Mobile Com-

munications

Jose Antonio

Portilla

Figueras

Mobile Communications

Jose Antonio Portilla Figueras

October 21, 2009

Mobile Com-

munications

Jose Antonio

Portilla

Figueras

Agenda

Topic 2: Case Study: The GSM Network

1 GSM System General Architecture

2 GSM Access network.

3 Traffic Models for the Air interface

4 Models for the BSS design.

5 UMTS and the path towards 4G

6 UMTS cell design

Mobile Com-

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GSM System ArchitectureGeneral Scheme

The network is divided into three major parts:

Switching System (SS)Base Station System (BSS)Operation and Maintenance Center (OMC)

Each of these contains a number of functional units whichmake up the entire system. The functional units are partsin the various hardware units.

Next slide shows a scheme of the structure of a GSMnetwork.

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GSM System ArchitectureGeneral Scheme

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GSM System ArchitectureFunctional Element Description: MSC

The Mobile services Switching Center (MSC) performs thetelephony switching functions of the system.

It also controls calls to and from other telephony and datasystems, such as the Public Switched Telephone Network(PSTN) and Public Land Mobile Network (PLMN).

In most GSM system, the VLR (see next section) isintegrated with the MSC in a MSC/VLR.

The MSC is responsible of the following functions

Setting up and controlling callsHandling speech path continuity of moving subscribers(handover).Location updating and location canceling in the locationregisters.

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GSM System ArchitectureFunctional Element Description: MSC

Provision of functions for signaling to and from BSC, MSsother GSM entities, other networks such as PSTN orISDN.

Administrative functions for defining data and handling ofthe mobile subscribers.

Security related functions which perform authentication.

Functions for IMEI check.

Receiving and delivering short messages from and to theMS.

charging and accounting.

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GSM System ArchitectureFunctional Element Description: Example of MSC

This a typical MSC machine (Inthis case of Siemens).

Processor, SwitchingMatrix,BSC port interfaces.

Of course, the building.

Between 5-6 Million Euros(Depends on the vendor, thecountry, the operator)

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GSM System ArchitectureFunctional Element Description: VLR

The Visitor Location Register (VLR) is a databasecontaining information about all MSs currently located inthe MSC service area.

The information is temporary and needed by the MSC toprovide service for visiting subscribers.

It can be seen as a distributed HLR.

When a MS roams into a new MSC service area, the VLRrequests data about the MS from the HLR.

If the MS makes a call , the VLR already has theinformation needed for call set-up.

This makes signaling between the two nodes over thenetwork unnecessary

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GSM System ArchitectureFunctional Element Description: GMSC

The Gateway MSC (GMSC) is the point in the PLMNwhere calls to mobile subscribers enter/leaves the GSMnetwork.

Each mobile terminating call must be routed via a GMSCin the home PLMN of the called MS.

It is required to distinguish between the element and thesignalling function.

The Gateway element is the physical element used asinterface to other networksThe signalling function is the functionality that asks theHLR about the position of the MS.

In most cases both things are implemented in the MSC.

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GSM System ArchitectureFunctional Element Description: HLR

The Home Location Register (HLR) is a database thatstores and manages subscriptions.

In a PLMN there usually is one, maybe two for securityissues.

For each subscriber, the HLR contains permanent datalike:

1 The associated numbers - MSISDN and IMSI.2 The customer portfolio.

The HLR also stores and updates dynamic data of thecustomer.

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GSM System ArchitectureFunctional Element Description: HLR functionality

The HLR provides the following functions (among others):

1 Definition of subscriber data.2 Maintenance of a database of mobile subscribers a3 Subscription to basic/supplementary services.4 Activation/deactivation of supplementary services.5 Functions for analysis of mobile subscriber numbers6 Handling of authentication data for mobile subscribers7 Communication with Authentication center.8 Functions for communication with GMSC and VLR using

the SS7.9 Statistical functions for collecting data regarding the

performance of the system.

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GSM System ArchitectureFunctional Element Description: AUC and EIR

The Authentication Center AUC is a database whichcontains the authentication keys. These keys aregenerated any time the HLR request it, and forwards themto the VLR. These keys are checked with the MS at eachaccess attempt.

The Equipment Identity Register (EIR) is a data basewhich stores the International Mobile station EquipmentIdentity (IMEI) for each MS equipment. It is verified ineach access.The main objective is to ensure that theequipment is not stolen. It has four lists:

1 White listed (permitted for use)2 Gray listed (should be tracked for evaluation)3 Black listed (barred)4 Unknown equipment

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GSM System ArchitectureFunctional Element Description: SMS Center

Although it is part of the Network Switching subsystem itis not shown in the figure of the first slide.

As its name shows the Short Message Service Center(SMSC) is a node dedicated to handle with the SMSservice. It has to receive and deliver SMS from MS insideand outside de PLMN.

The messages received are stored in the SMSC and theyare not sent to the ending MS until the network is under aspecified using threshold.

The cost of a SMSC is about 1-3 Millions Euros.

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GSM System ArchitectureFunctional Element Description: Base Station

The Base Station (BS) handles the radio interface to theMS. It is the radio equipment (transceivers and antennas)needed to serve the users in its coverage area in thenetwork.

We have to distinguish between the following concepts:

1 Site: It is composed of the civil engineering and thesupport and facilities to hold the equipment.

2 BTS/BS/RBS is the set of equipment in the site. Usuallya single site may be composed of a BTS for 900 MHz, anda BTS for 1800 MHz in GSM system.

3 Sector or cells. Normally the Base Station are divided intosectors, each one of them composes a cell.

4 TRX, Transmitter: It defines a radiochannel that is the setof a frequency (FDMA) and the time multiple access(TDMA).

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GSM System ArchitectureBTS types

The base stations/cells are usually classified attending tothe type of cell they are handling. A classical division isthe following .

