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CHAPTER --1

GSM INTRODUCTION

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GSM INTRODUCTION -----

1. Global System for Mobile communications (GSM: originally from Groupe Spcial

Mobile) is the most popular standard formobile phones in the world.

2. GSM is used by over 2billion people across more than 212 countries and territories.

3. GSM uses a variation of time division multiple access (TDMA) and is the most

widely used of the three digital wireless telephony technologies (TDMA, GSM, and

CDMA). 4. GSM digitizes and compresses data, then sends it down a channel with

two other streams of user data, each in its own time slot. It operates at either the 900

MHz or 1800 MHz frequency band.

4. GSM differs from its predecessors in that both signaling and speech channels are

digital call quality, and so is considered asecond generation (2G) mobile phone

system.

5. GSM standard is advantageous to both consumers (who benefit from the ability to

roam and switch carriers without switching phones) and also to network operators

(who can choose equipment from any of the many vendors implementing GSM).6. Newer version of GSM is Release97 which has packet data capabilities , by means

of GPRS (General Packet Radio Services ). Release 97 introduced higher speed

data transmission using Enhanced Data Rates for GSM Evolution (EDGE).

7. GSM, together with other technologies, is part of the evolution of wireless mobile

telemmunications that includes High-Speed Circuit-Switched Data (HCSD), GeneralPacket Radio System (GPRS), Enhanced Data GSM Environment (EDGE), and

Universal Mobile Telecommunications Service (UMTS).

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GSM OBJECTIVES---------

In June 1982, the European Conference of Postal and Telecommunications

Administrations (CEPT), created the Groupe Spcial Mobile (GSM) to develop a

standard for a mobile telephone system that could be used across Europe.Developing

the GSM has mainly two objectives ----

1. Pan -European roaming ,which offers compatibility throughout the European

continent &

2. Interaction with the integrated service digital network (ISDN), which offers the

capability to extend the single subscriber-line system to a multiservice system

with various services which are currently offered only through diverse

telecommunications networks.

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CHAPTER ---- 2

Comparison of mobile phone standards

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Comparison of mobile phone standards

Global System for Mobile Communications (AKA GSM, around 8085 % market share)

and IS-95 (AKA cdmaOne, around 1015 % market share

[1]

) are the two most prevalent

mobile communication technologies. Both technologies have to solve the same problem:

to divide the finite RF spectrum among multiple users.

TDMA (Time Division Multiple Accessunderlying technology used in GSM's 2G)

does it by chopping up the channel into sequential time slices. Each user of the channel

takes turns to transmit and receive signals. In reality, only one person is actually using the

channel at a specific moment. This is analogous to time-sharing on a large computer

server.

CDMA (Code Division Multiple Accessunderlying technology used in GSM's 3G and

IS-95's 2G) on the other hand, uses a special type ofdigital modulation called

spread spectrum which spreads the voice data over a very wide channel in pseudorandom

fashion. The receiver undoes the randomization to collect the bits together and produce

the sound.

For comparison, imagine a cocktail party, where couples are talking to each other in a

single room. The room represents the available bandwidth. In GSM, a speaker takes turns

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talking to a listener. The speaker talks for a short time and then stops to let another pair

talk. There is never more than one speaker talking in the room, no one has to worry about

two conversations mixing. In CDMA, any speaker can talk at any time; however each

uses a different language. Each listener can only understand the language of their partner.

As more and more couples talk, the background noise (representing the noise floor) gets

louder, but because of the difference in languages, conversations do not mix.

Comparison table

Feature NMT GSM UMTS IS-95 CDMA2000

Technology FDMA TDMA W-CDMA CDMA CDMA

Generation 1G 2G 3G 2G 3G

Digital No Yes Yes Yes Yes

Age 1981 1991 2001 1995 2000

Worldwide market

share[2]0% 80% 4% 0.6% 12%

Roaming Scandinavia Worldwide,200+countries

Worldwide Limited Limited

Handset

interoperabilityNone SIM card SIM card None

RUIM (notcommonly

implemented)

Common

InterferenceNone

Interfereswith someelectronics,

such as

amplifiers

None None None

Signal

quality/coverage

area

Goodcoverage

due to lowfrequencies

Goodcoverage

indoors on850/900MHz.

Repeaterspossible. 35

Smaller cellsand lowerindoors

coverage dueto 2100 MHz

frequency

Unlimitedcell size,

lowtransmitter

powerpermits

large cells

Unlimitedcell size, lowtransmitter

powerpermits large

cells

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km hardlimit.

Frequencyutilization/Call

density

Very lowdensity

0.2 MHz = 8timeslots.

Eachtimeslot canhold up to 2calls throughinterleaving.

5 MHz = 2Mbps. Eachcall uses 1.8-

12 kbit/sdepending on

chosenquality and

audiocomplexity.

