2. BTS Role in GSM Network
The BTS provides two-way radio communication
between the PSTN and Mobile Station (Mobile
Set) located in a single GSM cell. It also provides
a similar link between the mobile station and
the rest of the networks. The BTS provides on
interface for the digital baseband signals used by
the land based networks and the GSM radio
signals used by mobile station.
5. BTS Functions
As the principal interface between the PSTN and Mobile
Stations, the BTS performs four primary functions.
Transmission function: which manage the transfer of traffic
and control
data between the BTS and BSC.
Telecommunication functions: which manage the transfer
of traffic and
control data between the BTS and Mobile Station.
O&M function: which supervise the operation of the BTS.
Support function: which provides a logical and physical
environment in
which the BTS functions can be realized.
Communication between the
transmission, telecommunication, and O&M functions is
managed according to the OSI model. The BTS functions are
concerned with layer 1 (Physical), Layer 2 (Data Link), and
Layer 3 (Network) of this model.
6. Transmission Functions
To minimize operating costs, all data passed between
the BTS and BSC in Time division multiplexed onto a
single physical interface. This is the Abis
Interface, which carries all the data sent between the
BSC and BTS. Logical links between the BSC and BTS
handles the following information:
Signaling data used for control purposes
O&M data for the BTS transmission module
O&M data for the BTS entities
User data in the form of speech and data traffic.
7. Transmission Functions
Abis Interface:
For BTS and BSC multiplexing equipment is normally connected using
dedicated cabling. Other method of Abis Interface connection can
be used for BTS, where the installation of the dedicated cabling in
not possible. In this case, control of the transmission medium is in
the hands of third party.
Microwave Link (used where line of sight radio path is available.
Leased Line (Copper Cable or Fiber Optic used where the distance
between the BSC and BTS is too great for microwave).
Satellite Link (Used where Previous two methods are not possible
8. Telecommunication Function
There are two primary telecommunication
functions:
Baseband Functions:
Based band functions modulate and encode
traffic and signaling data from the BSC
according to GSM recommendations. This data
is then sent to the Mobile Stations using the
RF function. Traffic and signaling received
from the Mobile Stations is demodulated and
decoded to recover the baseband data.
9. Telecommunication Function
RF Function:
RF functions enable traffic and signaling to
be sent and received over the Air Interface
as a radio signal. A special link layer
protocol ensures the reliable transfer of
signaling data over the Air Interface.
For antenna Diversity, the
telecommunication function uplink path is
duplicated. The duplicated functions
intend from the antennas, through the RF
functions.
10. O&M Functions
O&M functions monitor and control the correct operation of the
BTS and its external interfaces. These function are shared between
the BTS and BSC. The BSC provides overall control.
The O&M function use Layer 2 links for BTS internal
communications. A terminal connected via an MMI is used for local
operator control of the BTS.
There are three categorized of O&M function:
Configuration Management
Fault Management
External Alarm Handling.
The O&M function also control the operation of the RF self-tests
and manage the actions required by the BTS recovery Strategy
11. Support Function
The support function provides a number of
services relevant to the internal working of
the BTS are:
Internal Power Supplies.
Internal Temperature Control.
Master Frequency.
Clock generation and distribution.
External alarm collection.
Internal self tests.
14. Port Address:
Formula:
16n + 1 ( n = shelf number )
This formula is for the first port of
each shelf. For remaining three ports
add 3 in the above formula for each
port.