Macrocells. With a coverage radius between 1.5 to 20 Km,mainly for rural environments with low traffic.Minicells.Coverage radius between 0.7 to 1.5 Km forsuburban and urban areas.Microcells. Coverage radius between 0.3-0.5 to 0.7 -1 Kmfor urban areas with high traffic.Picocells. Coverage radius up to 0.5 km. They are used indense urban areas with high traffic or to cover specialplaces like males or airport. They are usually traffic driven.

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GSM System ArchitectureBTS types

Figure: Macrocellfor Rural Areas Figure: Microcell

for Urban-SuburbanAreas

Figure: Picocell forDense Urban Areas

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GSM System ArchitectureBTS types and costs

The total cost of a site is the sum of several amounts anddepends, of course on the type of BTS.

1 Site acquisition and preparation: Between 30KEuros(Picocell) - 80 KEuros (Rural Macrocell)

2 BTS equipment, from 15KEuros (Picocell)- 40KEuros(Macrocell). It may additionally be increased by thenumber of sectors.

3 TRX, with an average cost of 3-4 KEuros.

Therefore the cost of the BTS can be estimated by.

CBTS = CS + CBTS · NSectors + CTRX · NTRX · NSectors

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GSM System ArchitectureBTS Functions

Radio transmission to and radio signal reception from MSs,

Equalizing and diversity functions to compensate forfading effects.

Quality measurements: uplink, downlink and neighboringBSs.

Report measurements to the BSC.

Time alignment measurements.

Transceiver and MS power control.

Broadcasting system information and paging messages.

Receiving channel requests from MSs.

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GSM System ArchitectureBase Station Controller

The BSC handles all radio related functions and is theBSSs center point. The BSC manages the entire radionetwork including:

1 Configuration of the network.2 Administration and remote control of the RBSs.3 Handling connections to MSs including handovers.

The capacity of a BSC is about 256 BTS, 512 cells and1020 TRX.

Sometimes the BSC may be integrated with the MSC inthe same location. Anyway, from the logical point of view,they continue being separate elements.

This usually happens in countries with customerconcentrates in some points (large cities).

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GSM System ArchitectureBSC example

Figure: Example of BSC

The cost of a BSCrounds 3 MillionEuros.

Figure: Typical values ofBSC features

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GSM System ArchitectureMobile Station and MSISDN

The mobile station (our mobile phone) is the only part in the mobilenetwork that is, in fact, mobile.

The mobile is physically divided into the Terminal Equipment (TE)and the Subscriber Identification Module (SIM)

The SIM contains customized information about the subscriber and isthe part that provides the mobility to the user.

Of course it contains the MSISDN and the correspondingauthentication Keys.

The MS is functionality divided into three parts.

1 Mobile Termination, which includes the Radio Modem, theUser interface and the set of RF equipment.

2 Terminal Adaptor (TA): It connects different dataterminals to the MT. It performs the protocol adaptingfunctions.

3 Terminal equipment (TE): With two types, TE1 for ISDNinterfaces and TE2 for no ISDN.

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GSM System ArchitectureMobile Station and MSISDN

The MSISDN number uniquely identifies a mobile telephonesubscription in the public switched telephone networknumbering plan. It is composed by:

Country Code

National Destination Code

Subscriber Number

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GSM System ArchitectureOperation and Support System

There are some part of the GSM network that are nottypically shown in the lectures: The Management Part andthe Intelligence Network. We will give a short look intothem.

OMC offers the customer cost effective support forcentralized, regional and local operations and maintenanceactivities required by a cellular network.

OMC is the functional entity from which the networkoperator monitors and controls the system.Most of OMC’s in Mobile Networks are are based onTelecommunication Management Network (TMN). TMNis a model for telecommunication networks management.The most important parts are:

1 Configuration management2 Fault management3 Performance management

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GSM System ArchitectureIntelligent Network

Intelligent Network(IN) techniques are a flexible andconvenient way to provide a large number of more variedservices to the customer

IN also allows highly personalized new services to beoffered.

The basic functions needed for IN services are

1 Triggering function used to determine if this is an IN callor not.

2 Functionality to store information about the IN services.3 Functionality to provide access to the IN services.4 Functionality to carry out the service.

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GSM System ArchitectureIntelligent Network

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GSM System ArchitectureIntelligent Network Functionalities

Now we show the main functionalities of the IN.

1 Service Control Function (SCF): contains the service logicand processing capability that is required to execute an INservice.

2 Service Switching Function (SSF): is the functional entitythat provides the mobile network with access to the INservices that reside in the Service Control Function (SCF).

3 Service Data Function (SDF): is the database function ofthe Intelligent Network. The SDF stores IN subscriber dataand network data. These data are accessed by the SCFduring the execution of the service.

4 Specialized Resource Function (SRF): provides specialcapabilities for the execution of some IN services.

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GSM System ArchitectureIntelligent Network Nodes

The above functionalities can be implemented in aMSC/VLR or as stand alone nodes. In this last case:

1 Service Control Point (SCP): Implements the SCF andoften also the SDF.

2 Service Switching Point (SSP): Implements the SSF.3 Service Switching Control Point (SSCP): Implements SSF,

SCF, and usually also the SDF.4 Service Data Point (SDP): Implements the SDF on a

UNIX station.5 Intelligent Peripherals (IPs): Special hardware

implementing the SRF

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GSM System ArchitectureIntelligent Network Nodes

The list of IN services is as long as detailed as you (orbetter said the operator) want.

A short list of them is:

1 Personal Number2 Prepaid Services3 Virtual Private Network4 Information and Business Services (Free numbers,

Universal Access Number and Premium Rate)