?Comparable

to UMTS

?Comparable

to UMTS

Battery life

Low, due tohigh

transmitter

power (1watt)

Very gooddue to simple

protocol,good

coverage and

mature,power-efficientchipsets.

Lower due tohigh

demands ofWCDMApower

control andyoung

chipsets.

Lower dueto high

demands ofCDMApowercontrol.

Lower due tohigh demands

of CDMApower control

and youngchipsets.

Handoff Hard Hard Soft Soft Soft

Breathing No No Yes Yes Yes

Intellectual property ?

Concentratedamong a few

industryparticipants

Concentratedamong a few

industryparticipants

Qualcomm Qualcomm

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CHAPTER ----3

AdvantagesAnd

Disadvantages of 2G GSM

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Advantages of 2G GSM GSM is mature; this maturity means a more stable network with robust features.

Less signal deterioration inside buildings.

Ability to use repeaters.

Talktime is generally higher in GSM phones due to the pulse nature of

transmission.

The availability ofSubscriber Identity Modules allows users to switch networks

and handsets at will, aside from a subsidy lock.

GSM covers virtually all parts of the world so international roaming is not a

problem.

The much bigger number ofsubscribers globally creates a betternetwork effect

for GSM handset makers, carriers and end users.

Disadvantages of 2G GSM Pulse nature of TDMA transmission used in 2G interferes with some electronics,

especially certain audio amplifiers. 3G uses W-CDMA now.

Intellectual property is concentrated among a few industry participants, creating

barriers to entry for new entrants and limiting competition among phone

manufacturers.[citation needed]

GSM has a fixed maximum cell site range of 35 km, which is imposed by

technical limitations.

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CHAPTER------4

GSM ARCHITECTURE

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GSM ARCHITECTURE ------------GSM consists of many subsystems which are as follows ---

1. The Mobile Station(MS)

2. Base Station subsystem(BSS)

3. Network and Swiching subsystem(NSS)

.

4 Operation subsystem(OSS) GSM

MS BSS NSS OSS

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Fig: Architecher of global system for mobilecommunications

1.The Mobile Station(MS)---- It may be a stand alone piece of equipment for certain services or support the

connection of external terminals.

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MS includes mobile equipment(ME) and a subscriber identity module (SIM) .

SIM a subscriber module which stores all subscriber related information.

ME can not be personali assigned to one subscriber .

When a subscribers SIM is inserted in ME of an MS , that MS belongs to subscriber

and call is deliver to that MS .

.2. Base Station Subsystem(BSS) -------------

The Base Station Subsystem (BSS) is the section of a traditional cellulartelephone networkwhich is responsible for handling traffic and signaling between a

mobile phone and theNetwork Switching Subsystem.

The BSS carries out transcoding The BSS carries out transcoding of speech channels,

allocation of radio channels to mobile phones, paging, quality management of

transmission and reception over the Air interface and many other tasks related to the

radio network.

BSS consists of a base transceiver station (BTS)and a base station controller (BSC)

which may cotrol several BTSs .

BTS contains an equipment of transmitting and receiving radio signals similar to ME

of an MS.

3. Network and Swiching subsystem(NSS)---------

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NSS includes main swiching of GSM.

It manages the communication between GSM users and other telecommunications

users.

It is owned and deployed by mobile phone operators and allows mobile phones to

communicate with each other and telephones in the widertelecommunications

network.

The architecture closely resembles a telephone exchange

The Network Switching Subsystem, also referred to as the GSM core network,

usually refers to the circuit-switched core network, used for traditional GSM services

such as voice calls, SMS, and Circuit Switched Data calls.

NSS management consists of ----

i) Mobile Service Switching Centre(MSC)

ii)Interworking Function(IWF)

iii)Home Location Register(HLR)----

The 'Home Location Register'or HLR is a central database that contains details

of each mobile phone subscriber that is authorized to use the GSM core network.

The HLR stores details of everySIM card issued by the mobile phone operator

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iv) Visitor Location Register (VLR)-----

The Visitor Location Register or VLR is a temporary database of the subscribers

who have roamed into the particular area which it serves.

Each Base Station in the network is served by exactly one VLR, hence a

subscriber cannot be present in more than one VLR at a time.

v)Gateway MSC(GMSC)

vi)Signaling Transfer Point(STP)

4.Operation subsystem--------

There are areas of OSS

i)Network operation and maintance functions

ii)Subscription management, including charging and billing

iii)Mobile equipment management

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A-Interface A-bis interfaceRadio

Air -interface

MSC

OAM

BTSBSC

MS

HLR

VLR

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fig: Functional Architecture and principal interfaces

CHAPTER-----5

Layer modeling (OSI model )

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Layer modeling (OSI model)---

The Open system Interconnection(OSI) of GSM consists of five layers---

Transmisson(TR)

Radio recorce management(RR)

Mobility management(MM)

Communition management(CM) and

Opertion, administration, and maintenance(OAM)

Users

Operators

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fig: The functional planes of GSM

The lower layers corresponds the short-time-scale function, the upper layers are long-

time-scale-functions.

