Unit 1 - Fundamentals of Communications.ppt

Current Trends & Technologies
Unit – I
Fundamentals of Communications

Syllabus
Fundamentals of Communications:
• Types of communication- Wired, wireless, mobile,
• Modes of transmission: Simplex, Half Duplex,
Full Duplex, Multiplexing techniques,
• History and evolution of wireless and mobile
systems,
• Transition and characteristics of 1G, 2G, 3G, 4G,
• Spectrum, regulations, and frequency allocation.

Significance of Human
Communication
• Communication is the process of
exchanging information.
• Main barriers are language and distance.
• Contemporary society’s emphasis is now
the accumulation, packaging, and exchange
of information.

Significance of Human
Communication
• Methods of communication: Face to face
• Signals
• Written word (letters)
– Electrical innovations:Telegraph
– Telephone
– Radio
– Television
– Internet (computer)

Communication Systems
• Basic components:
– Transmitter
– Channel or medium
– Receiver
• Noise degrades or interferes with
transmitted information.

General Model for Communication Systems

• The transmitter is a collection of electronic components and
circuits that converts the electrical signal into a signal suitable
for transmission over a given medium.
• The communication channel is the medium by which the
electronic signal is sent from one place to another.
• Types of media include
– Electrical conductors
– Optical media
– Free space
– System-specific media (e.g., water is the medium for sonar).

• A receiver is a collection of electronic components and circuits
that accepts the transmitted message from the channel and
converts it back into a form understandable by humans.
• A transceiver is an electronic unit that incorporates circuits that
both send and receive signals.
– Examples are:Telephones
– Fax machines
– Handheld CB radios
– Cell phones
– Computer modems

• Attenuation
– Signal attenuation, or degradation, exists in all media of
wireless transmission. It is proportional to the square of
the distance between the transmitter and receiver.
• Noise
– Noise is random, undesirable electronic energy that
enters the communication system via the
communicating medium and interferes with the
transmitted message.

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Transmission Media
• The transmission medium is the physical path by which a
message travels from sender to receiver.
• Computers and telecommunication devices use signals to
represent data.
• These signals are transmitted from a device to another in the
form of electric pulse or electromagnetic energy.
• Examples of Electromagnetic energy include power, radio
waves, infrared light, visible light, ultraviolet light, and X and
gamma rays.

11
Signals of low frequency (like voice signals) are generally transmitted as
current over metal cables.
It is not possible to transmit visible light over metal cables, for this class of
signals is necessary to use a different media, for example fiber-optic
cable.
Classes of Transmission media

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Twisted-pair cable
• Twisted pair consists of two conductors (normally copper), each
with its own plastic insulation, twisted together.
• Twisted-pair cable comes in two forms: unshielded and shielded
• The twisting helps to reduce the interference (noise) and crosstalk.

13
Unshielded Twisted-pair (UTP) cable
• Any medium can transmit only a
fixed range of frequencies!
• UTP cable is the most common
type of telecommunication
medium in use today.
• The range is suitable for
transmitting both data and
video.
• Advantages of UTP are its cost
and ease of use. UTP is cheap,
flexible, and easy to install.

14
Shielded Twisted (STP) Cable
• STP cable has a metal foil or
braided-mesh covering that
enhances each pair of
insulated conductors.
• The metal casing prevents
the penetration of
electromagnetic noise.
• Materials and manufacturing
requirements make STP
more expensive than UTP but
less susceptible to noise.

15
Coaxial Cable (or coax)
Coaxial cable carries signals of
higher frequency ranges
than twisted-pair cable.
Coaxial Cable standards:
RG-8, RG-9, RG-11 are
used in thick Ethernet
RG-58 Used in thin Ethernet
RG-59 Used for TV

16
Optical Fiber
• Metal cables transmit signals in the form of electric
current.
• Optical fiber is made of glass or plastic and transmits
signals in the form of light.
• Light, a form of electromagnetic energy, travels at
300,000 Kilometers/second ( 186,000 miles/second),
in a vacuum.
• The speed of the light depends on the density of the
medium through which it is traveling ( the higher
density, the slower the speed).

18
Unguided Media
• Unguided media, or wireless communication,
transport electromagnetic waves without using a
physical conductor. Instead the signals are broadcast
though air or water, and thus are available to anyone
who has a device capable of receiving them.

