ece401 lecture 4

8/3/2019 Ece401 Lecture 4

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LECTURE-4

BASIC CELLULAR

SYSTEM


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There are two basic cellular systems;

circuit-switchedsystem: AA circuitcircuit--switchedswitched networknetwork consistsconsists of of aa setset

ofof switchesswitches connectedconnected byby physicalphysical linkslinks..

AA connectionconnection betweenbetween twotwo stationsstations isis aa

dedicateddedicated pathpath mademade ofof oneone oror moremore linkslinks..

packet-switchedsystem:

It involves dividing data messages into

small bundles of information and transmitting them through the

communication networks to their intended

destinations using computer controlled

switches.


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Basic Analog Cellular system


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Consists ofthree subsystems:

1. Mobile units: control unit, a transceiver, and an

antenna system.2. Cell site. interface between the MTSO and themobile units.

has a control unit, radio cabinets, antennas, apower plant, and data terminals.

3. MTSO: The switching office, the centralcoordinating element for all cell sites,

Contains the cellular processor and cellularswitch.

It interfaces with telephone company zoneoffices, controls call processing, providesoperation and maintenance, and handles billingactivities.


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4.Connections.

The radio and high-speed data linksconnect the three subsystems.

Each mobile unit can only use onechannel at a time for its communicationlink.

But the channel is not fixed; it can be anyone in the entire band assigned by the

serving area, with each site havingmultichannel capabilities that canconnect simultaneously to many mobileunits.


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The MTSO is the heart of the analog

cellular mobile system: processor provides central coordination and

cellular administration.

The cellular switch, which can be either

analog or digital, switches calls toconnect mobile subscribers to other

mobile subscribers and to the

nationwide telephone network.


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It uses voice trunks and data links providing supervision links between the processor and the switch and betweenthe cell sites and the processor.

The radio link carries the voice and

signaling between the mobile unit andthe cell site.

The high-speed data links cannot betransmitted over the standard telephone

trunks and therefore must use eithermicrowave links or T-carriers (wire lines).Microwave radio links or T-carriers carry both voiceand data between cell site and the MTSO.


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Basic Digital Cellular System


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Abasic digital system consists of four elements:

mobile station, base transceiver station ,BTS, base station controller BSC, andswitching subsystems.

MS: mobile equipment (ME) and subscriber

identify module (SIM). SIM contains all subscriber-specific data storedon the MS side.

BTS: same function as the analog BTS, it hasthe Transcoder/Rate AdapterUnit(TRAU), which carries out coding anddecoding as well as rate adaptation in casedata rate varies.


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BSC: A new element in digital systems thatperforms the Radio Resource (RR)management for the cells under itscontrol.

B

SC also handles handovers, powermanagement time and frequencysynchronization, and frequencyreallocation among BTSs.

Switching subsystems:MSC: The main function of MSC is to

coordinate the setup of calls between MSand PSTN users.


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VLR (Visitor Location Register): A database of all

mobiles roaming in the MSCs area of control.HLR(Home Location Register): A centralized database

of all subscribers registered in a Public Land MobileNetwork (PLMN).

AUC (Authentication Center): Provides HLR with

authentication parameters and ciphering keys thatare used for security purposes.

EIR (Equipment Identity Register): A database forstoring all registered mobile equipment numbers.

IWF (Interworking Function): Provides the subscriberwith data services that can access data rate and protocolconversion facilities and interfaces with public andprivate data networks.


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EC (Echo Canceller):

Used on the PSTN side ofthe MSC for all voice circuits.

XC (Transcoder): Usually installs in each BTS.But for the cost reason, it can be installed in BSC

or MSC.OMC (Operational and Maintenance Centre):

This function resided in Analog MSC but becamea separated entity in digital systems.


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Packet-Switched System


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There are six elements: MS, Node B, RNC,

SGSN, GGSN, and GF . MS: Provides the voice and packet data services.

It is also called UE (User Equipment).

Node B: The name for base station in

GSM. RNC (Radio Network Controller): Controls the

radio resources of the Node Bs that are

connected to it. Its function is similar to BSC. A

device PCU (Packet Control Unit) converts the data stream into packet format.


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SGSN (Service GPRS SupportNode): Analogous

to MSC/VLRin the circuit-switched system.includes mobility management, security, andaccess control functions. It interfaces to HLR.

GGSN (Gateway GPR S SupportNode): Thepoint of interface with external packet datanetworks such as the Internet.

CGF (Changing Gateway Function): Mainly for

billing. RNS (Radio Network Subsystem): It consists ofRNC and Node B.

UTRAN consists of two or more RNS.


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Universal Terrestrial RadioAccess Network,


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Despite the fact that Nodes and RNC do not have

to be physically separated, there is a logicalinterface between them known as the Iub.

The RNC and its corresponding Node Bs arecalled the Radio Network Subsystem (RNS).

Therecanbemorethanone RNSpresentinaUTRAN.


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There are four interfaces connecting the UTRAN

internally or externally : Iu, Uu, Iub and Iur.The Iu interface is an external interface that

connects the RNC to the Core Network (CN).

The Uu is also external, connecting the Node B

with the User Equipment (UE).The Iub is an internal interface connecting theRNC with the Node B.

Iur interface which is an internal interface most

of the time, but can, exceptionally be an externalinterface too for some network architectures. Itconnects two RNCs with each other.

ece401 lecture 4

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