The transmission layer set up a connection between MS and BTS .

The RR layer refers to the protocol for the management of the transmission over the radio

interface and provides a stable link between the MS and BSC

The BSS performs the most of RR functions.

The management layer

1. manages the subscriber databases , including location data, and

2. manages the authentication activities , SIM,HLR, and AUC,

Transmission

RR

MMOAM

CM

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the NSS is the significant element in the CM layer. The following are the functions are

the parts of the CM layer ----

1. Call controlthe CM layer sets up calls , maintains calls, and releases calls. The

CM layer interacts among MSC/VLR, GMSC, IWF , AND HLR for managing

circuit-oriented services, including speech and circuit data.

2. Supplementary services management-- Allows users to have some control of

their calls in the network, and has specific variations from the basic services .

3. Short message service(SMS)---- related to the point-to point SMS .A SMS

service center (SMS -SC) may connect to several GSM networks. Short message

transmission requires setting up a signaling connection between the mobile station

and the MSC . The two functions of SMS are ----

i) Mobile-originated short message

ii) Mobile-terminated short message

CHAPTER ----6

Transmission

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Transmission ----

A 4-kHz analog speech signal converts to a 64 kbps digital signal , then down

converts to 13 kbps before modulation. Using a rate of 13-kbps instead of 64 kbps

allows the 13-kbps data rate transmission to occur over a narrowband channel . Since the

radio spectrum is a precious and li8mited resource, using less bandwidth per channel

provides more channels within a given radio spectrum.

Digital speech uses.

1. regular pulse excitation (RPE)---Generates the impulse noise to simulate the

nature of speech.

2. Linear prediction coding(LPC)----- Generates speech waveform by using a filter

with eight transmitted coefficients with a speech frame of 20 ms ; 260 bits

represent a 20ms speech frame .

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There are two modes of transmission in GSM , continuous (normal mode ) and

discontinuous .

The discontinuous transmission decreases the effective radio transmission encoding

of speech at 13 kbps from a bit rate around 500 bps without speech.

CHAPTER ---7

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GSM Channels and channel modes

GSM Channels and channel modes-------

Channel structure---- The services offered to users have four different modes,three data modes, and one speech mode. The radio transmission uses the physicalchannels.

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Fig:(b)

Fig: Interconnection with ISDN

(a)PSTN user to ISDN user, (b) GSM user to ISDN user

Physical Channels-----There are three kinds of physical channels , also called

traffic channels (TCHs):

1. TCH/F(Full rate)Transmits a speech code of 13 kbps or three data-mode rates,

12, 6, and 3.6 kbps.

2. TCH/H(half rate) --- Transmits speech code of 7 kbps or two data modes, 6 and

3.6 kbps .

Personal

computerPSTN ISDN

Personal

computer

Personalcomputer

GSM ISDNPersonalcomputer

Fig:(a)

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3. TCH/(one-eighth rate)Used for low-rate signaling channels, common channels,

and data channels.

Logical channels ----

Common channels. all the common channels are embedded in different traffic

channels They are grouped by the same cycles(51.8 BP) where BP is burst period i.e.

time slot which is 577micro sec.

Downlink common channels ----There are five downlink unidirectional channels,

shared or grouped by a TCH.

Frequency correction channels (FCCH)

Synchronization channels (SCH)

Broadcast control channels (BCCH

Paging and access grant channel(PAGCH)

Call broadcast channel (CBCH)

Uplink common channels -----The random access channel (RACH) is the only common

uplink channel RACH is the channel that the mobile station chooses to access the calls .

Signaling channels

Slow associated control channel (SACCH)

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CHAPTER ----8

TECHNICAL VIEW

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TECHNICAL VIEW--------

GSM is a cellular network, which means that mobile phones connect to it by

searching for cells in the immediate vicinity. GSM networks operate in four different frequency ranges.

Most GSM networks operate in the 900 MHz or 1800 MHz bands.

There are two types of frequency bands used in GSM.

In the 900 MHz band the uplinkfrequency band is 890915 MHz, and the

downlinkfrequency band is 935960 MHz.

This 25 MHz bandwidth is subdivided into 124 carrier frequency channels, each

spaced 200 kHz apart.

Time division multiplexing is used to allow eight full-rate or sixteen half-rate

speech channels perradio frequency channel.

There are eight radio timeslots (giving eightburstperiods) grouped into what iscalled a TDMA frame.

Half rate channels use alternate frames in the same timeslot. The channel data

rate is 270.833 kbit/s, and the frame duration is 4.615 ms.

The transmission power in the handset is limited to a maximum of 2 watts in

GSM850/900 and 1 watt in GSM1800/1900.

GSM has used a variety of voice codices to squeeze 3.1 kHz audio into between

5.6 and 13 kbit/s.

