Sistem SelulerPertemuan 12

Matakuliah : H0122 / Dasar TelekomunikasiTahun : 2008

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Mahasiswa dapat menyebutkan konsep seluler, evolusi teknologi dan karakteristik

layanan dan perkembangan teknologi.

Learning Outcomes

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• Konsep Seluler• Evolusi sistem seluler• Perkembangan teknologi seluler

Outline Materi

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• Underlying technology for mobile phones, personal communication systems, wireless networking etc.

• Developed for mobile radio telephone– Replace high power transmitter/receiver

systems•Typical support for 25 channels over 80km

– Use lower power, shorter range, more transmitters

Cellular System

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• Multiple low power transmitters– 100 w or less

• Area divided into cells– Each with own antenna– Each with own range of frequencies– Served by base station

•Transmitter, receiver, control unit– Adjacent cells on different frequencies to

avoid crosstalk

Cellular Network

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•Square– Width d cell has four neighbours at distance d and

four at distance •Better if all adjacent antennas equidistant•Simplifies choosing and switching to new antenna

•Hexagon– Provides equidistant antennas– Radius defined as radius of circum-circle

•Distance from center to vertex equals length of side

– Distance between centers of cells radius R– Not always precise hexagons

•Topographical limitations•Local signal propagation conditions•Location of antennas

Shape of Cells

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•Power of base transceiver controlled– Allow communications within cell on given

frequency– Limit escaping power to adjacent cells– Allow re-use of frequencies in nearby cells– Use same frequency for multiple conversations– 10 – 50 frequencies per cell

•E.g. – N cells all using same number of frequencies– K total number of frequencies used in systems– Each cell has K/N frequencies– Advanced Mobile Phone Service (AMPS) K=395,

N=7 giving 57 frequencies per cell on average

Frequency Reuse

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•D = minimum distance between centers of cells that use the same band of frequencies (called cochannels)

•R = radius of a cell•d = distance between centers of adjacent cells (d = R)•N = number of cells in repetitious pattern

– Reuse factor– Each cell in pattern uses unique band of frequencies

•Hexagonal cell pattern, following values of N possible–  N = I2 + J2 + (I x J), I, J = 0, 1, 2, 3, …

•Possible values of N are 1, 3, 4, 7, 9, 12, 13, 16, 19, 21, …

•D/R=√(3N)•D/d = √N

Frequency Reuse

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• Add new channels– Not all channels used to start with

• Frequency borrowing– Taken from adjacent cells by congested cells– Or assign frequencies dynamically

• Cell splitting– Non-uniform distribution of topography and

traffic– Smaller cells in high use areas

•Original cells 6.5 – 13 km•1.5 km limit in general•More frequent handoff•More base stations

Increasing Capacity

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• Cell Sectoring– Cell divided into wedge shaped sectors, – 3 – 6 sectors per cell– Each with own channel set– Directional antennas

• Microcells– Move antennas from tops of hills and large

buildings to tops of small buildings and sides of large buildings, even lamp posts

– Form microcells– Reduced power– Good for city streets, along roads and

inside large buildings

Increasing Capacity

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•Base station (BS) at center of each cell–Antenna, controller, transceivers–Controller handles call process–Number of mobile units may in use at a time

•BS connected to mobile telecommunications switching office (MTSO)–One MTSO serves multiple BS–MTSO to BS link by wire or wireless

•MTSO:–Connects calls between mobile units and from mobile to fixed telecommunications network

–Assigns voice channel, Performs handoffs–Monitors calls (billing)

•Fully automated

Operations

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Global Overview

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• Control channels– Setting up and maintaining calls– Establish relationship between mobile

unit and nearest BS• Traffic channels

– Carry voice and data

Channels

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•Mobile unit initialization– Scan and select strongest set up control channel– Automatically selected BS antenna of cell

•Usually but not always nearest (propagation anomalies)

– Handshake to identify user and register location– Scan repeated to allow for movement (Change of cell)– Mobile unit monitors for pages

•Mobile originated call– Check set up channel is free

•Monitor forward channel (from BS) and wait for idle– Send number on pre-selected channel

•Paging– MTSO attempts to connect to mobile unit– Paging message sent to BSs depending on called

mobile number– Paging signal transmitted on set up channel

Call in Single MTSO

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•Call accepted–Mobile unit recognizes number on set up channel–Responds to BS which sends response to MTSO–MTSO sets up circuit between calling and called BSs–MTSO selects available traffic channel within cells and notifies BSs

–BSs notify mobile unit of channel•Ongoing call

–Voice/data exchanged through respective BSs and MTSO

•Handoff–Mobile unit moves out of range of cell into range of another cell

–Traffic channel changes to one assigned to new BS, without interruption of service to user

Call in Single MTSO

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•Original cellular telephone networks•Analog traffic channels•Early 1980s in North America•Advanced Mobile Phone Service (AMPS)

First Generation (1G)

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•Higher quality signals, Higher data rates, Support of digital services

•Greater capacity•Digital traffic channels

–Support digital data, Voice traffic digitized–User traffic (data or digitized voice) converted to analog signal for transmission

•Encryption•Error detection and correction•Channel access

–Channel dynamically shared by users via Time division multiple access (TDMA) or code division multiple access (CDMA, IS-95)

Second Generation (2G)

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• Objective to provide fairly high-speed wireless communications to support multimedia, data, and video in addition to voice

• ITU’s International Mobile Telecommunications for the year 2000 (IMT-2000) initiative defined ITU’s view of third-generation capabilities as:

– Voice quality comparable to PSTN– 144 kbps available to users in vehicles over large areas– 384 kbps available to pedestrians over small areas– Support for 2.048 Mbps for office use– Symmetrical and asymmetrical data rates– Support for packet-switched and circuit-switched

services– Adaptive interface to Internet– More efficient use of available spectrum– Support for variety of mobile equipment– Flexibility to allow introduction of new services and

technologie

Third Generation (3G)

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• Telah dipelajari gambaran umum sistem seluler.

• Telah dipelajari evolusi telepon seluler.

Summary