Contents Telektronikk - Telenor

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UMTS
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per unit of
the geographical
area. The
ETE value is usually
calculated per
1000 users from
the Erlang value of a service
usage (calls per user •
mean holding time) multiplied
by the bit rate (kbit/s) for the service.
We then get a value of the demand for
information transfer in common for all
the services.
Several classes of operators can be defined
as well, like private, public, and residential.
Private operators will typically
be companies handling their own
employees, while a residential operator
handles a few users in the residence that
often are associated with a main user.
For a TGMS a strive for minimising the
number of radio interfaces and definition
of blocks related to the radio interface
that could be adapted to the situation
experienced are carried out. This invites
for the use of a layered and building
block approach to allow for such a flexibility.
Comparing a TGMS with the present
generations of systems, we recognise
that the latter have more or less been
designed for a limited number of services
and application areas. Therefore, the
parameters on the radio interface could
be tuned correspondingly.
Some of the services that could be supported
in a TGMS are depicted in Figure
3. Information bit rates potential up to
2 Mbit/s have been proposed. In addition,
studies are going on for even higher bit
rates, e.g. for mobile broadcasting.
We could compare this with the bit rate
supported in GSM, 13 kbit/s, and in
DECT, 32 kbit/s (although several slots
could be used for one connection). Natu-
rally, the highest bit rates will not be supported
in all the environments by a
TGMS. The highest bit rates may be
achieved for indoor connections while
some hundreds of kbit/s may be relevant
for outdoor over short distances (mobile
stations close to the base station). For
longer distances around 100 kbit/s could
be a limit for the information rate. However,
all these figures remain to be verified
for real cases.
3 Functionality in mobile
communications systems
The functionality present in a system can
be described in two steps: first, the various
sections, and second, the layers within
each of the sections. We may also look
upon this as a division between a horizontal
and a vertical description of such
systems.
3.1 Sections of a system
In principle, mobile telecommunications
systems have more or less the same functional
architecture for several system
generations, as illustrated in Figure 4.
However, the physical entities, protocols,
etc., that are included do vary, in addition
Figure 2
Several
application
environments for
future mobile
communications
systems
to the mapping from the functional entities
to the physical elements. Starting
from the users’ side, each user has an
identity, associated with a terminal (as a
fixed terminal identity or as a separate
unit, e.g. a Subscriber Identity Module,
SIM, in GSM). From GSM and onwards,
the subscription will be linked with the
user, i.e. according to the described role
model, and not to the terminal. Then, a
user could have an access device to ease
the identification and authentication procedures.
A mobile station includes the terminal
equipment and the mobile termination
(MT). The terminal equipment could also
be more complex than a telephone
device, e.g. like a PABX. In the systems
available so far, most mobile stations
consist of one physical unit. Such units
decrease in size and weight with the
development of technology. In addition,
some of them have the possibility to be
interconnected to standard terminal
equipment.
When a communication (information
transfer) need arises, a relationship between
the mobile station and a base station
is established. Such a need could be
initiated by the user or as a result of the
invocation of another type of procedures
defined in the system.
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