What is TETRA anyway?
TETRA is a wireless communication standard for Professional Mobile Radio
(PMR) and Private Access Mobile Radio (PAMR) applications, eg for public
safety organizations. Fast call setup times, closed user groups rather than calls
into the public switched telephone network, and group calls are some of the
features that make TETRA different from standards for public use like GSM. Both
duplex and simplex operation are supported – simplex meaning you have to
press a button while talking (the button is called PTT = "press to talk").
The standard comprises specifications for various applications and technologies,
as there are trunked mode (TMO), packet data (PDO), and direct mode (DMO)
operation. But most applications are expected to use TMO and DMO to exchange
speech and data; this part of the specification is called Voice + Data (V+D).
This version of the 4032 option supports signalling protocols for TMO supporting
simplex mode calls. TX measurements are supported for all the different TETRA
standards.
Some background information on TETRA
TETRA is a trunked radio standard defined by ETSI, the European Telecommuni-
cations Standards Institute. The scope, however, is not restricted to use within
Europe. Its primary use is for companies and organizations with frequent radio
communication needs; police organizations, transportation companies, taxis are
some examples of potential users. Of course, every organization and company
could have their own set of frequencies and infrastructure (base stations, re-
peaters). This is expensive both in terms of money (especially if the area cannot
be covered by one base station) and spectrum (which is limited). A trunked radio
network operator may instead offer services (air time) to many companies, thus
managing and administering some part of the spectrum and provide a regional
or national network with interfaces to international trunked networks and the
public switched telephone network.
The main advantages of a trunked network, when comparing it to cellular
systems like GSM, are the fast call setup (in simplex operation, you just press a
push-button and talk; the radio and the system will find an empty channel
immediately with virtually no delay) and the possibility of group calls. Also,
emergency services prefer to have a radio network of their own: in case of
disaster relief, cellular channels are usually blocked because everybody outside
the emergency services is already trying to make phone calls over the cellular
network.
Technically speaking, TETRA is a system applying the Time Division Multiple
Access (TDMA) method (plus the possibility of having multiple frequencies in
addition). This means, several users share one frequency: speech and data are
transmitted in digital format and multiplexed into timeslots. All of the four different
TETRA timeslots on one carrier bear different channels, so there can be as much
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Appendix TETRA MS Test
10-51
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