Page 40 - From GMS to LTE

26 From GSM to LTE-Advanced Pro and 5G

GSM band. To use GSM‐R, mobile phones need to be slightly modified to be able to
send and receive in this frequency range. This requires only minor software and hard-
ware modifications. To be also able to use the additional functionalities described
above, further extensions of the mobile device software are necessary. More about
GSM‐R can be found at http://www.uic.org/gsm‐r [19].

1.7.2 The Base Transceiver Station (BTS)
Base stations, which are also called base transceiver stations (BTSs), are the most visible
network elements of a GSM system (Figure 1.19). Compared to fixed‐line networks, the
base stations replace the wired connection to the subscriber with a wireless connection,
which is also referred to as the air interface. Base stations are also the most numerous
components of a mobile network. In Germany, for example, Telefonica O2 has over
18,000 GSM base stations and the other three network operators are likely to have
deployed similar numbers [20]. Figure 1.19 shows a typical base station antenna.
In theory, a base station can cover an area with a radius of up to 35 km. This area is
also called a cell. As a base station can only serve a limited number of simultaneous
users, cells are much smaller in practice, especially in dense urban environments. In
these environments, cells cover areas within a radius from 1 to 2 km in residential and
business areas, down to only several hundred meters with minimal transmission power
in heavily frequented areas like shopping centers and downtown streets. Even in rural
areas, a cell’s coverage area is usually less than 15 km, with the transmission power of
the mobile device of 1 or 2 W being the limiting factor in this case.
As the emissions of different base stations of the network must not interfere with
each other, all neighboring cells have to send on different frequencies. As can be seen
from Figure 1.20, a single base station usually has quite a number of neighboring

Figure 1.19 A typical antenna of a GSM base station. The optional microwave directional antenna
(round antenna at the bottom of the mast) connects the base station with the GSM network. Source:
Martin Sauter. Reproduced by permission of Martin Sauter.