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Originally, two codecs, named after the types of data channel they were allocated,

were used, called Half Rate (5.6 kbit/s) and Full Rate (13 kbit/s). These used a

system based upon linear predictive coding (LPC).

In addition to being efficient with bitrates, these codecs also made it easier to

identify more important parts of the audio, allowing the air interface layer to

prioritize and better protect these parts of the signal

GSM was further enhanced in 1997 with the Enhanced Full Rate (EFR) codec, a

12.2 kbit/s codec that uses a full rate channel.

Finally, with the development ofUMTS, EFR was refactored into a variable-rate

codec called AMR-Narrowband, which is high quality and robust against interference

when used on full rate channels, and less robust but still relatively high quality when

used in good radio conditions on half-rate channels.

Modulation Scheme----------

The modulationused in GSM is Gaussian minimum-shift keying(GMSK), a kind of

continuous-phase frequency shift keying. In GMSK, the signal to be modulated onto the

carrier is first smoothed with a Gaussianlow-pass filterprior to being fed to a frequency

modulator, which greatly reduces the interference to neighboring channels (adjacent

channel interference).

Bandwidth time product BT= 0.3

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Minimum means the minimum tone separation. GMSK utilizes

A small spectrum bandwidth to send a GSM carrier channel. The modulation rate of a

GSM carrier channel is 270 kbps.

Generating a GMSK

Waveform

GMSK as implemented by quadrature signal processing at baseband followquadrature modulator

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GMSK is based on MSK

Minimum Shift Keying Linear phase changes Spectrally efficient

At baseband, bit transitions are represented by

cycle sinusoid

MSK

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Frequency Hopping

In frequency hopping systems, the transmitter changes the carrier frequency according to

a certain "hopping" pattern . The advantage is that the signal sees a different channel and

a different set of interfering signals during each hop. This avoids the problem of failing

communication at a particular frequency, because of a fade or a particular interferer.

Slow and Fast Hopping

There are two kinds of frequency hopping Slow Frequency Hopping (SFH)

In this case one or more data bits are transmitted within one hop. An advantage is

that coherent data detection is possible. Often, systems using slow hopping also

employ (burst) error control coding to restore loss of (multiple) bits in one hop.

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Fast Frequency Hopping (FFH)

One data bit is divided over multiple hops. In fast hopping, coherent signal

detection is difficult, and seldom used. Mostly, FSK or MFSK modulation is used.

Slow frequency hopping is a popular technique forwireless LANs.

In GSM telephony, slow frequency hopping can be used, at the discretion of the network

control software. It avoids that a stationary terminal that happens to be located in a fade

looses its link to the base station.

As nearby hopping interferers are unlikely to continuously transmit in the same frequency

slot as the reference user, the near-far problem is less severe than in direct sequence(DS)

CDMA. Particularly for wireless LANs, where terminals can be located anywhere, this

advantage made SFH popular.

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Time division multiple access--------

Time division multiple access (TDMA) is a channel access method for shared

medium (usually radio) networks.

It allows several users to share the same frequency channel by dividing the signal

into different timeslots. The users transmit in rapid succession, one after the

other, each using his own timeslot. This allows multiple stations to share the same

transmission medium (e.g. radio frequency channel) while using only the part of

itsbandwidth they require.

TDMA is used in the digital 2Gcellular systems such asGlobal System for

Mobile Communications (GSM), IS-136,Personal Digital Cellular(PDC) and

iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT)standard forportable phones.

It is also used extensively in satellite systems, and combat-net radio systems.

TDMA frame structure showing a data stream divided into frames and those

frames divided into timeslots.

TDMA is a type ofTime-division multiplexing, with the special point that instead

of having one transmitterconnected to one receiver, there are multiple

transmitters. In the case of theuplinkfrom a mobile phone to abase station thisbecomes particularly difficult because the mobile phone can move around and

vary the timing advance required to make its transmission match the gap in

transmission from its peers.

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TDMA features

Shares single carrier frequency with multiple users

Non-continuous transmission makes handoff simpler

Slots can be assigned on demand in dynamic TDMA Less stringent power control than CDMA due to reduced intra cell interference

Higher synchronization overhead than CDMA

Advanced equalization is necessary for high data rates

Cell breathing (borrowing resources from adjacent cells) is more complicated than

in CDMA

Frequency/slot allocation complexity

Pulsating power envelop: Interference with other devices

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Burst and training sequences--------

In TDMA signal transmits in bursts. The time interval of the burst brings the

amplitude of a transmitted signal up from a starting value of 0 to its normal value . Then a

packet of bits is transmitted by a modulated signal Afterward, the amplitude decreases to

zero .

These burst occur only at the mobile station transmission or at the base station if the

adjacent burst is not transmitted.

There are trail bits and training sequence bits within a burst. The tail bits are three 0 bits

added at the beginning and at the end of each burst ,which provide the guard time.

