Contents Telektronikk - Telenor

user
access
device
106
sound/speech
video/image
data
mobile
specific
telephony Hifi-sound/-program
teleaction ISDN
video-telephony/-conference
message file transfer
location/navigation
telefax
inter-PABX/-LAN
1 10 100
kbit/s
1000
Figure 3 Some services that might be supported in a TGMS
terminal
mobile
station
mobile
termination
Figure 4 Functionality in mobile
communications systems
base
station
tranceiver
A base station system can be composed
of a transceiver and a controller. A
transceiver consists of the transmitter and
the receiver units for (de-)multiplexing,
frequency conversion, channel (de-)coding,
etc. A number of transceivers could
be controlled by a base station controller
that may perform channel allocation,
some cryptographic procedures, etc. A
switching function is normally a necessity
in any larger system. Control and
data functions are required for handling
the mobility, the services and the storage
of related information. Following the
architecture of an Intelligent Network
(IN) special resources could also be defined
implementing voice mail, answering
machines, etc.
Even though the functional entities are
depicted as separate units, the physical
implementation may vary, e.g. by connecting
the elements with a MAN
(Metropolitan Area Network), ref. e.g.
[5], [9].
base station
system
base station
controller
data
base
control
The section where mobile networks differ
most from other networks is naturally
the air interface, i.e. between the mobile
stations and the base stations, together
with the corresponding functional units.
For the other sections, we will find tasks
similar to those valid for most telecommunications
systems. These include both
the handling of user connections and the
signalling. However, specific considerations
due to the mobile nature of the
users/terminals must be included.
An additional aspect is that several operators/providers
may be involved, requiring
mechanisms for mutual recognition
of identities and rights.
As we find a high level of resemblance
between the wireless and fixed systems,
the reuse of functions and the integration
are topics of special interest. For integrating
a mobile system and a fixed network,
a number of integration levels can be
defined, e.g.:
- service
- signalling
- functional.
Here, integration means common use of
the relevant elements. For instance, by
special
recources
signalling integration the signalling messages
and the procedures are capable of
dealing with the requirements from each
of the systems (mobile and fixed terminals).
Two extreme integration schemes can be
described: firstly as a stand-alone solution
and secondly as a completely integrated
solution. The first case could be
requested to ease the introduction of
mobile systems. The latter solution could
be the most economic one according to
the scope considerations. However, some
enhancements of capabilities in the fixed
network may be needed for the fully integrated
solution, e.g. to allow for unrestricted
handovers between the various
application areas.
The integration solution also has impact
on the performance studies of these systems.
If the equipment examined is used
for handling a number of services,
the load impact from these
services should be included in the
study. Most likely, this would
increase the dimensionality of
the problem, at least before
applying techniques for reducing the
dimension.
3.2 Layers
In each of the sections described in the
previous part, a number of protocols can
be applied, depending on the integration
scheme chosen. For each of the protocols
certain aspects could be studied. Some
protocol stacks, as defined in international
standardisation organisations, are usually
elaborated. The number of layers
defined will depend on the configuration,
e.g. a single link, a network, and the efficiency
to be achieved, e.g. to avoid some
of the overhead information. In addition,
each top level protocol can be aimed for
controlling a few of the aspects relevant
for the system. For instance, one relationship
can be defined between the base
station controller and the mobile control
function, while another is defined between
the mobile station and the control
function. Naturally, these would have
different purposes. When the performance
of a link with related protocol processors
are examined, the characteristics
of each of the protocols could have an
impact on the resulting performance
measures.
In the physical layer (according to the
protocol stack) several of the mechanisms
present will influence the resulting
quality of a connection. Some of these
mechanisms are: