FDMA

Frequency Division Multiple AccessChannels divided by frequencyUplink / Downlink separated by frequency offset

Advantages

Symmetric uplink / downlink (bandwidth and power efficient, no channelswitching)Easy to implement

DisadvantagesInterference problems in shared radio spectrums

Inefficient usage of spectrum (each full duplex channel needs twofrequencies)

Examples: Radio, TV f

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Multiplexing - TDMA

Time Division Multiple AccessChannels divided by time

Uplink / Downlink separated by time slotUsually asymmetric uplink / downlink with dynamic reallocation

AdvantagesEfficient usage of spectrumEasy handoff, device can measure during idle slots

DisadvantagesInterference problems in shared radio spectrumsTime synchronization challengingLow frequency interference (time slot frequency)

NB: TDMA often combined withFDMA / frequency hopping

Examples: Bluetooth, GSMf

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Multiplexing CDMA

Code Division Multiple AccessChannels divided by code

Narrow band signal sent over a wide spectrum channelCodes are usually pseudo-random sequences (signal appears as noise)

AdvantagesSupports Cell frequency reuse (shared frequency band)

Support Soft handoffDisadvantages

Near / far problemInterference requires power control

Example: UMTSf

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Wireless Network Evolution

1933 First police radios

1938 First Walkie Talkie1946 Wireless Phone by AT&T

Invention of dynamic channel allocation(manual)Invention of frequency reuse by cells

Cell handover still too complex to handleautomatically1948 Invention of the transistor1959 Invention of the integrated circuit1964 First system with automatic channel allocation,duplex, no automatic handover1969 First cell-based system by Bell with automatichandover (in a train)


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Structure of basic mobile communication system

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1G Networks Analogue, 1980s

Based on analogue modulation (AM/FM) of radio carrier(no coding, no compression)Limited number of simultaneous calls due to limitedfrequency range frequency divisionCircuit switchedIn the beginning: no handover, no roamingData or voice

1G networks were planned to achieve maximum coveragewith the use of very few antennas

Examples;Advanced Mobile Phone System (AMPS) USA (1978)Total Access Communications System (TACS) UKC-Netz GermanyRadiocom 2000- France

NMT- Scandinavia


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Shortcomings of 1G (analog) systems

Limited capacity- could not cope with increase in the number ofsubscribersBulky equipmentLack of security- Analog signals could be interceptedPoor reliabilityIncompatibility between systems in different countries- Could not

support roaming

To improve on 1G systems, the European Conference of Posts andTelecommunications Administrations (CEPT) established the GroupeSpeciale Mobile (GSM) to set up a new standard

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Second Generation (2G) systems-Digital systems

Europe, Asia:

GSM (Global System for Mobile Communication)Full digital system (1987: Standard, 1990 first networks)FDMA + TDMA

America:D-AMPS (Digital AMPS, 1990 first networks)

Combined analogue / digital system

FDMA + TDMAcdmaOne (CDMA, 1994 first networks)

Full digital systemCDMA

Japan:PDC (Personal Digital Cellular, 1993, first networks)FDMA + TDMA


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Second Generation (2G) systems-Digital systems Contd

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Based on digital coding and compression (mainly voice)Efficient modulation to symbol / time rate

Circuit switched = end-to-end resource allocationDifferent techniques to increase number of simultaneous circuits(TDMA, FDMA, CDMA)Text service: SMSHandover and international roaming

Additional services beside voice

Advantages of 2G systemsEfficient use of radio resourcesSecurity for voice transmission

Possibility for data transmissionSupports use of Very Large Scale Integrated (VLSI) componentsallowing use of smaller and cheaper handsetsCompatible with ISDN land based networks


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Second Generation (2G) systems- Digital systems Contd

1997: WAP (Wireless Application Protocol) Forum createdData traffic in wireless telephony networksHandle characteristics of wireless network better thanTCP/IPWML (Wireless Markup Language) vs. HTML/HTTP

