Page 39 - From GMS to LTE

Global System for Mobile Communications (GSM) 25

Table 1.5 GSM frequency bands.

Band ARFCN Uplink (MHz) Downlink (MHz)
GSM 900 (primary) 0–124 890–915 935–960
GSM 900 (extended) 975–1023, 0–124 880–915 925–960
GSM 1800 512–885 1710–1785 1805–1880
GSM 1900 (North America) 512–810 1850–1910 1930–1990
GSM 850 (North America) 128–251 824–849 869–894
GSM‐R 0–124, 955–1023 876–915 921–960

of GSM is identical on both frequency bands, with the channel numbers, also referred
to as the Absolute Radio Frequency Channel Numbers (ARFCNs), being the only
difference (see Table 1.5).
While GSM was originally intended only as a European standard, the system soon
spread to countries in other parts of the globe. In North America, analog mobile networks
continued to be used for some time before second‐generation networks, which included
the use of the GSM technology, were introduced. As the 900 MHz and the 1800 MHz
bands were already in use by other systems the North American regulating body chose
to open frequency bands for the new systems in the 1900 MHz band and later on in the
850 MHz band.
The GSM standard is also used by railway communication networks in Europe and
other parts of the world. For this purpose, GSM was enhanced to support a number of
private mobile radio and railway‐specific functionalities and this version is known as
GSM‐R. The additional functionalities include the following:

The Voice Group Call Service (VGCS). This service offers a circuit‐switched walkie‐
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talkie functionality to allow subscribers who have registered to a VGCS group to
communicate with all other subscribers in the area who have also subscribed to the
group. To talk, the user has to press a ‘push to talk’ button. If no other subscriber
holds the uplink, the network grants the request and blocks the uplink for all other
subscribers while the push to talk button is pressed. The VGCS service is very
efficient, especially if many subscribers participate in a group call, as all mobile
devices that participate in the group call listen to the same timeslot in the downlink
direction. Further information about this service can be found in 3GPP TS 43.068 [16].
The Voice Broadcast Service (VBS). It is similar to VGCS, with the restriction that
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only the originator of the call is allowed to speak. Further information about this
service can be found in 3GPP TS 43.069 [17].
Enhanced Multi‐Level Precedence and Preemption (EMLPP). This functionality,
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which is specified in 3GPP TS 23.067 [18], is used to attach a priority to a point‐to‐point,
VBS or VGCS call. This enables the network and the mobile devices to automatically
preempt ongoing calls for higher priority calls to ensure that emergency calls (e.g. a
person has fallen on the track) are not blocked by lower priority calls and a lack of
resources (e.g. because no timeslots are available).
As GSM‐R networks are private networks, it has been decided to assign a private
frequency band in Europe for this purpose, which is just below the public 900 MHz