GSM Overview

GSM History

Analogue cellular telephone systems were experiencing exponential growth in Europe in the early 1980s, particularly in Scandinavia, United Kingdom, France and Germany. Each country developed its own proprietor system; hence it was incompatible with each other's equipment and operation.

CEPT (Conference of European Posts and Telegraphs) was form in 1982 due to incompatibility in the GSM equipment and operation throughout Europe. A study group called Groupe Spécial Mobile (GSM) within CEPT was responsible in developing a pan-European public land mobile system.

GSM now stands for Global System for Mobile Communication.

The proposed system had to meet certain criteria:

• Good subjective speech quality
• Low terminal and service cost
• Support for international roaming
• Ability to support handheld terminals
• Support for range of new services and facilities
• Spectral efficiency
• ISDN compatibility

GSM responsibility was transferred to the European Telecommunication Standards Institute (ETSI) in 1989, and phase I of the GSM specifications was published in 1990. Commercial service was started in mid-1991, and by 1993 there were 36 GSM networks in 22 countries.

 

Milestone Achievements of GSM Technology

High-speed data communication now available to over 100 million GSM users in 27 countries worldwide
179 Countries/Areas with GSM System
GSM Total Subscribers in May 2002 684.2 Million
24 Billion SMS messages sent per month through the GSM networks
SMS forecast for 2002 is 360 Billion
GSM accounts for 71% of the World's digital market and 68% of the World's wireless market

 

What is GSM

GSM, which stands for Global system for mobile/wireless communication, is the world standard for digital cellular communication for voice, fax, SMS and Data transmission. GSM is the name of a standardization group established in 1982 to create initially a common European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900/1800 MHz.

Cellular service uses of low-power transmitters where frequencies can be reused within a geographic area. The idea of cell-based mobile radio service was formulated Bell Labs in the early 1970s. However, the Scandinavian countries were the first to introduce cellular services for commercial use with the introduction of the Nordic Mobile Telephone (NMT) in 1981.

GSM and GPRS modem from a2b communication enables remote data retrieval, control and monitoring a reality for most companies and organizations. Applications for a2b Communication GSM and GPRS modem are diverse and most industry sectors have benefited from its ease-of- use, low power consumption, small form factor, Input and Output ports and 100% customizable to suit every application.

First Generation - The first generation (also known as 1G) of phones were analog devices with limited capabilities and relatively weak performance. First generation devices are still in use today, operating on the same analog networks that have been in place for decades.

Second Generation - 2G or second generation devices came into prominence during the late 1990s, supports digital communication. This in turn allows for high-quality voice services as well as for data transmission capabilities. Second generation devices meet the needs of most users today, but they are limited in several significant ways. The first limitation is one of compatibility. There are several competing and consequently incompatible - 2G digital standards in place throughout the world, including CDMA, TDMA and GSM. Another limitation of 2G is the lack of bandwidth inherent in circuit-switched networks. A circuit-switched consists of thousands of individual channels, called circuits, each of which accommodates one call (or one part of one call) at a time. A system like this works fine for voice communications when you want to have an uninterrupted conversation with someone else. But for data transmissions, circuit-switched networking is highly inefficient. That is why 2G devices, which operate on circuit-switched networks, are only capable of achieving maximum transmission speeds of 9.6Kbps to 14.4Kbps. A similar limitation caused by circuit-switched networks is the requirements that you log on to the network each time you want to access digital content. This is a hassle for mobile users who are always on the go and can't afford to waste 15 seconds or more logging on to the network to get a stock quote or read an email message. Unfortunately, this inconvenience is necessary because 2G networks treat data transmission just like a phone calls, with each transmission occupying a circuits for data purposes, there soon would be no circuits left to accommodate the people who want to make phone calls.

 

GSM Modem for Industrial and Commercial Application

How are Data and SMS (short message service) messages transferred across the GSM cellular networks

Transmitting Data and SMS messages over the digital GSM cellular networks requires firstly, a GSM modem that supports Data transmission and SMS messaging in bi-directional.

These modems are available in different sizes and chassis, which greatly depends on the I/Os and the power source it used.

The GSM modem components for data and sms interfaces are not actually modems as we traditionally understand them: the "modem" component you need to send and receive data actually resides at the network headquarters (also known as the Mobile Switching Centre, or MSC), using a special modem-like device called an IWU, or Inter Working Unit.

Data is sent digitally from the hardware via the I/O ports, through the GSM modem and then through the air to the IWU. The GSM modem and the data/sms interfaces thus act as one extended digital "serial" or "air-interface" link between the PC and the IWU, which now acts as the modem.

It is only when the digital data is received by the IWU that it is converted by the IWU to the analogue Frequency Shift Keys (FSK) tones characteristic of analogue modems, making it possible to connect via PSTN fixed-lines to an ordinary analogue modem. And if an ordinary modem sends data to your GSM modem, then the IWU converts the analogue tones received into the "digital data stream" suitable for transmission across the network to your GSM mobile.