The training sequence is a sequence known by the receiver which trains an equalizer, a

device which reduces the intersymbol interference.

The training sequence bits are inserted in the middle of a time slot some time is called a

midamble , for the same purpose as a preamble , so that the equalizer can minimize its

maximum distance with any useful bit.

There are eight different training sequences , with little between any two sequences to

distinguish the received signal from the interference signal .

There are several kinds of bursts :

1. Normal bursts

2. Access bursts

3. F and S bursts

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1.The normal burst used in TCH:

3. The F and S bursts ,used in FCCH and has the simplest format

3 57 1 26 1 57 3

7 41 1 35 3

3 38 1 64 1 38 3

2. Access bursts used in RACH

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Handover----

The GSM handover is not specified as a standard . It is a feature of mobile

assistance handover (MAHO) and is carried out within the unit.The mobile stationscans for another radio carrier under direction of a base station .It moniters those

time slots which are not its own assigned time slots for receiving the signal .

In this case , on the request of a base station, the signal strength of a

specified radio carrier is measured in one time frame , and on request , the

measurements are forwarded to the base station to asset in the handover process. This

is called MAHO .

fig : Handover in GSM

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The MSC uses two sets of information to decide whether a handover should be initiated

and which BTS is the candidate BTS for the handover . The two sets are ----

1. the signal strengths of the MS as received at the neighboring BTSs and

2. the strengths of neighboring BTSs received at the MS . The latter information is

from MAHO.

GSM provides handover processes for the following:

Quality (uplink/downlink).

Interference (uplink/downlink).

RF level (uplink/downlink).

MS distance.

Power budget.

More handover algorithms have been developed for specific applications, such as

microcellular, and are currently being implemented.

Mobile and wireless Communication

- Support for voice and data services

Total mobility

International access, chip-card enables use of access points of different

providers

Worldwide connectivity

One number, the network handles localization

High capacity

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Better frequency efficiency, smaller cells, more customers per cell

High transmission quality

High audio quality and reliability for wireless, uninterrupted phone calls at higher

speeds (e.g., from cars, trains)

Security functions

- Access control, authentication via chip-card and PIN

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CHAPTER----9

Cell Size in GSM

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Cell Size in GSM -------

There are four different cell sizes in a GSM networkmacro, micro, pico and

umbrella cells

The coverage area of each cell varies according to the implementation

environment.

Macro cells can be regarded as cells where thebase stationantenna is installed on

a mast or a building above average roof top level.

Micro cells are cells whose antenna height is under average roof top level; they

are typically used in urban areas.

Picocells are small cells whose coverage diameter is a few dozen meters; they are

mainly used indoors.

Umbrella cells are used to cover shadowed regions of smaller cells and fill in

gaps in coverage between those cells.

Cell horizontal radius varies depending on antenna height, antenna gain and

propagation conditions from a couple of hundred meters to several tens of

kilometers. The longest distance the GSM specification supports in practical use

is 35 kilometres (22 mi).

There are also several implementations of the concept of an extended cell, where the

cell radius could be double or even more, depending on the antenna system, the type

of terrain and the timing advance.

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Indoor coverage is also supported by GSM and may be achieved by using an indoor

picocell base station, or an indoor repeaterwith distributed indoor antennas fed

through power splitters, to deliver the radio signals from an antenna outdoors to the

separate indoor distributed antenna system.

These are typically deployed when a lot of call capacity is needed indoors, for

example in shopping centers or airports. However, this is not a prerequisite, since

indoor coverage is also provided by in-building penetration of the radio signals from

nearby cells.

CHAPTER ------10

Services Provided by GSM

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Services Provided by GSM:

GSM services are a standard collection of applications and features available to mobile

phone subscribers all over the world.

The design of the service is moderately complex because it must be able to locate a

moving phone anywhere in the world, and accommodate the relatively small battery

capacity, limited input/output capabilities, and weak radio transmitters on mobile devices.

1. General Packet Radio Service (GPRS)

Apacket-switched connection chops data into distinct chunks, known as

packets, which may arrive at their destination via different routes, at different

times, out of sequence, or (hopefully only occasionally) not at all. An

intermediate protocol, like TCP, might be used to ensure the original datastream is reassembled at the destination (by putting packets in order and

retransmitting missing ones, if necessary).

The advantage of packet-switched connections is that bandwidth is only used

when there is actually data to transmit

Telecommunication services can be classified into

1. Bearer Services,

2. Teleservices, and

3. Supplementary Services.

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When a call is made from a GSM Mobile Station, the type of service requested is

indicated in the set-up message. This means that the GSM operator has the option to treat

emergency calls differently by allowing mobile equipment without a SIM card to make

them.

4. Bearer Services:

A bearer service provides the capacity necessary to transmit

appropriate signals between two access points providing an interface to the network. In

GSM asynchronous and synchronous data transmission rates upto 9.6 kbps are supported.