19
Unguided Media
•There are four basic types of transmissions standards for
wireless networking.
•These types are produced by the Institute of Electrical and
Electronic Engineers (IEEE).
•These standards define all aspects of radio frequency
wireless networking.
•They have established four transmission standards; 802.11,
802.11a, 802.11b, 802.11g.

20
Unguided Media
• The basic differences between these four types are
connection speed and radio frequency.
• 802.11 and 802.11b are the slowest at 1 to 2 Mbps and upto
11Mbps respectively.
• They both operate off of the 2.4 GHz radio frequency.
• 802.11a operates off of a 5 GHz frequency and can transmit
up to 54 Mbps.
• 802.11g operates off of the 2.4 GHz frequency and can
transmit up to 54 Mbps.
• Actual transmission speeds vary depending on such factors
as the number and size of the physical barriers within the
network and any interference in the radio transmissions.

Types of electronic communication
• Electronic communications are classified according to
whether they are One-way (simplex) or two-way (full
duplex or half duplex) transmissions
• Analog or digital signals

Types Of Transmission Mode
1. Simplex Transmission Mode.
2. Half Duplex Transmission Mode
3. Full Duplex Transmission Mode.

Simplex Mode
• In simplex mode transmission, information
is sent in only one direction.
• Device connected in simplex mode is
either send only or receive only; that is one
device can only send, other device can
only receive.
• Communication is unidirectional.

Simplex Transmission
• This type of communication is one-way.
Examples are:
– Radio
– TV broadcasting
– Beeper (personal receiver)

Half Duplex Mode
• In half duplex transmission data can be
sent in both the directions, but only in one
direction at a time.
• Both the connected device can transmit
and receive but not simultaneously.
• When one device is sending the other can
only receive and vice-versa.

Half Duplex
• The form of two-way communication in
which only one party transmits at a time is
known as half duplex. Examples are:
– Police, military, etc. radio transmissions
– Citizen band (CB)
– Family radio
– Amateur radio

Full Duplex Mode
• In full duplex transmission, data can be sent
in both the directions simultaneously.
• Both the connected devices can transmit and
receive at the same time.
• Therefore it represents truly bi-directional
system.
• In full duplex mode, signals going in either
Direction share the full capacity of link.

Full Duplex
• When people can talk and listen simultaneously, it is called full
duplex. The telephone is an example of this type of
communication.

Analog Signals
• An analog signal is a smoothly and
continuously varying voltage or current.
• Examples are:
– Sine wave
– Voice
– Video (TV)

Digital Signals
• Digital Signals
• Digital signals change in steps or in discrete
increments.
– Most digital signals use binary or two-state
codes. Examples are:Telegraph (Morse code)
– Continuous wave (CW) code
– Serial binary code (used in computers)

Unit 1 - Fundamentals of Communications.ppt

• Digital Signals
– Many transmissions are of signals that originate
in digital form but must be converted to analog
form to match the transmission medium. Digital
data over the telephone network.
• Analog signals. They are first digitized with an
analog-to-digital (A/D) converter.
• The data can then be transmitted and processed by
computers and other digital circuits.

Modulation and multiplexing
• Modulation and multiplexing are electronic
techniques for transmitting information
efficiently from one place to another.
• Modulation makes the information signal
more compatible with the medium.
• Multiplexing allows more than one signal to
be transmitted concurrently over a single
medium.

• Frequency
• Frequency is the number of cycles of a
repetitive wave that occur in a given period of
time.
• A cycle consists of two voltage polarity reversals,
current reversals, or electromagnetic field
oscillations.
• Frequency is measured in cycles per second (cps).
• The unit of frequency is the hertz (Hz).

• Example 1 - (1) Cycle
• One cycle, specified event, is measured 1
second in time which equals 1 Hz.
• Alternating current is defined as a single
change from up to down to up, or as a
change from positive, to negative to positive

• Example 2 - (5) Cycles
• Five cycles, specified events, measured 1
second in time which equals 5 Hz.

• Wavelength is the distance occupied by
one cycle of a wave and is usually
expressed in meters.
• Wavelength is also the distance traveled by
an electromagnetic wave during the time of
one cycle.
• The wavelength of a signal is represented
by the Greek letter lambda (λ).

• Wavelength is the distance between similar
points on two back-to-back waves.

