Mobile Communication
General Information
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Mobile radio communication allows to establish connection to from
the mobile subscriber irrespective of their geographical location
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Mobile requires radio switching networks, namely digital cellular
mobile radio networks
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Via the radio interface the mobile subscriber MS can access the mobile
radio network, known as radio interface
Mobile Communication
General Information
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On the stationary network side the radio interface is served by base
station = BS
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On the mobile network side, the subscriber uses mobile equipment
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A fully digital interface, as employed in GSM/DCS is the basis of
digital mobile radio network.
Digital cellular Mobile Radio Network
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The smallest service area in a mobile
radio network are called radio cells.
The totality of these cells forms a so
called cellular mobile radio network
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Every cell is served by a base station
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The base stations are connected to the
mobile switching centre = MSC
in star shaped configuration
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The MSC are linked to each other and
also function as gateway to the fixed
networks (e.g. PSTN)
GSM
GSM is a standard for global system for mobile communications
GSM 900:

GSM is a standard for digital cellular mobile radio networks (PLMN) with the
digital transmission in the 900 MHz band
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GSM 900-PLMN are designed for extensive radio coverage even in rural areas
and have a maximum cell radius of 35km
DCS 1800 (Digital cellular system for 1800 MHz bandwidth)

Variant of the GSM standard, which uses the 1800 MHz band for the radio
interface
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DCS 1800 is designed for radio coverage in the areas with very high
subscriber density
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In DCS 1800 the cells have radius upto 8km, due to this comparatively small
transmit capacity it is possible to use very small size equipment
Service Concept in GSM/DCS
In GSM/DCS PLMN, mobile subscribers are offered three service
Categories
Service Concept in GSM/DCS
Bearer Services:
Bearer services are the pure transport service, with the bearer services the
network functions required for a specific type of message transmission are
clearly defined. These network functions involve for example the support
of various data transmission rates(300b/s to 9.6kb/s) and modes (circuit or
packet switched, synchronous or asynchronous).
Service Concept in GSM/DCS
Teleservices:

With teleservices , not only the transport functions required for a
connection setup, but also the features and the characteristics of the
terminal equipment are clearly defined e.g., a specific signal protocol
between the terminals
Teleservices are provided upto the user access point at the terminal
Equipment. Example fax service and short message service etc.
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Service Concept in GSM/DCS
Supplementary services:


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Bearer and teleservises are also called the basic services
Supplementary services cannot be assigned to the users without basic
services
Supplementary service enhances or modifies the basic services
telephony i.e., call forwarding, call charge display, call hold
Functional Network Architecture
The GSM/DCS system consists of three subsystems
Network components of radio subsystem
The radio subsystem (RSS) consists of
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Mobile Equipment
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Base Station
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Radio Interface
Network components of radio subsystem
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The base station (BS) terminates the radio interface (Um) on the
stationary network side
The base station includes
Base transceiver station (BTS)
Base Station Controller (BSC)
Transcoding & Rate Adaptation Unit
Network components of radio subsystem
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A BSC can control several BTS
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The interface between the BSC and
BTS is called Abis interface
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The BSC,TRAU and BTS form a
unit which is called Base station
System

Every BSC contained in the
network controls one base station
system (BSS)
Network components of radio subsystem
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The BTS provides the cell with radio
interface which means that it provides
the radio channel and sends the cell
descriptive parameters such as
transmit capacity, name of the cell etc
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The BSC is responsible for intelligent
functions in BSS
It controls several BTS
It distributes traffic channel
connections from SSS to BTS
The Network Component TRAU
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The Transcoding and rate adaptation unit adapts the 64kb/s (speech,
data) from the MSC to the comparatively low transmission rate of the
radio interface
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TRAU consists of two functional units
The trancoder (TC) for the speech compression
The rate adaptor (RD) for data rate adaptation
TRAU interfaces are called
A interface (to the SSS(MSC))
Asub interface to the BSC (can carry four times no of
channels carried by A interface)
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The Network Component TRAU
The Network Component TRAU
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TRAU can be installed on The
MSC site, the network operator can
save the line cost