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GSM Technologies

Introduction. The development of GSM started in the early 1980s. It was seen then as the mainstay of the plans for Europe´s mobile communication infrastructure for the 1990s. Today, GSM and its DCS 1800 and PCS 1900 versions have spread far beyond Western Europe with networks installed across all continents.The story begins in 1982 when the European Conference of Posts and Telecommunications Administrations (CEPT), consisting then of the telecommunication administrations of twenty six nations made two very significant decisions. The first was to establish a team with the title "Groupe Spéciale Mobile" (hence the term "GSM", which today stands for Global System for Mobile Communications) to develop a set of common standards for a future pan-European cellular network. The second was to recommend that two blocks of frequencies in the 900 MHz band be set aside for the system.The CEPT made these decisions in an attempt to solve the problems created by the uncoordinated development of individual national mobile communication systems using incompatible standards. The impossibility of using the same terminal in different countries whilst traveling across Europe was one of these problems; another was the difficulty of establishing a Europe-wide mobile communications industry that would be competitive in world markets due to the lack of a sufficiently larger home market with common standards - with its attendant economies of scale.
By 1986 it was clear that some of these analogue cellular networks would run out of capacity by the early 1990s. As a result, a directive was issued for two blocks of frequencies in the 900 MHz band, albeit somewhat smaller than recommended by the CEPT, to be reserved absolutely for a pan-European service to be opened in 1991.
In the meantime the GSM members were making excellent progress with the development of agreed standards. One major decision was to adopt a digital rather than an analogue system.
The digital system would offer improved spectrum efficiency, better quality transmission and new services with enhanced features including security. It would also permit the use of Very Large Scale Integration (VLSI) technology which would lead to smaller and cheaper mobiles, including hand held terminals. Finally, a digital approach would complement the development of the Integrated Services Digital Network (ISDN) with which GSM would have to interface.
GSM initially stood for Group Spécial Mobile, the CEPT (Conference of European Posts & Telegraphs) formed the group to develop a Pan-European cellular system to replace the many systems already in place in Europe that were all incompatible.The main features of GSM were to be International Roaming ability, good sound quality, small cheap handsets and ability to handle high volumes of users. GSM was taken over in 1989 by the ETSI (European Telecommunications Standards Institute) and they finalised the GSM standard in 1990. GSM service started in 1991. It was also renamed this year to Global System for Mobile communications (GSM).
Today there are approx. 105 countries with GSM networks or planned networks and many more are planned with around 32 million subscribers world wide on the 139 networks. This accounts for over 25% of the world's cellular market.
The MoU "Memorandum of Understanding" has over 210 members from 105 countries, this organisation meets ever three to four months to look at new or better implementations to the GSM system.
The MoU has a website that goes into more details at http://www.gsmworld.com.
Highlights. 1982 CEPT forms Groupe Spéciale Mobile (GSM) and recommends reservation of frequencies in 900 MHz band for future pan-European cellular system.1987 Memorandum of Understanding (MoU) signed in Copenhagen by operators from thirteen European countries.
1992 First commercial GSM networks start to come into service.
1992 First international roaming agreement signed between Telecom Finland´s and Vodafone (UK´s) GSM networks.
1992 Australian operators are first non-European operators to sign the MoU.
1993 Status report: thirty GSM networks in (end) service worldwide with more than one million customers. Seventy MoU members from forty five countries.
1994 Status report: sixty GSM networks in service (end) worldwide with more than four million customers. Over one hundred MoU members from sixty countries.
1995 Status report: one hundred and twenty (end) GSM networks in service worldwide with more than twelve million customers. Over one hundred and fifty MoU members from ninety countries.
GSM Requirements The quality of Voice in the GSM system must be better then that achieved by the 900MHz analogue systems over all the operating conditions.
The system must offer encryption of user information
The system must operate in the entire frequency band 890-915MHz and 935-960MHz.
An international standardised signaling system must be used to allow the interconnection of mobile switching center's and location registers.
Minimise modifications to the existing fixed public networks.
Design the system so handset costs are minimised
Handsets must be able to be used in all participating countries
Maximum flexibility for other services like ISDN
System should maximise the functions and services available to cater for the special nature of mobile communications.
GSM Information 
With digital, sound quality is sharp and clear. Background sounds and static are vastly reduced and crossed-line conversations are also eliminated. In comparison with analogue there are also far fewer dropouts, and overall the quality is more like that of a fixed telephone.
Unlike analogue, everything you say and send within the digital network is safe and secure. Some features are user authentication that prohibits unauthorised access, encryption key distribution that guarantees the privacy of the call and caller identification restrictions that can prevent the delivery of the calling users number to the receiver.
With digital, better technology means better battery life. You get up to twice as much talk time from each battery charge, compared with analogue. In addition the digital service allows more calls to be handled at any one time, therefore reducing congestion in areas of dense population and high usage.
With digital, you are able to use your mobile phone, and number in other countries around the world who operate a GSM network. Click HERE to view the list of GSM operators around the world. Or you can just take your SIM card and use another GSM phone. Your home carrier must have a roaming agreement in place and must be notified before leaving so that you can be activated in that country. All you need to do is switch on the phone at your destination and you will automatically log into the network. Dependent on the country you can still use your old SIM, but some countries will require you to get a loan SIM from your carrier before going there. This will give you a new number whilst in that country but you can easily set up a diversion to the new number if need be.