• Amplitude is the height, force or power of
the wave

• Phase can be measured in distance, time, or
degrees.
• If the peaks of two signals with the same
frequency are in exact alignment at the
same time, they are said to be in phase.
• Conversely, if the peaks of two signals with
the same frequency are not in exact
alignment at the same time, they are said to
be out of phase.

• Below is an example of 2 wave forms 90
degree out of phase.

Modulation
• In analog transmission, the sending device produces a high
frequency signal (a sine wave) that acts as a basis for the
information signal. This base signal is called the carrier
signal.
• Digital information is then modulated on the carrier signal
by modifying one or more of its characteristics (amplitude,
frequency, phase). This kind of modification is called
modulation and the information signal is called a
modulating signal.

• For any analog modulator type, there are
two inputs and one output. The two inputs
are modulating signal (i.e. analog
information to be transmitted) and carrier
signal waveform. The output is referred as
modulated waveform.

Amplitude Modulation(AM)
• Amplitude Modulation(AM) is the
modulation technique in which carrier
amplitude varies based on analog baseband
information signal to be transmitted using
wireless device. one of the application of
amplitude modulation is radio.

Frequency Modulation
• Frequency Modulation(FM) is the
modulation technique in which carrier
frequency varies based on analog baseband
information signal to be transmitted using
wireless device.

Phase Modulation
• Phase Modulation(PM) is the modulation
technique in which carrier phase varies
based on analog baseband information
signal to be transmitted using wireless
device.

Multiplexing
• Multiplexing is the set of techniques that allows the
simultaneous transmission of multiple signals across a
single data link.
• A Multiplexer (MUX) is a device that combines several
signals into a single signal.
• A Demultiplexer (DEMUX) is a device that performs the
inverse operation.

• Multiplexing means “sharing a medium”. It
is a form of data transmission in which one
communication channel carries several
transmissions at the same time. In simple
words, the method of dividing a single
channel into many channels so that a
number of independent signals may be
transmitted on it is known as Multiplexing.

• Frequency Division Multiplexing-FDM
• In FDM the available bandwidth is divided into a
number of smaller independent logical channels
with each channel having a small bandwidth. It
assigns “frequency ranges” to each “user” or
“signal” on a medium. Thus, all signals are
transmitted at the same time, each using different
frequencies. The method of using a number of
carrier frequencies, each of which is modulated by
an independent signal is in fact frequency division
multiplexing.

• Time Division Multiplexing
• In TDM, sharing is accomplished by dividing
available “transmission time” on a
medium/channel among users.
• Each user of the channel is allotted a small time
interval during which he transmits a message.
Total time available in the channel is divided, and
each user is allocated a time slice. In TDM, users
send message sequentially one after another. Each
user can use the full channel bandwidth during the
period he has control over the channel.

Frequency-division Multiplexing (FDM)
• FDM is an analog technique that can be applied when the bandwidth of
a link is greater than the combined bandwidths of the signals to be
transmitted.

• In FDM signals
generated by each
device modulate
different carrier
frequencies. These
modulated signals are
combined into a single
composite signal that
can be transported by
the link.
FDM is an analog multiplexing technique
that combines signals.

• In FDM signals generated by each device modulate
different carrier frequencies. These modulated signals are
combined into a single composite signal that can be
transported by the link.
• Carrier frequencies are separated by enough bandwidth to
accommodate the modulated signal.
• These bandwidth ranges are the channels through which
various signals travel.
• Channels must be separated by strips of unused bandwidth
(guard bands) to prevent signal overlapping.

Example
Assume that a voice channel occupies a bandwidth of 4
KHz. We need to combine three voice channels into a link
with a bandwidth of 12 KHz, from 20 to 32 KHz. Show
the configuration using the frequency domain without the
use of guard bands.
Solution
Shift (modulate) each of the three voice channels to a
different bandwidth, as shown in Figure

Wave-division Multiplexing (WDM)
• Wave-division multiplexing is conceptually the same as
FDM, except that multiplexing and de-multiplexing
involve light signals transmitted through fiber-optic
channels.
• The purpose is to combine multiple light sources into one
single light at the multiplexer and do the reverse at the de-
multiplexer.
• Combining and splitting of light sources are easily handled
by a prism.

Time-division Multiplexing (TDM)
• Time-division multiplexing (TDM) is a digital process that can be
applied when the data rate capacity of the transmission medium is
greater than the data rate required by the sending and receiving
devices.

TDM
TDM is a digital multiplexing technique to
combine data.

