UNIT-5
CELLULAR AND SATELLITE
COMMUNICATION
TOPICS in UNIT 5
DISCUSSION OUTLINE
• Introduction to Cellular Technology
• Evolution of Cellular Technology
• Various generation of Cellular Technology
Cellular Communication
• Cellular
communication is
a
form
of communication technology that enables the use of
mobile phones.
• Each cell is allocated a given number of frequencies
(or channels) that allow a large number of subscribers
to conduct conversations simultaneously.
• A cellular system comprises a core network that
connects to base stations with antennas on towers that
span up to 20 miles in diameter.
• GSM
and
CDMA
are
the
two
major cellular technologies.
Advantages
•
•
•
•
•
•
Advantages of the cellular system :
High capacity.
Reduced in process.
Less transmission power.
Reduced set up times.
It reduced the interference which increases the total
system capacity.
• It improved S/N ratio.
• Reduced the cluster size.
• More robust against the failure of single components.
Evolution
• Mobile telephone service began in 1940s and were
called MTSs-Mobile Telephone systems.
• Manually operated.
• It uses FM with frequency of 35MHz to 45MHz both
mobile unit and base station.
• In 1947 AT&T introduced a Radio telephone service
called highway service between New York and
Boston.
• The system is operated in 35MHz to 45MHz band.
• In 1960 AT&T introduced direct dialing full duplex
mobile telephone service.
Evolution
• In 1964 IMTS-Improved Mobile Telephone System
was introduced.
• No need of an operator.
• It used several carrier frequencies and handled several
simultaneous mobile conversation at the same time.
• It covered wide area using a single base station
transmitter.
• Both IMTS and MTS base station transmitters
outputted the powers in the range 100W to 200W .
• The mobile units transmitted between 5W and 25W.
Evolution
Evolution
Generation
Generation
Generation
Generation
Generation
Generation
Generation
Generation
Generation
Generation
Generation
Generation
Generation
Comparison
3G and 4G
5G
5G
5G
1G to 5G
Fundamental Concepts
• The key principles of cellular telephone is determined
by subdividing a large geographic area called a
coverage zone into small sections called as Cells.
• The concept of frequency reuse is used to increase the
capacity of a mobile telephone channel.
• In general cellular telephone systems allows a large
number of users to share the limited number of
common usage radio channels available in a region.
• It provides faster and efficient call processing.
Fundamental Concepts
Cellular Concepts
• With the cellular concept each area is further divided
into hexagonal shaped cells that fit together to form a
honey comb pattern.
• The hexagon shape was chosen because it provides
the most effective transmission while eliminating
gaps between adjacent cells.
• A cell is defined by its physical size and more
importantly by the size of its population and traffic
patterns.
• The physical size of a cell varies, depending on user
density and calling patterns.
Cellular Concepts
• The large cells called as Macrocells have a radius
between 1mile and 15 miles with BS transmits power
between 1W and 6W.
• The smallest cells called as Microcells typically have
a radius of 1500 feet or less with BS transmits powers
between 0.1W and 1W.
• Microcells are used in high density areas such as
large cities and inside buildings.
• The mobile unit is able to identify as either fast or
slow moving thus allowing cell transfer and update
locations.
Metropolitan Area
Excitation of cell
Excitation of cell
Cellular Telephone
Frequency Reuse
• Frequency reuse is the process in which the same set
of frequencies can be allocated to more than one cell
provided the cells are separated by sufficient distance.
• Cells using the same set of radio channels can avoid
mutual interference provided they are properly
separated.
• Each cell BS is allocated a group of channel
frequencies that are different those of neighboring
cells.
• The BS antennas are chosen to achieve a desired
coverage pattern within the cell.
Frequency Reuse
Frequency Reuse
Frequency Reuse
Frequency Reuse
Problem
FRF
Tessellate
Co Channel Cells
Co Channel Cells
Interference
• Interference is defined as any unwanted signal mixes
up with the useful signal.