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2.5G Networks

Involved packet based add-on to 2G networks

GSM:GPRS (use free timeslots for data)EDGE (use free timeslots for data, with more efficient modulation)

CDMA

CDMA2000 1x-RTT (Single Carrier Radio TransmissionTechnology)CDMA2000 air interface, also allows data transport


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3G Networks

EuropeUMTS (Universal Mobile Telephone System) (W-CDMA)

America, Japan, Koreacdma2000 (Code Division Multiple Access)

ChinaTD-SCDMA (Time Division-Synchronous Code Division MultipleAccess)

Based on digital coding and compressionAll based on code division multiple access to increase number ofsimultaneous callsCircuit switched and packet data

Handover and international roamingMany additional services besides voice

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Mesh Networks

A network of interconnected (wireless) nodes (full or partialmesh)

The network handles many-to-many connections and iscapable of dynamically updating and optimizing theseconnections

Mostly based on WLAN (802.11) technology, frequency bands without license + IP backbone (xDSL)

Various multiplexing techniques, high data rate (up to 100Mb/s), short range (< 100 m)

Several trials in larger cities, sometimes grass root

approaches


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WiMAX

WiMAX- Worldwide Interoperability for Microwave Access

Fixed / Nomadic WiMAXIEEE 802.16d or 802.16-2004for covering the last mile OFDM, high data rate (up to 70 Mb/s), wide range (up to 48km)

Devices: outdoor and indoor installed CPE (CustomerPremises Equipment)Frequencies: 2.5 GHz, 3.5 GHz and 5.8 GHz (licensed andlicense free)

Mobile WiMAX Mobile

IEEE 802.16eUsage: Long-distance mobile wireless broadbandDevices: PC Cards, Notebooks and future handsets


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Beyond 3G Networks

HSPA (High Speed Packet Access)3.5G: HSDPA (High-Speed Downlink Packet Access3.75G: HSUPA (High-Speed Uplink Packet Access)

4G New Technologies: HSPA+, LTE, WiMAX+

Pure packet switched IP-based networksIncreased data rates (beyond 100 Mb/s)Transparent vertical handovers between different networktechnologies (including WLAN, WiMAX, etc.)


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GSM Cellular Structure

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GSM Architecture- Overview

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Abbreviations

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GSM Sub-systems

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Mobile station (MS)

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Mobile Station (MS) Contd

The two parts of the MS allows a distinction the actual equipment andthe subscriber using it

The IMSI identifies the subscriber within the GSM networkThe MS ISDN is the actual telephone number a caller uses to callanother party/personThe IMEI maybe used to block certain types of equipment fromaccessing the network if they are unsuitable. It can also be used tocheck for stolen equipment

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Base Station Subsystem (BSS)

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Handover (Hand-off)

Refers to the process of transferring an on-going mobile phone call ordata session from one cell and/or base station to another geographically

adjacent cell and/or base station as the user is in motion.In properly functioning networks, the process occurs smoothly withoutgaps in communication and is usually unnoticeable to the cellularnetwork userTypes of handover;

Hard Handover: Allows active connection to one base station at a time. It requiresthe connection to the original base station to be broken before establishingconnection with the new base station. It is used in GSM and analog cellularnetworksSoft Handover: Allows simultaneous active connections to multiple base stationsand does not require the original connection to be broken down. It offers smoother

caller transition with lesser chances of break down in communication. It iscommonly used in single frequency systems such as CDMA, WCDMASofter Handover: Allows mobile stations to communicate with more than onesector managed by the same base station especially in UMTS networksInter RAT Handover: Allows MS to communicate between different Radio AccessTechnologies(RAT) e.g GSM and WCDMA

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BSS Network Topologies

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NSS Contd

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Functions of MSC

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Visitors Location Register (VLR)

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Home Location Register (HLR)

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Equipment Identity Register (EIR)

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Gateway MSC (GMSC)

Lec 2-Wireless Technology Generations

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