• TDM can be implemented in two ways: synchronous TDM
and asynchronous TDM.
• In synchronous time-division multiplexing, the term
synchronous means that the multiplexer allocates exactly
the same time slot to each device at all times, whether or
not a device has anything to transmit.
• Frames
Time slots are grouped into frames. A frame consists of a one
complete cycle of time slots, including one or more slots
dedicated to each sending device.

Framing Bits
Because the time slot order in a synchronous TDM system
doest no vary from frame to frame, very little overhead
information needs to be included in each frame. However,
one or more synchronization bits are usually added to the
beginning of each frame.
These bits, called framing bits, allows the demultiplexer to
synchronize with the incoming stream so that it can
separate the time slot accurately.

Asynchronous TDM
• Synchronous TDM does not guarantee that the full
capacity of a link is used. Because the time slots are pre-
assigned and fixed, whenever a connected device is not
transmitting, the corresponding slot is empty.
• Asynchronous time-division multiplexing, or statistical
time-division multiplexing, is designed to avoid this type
of waste.
• Like synchronous TDM, asynchronous TDM allows a
number of lower-speed input lines to be multiplexed to a
single higher-speed line. However, in asynchronous TDM
the total speed of the input lines can be greater than the
capacity of the link.

•In an asynchronous system,
if we have n input lines, the
frame contains no more than
m slots, with m less than n.
•The number of time slots in
an asynchronous TDM
frame (m) is based on
statistical analysis of the
number of input lines that
are likely to be transmitting
at any given time.
•In this case any slot is
available to any of the
attached input lines that has
data to send.

Examples of Asynchronous TDM Frames

Asynchronous TDM
Addressing and Overhead
• In asynchronous TDM each time slot must carry an
address telling the de-multiplexer how direct the data. This
address, for local use only, is attached by the multiplexer
and discarded by the de-multiplexer once it has been read.

Evolution of Mobile Wireless
Communication Networks
Mobile Cellular Network evolution has been
categorized in to ‘generations’

Cellular Network Basics
• Cellular network/telephony is a radio-based technology; radio
waves are electromagnetic waves that antennas propagate
• Most signals are in the 850 MHz, 900 MHz, 1800 MHz, and 1900
MHz frequency bands
Cell phones operate in this
frequency range

Cellular Network
• Base stations transmit to and receive from mobiles at the
assigned spectrum
– Multiple base stations use the same spectrum (spectral reuse)
• The service area of each base station is called a cell
• Each mobile terminal is typically served by the ‘closest’ base
stations
– Handoff when terminals move

Cellular Network Generations
• It is useful to think of cellular Network/telephony
in terms of generations:
– 1G: Analog cellular telephony
– 2G: Digital cellular telephony
– 3G: High-speed digital cellular telephony (including
video telephony)
– 4G: IP-based “anytime, anywhere” voice, data, and
multimedia telephony at faster data rates than 3G
(deployed in 2014–2015)

Evolution of Cellular Networks
1
G
2
G
3
G
4
G
2.5
G

The First Generation System
1G (Analog)
• In 1980 the mobile cellular era had started, and
since then mobile communications have
undergone significant changes and experienced
enormous growth.
• First-generation mobile systems used analog
transmission for speech services.
• In 1979, the first cellular system in the world
became operational by Nippon Telephone and
Telegraph (NTT) in Tokyo, Japan.

1G
• Two years later, the cellular epoch reached
Europe.
• In the United States, it was launched in 1982.
• All these systems offered handover and
roaming capabilities but the cellular networks
were unable to interoperate between countries.
• This was one of the inevitable disadvantages of
first-generation mobile networks.

The Multiple Access Problem
• The base stations need to serve many
mobile terminals at the same time (both
downlink and uplink)
• All mobiles in the cell need to transmit to
the base station
• Interference among different senders and
receivers
• So we need multiple access scheme

Multiple Access Schemes
• Frequency Division Multiple Access (FDMA)
• Time Division Multiple Access (TDMA)
• Code Division Multiple Access (CDMA)
3 orthogonal Schemes:

Frequency Division Multiple
Access
• Each mobile is assigned a separate frequency channel for the
duration of the call
• Sufficient guard band is required to prevent adjacent channel
interference
• Usually, mobile terminals will have one downlink frequency band
and one uplink frequency band
• Different cellular network protocols use different frequencies
• Frequency is a precious and scare resource. We are running out of it
– Cognitive radio
frequency