GSM Network comprises three parts, Mobile Station (MS) which is similar to a cordless phone with extra features, the Base Transceiver Station (BTS) that controls the connection with the Mobile Station, the Base Station Controller (BSC) that controls multiply Base Transceiver Station's and then the rest of the network covered further below..
Mobile Station (MS)A Digital Mobile Phone and a SIM card make up the Mobile Station. The SIM (Subscriber Identity Module) is a card that fits into your handset and is one of two sizes - either full size (same size as a credit card) or the smaller plug in version. The SIM microprocessor is based on a silicon chip which is designed to tolerate temperatures between -25 Degrees Celsius and +70 Degrees Celsius, and will also withstand up to 85% humidity. However silicon is fragile and, therefore, if the card is tampered with, physically or electronically, the card will be rendered useless.
The SIM contains all of your identification details, such as your IMSI (International Mobile Subscriber Identity. This is a numeric string, where the first 3 digits represent the country where the SIM is from, the next represent the operator in that specific country. The other digits represent the subscribers identity in his home-network), phone memories, billing information, SMS text messages, pin numbers and international roaming information.
A IMEI (International Mobile Equipment Identity) card is the serial number of the GSM phone that is the equivalent of the ESN number in a Analogue Phone, this is fixed in the phone and cannot be changed. The SIM card contains a IMSI (International Mobile Subscriber Identity) number that identifies the user to the network along with other user and security information.
Base Transceiver Station (BTS)The Base Transceiver Station consists of a radio transceiver with antenna that covers a single cell. It handles the communications with the MS via radio interface.BTS are all connected together to allow you to move from one cell to another. The antenna can take on various forms, in the UK lampposts are being used, but normally it has three directional cells.
Base Station Controller (BSC)The Base Station Controller manages multiple BTS's. It controls the allocation and release of radio channels and handovers between cells.
A series of BTS's are connected to each Base Station Controller, the BSC keeps a eye on each call and decides when to pass the call off to another BTS and to which one.
The Rest of the NetworkSeveral BSC's are controlled by the Mobile service Switching Center (MSC), the MSC works with four databases (HLR, VLR, EIR and the AuC) and together they manage the communications between Mobile Station user and the other network types. Each of the databases has a separate job, these are as follows
Mobile Switching Center (MSC) The Mobile Switching Center is the interface between the base station system and the switching subsystem of the mobile phone network. Furthermore, the MSC is also the interface between the cellular network and the PSTN. The MSC generates all billing records and ensures that all usage is directed to the appropriate account. The MSC has a relatively complex task, as unlike a conventional telephone exchange, when GSM subscribers make calls they could be anywhere within the network. The MSC must ensure that calls are routed through to those subscribers, wherever they are and wherever they move to throughout the duration of each cell. This situation becomes even more complex when two mobile subscribers wish to contact each other from two distant locations. 
In order to simplify the subscriber management function, a specific service area is allocated to each MSC. The MSC has to control the switching of tariff to and from the subscribers within it's service area which involves the coordination of all radio resources and the inter cell hand-off activities. 
Home Location Register (HLR) The HLR is the central data base for all the subscribers which contains details on the identity of each subscriber, the services to which they have access and the locations where the subscriber was last registered. 
