Thursday, July 17, 2008

GSM Specifications

Before looking at the GSM specifications, it is important to understand the following basic terms:

bandwidth—the range of a channel's limits; the broader the bandwidth, the faster data can be sent
bits per second (bps)—a single on-off pulse of data; eight bits are equivalent to one byte
frequency—the number of cycles per unit of time; frequency is measured in hertz (Hz)
kilo (k)—kilo is the designation for 1,000; the abbreviation kbps represents 1,000 bits per second
megahertz (MHz)—1,000,000 hertz (cycles per second)
milliseconds (ms)—one-thousandth of a second
watt (W)—a measure of power of a transmitter

Specifications for different personal communication services (PCS) systems vary among the different PCS networks. Listed below is a description of the specifications and characteristics for GSM.

frequency band—The frequency range specified for GSM is 1,850 to 1,990 MHz (mobile station to base station).
duplex distance—The duplex distance is 80 MHz. Duplex distance is the distance between the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart.
channel separation—The separation between adjacent carrier frequencies. In GSM, this is 200 kHz.
modulation—Modulation is the process of sending a signal by changing the characteristics of a carrier frequency. This is done in GSM via Gaussian minimum shift keying (GMSK).
transmission rate—GSM is a digital system with an over-the-air bit rate of 270 kbps.
access method—GSM utilizes the time division multiple access (TDMA) concept. TDMA is a technique in which several different calls may share the same carrier. Each call is assigned a particular time slot.
speech coder—GSM uses linear predictive coding (LPC). The purpose of LPC is to reduce the bit rate. The LPC provides parameters for a filter that mimics the vocal tract. The signal passes through this filter, leaving behind a residual signal. Speech is encoded at 13 kbps.

Global System for Mobile Communication (GSM)

GSM Subscriber Services

There are two basic types of services offered through GSM: telephony (also referred to as teleservices) and data (also referred to as bearer services). Telephony services are mainly voice services that provide subscribers with the complete capability (including necessary terminal equipment) to communicate with other subscribers. Data services provide the capacity necessary to transmit appropriate data signals between two access points creating an interface to the network. In addition to normal telephony and emergency calling, the following subscriber services are supported by GSM:

dual-tone multifrequency (DTMF)—DTMF is a tone signaling scheme often used for various control purposes via the telephone network, such as remote control of an answering machine. GSM supports full-originating DTMF.
facsimile group III—GSM supports CCITT Group 3 facsimile. As standard fax machines are designed to be connected to a telephone using analog signals, a special fax converter connected to the exchange is used in the GSM system. This enables a GSM–connected fax to communicate with any analog fax in the network.
short message services—A convenient facility of the GSM network is the short message service. A message consisting of a maximum of 160 alphanumeric characters can be sent to or from a mobile station. This service can be viewed as an advanced form of alphanumeric paging with a number of advantages. If the subscriber's mobile unit is powered off or has left the coverage area, the message is stored and offered back to the subscriber when the mobile is powered on or has reentered the coverage area of the network. This function ensures that the message will be received.
cell broadcast—A variation of the short message service is the cell broadcast facility. A message of a maximum of 93 characters can be broadcast to all mobile subscribers in a certain geographic area. Typical applications include traffic congestion warnings and reports on accidents.
voice mail—This service is actually an answering machine within the network, which is controlled by the subscriber. Calls can be forwarded to the subscriber's voice-mail box and the subscriber checks for messages via a personal security code.
fax mail—With this service, the subscriber can receive fax messages at any fax machine. The messages are stored in a service center from which they can be retrieved by the subscriber via a personal security code to the desired fax number.

Supplementary Services

GSM supports a comprehensive set of supplementary services that can complement and support both telephony and data services. Supplementary services are defined by GSM and are characterized as revenue-generating features. A partial listing of supplementary services follows.

call forwarding—This service gives the subscriber the ability to forward incoming calls to another number if the called mobile unit is not reachable, if it is busy, if there is no reply, or if call forwarding is allowed unconditionally.
barring of outgoing calls—This service makes it possible for a mobile subscriber to prevent all outgoing calls.
barring of incoming calls—This function allows the subscriber to prevent incoming calls. The following two conditions for incoming call barring exist: baring of all incoming calls and barring of incoming calls when roaming outside the home PLMN.
advice of charge (AoC)—The AoC service provides the mobile subscriber with an estimate of the call charges. There are two types of AoC information: one that provides the subscriber with an estimate of the bill and one that can be used for immediate charging purposes. AoC for data calls is provided on the basis of time measurements.
call hold—This service enables the subscriber to interrupt an ongoing call and then subsequently reestablish the call. The call hold service is only applicable to normal telephony.
call waiting—This service enables the mobile subscriber to be notified of an incoming call during a conversation. The subscriber can answer, reject, or ignore the incoming call. Call waiting is applicable to all GSM telecommunications services using a circuit-switched connection.
multiparty service—The multiparty service enables a mobile subscriber to establish a multiparty conversation—that is, a simultaneous conversation between three and six subscribers. This service is only applicable to normal telephony.
calling line identification presentation/restriction—These services supply the called party with the integrated services digital network (ISDN) number of the calling party. The restriction service enables the calling party to restrict the presentation. The restriction overrides the presentation.
closed user groups (CUGs)—CUGs are generally comparable to a PBX. They are a group of subscribers who are capable of only calling themselves and certain numbers.