Time Division Multiple Access
• Time is divided into slots and only one mobile
terminal transmits during each slot
• Each user is given a specific slot.
Guard time – signal transmitted by mobile terminals at
different locations do no arrive at the base station at the same
time

Code Division Multiple Access
• Use of orthogonal codes to separate different transmissions
• Each symbol of bit is transmitted as a larger number of bits
using the user specific code – Spreading
– Bandwidth occupied by the signal is much larger than the
information transmission rate
– But all users use the same frequency band together
Orthogonal
among users

The Second-generation
2G & 2.5G (Digital)
• Second-generation (2G) mobile systems were introduced in the
end of 1980s.
• Low bit rate data services were supported as well as the
traditional speech service.
• Compared to first-generation systems, second-generation (2G)
systems use digital multiple access technology, such as TDMA
(time division multiple access) and CDMA (code division
multiple access).
• Consequently, compared with first-generation systems, higher
spectrum efficiency, better data services, and more advanced
roaming were offered by 2G systems.
• In Europe, the Global System for Mobile Communications
(GSM) was deployed to provide a single unified standard.
• This enabled seamless services through out Europe by means of
international roaming.

2G & 2.5G
• Global System for Mobile Communications, or
GSM, uses TDMA technology to support multiple
users.
• New technologies have been developed based on the
original GSM system, leading to some more
advanced systems known as 2.5 Generation (2.5G)
systems.
• The move into the 2.5G world began with General
Packet Radio Service (GPRS).
• GPRS is a radio technology for GSM networks that
adds packet-switching protocols.

2G & 2.5G
• Packet switching is a technique whereby the
information (voice or data) to be sent is broken
up into packets, of at most a few Kbytes each,
which are then routed by the network between
different destinations based on addressing data
within each packet.
• GPRS is the most significant step towards 3G.

GSM
• Abbreviation for Global System for Mobile
Communications
• Concurrent development in USA and
Europe in the 1980’s
• The European system was called GSM and
deployed in the early 1990’s

GSM Services
• Voice, 3.1 kHz
• Short Message Service (SMS)
– 1985 GSM standard that allows messages of at most 160 chars.
(incl. spaces) to be sent between handsets and other stations
– Over 2.4 billion people use it; multi-billion $ industry
• General Packet Radio Service (GPRS)
– GSM upgrade that provides IP-based packet data transmission up
to 114 kbps
– Users can “simultaneously” make calls and send data
– GPRS provides “always on” Internet access and the Multimedia
Messaging Service (MMS) whereby users can send rich text,
audio, video messages to each other
– Performance degrades as number of users increase
– GPRS is an example of 2.5G telephony – 2G service similar to 3G

GSM Channels
• Physical Channel: Each timeslot on a carrier is referred to as a
physical channel
• Logical Channel: Variety of information is transmitted
between the MS and BTS. Different types of logical channels:
– Traffic channel
– Control Channel
Downlink
Uplink
Channels

GSM Frequencies
• Originally designed on 900MHz range, now also
available on 800MHz, 1800MHz and 1900 MHz
ranges.
• Separate Uplink and Downlink frequencies
– One example channel on the 1800 MHz frequency band,
where RF carriers are space every 200 MHz
1710 MHz 1880 MHz
1805 MHz
1785 MHz
UPLINK FREQUENCIES DOWNLINK FREQUENCIES
UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 95MHZ

The Third-generation
3G
• In EDGE, high-volume movement of data was possible,
but still the packet transfer on the air-interface behaves
like a circuit switch call.
• Thus part of this packet connection efficiency is lost in
the circuit switch environment.
• Moreover, the standards for developing the networks
were different for different parts of the world.
• Hence, it was decided to have a network which provides
services independent of the technology platform and
whose network design standards are same globally.
• Thus, 3G was born.

3G
• The International Telecommunication
Union (ITU) defined the demands for 3G
mobile networks with the IMT-2000
standard.
• An organization called 3rd Generation
Partnership Project (3GPP) has continued
that work by defining a mobile system that
fulfills the IMT-2000 standard.

3G
• 3G networks enable network operators to offer users
a wider range of more advanced services while
achieving greater network capacity through
improved spectral efficiency.
• Services include wide-area wireless voice
telephony, video calls, and broadband wireless data,
all in a mobile environment.
• Additional features also include HSPA (High Speed
Packet Access) data transmission capabilities able to
deliver speeds up to 14.4 Mbps on the downlink and
5.8 Mbps on the uplink.