5.Supplementary Services:

The supplementary services basically consist of call forwarding and call barring.

5.1 Call Forwarding:

The Call Forwarding Supplementary Service is used to divert calls from the

original recipient to another number, and is normally set up by the subscriber himself. It

can be used by the subscriber to divert calls from the Mobile Station when the subscriberis not available, and so to ensure that calls are not lost. A typical scenario would be a

salesperson turns off his mobile phone during a meeting with customers, but does not

with to lose potential sales leads while he is unavailable.

5.2 Call Barring:

The concept of barring certain types of calls might seem to be a supplementary

disservice rather than service. However, there are times when the subscriber is not the

actual user of the Mobile Station, and as a consequence may wish to limit its

functionality, so as to limit the charges incurred. Alternatively, if the subscriber and user

are one and the same, the Call Barring may be useful to stop calls being routed to

international destinations when they are routed. The reason for this is because it is

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expected that the roaming subscriber will pay the charges incurred for international re-

routing of calls. So, GSM devised some flexible services that enable the subscriber to

conditionally bar calls.

Newer GSM Services:

1. Number Identification:

Calling Line Identification Presentation: This service deals with the

presentation of the calling party's telephone number. The concept is for thisnumber to be presented, at the start of the phone ringing, so that the called

person can determine who is ringing prior to answering. The person

subscribing to the service receives the telephone number of the calling party.

Calling Line Identification Restriction: A person not wishing their

number to be presented to others subscribes to this service. In the normal

course of event, the restriction service overrides the presentation service.

Connected Line Identification Presentation: This service is provided to

give the calling party the telephone number of the person to whom they are

connected. This may seem strange since the person making the call should

know the number they dialled, but there are situations (such as forwardings)

where the number

2 .Multi-Party:

Multi-Party Service: This service is similar to a conference type service, in

that several calls may be connected with all parties talking to each other.

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CHAPTER---11

Conclusion

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Conclusion:

Thus it seems that probably the potential of GSM is not fully realized

till date. The real power of its capabilities is yet to be harnessed and will

influence the human life in a big way in the future. The future has a lot to

see in terms of the new generation state-of-the -art cellular phones and other

devices being used in common.

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CHAPTER----12

Overview of GSM

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Overview of GSM-----------

Summary of physical layer parameters----TDMA Structure 8 time slots per radio carrier

Time slots .577 ms

Frame interval 8 time slots =4.615ms

Radio carrier no. 124 radio carrier (935-960mhz uplink

890-915mhz downlink)

Modulation Scheme Gaussian MSK BT=.3

Frequency hopping Slow frequency hopping 217hops/s)

GSMs Strenth--------

GSM is first to apply the TDMA scheme developed for mobile radio

systems . It has several features ----

1. Roaming in European countries

2. Use of SIM cards

3. Control of transmission power

4. Discontinuous transmission

5. Mobile assisted handover

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Convolution coding

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CHAPTER--- 1

Abstract

Abstract

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Channel coding refers to the class of signal transformations designed toimprove communication performance by enabling the transmitted signals to betterwithstand the effects of various channel impairments, such as noise , interference, and

fading. These signal processing techniques can be thought of as vehicles foraccomplishing desirable system trade offs (e.g., error performance vs. bandwidth, powervs. bandwidth).

The primary objective of spectrally efficient modulation techniques is tomaximize bandwidth efficiency. The increasing demand for digital transmission channelshas led to the investigation of spectrally efficient modulation technique to maximizebandwidth efficiency and thus help to ameliorate the spectral congestion problem.

The channel coding techniques viz. Linear Block Code, Convolutional Codeetc. have generally not been associated with voice grade telephone channels. Recently,

however, there has been considerable interest in techniques that can provide coding gainfor bandlimited channels. The motivation is to enable the reliable transmission of higherdata rate over voice grade channels.

In this design, various aspects of information theory are studied and aConvolutional encoder is implemented

CHAPTER----2

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INFORMATION THEORY ANDCODING

INFORMATION THEORY AND

CODING

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For its efficient and reliable operation a digital communication system dependsupon different types of encoders and decoders along with some other equipment.Decoders are used to decode the original bit stream from the encoded bit stream. Theencoders are used for two purposes:

Source coding

Channel coding

In this section I will discuss about these two types of coding used in digitalcommunication system, so that we can get a clear concept of coding. Source coding andchannel coding play a very important role in design of an efficient and a reliablecommunication system.

In the present section, first I will discuss some information theoretic terms (in detail),

which are frequently used in the coding theoy, then I will discuss about the coding

CHAPTER ----3

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Coding theory

Coding theory------

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Coding theory is a branch ofmathematics and computer science dealing with the error-

prone process of transmitting data across noisy channels, via clever means, so that a large

number of errors that occur can be corrected. It also deals with the properties of codes,

and thus with their fitness for a specific application.

