Cellular systems allow mobile users to communicate wirelessly using a network of base stations and switches. A mobile station communicates with the nearest base station, which connects to a mobile switching center. The switching center routes calls between mobile stations and the public switched telephone network. Coverage areas are divided into cells served by individual base stations to allow frequency reuse that improves system capacity.

1. INTRODUCTION
TO CELLULAR
ARCHITECTURE

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3. Fundamental architecture of Cellular System
MOBILE STATION BASE STATION MOBILE
SWITCHING
CENTRE (MSC)
PUBLIC SWITCHED
TELEPHONE
NETWORK (PSTN)A station in the
cellular radio service
intended for use
while in motion at
unspecified locations.
Mobile station may
be hand held
personal units
(Portables) or
installed in vehicles
(Mobiles)
A fixed station in a
mobile radio system used
for radio communication
with mobile stations.
Base stations are located
at the centre or on the
edge of a coverage region
and consists of radio
channels and
transmitter and
receiver antennas
mounted on a tower.
Switching centre which
coordinate the routing
of calls in a large
service area. In cellular
radio system the MSC
connect the cellular base
station and the mobiles
to the PSTN. An MSC is
also called a Mobile
Telephone Switching
Office (MTSO).
PSTN (public switched
telephone network) is the
world’s collection of
interconnected voice-oriented
public telephone networks.
PTSN comprises all the
switched telephone
networks around the world
that are operated by local,
national or international
carriers.

4. Cellular System to cover a geographical area
BASE STATION
MOBILE STATION
CELL
A cell is the geographic area that
is covered by a single base
station in a cellular network.

5. Detailed View of GSM Architecture
A base transceiver station (BTS) is a piece of equipment that
facilitates wireless communication between user equipment (UE) and a
network. UEs are devices like mobile phones (handsets), WLL phones,
computers with wireless Internet connectivity.
A base station controller (BSC) is a network element that controls and
monitors a number of base stations and provides the interface
between the cell sites and the mobile switching center (MSC).
The Home Location Register is a database from a mobile network in
which information from all mobile subscribers is stored. The HLR
contains information about the subscribers identity, his telephone
number, the associated services and general information about the
location of the subscriber.
The Visitor Location Register (VLR) is a database contains the exact
location of all mobile subscribers currently present in the service area
of the MSC. This information is necessary to route a call to the right
base station. The database entry of the subscriber is deleted when the
subscriber leaves the service area.
The Authentication Centre (AUC) is a function in a GSM network used
for the authentication a mobile subscriber that wants to be connected
to the network. Authentication is done by identification and
verification of the validity of the SIM. Once the subscriber is
authenticated, the AUC is responsible for the generation of the
parameters used for the privacy and the ciphering of the radio link.
Operation Maintenance Center (OMC) is used to monitor and maintain the
performance of each Mobile Station (MS), Base Station (BS), Base Station
Controller (BSC) and Mobile Switching Center (MSC) within a GSM system.
Integrated Services Digital Network (ISDN) is a set of communication
standards for simultaneous digital transmission of voice, video, data, and other
network services over the traditional circuits of the public switched telephone
network.

6. GSM Channels
MOBILE STATION BASE STATION MOBILE SWITCHING
CENTRE (MSC)
PUBLIC SWITCHED
TELEPHONE NETWORK
(PSTN)
Wireless Access through Radio Channels Wired Communication – Back Bone Networks
The communication between the MS and
BS are defined by CAI (Common Air
Interface) Standard.
VOICE AND
DATA
CHANNEL
CONTROL
CHANNEL
FORWARD VOICE
CHANNEL
REVERSE VOICE
CHANNEL
FORWARD CONTROL
CHANNEL
REVERSE CONTROL
CHANNEL
Used for voice transmission
from BS to MS
Used for voice transmission
from MS to BS
Used for setting up the calls
and exchanging the control
messages

7. Channel Access Mechanisms
In real time scenario a single Base
Station will serve several Mobile
Stations simultaneously. This gives
raise to 2 important questions
1. How Full duplexing is
achieved?
2. How mobile users share the
available finite amount of
spectrum
Full Duplex can be achieved by
 Frequency Division Duplexing (FDD):
Frequency-division duplexing (FDD) is a method for establishing a full-duplex
communications link that uses two different radio frequencies for transmitter and
receiver operation. FDD operation normally assigns the transmitter and receiver
to different communication channels. One frequency is used to communicate in
one direction, and the other frequency is required to communicate in the opposite
direction. The transmit direction and receive direction frequencies are separated
by a defined frequency offset.
 Time Division Duplexing (TDD):
Time division duplex (TDD) refers to duplex communication links where uplink is
separated from downlink by the allocation of different time slots in the
same frequency band.

8. How Mobile Users Share the Available
Spectrum:
 The Basic Resource for Wireless
Communication is Radio Spectrum. This is
to be shared among multiple users.
 Multiple Access schemes are used to allow
many mobile users to share
simultaneously a finite amount of radio
spectrum.
 The sharing of spectrum is required to
achieve high capacity by simultaneously
allocating the available bandwidth or
channel to multiple users
 Duplexing is needed to allow subscribers
send and receive information
simultaneously. Ex : Mobile Systems
Note:
This must be done without severe degradation
in the performance of the system

9. Summary
• Basic Components and definition
• Architecture of Cellular Systems
• CAI Standards for GSM channels
• Concepts of Duplexing
• Concepts of Multiple Access Techniques