• The two major kind of interferences that occur in
cellular communication are:
• 1. Co-Channel Interference
• 2. Adjacent Channel Interference
Co-Channel Interference-CCI
Co-Channel Interference-CCI
Co-Channel Interference-CCI
Co-Channel Reuse Ratio Q
Co-Channel Reuse Ratio Q
CCI
• Co-channel interference can be described as
interference between the signals from co-channel
cells.
• Co-channel interference comes from a device using
the same channel.
• Co-channel majorly occurs on the same channel.
• A large co-channel reuse ratio improves the
transmission quality because of the smaller level of
co-channel interference.
• To reduce co-channel interference and provide
efficient isolation, Co-channel cells are physically
separated by a minimum distance.
Adjacent Channel Interference ACI
Adjacent Channel Interference ACI
Adjacent Channel Interference ACI
ACI
• Adjacent channel interference can be described as the
interference that results from the signal that is
adjacent in frequency to the required signal.
• Adjacent channel interference comes from channels
on nearby frequencies.
• Adjacent channel interference occurs from a different
channel.
• Adjacent channel interference can also be caused by
frequency reuse and when the frequency reuse is high
there are more chances for interference because of
operation.
• The adjacent channel interference can be minimized
by proper filter and channel assignment strategy.
Cell –Splitting and Sectoring
Cell Splitting
• Cell splitting is when the area of a cell or independent
component coverage areas of a cellular system is
further divided thus creating more cell areas.
• The purpose is to increase the channel capacity and
improve the availability and reliability of a cellular
telephone network.
• Splitting cell areas creates new cells providing an
increase in the degree of frequency reuse thus
increasing the channel capacity of the network.
• Cell splitting is the resize or redistribution of cell
areas.
Cell Splitting
• It is the process of subdividing highly congested cells
into smaller cells each with their own BS and set of
channel frequencies.
• Cell splitting allows a systems capacity to increase by
replacing large cells with several smaller cells while
not disturbing the channel allocation scheme to
prevent interference between cells.
• In fig. Macrocells are divided into mini cells which
are further divided into microcells as traffic density
increases.
• Each time a cell is split its transmit power is reduced,
decreases the cell radius and maintain same Q.
Cell Splitting
Cell Sectoring
• Another means of increasing the channel capacity of
a cellular telephone system is to decrease the D/R
ratio while maintaining the cell radius.
• In a cellular telephone system CCI can be decreased
by replacing a single omni directional antennas with
several directional antennas each radiating with in a
smaller area.
• These smaller areas are called sectors and decreasing
the co channel interference while increasing capacity
by using directional antennas is called Sectoring.
• A cell is normally partitioned into 60 degree or 120
degrees.
Cell Sectoring
Cell Sectoring
Advantages
•
•
•
•
Better S/I ratio.
Reduces interference.
Increases capacity.
Reduces cluster size.
• More freedom in assigning channel.
Roaming and Handoff
• Roaming enables
a mobile subscriber
to
automatically make and receive voice calls, send and
receive data, or access other services when travelling
outside the geographical coverage area of their home
network, by means of using a visited network.
• When your phone is roaming, it means you're able to
use your mobile phone outside of your provider's
coverage area.
• Roaming charges may apply when you travel and
leave your 'home' network area and 'roam' onto the
network or coverage area of another provider.
Roaming and Handoff
• In short, roaming is a term used to describe the
ability of phones to connect to the network of a
different carrier, abroad or at home in order to offer
users the same features they use while on their
“home” network – making and receiving calls and
text messages and surfing the web.
• The transfer of a mobile unit from one base station’s
control to another base station’s control is called a
Handoff or Handover.
• Handoff’s should be performed as infrequently as
possible and be completely transparent to the
subscriber.
Handoff
• A handoff consists of four stages:
1. Initiation
2. Resource Reservation
3. Execution
4. Completion
• A connection that is momentarily broken during the
cell to cell transfer is called as Hard Handoff.