All subscriber administration procedures are communicated to the HLR where the data is stored until it is required by another part of the Public Land Mobile Network (PLMN). The two key references used to route calls to each subscriber are the International Mobile Subscriber Identity (IMSI) and the Mobile Subscriber Integrated Services Digital Network (MSISDN) number. The IMSI is the unique number allocated to the subscriber which is stored in the SIM Card and is used by the network for internal communications. When the SIM Card is inserted into a Mobile Equipment it becomes a Mobile Station. The MSISDN is the subscriber's mobile number which is linked to the IMSI in the HLR. Incoming calls to a subscriber are translated back to the IMSI at the HLR thus enabling them to be delivered to the Mobile Station. 
Once the Mobile Station's MSISDN has been used to identify the IMSI, the HLR verifies the subscription records to ensure that the call can be delivered to the last known location of the Mobile Station. 
Visitor's Location Register (VLR) The VLR is a database that is linked to an MSC and temporarily stares information about each Mobile Station within the area served by that MSC. The information that is temporarily stored in the VLR is sufficient to allow any Mobile Station within that MSC area to make and receive calls. This includes the Mobile Station's identity, the area in which it was last registered and data pertaining to the subscriber and any supplementary services that have been selected by the subscriber. The MSC refers to the VLR each time that a Mobile Station attempts to make a call in order to verify that the request can be fulfilled. This process is to establish that no call restrictions or call barring instructions are in place. 
Equipment Identity Register (EIR) The EIR ensures that all Mobile Equipment's are valid and authorised to function on the PLMN. Three categories exist on the EIR, a white list, a gray list and a black list. The white list comprises the IMEI ranges of all the Mobile Equipment's that have been approved by any one of the three European, GSM approval centers. Any Mobile Equipment that appears on the gray list will be allowed to function but will trigger an alert to the network operator. This facility allows the network operator to identify any subscriber that is using a lost or stolen Mobile Equipment. 
Mobiles that are lost or stolen can be blacklisted which will prevent them from functioning on the home PLMN or on other PLMNs around the world. 
Central Equipment Identity Register (CEIR) A central EIR is managed by the MoU Permanent Secretariat in Dublin, Ireland. Every MoU member is committed to linking their network's EIR to the CEIR by January 1995. The advantage in having the CEIR concept is that it empowers each network operator to restrict or prevent the operation of any given MS throughout all PLMNs that are linked up to the CEIR. 
Authentication Center (AUC) The authentication center is used to validate the SIM Card being used by the Mobile Station. Secret information that is held in the AUC and which is also contained within the SIM Card is used to perform a complex mathematical calculation. Authentication occurs if the results of these two calculations agree. 
SMSC (SMS Center or Service Center), the SMSC handled all the SMS messages that are sent. The messages are sent on a data channel so you can receive them whilst on a call. GMSC (Gateway MSC), is a gateway switch where the call is directed when setting up a call to a GSM user. The GMSC looks for the subscriber by interrogating the right HLR which then interrogates the VLR and routes the incoming call towards the MSC where the subscriber can be reached The frequency bands allocated are 890-915MHz and 935-960MHz. Half is used for transmitting and the other half is used for receiving. To allow maximum number of users access, each band is subdivided into 124 carrier frequencies spaced 200KHz apart, using FDMA techniques. By applying TDMA techniques, each of these carrier frequencies is further subdivided into time slots which provide each user with the carrier frequency for approximately 0.577ms. This equates to approx. 217 jumps per second, but amongst a very small frequency range so encryption is a must for proper security of calls. In fact it is not exactly that, it is hopping 13 times every 60 ms, which gives 13/0.06 per second. 0.577ms = 13 frames/60 ms /8 time slots There is also an extension band of 15 MHz in both directions. There is also DCS 1800 which is equivalent to GSM but at 1800 MHz and the USA will use the 1900 MHz band for what they call the PCS (which is either CDMA or GSM like). 


