Uses 3G mobile broadband

UMTS and GSM - a comparison of technology

Mobile broadband internet has become a reality with UMTS. We'll show you what techniques are used to send more data through the air.
Image: cristimatei - Fotolia.com UMTS (Universal Mobile Telecommunications System) is also referred to as the third generation of mobile communications (3G). The first mobile network in Germany was the A-Netz, which was introduced in 1958 and has since been discontinued. It was replaced by the B network in the 1970s, which was followed by the C network in the 1980s. This analog network of Deutsche Telekom, which was discontinued at the end of 2000, still belongs to the first generation of mobile communications.

Mobile broadband internet has become a reality with UMTS. We'll show you what techniques are used to send more data through the air.
Image: cristimatei - Fotolia.com The second are the digital D and E networks based on the GSM standard, which will continue to operate with the introduction of the UMTS standard. The UMTS licenses are initially granted in Germany until 2020, the GSM licenses until 2016.

TDMA and WCDMA - the carrier technologies of GSM and UMTS

So that the many different mobile radio devices in a network do not interfere with each other, there are different methods of telling the devices apart. The simplest method is used with analog radio. All transmitters work on different frequencies. To listen to a particular station, you simply select the relevant reception frequency. The disadvantage of this method, which is also called frequency division multiplex: You need a separate transmitter for each possible frequency. A base station that is supposed to serve ten cell phones would therefore also have to have ten separate transmitting and receiving parts (transceivers). This is complex and expensive.

Time division multiple access (TDMA) is predominantly used in a GSM network. This means that different devices transmit one after the other on one frequency. Each device only has a specific short time slot available for its data or voice transmission. Here is an example: A transmitter transmits data in time slots that are 1/100 of a second long. The first 1/100 of a second data is then transferred to the mobile phone 1. The next 1/100 of a second is on Handy 2, and so on. After about five to eight cell phones, the rotation starts all over again, so that each cell phone is supplied several times per second.

UMTS, on the other hand, is based on the so-called WCDMA method (Wideband Code Division Multiple Access), which differs greatly from the time division multiplex method used up to now. The base station assigns a different code to each cell phone in its transmission area, which the cell phone can use to filter out the specific user data from the overall data stream. Similarly, the cell phones also receive different codes in order to send their data back to the base station. Similar to GPRS, the participants automatically share the total available bandwidth of the radio cell. This increases the transmission speed and the network resources can be used optimally. Another plus point of the procedure: The participant is always online. Disadvantage of the method: The maximum transmission rate decreases with the distance between the cell phone and the radio mast and with the speed at which the cell phone is moved (for example in a car or train).

Data in GSM networks

With GSM it was originally intended that all devices share the entire possible data transmission rate equally. The individual part is also referred to as a virtual channel. With the GSM standard, this has a maximum data transmission rate of 9.6 kBit / s, or 14.4 kBit / s in compressed mode with reduced error correction. This bandwidth is suitable for voice transmissions, but excruciatingly slow for data transmissions.

To mitigate this disadvantage, three technologies are available for GSM networks: HSCSD, GPRS and EDGE make it possible to bundle several virtual data channels in order to increase the transmission rate.

With HSCSD, the mobile radio device uses up to four fixed data channels and thus enables transmission rates of a total of 57.6 kBit / s. The problem with this is that all channels remain busy even when the user is not transmitting any data, for example because he is reading an e-mail or a website. HSCSD is now out of date and is only available to Vodafone and Alt-E-Plus customers.

GPRS compensates for this disadvantage by dynamically allocating each mobile device a share of the total capacity reserves available in the network. GPRS works in a packet-oriented manner, no fixed data channels are reserved. A disadvantage of GPRS: If there is no capacity reserves because the network is already very busy or because many users want to transmit data at the same time, the transmission rate drops towards zero. EDGE technology is an improvement on GPRS technology and uses optimized modulation methods so that the maximum usable data throughput can increase to up to 473 kBit / s.

Data in UMTS networks

Another difference between GSM and UMTS technology lies in the bandwidth of the frequencies used. In the D and E networks, this is around 200 kHz. With UMTS, on the other hand, it is 5 MHz - that is 25 times the value. These large frequency spectra enable the fast data transmission rates with UMTS.

In addition, UMTS networks are characterized by a new type of cell structure. The smallest cell is the picocell with a diameter of less than a hundred meters. So-called 'hot spots', office buildings, hotels, airports, trade fairs and the like are supplied with picocells. The micro cell with an extension of up to several kilometers supplies entire urban areas. For suburbs there is the macro cell with a range of over 20 kilometers. Hyper and umbrella cells, which are also referred to as world cells in the global UMTS concept, can reach an expansion of several hundred kilometers.

UMTS can theoretically enable transmission rates of up to 2 Mbit / s. With HSPA technology or HSPA +, even higher bandwidths of up to 42.2 Mbit / s and more are possible.

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