what is digital cellular system?

What kind of information will you get from this blog?

1. What are digital cellular systems?
2. What are the advantages of digital cellular systems?
3. What are the differences between analog and digital cellular systems?
4. What is a global system for mobile and its types?
5. Architecture of GSM

 

Digital cellular systems:  

The digital cellular systems are GSM, CDMA, PDC, NA-TDMA and 1800-DCS. The cordless phone systems are DECT and CT-2 techniques digital cellular systems can use frequency division multiple access time division multiple access and code division multiple access. If a multiple-access technique is selected for a definite system, all the functions, protocols, and networks are connected with that technique.

 

Advantages of cellular system:

 The advantages of digital cellular systems are given

1. There is to be a ten-time capacity increase over analog systems.
2. Reduced RF transmission power and provides longer battery life.
3. They give international and wide-area roaming capability.
4. provide better security against fraud.
5. They give encryption for information security and privacy.
6. The compatibility with ISDN, leading to a wider range of services.
7. Ability to operate in small cell environments.

 

Differentiate between analog and digital cellular system:

 The differences between analog and digital cellular systems are given below-

Digital cellular systems	Analog cellular systems
Digital systems have an improved performance in high cochannel interference (CCI) and adjacent channel interference environments	Analog systems do not have an improved performance in high co-channel interference and  adjacent channel interference environment.
Digital cellular systems have international and wide area roaming capability.	These facilities are not provided by analog cellular systems.
They have ability to operate in small cell environments.	This is not possible in analog cellular systems.
These are compatible with ISDN, leading to wider range of services. wider range of services.	Analog cellular systems are not compatible with ISDN, leading to
They have encryption capability for information security and privacy.	These are not possible in analog cellular systems.
Digital cellular systems have reduced RF transmission power and longer battery life.	In analog cellular systems these are not possible.
Digital technology makes it possible to introduce new services.	These are not supported by AMPS or other analog systems.
For a fixed allocation of spectrum a large increse in capability implies corresponding reductions in cell size.	Here these are not possible.

 

 

GSM (Global system for mobile communications) : 

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 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 given 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.

 

Characteristics of the initial GSM standard :

1. A fully digital system utilizing the 900 MHz frequency band.
2. The TDMA over radio carriers with 200 kHz carrier spacing.
3. The eight full rate or sixteen half rate TDMA channels per carrier
4. The user/terminal authentication for fraud control.
5. Full international roaming capability
6. Encryption of speech and data transmissions over the radio path.
7.  Low speed data services upto 9.6 kbits/sec. 
8. Compatibility with ISDN for supplementary
9.  Support of short message service (SMS).
10. GSM supports a range of basic and supplementary services and these services are defined in terms analogous to those for ISDN.

 

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

PUBLICBLOGS.IN

Architechture of GSM : 

The sub-systems of GSM are given below-

1. Mobile station sub-system
2. Base station sub-system
3. Network and switching sub system
4. Operation sub-system

Mobile station sub-system : The mobile station consists of all user equipment and software required for communication with a GSM network. An mobile station contains SIM, which holds all user specific information that is required to GSM. While an 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 programmable soft keys. Further interfaces comprise computer modems.

IrDA or bluetooth, typical MSs e.g., mobile phones, comprise many more vendor-specific functions and components such as cameras, finger-print sensors, address book and internet browsers.

 

Base Station Sub-system (BSS) - The base station sub-system has a base station controller (BSC) and one or more subtending base transceiver stations (BTS). BSS is responsible for all functions related to the radio resource (channel) management. This includes the management of radio channel configuration with respect to use as speech, data, or signaling channels, allocation 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 -

• Handoff Management

1. Collect signal quality data from adjacent base station systems
2. analyze signal quality data and determine handoff requirement
3. Keep MSC informed regarding handoff activity

• 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 raido interface

• Digital signal processing

1. Transcoding and rate adaption
2. Channel coding and decoding

• Frequency hopping and power control

1. Assignment of frequency-hop sequence an start time
2. Assignment of effective radiated power values to mobile stations

 

Network and Switching Sub-system: The heart of the GSM system is formed by the network and switching sub-system (NSS). Refer figer, 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 -

• Mobile Services Switching Centre (MSC) - MSCs are high performance digital ISDN switches. They setup 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.

• 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 world wide GSM networks. All these user-specific information elements only exist once for each user in a single HLR, that also supports charging and accounting.

 

• Visitor Location Register (VLR) - The VLR associated to each MSC is very dynamic data base that stores all important information required for the MS users currently in the LA which is associated to the MSC. When a new MS comes into an LA, the VLR is responsible for, it copies all relevent information for this user from the HLR. This hierarchy of VLR and HLR avoids frequent HLR updates and long-distance signaling of user information.

 

• Operation sub system- Operating sub-system organization is shown blow

 

There are three areas of OSS-

1. Mobile equipment management
2. Network operation and maintenance functions
3. Subscrip-tion 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 

From this blog you are going to learn about digital cellular systems it's advantages and how it is different from analog cellular systems. it's  Architecture of GSM