Why there is a single frequency in 3G

UMTS - Universal Mobile Telecommunications System

UMTS is a 3rd generation (3G) cellular technology that was originally intended to replace GSM (2nd generation, 2G). But it never got that far. For UMTS, GSM is still the fallback in the cellular network.
UMTS technology is based on packet-oriented switching and the Internet protocol in order to create the conditions for mobile communication services.

  • Video telephony / video conference
  • Internet access
  • Email and data transfer
  • eCommerce / online shopping
  • Financial services / mobile banking
  • Music / video on demand
  • Mobile radio and television
  • Information services
  • navigation
  • Telematics

UMTS is part of the IMT-2000 family, the umbrella term for the 3rd generation (3G) of mobile radio systems. UMTS was initiated by the European (ETSI) and the Japanese (ARIB) standardization organizations. The Japanese in particular were in a hurry, as bottlenecks in the Japanese mobile network were to be feared. That is why the first public UMTS network went live in Japan in October 2001.

Replace UMTS by 2020

In the terms and conditions of Deutsche Telekom there is a note that the 3G mobile radio technology UMTS and HSPA is "only available until December 31, 2020, subject to an extension". It should look similar with the other network operators. Concrete statements as to when 3G will no longer be available will be difficult to make.

The following facts must be taken into account when using 3G cellular technology:

  • From 2021 and 2023, the 3G frequencies will be used for 5G mobile communications.
  • The 3G networks were never available nationwide across Germany.
  • Cellular modems and routers with UMTS were always dependent on an automatic fallback to 2G networks (GSM and GPRS).
  • If additional devices are added due to the shutdown of 3G and the resulting fallback, individual 2G cells can be overloaded, which is why all communication is only possible to a limited extent or even fails completely.
  • The network operators are busy expanding their networks for LTE and 5G. The capacities for 2G and 3G will be reduced.

2G and 3G are not future-proof. Only LTE will partially be included in the 5G standard and will continue to be available and is therefore future-proof.

Future-proof standards are available with LTE-Cat-1 and LTE-Cat-M1. LTE-Cat-1 in particular is an ideal replacement for the previous use of UMTS and GPRS until 5G is available nationwide in Germany.

Frequency ranges

The UMTS specification provides for two different modulation methods, which also differ in the frequency ranges used.

 Access procedureFrequency ranges
FDDFrequency division multiplex1.920 ... 1.980 GHz (uplink)
2.110 ... 2.170 GHz (downlink)
TDDTime division multiplex1.900 ... 1.920 GHz
2.010 ... 2.025 GHz

The access method for FDD uses the frequency ranges 1.920 to 1.980 GHz and 2.110 to 2.170 GHz. TDD uses the frequency ranges 1.900 to 1.920 GHz and 2.010 to 2.025.
If the frequency band is divided into frequency carriers, there are 12 frequency carriers in the FDD frequency range, each with 5 MHz in the uplink and downlink direction. The duplex spacing is 190 MHz.
7 unpaired frequency carriers of 5 MHz each are defined for the TDD frequency band. The UMTS frequencies were allocated in 5 MHz blocks. In Germany, 2 duplex frequency carriers were auctioned to 6 mobile phone providers and 5 of the 7 unpaired blocks to 5 mobile phone providers. 2 of the unpaired blocks are still free. They serve as a protective distance to the neighboring DECT frequency range.

UMTS in the 900 MHz band

Mobile communications suffer from the fact that the network capacity is limited and many participants have to share the limited bandwidth. In addition, the utilization of cellular networks has increased significantly due to low tariffs and new applications. In many places mobile communications with UMTS can only be used to a limited extent because there is not enough capacity available in the frequency spectrum. In order to increase the network capacity, additional frequencies are required, which are unfortunately not available.

So far, part of the 900 MHz band has been reserved for GSM. However, because the frequency bands below 1 GHz have more favorable propagation conditions, which enables larger radio cells and better indoor coverage, the link between the 900 MHz band and GSM has been lifted. The frequency usage of the 900 MHz band has been revised in Europe and allows the use of UMTS / HSPA.

In order for this to work in practice, two problems have to be solved. One problem is the frequency distribution. A contiguous channel bandwidth of 5 MHz is necessary for UMTS. But the division of the 900 MHz band was originally made according to the requirements of GSM. A channel bandwidth of 200 kHz is sufficient here.
In addition, the mobile phones must also support UMTS in the 900 MHz band.

CAMEL - Customized Applications for Mobile Network Enhanced Logic

The UMTS specification not only deals with the technical side, i.e. the transmission technology for mobile applications, but also new services. Within the specification, this is dealt with under the generic term CAMEL. This includes services and applications such as location-based services and flexible billing models such as home zone tariffs or prepaid services. Due to the faster transmission speed, many applications are possible that do not exist with GSM.

Multi-call and dual mode

With UMTS, some important innovations were introduced in mobile communications. The multi-call functionality enables the establishment and use of multiple connections via a mobile device. For example, it is possible to make phone calls and surf the Internet at the same time.
The dual mode allows all UMTS cell phones to use the GSM or GPRS network. It is one of the most important features. This is the only way to be able to make calls anywhere. It is even conceivable that the GSM network will remain as a backup if UMTS cannot be expanded down to the last corner or in order to distribute the increasing use of mobile radio and the resulting high network load over two radio networks.

Transmission speed

In practice, one speaks of 384 kBit / s (up to 120 km / h) as the theoretical maximum with an unloaded UMTS network. With increasing speed, e.g. B. when driving a car or train, the speed goes back to 144 kBit / s (up to 500 km / h).
Thanks to HSPA, the transmission speed increases to 7.2 Mbit / s. With HSPA + even 168 Mbit / s should be possible.

Cell management

The data rate is reduced when a radio cell is heavily used. In order to avoid the breakdown of the radio interface, this radio cell reduces its coverage area. They are then referred to as pumping cells (cell breathing).
The same thing happens when a participant moves on the edge of the cell. The loss of signal must then be compensated for by increasing the transmission power. However, there is only a maximum transmission power available within the cell, which must not be exceeded. An increase in the transmission power for one subscriber thus leads to a reduction in the transmission power for the other subscribers. In this case, too, the cell protects itself against overload by reducing the cell radius. The subscribers who are at the edge of the cell are then transferred to a neighboring UMTS cell via soft handover or there is a handover to the GSM network. The participant will hardly notice this process during a voice connection. In the case of a data connection, this means that the connection briefly breaks down and must first be re-established. That can take a few seconds.

UMTS technology

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