There are two classes of codes.

1. Source coding (Data compression)

2. Channel coding (Forward error correction)

The first, source encoding, attempts to compress the data from a source in order to

transmit it more efficiently. We see this practice every day on the Internet where the

common "Zip" data compression is used to reduce the network load and make files

smaller. The second, channel encoding adds extra data bits, commonly called redundancy

bits, to make the transmission of data more robust to disturbances present on the

transmission channel. The ordinary user may not be aware of many applications using

channel coding. A typical music CD uses a powerful Reed-Solomon code to correct for

scratches and dust. In this application the transmission channel is the CD itself. Cell

phones also use powerful coding techniques to correct for the fading and noise of high

frequency radio transmission. Data modems, telephone transmissions, and of courseNASA all employ powerful channel coding techniques to get the bits through.

CHANNEL ENCODING-----

Channel encoding theory is to find codes which transmit quickly, contain many

valid code words and can correct or at least detect many errors. While not

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mutually exclusive, performance in these areas is a trade off. So, different codes

are optimal for different applications.

The needed properties of this code mainly depend on the probability of errors

happening during transmission. In a typical CD, the impairment is mainly dust or

scratches. Thus codes are used in an interleaved manner. The data is spread out

over the disk. Although not a very good code, a simple repeat code can serve as

an understandable example. Suppose we take a block of data bits (representing

sound) and send it three times. At the receiver we will examine the three

repetitions bit by bit and take a majority vote. The twist on this is that we don't

merely send the bits in order. We interleave them. The block of data bits is first

divided into 4 smaller blocks. Then we cycle through the block and send one bit

from the first, then the second, etc. This is done three times to spread the data out

over the surface of the disk. In the context of the simple repeat code, this may not

appear effective. However, there are more powerful codes known which are very

effective at correcting the "burst" error of a scratch or a dust spot when this

interleaving technique is used.

The term algebraic coding theory denotes the sub-field of coding theory where the

properties of codes are expressed in algebraic terms and then further researched.

Algebraic Coding theory, is basically divided into two major types of codes

1. Linear block codes

2. Convolutional codes

It analyzes the following three properties of a code -- mainly:

code word length total number of valid code words

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Channel Coding Theorem:

The channel coding theorem for a DMC is stated as follows:

Given a DMS X with entropy H (X) bits/symbol and a DMC with a capacity Cs

bits/symbol, if H (X) C, there exist a coding scheme for which the source output can be

transmitted over the channel with an arbitrarily small probability error.

Conversely, if H (X) > Cs, it is not possible to transmit information over the channel with

an arbitrarily small probability error. Note that the channel-coding theorem only asserts

the existence of code but it does not tell us how to construct these codes.

The block diagram the communication channel is shown in the fig at next page.

Applications of coding theory

Another concern of coding theory is designing codes that help synchronization. A code

may be designed so that a phase shift can be easily detected and corrected and that

multiple signals can be sent on the same channel. There is an interesting class of codes

we see every day on our cell phones. These are the Code Division Multiple Access

(CDMA) codes.

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CONVOLUTIONAL

ENCODING

In telecommunication, a convolutional code is a type oferror-correcting

code in which (a) each m-bitinformation symbol (each m-bit string) to be

encoded is transformed into an n-bit symbol, where m/n is the code rate (n

m) and (b) the transformation is a function of the last kinformation symbols,

where kis the constraint length of the code.

Where convolutional codes are used

Convolutional codes are often used to improve the performance of digital

radio, mobile phones, satellite links, and Bluetooth implementations.

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CHAPTER----4

Convolution codes

Convolution codes ----

To convolutionally encode data, start with kmemory registers, each holding 1 input bit.Unless otherwise specified, all memory registers start with a value of 0. The encoder has

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n modulo-2 adders, and ngenerator polynomials one for each adder (see figurebelow). An input bit m1 is fed into the leftmost register. Using the generator polynomialsand the existing values in the remaining registers, the encoder outputs n bits. Now bitshift all register values to the right (m1 moves to m0, m0 moves to m-1) and wait for thenext input bit. If there are no remaining input bits, the encoder continues output until all

registers have returned to the zero state.

The figure below is a rate 1/3 (m/n) encoder with constraint length (k) of 3. Generatorpolynomials are G1 = (1,1,1), G2 = (0,1,1), and G3 = (1,0,1). Therefore, output bits arecalculated (modulo 2) as follows:

n1 = m1 + m0 + m-1n2 = m0 + m-1

n3 = m1 + m-1.

mk stage shift registeri/p seq. shifted k bit at a time

1 -----------

n mod-2 adders

1 2 3 ------ n

Encoded Output Sequence

The integer m is a parameter known as the constraint length of the convolution code. Inpractice , n and k are small integers and m is varied to control redundancy. The constraintlength represents the no. of k bit shifts over which a single information bit can influencethe encoder output. Since there are n code bits for each input group of k message bits, thecode rate is k/n message bit per code bit, where k

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In present case convolution encoder is for 1/3 rate .the four outputs of shift registerare s1,s2 , s3 and s4 .