UMTS Technology

UMTS (Universal Mobile Telephone Service) is a Third Generation (3G) mobile system being developed within the ITU's IMT-2000 framework. 

UMTS has the support of many major telecommunications operators and manufacturers because it represents a unique opportunity to create a mass market for highly personalised and user friendly mobile access to the Information Society. 

UMTS seeks to build on and extend the capability of today's mobile, cordless and satellite technologies by providing increased capacity, data capability and a far greater range of services using an innovative radio access scheme and an enhanced, evolving core network. 

Spectrum for UMTS 
WRC'92 identified the frequency bands 1885-2025 MHz and 2110-2200 MHz for future IMT-2000 systems, with the bands 1980-2010 MHz and 2170-2200 MHz intended for the satellite part of these future systems. 

How and When? 
For the commercial and technical success of UMTS, and to meet its 2002 launch deadline, a number of steps are being undertaken by manufacturers, standards bodies, operators and regulators around the world: 

- Creating an adequate regulatory framework 
- Ensuring availability of licences 
- Allocating adequate spectrum to operators 
- Producing timely UMTS standards 
- Encouraging simultaneous uptake of UMTS in several countries to stimulate uptake of services in a world-wide market. 
- Full commercial phase (2002-2005), with performance and capability enhancements, and the introduction of new, sophisticated UMTS services


TDMA Technology

TDMA is short for Time Division Multiple Access, a technology for delivering digital wireless service using TDM (which itself is short for time-division multiplexing).

TDM is a type of multiplexing that combines data streams by assigning each stream a different time slot in a set. TDM repeatedly transmits a fixed sequence of time slots over a single transmission channel. Within T-Carrier systems, such as T-1 and T-3, TDM combines Pulse Code Modulated (PCM) streams created for each conversation or data stream.

TDMA works by dividing a radio frequency into time slots and then allocating slots to multiple calls. In this way, a single frequency can support multiple, simultaneous data channels. TDMA is used by the GSM digital cellular system.


CDMA Technology

What are the benefits of CDMA? TOP
CDMA brings several major benefits over other similar technologies. CDMA offers the greatest network capacity to serve more subscribers with the same amount of infrastructure costs. It has the clearest and most achievable path to future higher speed standards. CDMA operators provide broad coverage in the US and abroad. It is the wireless technology that will provide the highest transmission speed in the next few years.

Which wireless operators deploy CDMA systems? TOP
In the US, Verizon (Bell Atlantic, GTE, AirTouch, Primeco PCS) and Sprint PCS provide the largest CDMA footprint that covers most of the U.S. Regional CDMA carriers include Qwest Wireless and Alltel.
Korean operators are among the largest CDMA carriers in the world. SK Telecom, KT Freetel and LG share more than 27 million CDMA subscribers in Korea.

What is the difference between cdmaOne and cdma2000? TOP
CdmaOne is the commercial term branded by CDMA Development group (CDG) for all IS-95 based CDMA systems. Cdma2000 is the commercial name for next generation high-speed data and voice transmission, including 1XRTT and beyond. Cdma2000 1x allows a maximum data speed of 144 kbps initially and ultimately to 307 Kbps. It will potentially increase network capacity by as much as 80% over cdmaOne. CDMA wireless operators around the world have committed to deploy cdma2000 1x.

Is CDMA the only technology capable of delivering wireless communications solutions? TOP
No. There are many competing technologies that currently offer either wireless voice and/or data. These include GSM, TDMA and CDPD. In addition there are also many next generation wireless data solutions that will compete with future evolutions in CDMA technology. These include GPRS, EDGE, and W-CDMA.

Why is AirPrime focused on CDMA? TOP
AirPrime has strategically put its focus on CDMA as its core technology for wireless communications solutions because CDMA technologies form the basis of the ultimate standards of worldwide wireless technologies. CdmaOne, the fastest growing wireless technology in the world, will migrate to cdma2000. All other wireless technologies, such as GSM, TDMA, GPRS and EDGE, will eventually be replaced by W-CDMA, which is also a CDMA technology. With laser-like focus on CDMA, AirPrime is positioned to deliver the best in class wireless solutions for North America and the world markets.

How is AirPrime using CDMA technology? TOP
AirPrime is developing wireless communications modules and software based on CDMA technology for worldwide OEMs, including manufacturers of PCs, PDAs, Internet appliances, and mobile communications solutions for other consumer products.