If one GSM modem sends data or sms to another GSM modem, then there's no need for an analogue-to-digital conversion since the entire "air interface" is already digital, as is required by the GSM specification.

 

The benefits of GSM modem and GSM Technology

There's more than one way to obtain data from remote devices these days. You can get full system access for data collection and system control through the use of existing GSM Network infrastructure and specialise GSM modems.

Converging the world of GSM and Internet Technology has to be one of the remarkable applications of technology in the Industrial and Commercial sector. This capability lets company personnel check the latest data from a remote device 365 days a year and 24 hours a day. Key personnels can read data or be alerted of any system failure whilst traveling or attending to other matters, this means staff can perform countless other feats that were impossible only a decade ago. With a2b Communication GSM solution it is now possible for company to implement "anywhere-anytime" technology using GSM modem and Internet enabled system.

2G (second generation) are capable of transmitting digital bits across the radio spectrum at rates that typically range between 9.6Kbps and 14.4 Kbps. In North America, digital wireless networks adhere to one of three standards:

CDMA (Code-Division Multiple Access)
TDMA (Time Division Multiple Access)
GSM (Global System for Mobile communications)

GSM is far the most popular standard in the World and particularly successful throughout Europe. What is important to know is that the three standards are incompatible with one another.

 

What are the differences between 2G and 2.5G/Pre 3G Devices

2G technologies offer narrowband access and slow data rates (the typical speed is from 9.6Kbps and 14.4Kbps) and designed primarily for voice or short bursts of text data. Whilst, 2.5G/Pre 3G technology offers 144Kbps and beyond and designed for data such as multimedia.

This new generation of wireless networks is meant to serve as a bridge between the existing 2G standards of GSM, CDMA & TDMA and the future standards of 3G, as defined by the ITU; an international organisation within the context of the United Nations to coordinate the development of telecommunications systems throughout the world.

 

The 2.5G standards

Several networking technologies have been proposed to bridge the gap between the second and third generations of wireless technology, but two stand out as the most prevalent: GPRS (General Packet Radio Service) and CDMA2000 1XRTT.

Both are packet-switched (data broken into groups, called packets, transmit individually across a network) networks as opposed to circuit-switched (data that transmits across dedicated channels, called circuits) networks, which essentially means they are designed to function more like the Internet than like a voice network. Similarly, both offer tremendous improvements in data transmission speed and always-on connectivity.

 

More on GPRS

Theoretically, GPRS can offer a maximum transmission rate in excess of 115Kbps and real-world throughput of 20 Kbps to 50 Kbps, GPRS serves as a data overlay (complementary networking layer) to GSM. The overlay lets wireless carriers send data across the existing network without replacing the GSM infrastructure. When you consider that GSM is by far the most common networking standard throughout the world, the real advantage of GPRS becomes apparent.

The next step in the GSM/GPRS migratory path is EDGE (Enhanced Data for GSM Evolution; also referred to as Enhanced Data GSM Environment and Enhanced Data Rates for Global Evolution), which is a GPRS enhancement that offers transmission rate of 384Kbps.

Mini Glossary for GSM

• ADPCM - Adaptive Differential Pulse Code Modulation
• Bandwidth-the range of a channel's limits; the broader the bandwidth, the faster data can be sent
• BSS - Base Station System
• BER - Bit Error Rate
• Bits per second (bps)-a single on-off pulse of data; eight bits are equivalent to one byte
• CDMA - Code Division Multiple Access. A wide-band spread-spectrum network technology.
• Frequency-the number of cycles per unit of time; frequency is measured in hertz (Hz).
• Frequency Band-The frequency range specified for GSM is 1,850 to 1,990 MHz (mobile station to base station).
• FDMA - Frequency Division Multiple Access
• 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
• PCH - Paging CHannel. Used by the network to inform the MS of an incoming call (downlink).
• PCM - Pulse Code Modulation
• PCN - Personal Communications Network/Public Communications Network. A term historically used to mean GSM at 1800Mhz. Now known as GSM1800
• PDU - Protocol Data Unit. Encoding method for data being transferred to/from a handset over the network.
• 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.
• Watt (W)-a measure of power of a transmitter

 

GSM Subscriber Services

There are two types of services offered through GSM Modem and GSM Network. These are Telephony services, which is also known as Teleservices and Data also known as bearer services. GSM telephony services are predominantly voice call services, which enables other subscribers to communicate with other connected users. GSM data services provide connectivity between two access points creating an interface to the network.

In addition to normal telephony and emergency calling, the following services are supported by GSM:

• Dual-Tone Multi-Frequency (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 3 - 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 (SMS) - 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 the subscriber via a personal security code to the desired fax number can retrieve them.

 

GSM Supplementary Services

GSM supports a comprehensive set of supplementary services that can complement and support both telephony and data services.

• Advice of Charge
• 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.
• Close User Group
• 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.
• Explicit Call Transfer
• 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.