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# Global System Mobile: Implentation, Architecture and Advantages

2245 words (9 pages) Essay in Information Technology

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The GSM standard

GSM (Global System Mobile) is a free standard system for digital mobile telephony. A GSM device can connect to a GSM network and send and receive messages, faxes, surf the Internet, securely access the computer network of a private company, as well as other digital functions that include data transmission, SMS, MMS… GSM was developed by the European Telecommunications Standards institute (ETSI) and it was first deployed in Finland in December 1991.

The GSM standard is considered, in terms of its transmission speed and other features, a second-generation system (2G). The third-generation UTMS standards and the fourth-generation LTE advanced standards that followed do not form part of the GSM standard.

## 1.    Worldwide implementation

The GSM association claims to have a total of 4300 million connected devices[1] which represents approximately the 90% of all the global terminals in use. It is present in 200 different countries, being the predominant standard in Europe, South America, Asia and Oceania, and with a great extension in North America[2].

The worldwide implementation of this system has brought some advantages for both customers and service providers. At customer level, it allows to subscribe to the network from any terminal using an identity chip, mostly know as SIM. For service providers, the fact that GSM is a free standard exempt them from having to pay for licenses and makes easier agreements between companies from different countries, minimizing adaptation costs. Another important advantage is the global number for emergencies, the 112, making easier that travellers from anywhere in the world can communicate emergency situations without the need to know a local number.

## 2.    Frequency bands

The GSM standard has been implanted in the following frequency bands[3]:

 Band Name Channels Notes GSM 850 GSM 850 128-251 Used in EE. UU, South America and Asia GSM 900 P-GSM 900 0-124 Used in Europe E-GSM 900 974-1023 R-GS 900 n/a GSM1800 GSM 1800 512-885 GSM1900 GSM 1900 512-810 Used in North America

Table 1. GSM frequency bands

## 3.    Network architecture and operation

The biggest trouble when designing the network structure for a mobile telephone system is to face the limitation of the range of available frequencies. Each conversation, or in short, each data traffic client needs a minimum of bandwidth for which the transmission can be carried out correctly. Each operator in the market is assigned a certain bandwidth in certain delimited frequencies that must be distributed for sending and receipting traffic to all its users. Therefore, a single antenna can’t be used for all the users at the same time, since the bandwidth would not be enough. In addition, the ranges in which the different users emit should be separated to avoid interferences between their shipments.

The structure of a GSM network is subdivided into layers that work, summarizing, in the following way. The Base Station (BS) solves the problem of accessing the channel’s end. The Network and Switching System (NSS) takes care of the routing one side, and on the other side of subscriber identification, charging and access control. In the following paragraphs is explained with more detail.

Image 1. The structure of a GSM network

### 3.5 Base Stations or BSS

As it was said before, the system must be able to support a large load of users using the network at the same time. If there were only one antenna for all users, the available radio-electric space would saturate very quickly. The solution for this is to reuse the available frequencies. Instead of using a single antenna for an entire city, many are placed, and the system is programmed so that each antenna uses different frequencies from its neighbours, but same as other antennas outside its range. Each antenna has certain frequency range, which corresponds to a certain number of radioelectric channels.

In addition, the antennas are provided with the necessary network electronics to communicate with the NSS, so they can take care of the management of the radio interface. The whole antenna with its electronics and its connection with the rest of the network is called Base Station Subsystem (BSS). The geographic area which a BS provides coverage is called a cell. This distribution system of the bandwidth is sometimes called Space Division Multiple Access (SDMA) or special division.

The use of the SDMA requires an additional layer of network that was introduced for the first time in the GSM standard called Base Station Controller (BSC) that works as an intermediary between the hearth of the network and the antennas and takes care of the frequency distribution and the power control of terminals and Base Stations.

A base station can reach a radius of coverage around it from several hundred meters to a practical maximum of 35 kilometres in rural areas[4]. However, and given that the number of users that can attend each BS is limited by the width of band that the BSC assigns to each BS, and although it could be thought that the base stations should have a great power to cover a larger area, it has a maximum rated power of 320 W and in fact always emit the smallest possible power to avoid interfering with distant cells that could use the same frequency range, which is why it is rare that more than 40W models are installed.