3G
• The first commercial 3G network was launched by
NTT DoCoMo in Japan branded FOMA, based on
W-CDMA technology on October 1, 2001.
• Roll-out of 3G networks was delayed in some
countries by the enormous costs of additional
spectrum licensing fees.
• In many countries, 3G networks do not use the same
radio frequencies as 2G, so mobile operators must
build entirely new networks and license entirely
new frequencies.

4G
• In contrast to 3G, the new 4G framework to be
established will try to accomplish new levels of user
experience and multi-service capacity by also
integrating all the mobile technologies that exist.
• This network will be less expensive and data
transfer will be much faster.
• 4G mobile communication services started in 2010
and become mass market in about 2014-15.
• Peak data rate of 1 Gbps for downlink (DL) and 500
Mbps for uplink (UL).

Mobile Station (MS)
• MS is the user’s handset and has two parts
• Mobile Equipment
– Radio equipment
– User interface
– Processing capability and memory required for
various tasks
• Call signalling
• Encryption
• SMS
– Equipment IMEI number
• Subscriber Identity Module

Subscriber Identity Module
• A small smart card
• Encryption codes needed to identify the subscriber
• Subscriber IMSI number
• Subscriber’s own information (telephone directory)
• Third party applications (banking etc.)
• Can also be used in other systems besides GSM, e.g., some
WLAN access points accept SIM based user authentication

Base Station Subsystem
• Transcoding Rate and Adaptation Unit (TRAU)
– Performs coding between the 64kbps PCM coding used in the
backbone network and the 13 kbps coding used for the Mobile
Station (MS)
• Base Station Controller (BSC)
– Controls the channel (time slot) allocation implemented by the
BTSes
– Manages the handovers within BSS area
– Knows which mobile stations are within the cell and informs the
MSC/VLR about this
• Base Transceiver System (BTS)
– Controls several transmitters
– Each transmitter has 8 time slots, some used for signaling, on a
specific frequency

Network and Switching
Subsystem
• The backbone of a GSM network is a telephone network with
additional cellular network capabilities
• Mobile Switching Center (MSC)
– An typical telephony exchange (ISDN exchange) which supports
mobile communications
– Visitor Location Register (VLR)
• A database, part of the MSC
• Contains the location of the active Mobile Stations
• Gateway Mobile Switching Center (GMSC)
– Links the system to PSTN and other operators
• Home Location Register (HLR)
– Contain subscriber information, including authentication information in
Authentication Center (AuC)
• Equipment Identity Register (EIR)
– International Mobile Station Equipment Identity (IMEI) codes for e.g.,
blacklisting stolen phones

Home Location Register
• One database per operator
• Contains all the permanent subscriber information
– MSISDN (Mobile Subscriber ISDN number) is the
telephone number of the subscriber
– International Mobile Subscriber Identity (IMSI) is a 15 digit
code used to identify the subscriber
• It incorporates a country code and operator code
– IMSI code is used to link the MSISDN number to the
subscriber’s SIM (Subscriber Identity Module)
– Charging information
– Services available to the customer
• Also the subscriber’s present Location Area Code,
which refers to the MSC, which can connect to the MS.

Other Systems
• Operations Support System
– The management network for the whole GSM network
– Usually vendor dependent
– Very loosely specified in the GSM standards
• Value added services
– Voice mail
– Call forwarding
– Group calls
• Short Message Service Center
– Stores and forwards the SMS messages
– Like an E-mail server
– Required to operate the SMS services

Location Updates
• The cells overlap and usually a mobile
station can ‘see’ several transceivers
(BTSes)
• The MS monitors the identifier for the BSC
controlling the cells
• When the mobile station reaches a new
BSC’s area, it requests an location update
• The update is forwarded to the MSC,
entered into the VLR, the old BSC is
notified and an acknowledgement is passed
back

Handoff (Handover)
• When a call is in process, the changes in
location need special processing
• Within a BSS, the BSC, which knows the
current radio link configuration (including
feedbacks from the MS), prepares an available
channel in the new BTS
• The MS is told to switch over to the new BTS
• This is called a hard handoff
– In a soft handoff, the MS is connected to two
BTSes simultaneously

