GSM Technology

GSM technology arose from the union of many European countries. Initially, GSM was the acronym for Global Spécial Mobile, but soon came to mean Global System for Mobile. It was created with the intention of becoming a unified standard telephony able to replace several proprietary standards used in the first generation of cellular networks. The first GSM network went into operation in 1991 in Finland, and the pattern became popular so quickly became a dominant force in the world.

The standardization around the GSM ended up being one of the main factors that led to the popularization of mobile phones and smartphones, as the use of a common standard allowed the costs fall and the same devices were sold in different countries, with only minor changes in software and functions.

Versão em Português.

gsm

The most basic access technology in the GSM is the CSD (Circuit Switched Data), a system allowing connections to 9.6 kbit but was still a fee per minute, just as a voice call. In the CSD, the connection was made by the apparatus itself, without the need for an external modem. Since the connection was very slow, it ended up being usable only for light fares, how to replace SMS and emails.

GPRS

GPRS (considered a 2.5G technology) was the first choice of web access over the cellular network really usable. It is an entirely digital system based on packet transmission, a fee according to the amount of data transferred and not by connection time.

In GPRS slots (or channels) of data are used with 8 to 20 kbits each, in accordance with the modulation system used. The CS-4, used only when the unit is near to the antenna, offers the full 20 kbits. As the signal amount falls, begins to be used CS-3 (14.4. Kbits), CS-2 (12 kbits) or CS-1 (8 kbits).

In the system adopted by most phone companies are used a total of five slots, 4 of them to download and upload, resulting in 32-80 kbits to download and 8-20 kbits for upload. However, the rates obtained in practice are somewhat below that, due to lost packets and retransmissions.

It is common for speeds of GPRS connections are compared to the dial-up modems, but in practice they end up seeming slower, due to the enormous connection latency. While on a modem connection latency is around 100-200 ms, the GPRS is usually between 500 and 1000 ms, according to the signal quality and the number of relay stations where he needs go to reach the center.

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Currently, GPRS is the simplest mode of connection offered by GSM operators, used as a fallback in the areas where the UMTS or GPRS, keeping the same structure GSM, but implements a new modulation system that multiplies the speed connection by three. Despite the increase in speed, EDGE is not considered a 3G technology, but 2.75G.

EDGE

In EDGE are used nine modulation systems, ranging from MCS-9 (59.2 kbits per time slot) to the MCS-1 (8.8 kbits) through intermediate stages of 54.4, 44.8, 29.6, 22.4, 17.6, 14.8 and 11.2 kbits, according to the amount of the signal. As in GPRS four time slots are used for downloading and uploading to one time slot, resulting in 35.2 to 236.8 kbits for download and 8.8. to 59.2 kbits for upload.

Even in GSM networks already upgraded to EDGE, GPRS is still available, serving devices that do not support the EDGE, as in the case of older models as well as many of the appliances “made-in-China” sold in the informal market.

There is no practical difference in signal range between EDGE and GPRS, so the devices using EDGE continue to use the system regardless of signal quality. However, the EDGE access speed falls faster as the signal gets weaker and, in areas where the signal is bad, the difference between the two is very small (35.2 against 32 kbits).EDGE can be expanded to 8 slots, which doubles speed, allowing to reach 473.6 kbits and two telephone companies can be combined into a single connection, again doubling the download rate, which is now nearly 1 megabit. This technology is called EDGE Evolution and can be used by operators as an internal solution between EDGE and UMTS (3G). However, it was never used by the Brazilian telephony companies, which preferred to migrate straight to 3G.

Although the transfer speed “gross” is relatively high, the connections via EDGE working with a very high latency, which makes loading of much slower pages. In the GPRS access connections it is even worse, since the latency is combined with a low transfer rate. In general, surfing via EDGE is not unlike the experience of surfing using a 56k modem, and a connection via GPRS resembles a modem connection with a bad line.

GSM Technology Operating Scheme.

3G

On the other hand, things are much better in 3G, where there have been great improvements on both fronts. In an area with good coverage, you can even make VoIP calls comfortably and with an unlimited data plan, you can risk downloading a CD ISO or download other large files.

The major problem in using a 3G connection through the cell is the high speed transmission of data causes the battery runs out quickly. In most of the models, the autonomy to transfer data continuously (as when doing a download) is less than two hours, so that a USB charger turns out to be an important accessory for those who access using the notebook.

Of course, the device is able to save power when data is not being transferred, so that if you use the connection only to navigate and perform other basic tasks, with a low volume of data transfer, the battery can last several hours.

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Font

MORIMOTO, Carlos Eduardo. Smartphones, guia prático / Carlos Eduardo Morimoto. – Porto Alegre: Sul Editores, 2009. Pages 308-310. (with adaptations and updates)

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