GSM Network Areas

The GSM network is made up of geographic areas. As shown in , these areas include cells, location areas (LAs), MSC/VLR service areas, and public land mobile network (PLMN) areas.

The cell is the area given radio coverage by one base transceiver station. The GSM network identifies each cell via the cell global identity (CGI) number assigned to each cell. The location area is a group of cells. It is the area in which the subscriber is paged. Each LA is served by one or more base station controllers, yet only by a single MSC. Each LA is assigned a location area identity (LAI) number.

An MSC/VLR service area represents the part of the GSM network that is covered by one MSC and which is reachable, as it is registered in the VLR of the MSC .

The PLMN service area is an area served by one network operator .

Standard Operation Procedure's

Drive Test SOP

How To:

Drive Test Using TEMS Investigation GSM

I. Starting TEMS

First, make sure TEMS investigation GSM is already installed

1.1 Start TEMS from Start Menu

1.2 This is TEMS investigation GSM user interface

II. Connect Devices

First, make sure all devices are already connected to the laptop.

2.1 Before we start, we must identify equipment first. Click the Identify Equipment button on the Equipment Control toolbar.

A dialog named "Port Properties" will appear

make sure that mobile station and GPS is connected to a COM port on your computer and the COM port you use is checked. Than Click OK

2.2 TEMS Investigation now scans the COM ports for external devices and enables these devices automatically. A Port Configuration window is opened (if not open, you can look at configuration tab), showing the progress of the scan. When it is finished (after a few seconds), the text "Ready" is displayed at the bottom of the Port Configuration. Red circle in the icons means the device is not yet connected.

If automatic identify can’t find your equipment, you can add them manually:

Choose your Port and Equipment, and click “OK”:

2.3 To receive data from the mobile and GPS, you must connect those devices:

Click “Connect All” on the Connections Toolbar.

If the connection is successful, then red circle in the icon will change into green circle.

2.4 If you want to disconnect the device, just click “Disconnect all” from the Toolbar:

III. Recording

Before start recording, you should open maps (or GeoSet) and cell definition

3.1 Open Map

You can view map window in the Map worksheet above the status bar.

In the Map Window you’ll see map toolbar. To open Map, click “Open map”

Locate and select your Map Files and click open:

or for fast layering, you can open “GeoSet” instead :

3.2 Open Cell Definition

From Menu Bar, click Configuration, and click Cell Definition :

than Cell Definition window is shown. Click “Open”

Locate and select your Cell Name Files (*.cel) and click open:

3.3 Start Recording

You can start recording by clicking Record Button on the toolbar

Then you’ll be ask name of log file and where to save it.

3.4 Stop Recording

If you want to stop recording, just click Stop button on the toolbar:

3.5 Replay Log File

If you want to replay your log file (or to make sure you’ve recorded well), click “Open logfile” on the tool bar :

Warning: You can replay Log file only if your devices is disconnected

IV. Testing Mode

4.1 Idle Mode

In idle mode, the mobile station is standby and not making any call. You can just click record button to start recording idle mode. Use Idle Mode to test sectorization and cross feeder on the night of cut over.

4.2 Idle Lock and Idle Prevent

When the mobile station is in idle mode, it can be locked to one channel or to a set of channels. This inhibits all reselections to other channels, regardless of the signal strength and quality of neighboring cells. The inverted operation is also possible, namely to prevent reselection to a specified channel set.

^Click ^{on the toolbar, and select which channel you want to lock}

^{To reset the lock on channel function, simply click} ^{on the toolbar.}

There is another way to lock on channel,by using Equipment Properties :

^Click ^{on the toolbar.}

To prevent reselection to a specified channel set, just choose Prevent Function :

4.3 Dedicated Mode

In dedicated mode, the mobile station is making a call. You can do it by either ^{using the TEMS mobile phone, or click redial} ^{on the toolbar}.

^{To terminate an ongoing call, simply click} ^{on the toolbar}

4.4 Force Handover and Prevent Handover

When the mobile station is in dedicated mode, you can manipulate handovers. Specifically, you can do one of the following:

Prevent handover to specified channels. The mobile then reports no signal strength for these channels.

Force handover to a specified channel, or restrict handovers to a chosen channel set. The mobile then reports a RxLev of 63 for any such cell, 10 for the serving cell and no RxLev for other neighboring cells.

^Click ^{(Equipment Properties) on the toolbar}

To Force handover, simply select “Target HO” Function, and choose target channels.

To Prevent handover, simply select “Prevent HO” Function, and choose target channels.

4.5 Command Sequence

Command sequences are used to automate testing of voice as well as data. They allow you to prerecord all the commands to be given to the mobile stations during a drive test. Use command sequence for NQI drive test.

Go to menu bar, click “Control” and than click “Command Sequence”:

If you’ve created Command Sequence before, just open the file:

4.6 GPRS Test

Before doing GPRS test, your mobile phone has to be configured based on operator parameter. Example of manual configuration is presented on Appendix 1.

To start Testing, press Record, Browse using WAP browser on the mobile phone. Wait until you hear “GPRS attached” and “PDP context activated”. Start browsing for a few second, and than close your wap browser. You will hear “GPRS Detached”. You may click Stop to stop recording.

V. Exporting Log File

To process log file data to other software (e.g MapInfo), you have to export the logfile first. Go to Menu Bar, click “Logfile” and than click “Export Logfile”