• A hard handoff is a break- before-make process.
• With a hard handoff a mobile unit breaks its
connection with one base station before establishing a
voice communications with a new base station.
Handoff
• Hard hand off generally occurs when a mobile unit is
passed between disjointed systems with different
frequency assignments, air interface characteristics or
technologies.
• A flawless hand off is called a soft handoff and
normally takes app 200ms which is imperceptible to
mobile users.
• With a soft handoff a mobile unit establishes a
contact with a new base station before giving up its
current radio channel by transmitting coded speech
signals to two base stations simultaneously.
Handoff
• Both base stations send their received signals to the
MTSO which estimates the quality of the two signals
and determines when the transfer should occur.
• A soft handoff requires that the two base station
should operate synchronously with one another.
• In fig the mobile unit is moving away from base
station 1. When the mobile unit is at positions W and
X it is well within the range of base station 1 and very
distant from base station 2.
• When the mobile unit reaches position Y it receives
signal from base station 1 and base station 2 app the
same power level and the two BS setting up for a
handoff.
Handoff
Handoff
• When the mobile unit crosses cell 1 into cell 2 the
handoff should be executed and completed.
• Computers at cell site controllers should transfer calls
to cell to cell with minimal disruption and
degradation in the quality of transmission.
• The computers uses handoff decision algorithms
based on variation in signal strength and signal
quality.
• Handoffs can be initiated when the signal strength
measured by either the base station or the mobile
unit’s receiver falls below a predetermined threshold
level.
Handoff
• During a handoff information stored in the first base
station is transferred to the new base station.
• A condition called blocking occurs when the signal
level drops below a usable level and there are no
usable channels available in the target cell to switch
to.
• The four steps involved in handoff process is given
below:
Handoff
Comparison
GSM
• The Global
System
for
Mobile
Communications (GSM) is a standard developed by
the European
Telecommunications
Standards
Institute (ETSI) to describe the protocols for
second-generation (2G) digital cellular networks used
by mobile devices such as mobile phones and tablets.
It was first deployed in Finland in December 1991.
• It was formed by a study group called Groupe
Special Mobile.
• By the mid-2010s, it became a global standard for
mobile communications achieving over 90% market
share, and operating in over 193 countries and
territories.
GSM
GSM
GSM Services
GSM Services
GSM Architecture
GSM Architecture
• The three primary subsystems of GSM are
1. BSS – Base station subsystem
2. NSS- Network switching subsystem
3. OSS- Operational support subsystem
• The BSS is sometimes known as the radio subsystem
because it provides and manages radio frequency
transmission paths between mobile units and mobile
switching center.(MSC)
• It also manages the radio interface between mobile
units and all other GSM subsystem.
• Each BSSs consists of many base station controllers
BSC’s which connect the MCS to the NSS .
GSM Architecture
• The NSS manages the switching functions for the
system and allows the MSCs to communicate with
the other telephone networks such as PSTN and
ISDN.
• The OSSs supports operation and maintenance of the
system and allows engineers to monitor, diagnose and
trouble shoot of every aspect of GSM network.
• GSM was originally designed for 200 fill duplex
channels in the 900MHz band.
• A 890MHz to 915MHz is used for MS to BS and
935MHz to 960MHz for BS to MS.
GSM Architecture
Advantages
•
•
•
•
More suitable network with robust features.
No roaming charges on International calls.
Worldwide connectivity and extensive coverage.
SAIC and DAIC techniques used in GSM provide
very high transmission quality.
Limitations
• Limitations of GSM is
• that multiple users share the same bandwidth.
• With enough users, the transmission
encounter interference.
can
Applications
• GSM technology is being mostly used for talking to
family, friends and business colleagues.
• we use communication feature of Telephone landlines
for internet, e-mail, data connectivity, remote
monitoring,
computer
to
computer
communication, security systems.
Applications