Roaming
• When a MS enters another operators network,
it can be allowed to use the services of this
operator
– Operator to operator agreements and contracts
– Higher billing
• The MS is identified by the information in the
SIM card and the identification request is
forwarded to the home operator
– The home HLR is updated to reflect the MS’s
current location

3G Overview
• 3G is created by ITU-T and is called IMT-
2000

3.5G (HSPA)
High Speed Packet Access (HSPA) is an merger of two mobile
telephony protocols, High Speed Downlink Packet Access
(HSDPA) and High Speed Uplink Packet Access (HSUPA), that
extends and improves the performance of existing WCDMA
protocols
3.5G introduces many new features that will enhance the UMTS
technology in future. 1xEV-DV already supports most of the
features that will be provided in 3.5G. These include:
- Adaptive Modulation and Coding
- Fast Scheduling
- Backward compatibility with 3G
- Enhanced Air Interface

4G (LTE)
• LTE stands for Long Term Evolution
• Next Generation mobile broadband
technology
• Promises data transfer rates of 100 Mbps
• Based on UMTS 3G technology
• Optimized for All-IP traffic

Spectrum
• All wireless communications signals travel
over the air via radio frequency.
• The TV broadcast you watch, the radio
program you listen to, the GPS device that
helps get you where you're going, and the
wireless phone service you use to make phone
calls - all use invisible airwaves to transmit
bits of data through the air.
• "Spectrum" is the range of radio frequencies
available.

Spectrum (Cont..)
• The easiest way to understand what spectrum really is
and how it provides services is to look at your radio.
• When you tune your radio to 93.5 FM, you are tuning
into a station that is broadcasting at 93.5 megahertz.
• If you want to a listen to a different station, you turn the
dial to another frequency like 98.3 FM and a different
radio station will be transmitting over that particular
frequency.
• No two stations transmit over the same spectrum at the
same time in the same area, because if they did, they'd
cause interference with one another.

Regulations
• The radio frequency spectrum is not an
inexhaustible resource.
• It is a very precious resource which must be
managed to ensure efficient and equitable
access for the services which use it.

Why Manage Spectrum?
• Administration of a natural resource -- key
to economic health of telecommunications.
• Addresses international and domestic
components.
• Ensures interference-free access to the radio
frequency spectrum for as many users and
as many uses as is possible.
• Large revenue generator.

Regulating Authority
• Each country has is own way or body for spectrum
management.
• Telecom Regulatory Authority of India (TRAI) was
established on February 20, 1997 to regulate telecom
services and tariffs in India.
• Earlier regulation of telecom services and tariffs was
overseen by the Central Government of India.
• In USA The Federal Communications Commission
(FCC) is an independent agency of the United States
government, to regulate interstate communications by
radio, television, wire, satellite, and cable in all 50
states, the District of Columbia and U.S. territories.

Frequency Allocation
• Auction of spectrums was introduced in the
telecommunication market after the failure of the
administrative process of allocating spectrum.
• In auction theory, an auction takes place when there is a
seller who wishes to allocate an object to one of ‘n’
buyers.
• Auctions use a price mechanism to allocate spectrum.
• Auction of spectrum can be used to increase efficiency
and earn maximum revenue.
• However, auctions of spectrum also have certain
drawbacks such as higher price of telecom services due
to high license fees.

• Some of the different types of auction formats
are:
• First-price sealed bid auction: The highest
bidder wins the auction. Such highest bidder
pays an amount equal to the bid amount and it
is not essential that the bidder with the highest
value will place the highest bid. The bid is
based on the speculation what other bidders
will be bidding.

• Second-price sealed bids auction (Vickery
auction): This procedure of auction is similar
to first price sealed bid auction. The highest
bidder wins the auction but he has to pay the
price equal to the second highest bid.
• Dutch auction: The auctioneer quotes the
highest price for the subject matter of the
auction and gradually decreases price. The
first one to bid for it wins the auction.

• English or Japanese auction: In English auction, the auctioneer
quotes the minimum price and the buyer bids an amount higher
than the minimum price.
• The bidding is closed when there is no increase in the amount
and the highest bidder wins the auction.
• The other variant of English auction is Japanese auction.
• In this format, the auctioneer quotes a low price and gradually
increases the price which is pre-determined.
• The bidders should show willingness to buy at the price quoted
by the auctioneer.
• The bidding closes when only one bidder is left, who is willing
to buy the object at the price quoted by the auctioneer.

Unit 1 - Fundamentals of Communications.ppt

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