Therefore, in areas where there is a large concentration of users such as cities, a large number of BS of very limited power should be installed and in areas of lower density of use such as rural areas the number of stations can be reduced and its power higher. This also ensures a longer battery life of the terminals and less use of power from the base stations.

### 3.1 Base Station Controller (BSC)

The communication should not be interrupted because a user moves and leaves the coverage area of a BS. Both the user terminal and the BS calibrate the power levels with which they send and receive the signals and inform the base station or BSC accordingly. In addition, usually several base stations at the same time can receive the signal from a terminal and measure its power. In this case, the BSC sends the terminal to another contiguous station, less saturated, even though the terminal must emit more power. Therefore, the work of the BSC is also to control the power and the frequency at which they emit both terminals and BSs.

### 3.2 The Network and Switching System (NSS)

The Network and Switching System (NSS) is the logical layer of call routing and data storage. Each BSC is connected to the NSS and NSS is responsible for three tasks:

• Routing the transmission to the BSC.
• Provide interconnection with the networks of other operators
• Provide connection to the Subscriber Identification subsystem and operator databases, which give the user permission to use the network services according to their type of payment and payment status (base location and visitor records, HLR and VLR).

### 3.3 The Mobile Switching Central (MSC)

The Mobile Switching Central (MSC) is responsible for initiating, terminating and channelling calls through the BSC and BS corresponding to the called subscriber.

### 3.4 Home Location Register (HLR) and Visitor Location Register (VLR)

The Home Location Register (HLR) is a database that stores the user’s position within the network, whether it is connected or not and the characteristics of its subscription (services it can and cannot use, type of terminal, etc.). It is rather permanent in character; each mobile phone number is assigned to a specific and unique HLR, which is managed by its mobile operator.

The Visitor Location Register (VLR) is a more volatile database that stores for the area covered by an MSC, the identifications permissions types of subscription and locations in the network of all the active users at that moment and in that section of network. When a user registers in the network, the VLR of the section to which the user is connected contacts the HLR of the user’s origin and verifies whether he can make calls according to his type of subscription. This information remains stored in the VLR while the user terminal is on and refreshes periodically to avoid fraud.

The 4G (LTE) standard presents some serious advantages against the previous standards, the 3G developed by 3GPP, and the 2G GSM standard. Probably the most significant advantage is the higher speed. Due to the use of higher frequency bands, its results on a speed transmission due to 10 times the previous technologies. Another advantage is the higher capacity. The use of multiple antenna transmission as well as OFDM in the air interface makes that LTE can support up to 200 active data clients at full speed for every 5MHz cell[5], compared to 3G tower that could only support between 60 and 100 clients. Other advantage related is reduced latency. In the LTE architecture there are no circuit switched components. This makes the network architecture simpler and radio management faster, which results in a very low latency that can be even lower than 5ms.

There are other more technically advantages in the 4G LTE system like the spectral efficiency, the flexible bandwidth usage or the “cell breathing” technique that provides a better administration of the percentage of cell shrinkage.

## 5G Enhancements

The 5G is the fifth generation of cellular mobile communications, succeeding the previous mentioned generations. The performance enhancements that any 5G network aims to reach are:

• A peak data rate of 20 Gbit/s.
• An average data rate of 1 Git/s.
• A latency of 1m.
• A maximum speed of handoff of 500km/h.
• A connection density of

${10}^{6}/{\mathit{km}}^{2}$

.

• An energy efficiency equal to 4G.
• A spectrum efficiency equal to 4 times the 4G efficiency.
• An area traffic capacity of 10 Mbit/s/

${m}^{2}$

.

[1]GSM World (2010). Market Data Summary. [online] Available at: https://web.archive.org/web/20100521013451/http://www.gsmworld.com/newsroom/market-data/market_data_summary.htm

[2]GSM World (2010). Market Data and Analysis. [online] Available at: https://web.archive.org/web/20100603074806/http://www.gsmworld.com:80/newsroom/market-data/market_data_and_analysis.htm

[3] Radio-electronics.com. (2018). GSM Frequencies | GSM Channels & Frequency Bands | Radio-Electronics.Com. [online] Available at: https://www.radio-electronics.com/info/cellulartelecomms/gsm_technical/gsm-frequency-frequencies-bands-allocations.php

[4] Balanis, Constantine A. (2005). Antenna Theory: Analysis and Design. 1 (3rd ed.). John Wiley and Sons. p. 4. ISBN 047166782X.

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