Information On Other Wireless Technologies

What is GSM? TOP
GSM (Global System for Mobile) communications is a digital technology developed in Europe during the 1980s and first deployed in the early 1990's. Today it is widely used in Europe and Asia Pacific. Commonly referred to as a second-generation (2G) technology, GSM networks serve roughly half of the total wireless voice subscriber base in the world.

What is TDMA? TOP
TDMA (Time Division Multiple Access), also commonly referred to as D-AMPS (Digital Advanced Mobile Phone System), works by dividing an original AMPS channel narrow radio channel into time framed slots to increase capacity. TDMA, which is widely used in the US, South America and parts of theAsia Pacific region for wireless voice communications, supports a circuit-switched data rate of 9.6 kpbs, although no operator in the U.S. has deployed such service.

What is CDPD? TOP
CDPD (Cellular Digital Packet Data) is an overlay technology using the existing AMPS (Advanced Mobile Phone System) analog cellular infrastructure. CDPD systems share the same set of cellular frequencies with AMPS. CDPD is an IP-based, packet-switched network that supports a maximum raw data speed of 19.2 kpbs. AT&T Wireless and Verizon are two of the major operators who support CDPD today in the U.S.

What is GPRS? TOP
GPRS (General Packet Radio Service) is the next generation data technology for GSM. GPRS can send data at speeds ranging from 9.6 kpbs to 57.6 kpbs by combining three to six voice channels in the TDMA system. GPRS is expected to be widely deployed in Europe within the coming year.

What is EDGE? TOP
EDGE (Enhanced Data rate for GSM Evolution) is an evolutionary 3G technology based on existing GSM and TDMA/IS-136 standards. EDGE will allow more data (up to 384 Kbps) to be transmitted over the TDMA radio frequency once channel quality improves.

What is W-CDMA and how does it differ from cdmaOne and cdma2000? TOP
CdmaOne and cdma2000 are based on the same standard where cdma2000 technologies represent the evolution of cdmaOne. W-CDMA or Wideband CDMA is also a CDMA technology that has different system parameters and implementation details. W-CDMA and cdma2000 are not fully compatible, but there is ongoing effort to minimize their differences to reduce costs and complexity of future wireless devices that support both technologies. W-CDMA will be deployed in Japan, Europe and Asia Pacific, while cdma2000 will be deployed in North America and Asia Pacific.

What are the relationships of all these technologies? TOP
CdmaOne will evolve to cdma2000, which is a 3G world standard. GSM and TDMA will migrate to GPRS and then EDGE. Eventually, GPRS and EDGE systems will be replaced by W-CDMA, the other 3G world standard.

Analog Technology

AMPS Advanced Mobile Phone System AMP's was developed by Bell Labs in the late 1970's and was released in the USA in 1983. It uses the 800MHz band and is currently the largest Analog standard used.
C450 C-450 Installed in South Africa during the late 1980's. Uses a 450MHz band.
C-Netz C-Netz Launched first in 1981 in Sweden by the Comvik network, found mainly in Germany and Austria.
JTAC Japanese Total Access Communications System Motorola system similar to AMPS. First installed in the UK in 1985. Utilises the 900MHz band.
HICAP NTT-HICAP High capacity version of NTT
N-AMPS Narrowband Advanced Mobile Phone Systems Developed by Motorola as a migrationary step between Analog and Digital. Three times the capacity of AMPS utilising the same band.
NMT450 Nordic Mobile Technologies Developed by Ericsson and Nokia to operate in the rugged terrain in the Nordic countries. Range 25km. Utilises the 450MHz band and uses FDD FDMA.
NMT900 Nordic Mobile Technologies Developed by Ericsson and Nokia to operate in the rugged terrain in the Nordic countries. Range 25km. Utilises the 900MHz band and uses FDD FDMA.
NMT-F Nordic Mobile Technologies - France French version of NMT
NTT Nippon Telegraph and Telephone Original Japanese Analog system.
RC2000 Radiocom 2000 French System released in November 1985
TACS Total Access Communications System Motorola system similar to AMPS. First installed in the UK in 1985. Utilises the 900MHz band.

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