GSM (Global System for Mobile Communication)

In this blog, we will explore an important topic of Cellular and Mobile Communication. In this blog, we will learn what GSM (Global System for Mobile Communication) is, its architecture, and its sub-systems.

What is GSM or Global System for Mobile Communication?

In the world today, the most successful digital mobile telecommunication system is GSM. It is used by over 800 million people in more than 190 countries. In the 1980s, Europe had numerous coexisting analog mobile phone systems, which were often based on similar standards but ran on slightly different carrier frequencies.

To avoid this situation for a second generation fully digital system, the Group Special Mobile (GSM) was founded in 1982 Soon, this system was named the global system for Mobile Communications (GSM) with the specification process lying in the hands of ETSI (European telecommunication standard institute), (GSM association 2002) In the context of UMTS (Universal mobile telecommunication system) and the creation of 3GPP (Third generation partnership project) the whole development process of GSM was transferred to 3GPP and further development is combined with 3G development, 3GPP assigned new numbers to all GSM standards.

What are the characteristics of the initial GSM or Global System for Mobile Communication Standard?

The characteristics of the initial GSM standard can be summarized as follows-

(i) A fully digital system utilizing the 900 MHz frequency band.

(ii) The TDMA over radio carriers with 200 kHz carrier spacing.

(iii) The eight full-rate or sixteen half-rate TDMA channels per carrier.

(iv) The user/terminal authentication for fraud control.

(v) Full international roaming capability.

(vi) Encryption of speech and data transmissions over the radio path.

(vii) Low-speed data services up to 9.6 kbits/sec.

(viii)Compatibility with ISDN for supplementary

(ix) Support of short message service (SMS).

(x) GSM supports a range of basic and supplementary services and these services are defined in terms analogous to those for ISDN.

Draw the GSM architecture and explain each sub-system.

The sub-systems of GSM are given below -

(i) Mobile Station Sub-system- The mobile station consists of all user equipment and software required for communication with a GSM network. A mobile station contains a SIM, which holds all user-specific information that is required for GSM. While a mobile station can be identified by the international mobile equipment identity (IMEI), a user can personalize any MS using his or her SIM. Without SIM, only emergency calls are possible.

Apart from the telephone interface, an MS can also offer other types of interfaces to users with display, loudspeaker, microphone, and MS BSS programmable soft keys. Further interfaces comprise computer modems, IrDA or Bluetooth, and typical MSs e. g., mobile phones, which comprise many mons Irodor-specific functions and components such as cameras, fingerprint sensors, address book, and internet browsers.

(ii) Base Station Sub-system (BSS) - The base station sub-system has a base station controller (BSC) and one or more such tending base transient ha a hashes (BOS) BSS is responsible for all function agreement the radio resource (channel) management. This includes data, or ehf radio channel (configuration with respect to use as speech, data, or signaling channels, allocating and release of channels for call setup and release, control of frequency hopping, and transmit power at the mobile station (MS).

Thus, the range of functions performed by the BSS includes the following -

a) Handoff Management - 

(1) Collect signal quality data from adjacent base station systems

2) Analyze signal quality data and determine handoff requirements

(3) Keep MSC informed regarding handoff activity.

(b) Radio Resource Control -

(1) Configuration of radio channels

(2) Selection, allocation, and de-allocation of radio channels

(3) Monitoring of radio channel busy/idle status

(4) Encryption of radio interface.

(c) Digital Signal Processing -

(1) Transcoding and rate adaption

(2) Channel coding and decoding.

(d) Frequency Hopping and Power Control -

(1) Assignment of frequency-hop sequence and start time.

(2) Assignment of effective radiated power (ERP) values to mobile stations.

(iii) Network and Switching Sub-system- The heart of the GSM system is formed by the network and switching sub-system (NSS). Refer to the Figure, the NSS connects the wireless network with standard public networks, performs handovers between different BSSs, comprises functions for worldwide localization of users, and supports charging, accounting, and roaming of users between different providers in different countries. The NSS has the following switches and databases -

(a) Mobile Services Switching Centre (MSC) - MSCs are high-performance digital ISDN switches. They set up connections to other MSCs and to the BSCs via the A interface. Therefore, MSCs form the fixed backbone network of a GSM system. Typically, an MSC manages many BSCs in a geographical region. A gateway MSC (GMSC) has additional connections to other fixed networks, like PSTN and ISDN.

Using additional interworking functions (IWF), an MSC can also connect to public data networks (PDN) like X.25. An MSC manages all signaling required for connection setup. connection release and handover of connections to other MSCs. To achieve this, the standard signaling system No.7 (SS7) is used.

An MSC also performs all functions required for supplementary services such as call forwarding, multiparty calls, reverse charging, etc.

(b) Home Location Register (HLR) - HLR is the most important database in a GSM system as it stores all user-relevant information. This contains static information, such as the mobile subscriber ISDN number (MSISDN), subscribed services, and the authentication key K.

In addition, dynamic information is required, for example, the current location area (LA) of the MS. When MS leaves its current LA, the information in the HLR is updated. This information is essential to localize a user in the worldwide GSM networks. All these user-specific information elements only exist once for each user in a single HLR, that also supports charging and accounting.

(c) Visitor Location Register (VLR) - The VLR associated with each MSC is a very dynamic database that stores all important information required for the MS users currently in the LA which is associated with the MSC. When a new MS comes into an LA, the VLR is responsible for, it copies all relevant information for this user from the HLR.

This hierarchy of VLR and HLR avoids frequent HLR updates and long-distance signaling of user information.

(iv) Operation Sub-system- The operating sub-system organization is shown in the figure.

There are three areas of OSS-

(a) Mobile equipment management.

(b) Network operation and maintenance functions

(c) Subscription management, including charging and billing

These operations need interaction among some or all of the infrastructure equipment. In any existing network, OSS can be implemented.

Conclusion -

In the world today, the most successful digital mobile telecommunication system is GSM. It is used by over 800 million people in more than 190 countries. In the 1980s, Europe had numerous coexisting analog mobile phone systems, which were often based on similar standards but ran on slightly different carrier frequencies. In this blog, we have learned about the GSM, its architecture, and each sub-system. I hope you all like this blog.

Do you dream of turning your thoughts and words into income ? join us now and become blogger now.

PUBLICBLOGS.IN