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Elektromagnetische Felder

LTE – Long Term Evolution

  • LTE is a digital mobile communications technology and is considered the successor to UMTS (Universal Mobile Telecommunications System). In Germany, LTE is operated in three frequency bands. The frequencies used are around 800, 1800, and 2600 MHz.
  • As with GSM and UMTS mobile communications technologies, the areas to be served with mobile communications are divided into so-called cells. The cells are supplied by stationary transmitter stations (base stations).
  • The maximum transmitter power of LTE terminals is 200 milliwatts. Depending on the quality of the radio connection to the base station, the devices can theoretically reduce the actual transmitter power to 0.1 microwatts.

Like UMTS and its extensions HSPA (High Speed Packet Access) and HSPA+, also LTE is still allocated to the third generation of mobile communications (3G). That is why the designation 3.9G is sometimes used for LTE. Only its advancement, LTE-Advanced, meets all requirements imposed on mobile communications technologies of the fourth generation (4G) by standardisation bodies. In Germany, LTE has been available since the end of 2010 and LTE-Advanced was introduced in late 2014.

LTE is a broadband technology and contributes to wide area coverage with broadband services (The Federal Government’s Broadband Strategy).

Frequencies

In Germany, LTE is operated in three frequency bands. The frequencies used are around 800, 1800, and 2600 MHz. The frequency range around 800 MHz had been utilised for the terrestrial broadcasting of television programmes before LTE was introduced. The reallocation of frequencies is associated with the term "digital dividend". The frequency range around 1800 MHz has already been employed for mobile communications previously (GSM1800). Only the use of the frequency band around 2600 MHz is new in mobile communications.

It can be anticipated that LTE will also be operated in frequency ranges for which new licences were auctioned in 2015. These include frequencies in the 700-megahertz range which will gradually be freed up for mobile broadband owing to the switchover of radio broadcasting to DVB-T2 ("digital dividend II") starting from 2017. In addition, frequency ranges around 900 and 1800 megahertz were auctioned which already had been used for mobile communications before and in which LTE can now be operated as well (so-called "spectrum refarming"). In addition there are new licences for frequencies just below 1500 MHz.

LTE can also be operated in the frequency range around 2000 MHz, the licences for which were already auctioned in 2010. Currently this range is used for UMTS or HSPA/HSPA+.

Functional Principles

As with GSM and UMTS mobile communications technologies, the areas to be served with mobile communications are divided into so-called cells. The cells are supplied by stationary transmitter stations (base stations). The base stations with their antennas serve as transmitters and receivers of high-frequency electromagnetic fields by means of which the wireless communication with the terminals of the customers is carried out.

Similar to the preceding expansion levels of the mobile telephone networks, LTE particularly allows increased transmission rates. LTE networks are predestined for data intensive services (HD video streaming, telemedicine, data synchronisation etc.). As with wired internet, data are transmitted exclusively in packets which - compared to other mobile communications technologies - allows very short reaction times (latency times) and offers advantages for example when calling up websites or when playing "online games". Voice telephony is also possible using LTE.

Channel access methodsshow / hide

Just as with UMTS, information transfer in LTE networks does not require the rigid time slot technique known from GSM. In contrast to UMTS, in LTE even larger and more flexible channel bandwidths (up to 20 MHz, with LTE-Advanced by channel aggregation up to 100 MHz) and thereby higher data transmission rates are possible. Therefore, a method different than UMTS has to be employed to distribute the transmission capacity among the simultaneously active users in a cell.

LTE uses Orthogonal Frequency Division Multiplexing Access (OFDMA) as coding and access methods in the base stations and Single Carrier Frequency Division-Multiplexing Access (SC-FDMA) on the terminal side. Both methods are comparable to the OFDM method which is also used for WLAN, DVB-T or WiMAX and thus do not represent any substantial innovation from a radiation protection point of view. The methods OFDM and OFDMA have been described among other things in a research project on the topic of WiMAX commissioned by the BfS (see final report, part 1, page 29 and following).

Modulation methodsshow / hide

The various modulation methods used for LTE are already known from other mobile radio applications and do not represent any substantial innovation either.

Duplexingshow / hide

Frequency division duplexing is used to separate the data sent by the base station from that sent by the terminal. This means that another frequency band is utilised for the connection from the base station to the terminal than in the opposite direction.

An alternative method is so-called time division duplexing in which the same frequency band is alternately used for both directions of the connection leading to a more pulsed signal form. However, it has not been employed in Germany so far.

Transmitter power of base stations and terminals

The maximum transmitter power of an LTE base station depends, among other things, on the size of the mobile radio cell to be served. Typical transmitter powers range from 20 to 50 watts per antenna. As with GSM and UMTS, one site often serves three sectors, covering an angle of 120° each, with one radio channel each.

In many cases, a new technology, the so-called MIMO antenna technology (Multiple Input Multiple Output) is used at the base station side. Here, signals containing the same information are emitted by two different antennas. This allows for larger bandwidths and faster data transmission.

The maximum transmitter power of LTE terminals is 200 milliwatts. Depending on the quality of the radio connection to the base station, the devices can theoretically reduce the actual transmitter power to 0.1 microwatts.

State of 2017.05.09

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