These outputs are inputted in a combinations of ex-or gates to produce a three bitconvolved output u1, u2, and u3 as according to the following generator polynomial.

U1=s1;

U2=s1+s2+s3+s4;

U3=s1+s4+s3.

Application of Convolution codes

Convolutional codes are used in voice band modems (V.32, V.17, and V.34) and in GSMmobile phones, as well as satellite and military communication devices.

Here the idea is to make every codeword symbol be the weighted sum of the various

input message symbols. This is like convolution used in LTI systems to find the output ofa system, when you know the input and impulse response.

So we generally find the output of the system [convolutional encoder] , which is theconvolution of the input bit, against the states of the convolution encoder, registers.

Fundamentally, convolutional codes do not offer more protection against noise than anequivalent block code. In many cases, they generally offer greater simplicity ofimplementation over a block code of equal power. The encoder is usually a simple circuitwhich has state memory and some feedback logic, normally XOR gates. The decoder canbe implemented in software or firmware.

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CHAPTER ---5

IMPLEMENTATION AND CIRCUIT DESIGN

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IMPLEMENTATION AND CIRCUIT DESIGNThe encoder circuits are usually constructed with a number of adders

(mod2) and memory devices. For digital circuits mod2 adders can be constructed

with XOR logic and memory device by Shift Registers.

Encoder for 1/3Rate:A convolutional encoder transforms k bits of data into n bit codes, but the

coder output depends on the earlier blocks of data that have been processed by

the coder. The general block diagram for an encoder of1/3 rate which is

implemented through hardware is shown in figure 1, where the parameters are:

R = 1/3, n = 3, and constraint length k = 1.

The circuit for this encoder is shown in figure 2. In this circuit an eight bit

serial in parallel out shift register and eight XOR gates are used. Manual clock

has been used to simplify and observe the working of the circuit.

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Hardware Description:For the design of encoder n =3, k =1, K = 3, we need

data source

shift register

mod 2 adders

Different blocks and components are described as follows:

Data Source:For this I have used

5V power supply

1 SPDT switch

In this

5V Logic State 1

0V Logic State 0

SPDT is such type of switch in which when one pole is one side the ground

is connected and logic state 0 is obtained. While when pole is at the other side,

supply voltage is connected and logic state 1 is obtained.

Shift Registers: A group of cascaded flip-flops used to store related bits of

information is known as a register. A register that is used to assemble and store

information arriving from a serial source is called a shift register. Each flip flop

output of a shift register is connected to the input of the following flip flop and a

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Mod 2 Adder:For this XOR IC 7486 is used. This is a quad 2 input XOR gate.

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Clock:For controlling the operation of the flip flop in the shift register we need

clock cycles which have been generated by 555timer.

For generation of clock f on time 0.5 secs, we want:

Components: Unit

555timer IC 1

10 k resistance 2

100K resistance 1

0.1 F capacitance 2

1000 F capacitance 1

At the pin 3 of timer IC we can obtain clock.

7486 Quadruple 2-Input Exclusive ORGate

These devices contain four independent 2-input exclusive

OR-Gates. They perform the Boolean function Y = A B

= AB + A B in positive logic.

A common application is as a true/ complement 2-input

element. If one of the inputs is low, the other input will be

reproduced in true form at the output. If one of the inputs is

high, the signal on the other input will be reproduced

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inverted at the output. Our component SN7486 is

characterized for operation from 0 0C to 70 0C.

Every IC s characterized by its own

pin architecture,

The architecture for our IC is given as

adjacent showing the top view of the

IC

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Application of Exclusive OR logic:

An exclusive-OR gate has many applications, some of

which can be represented better by alternative logic

symbols.

These are five equivalent Exclusive-OR symbols valid for

an 86 or LS86A gate in positive logic; negation may be

shown at any two ports.

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POWER SUPPLY UNIT

A necessary part of the electronic system is Power

supply . we oftenly use +5volt supply ,all the linear ICs

(OPMP) Requires +15volt supply.

For our work +5 volt supply is enough .

. A d.c. power supply which maintain the output voltage

constant irrespective of a.c. mains fluctuation or load

variation is known as regulated d.c.power supply.

A regulated power supply consists of an ordinary power

supply and voltage regulating devices. The output of

ordinary power supply is fed to the voltage regulator

which produces the final output. The output voltage

remains constant whether the load current changes or

there are fluctuations in the input dc voltages.

COMPONENT USED:

A 12-0-12step down transformer-200ma

Electrolytic capacitor of 1000F

Regulator IC 7805

4 diode IN 4007

LM 7805

Features

Output Current up to 1A

Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V

Thermal Overload Protection

Short Circuit Protection

Output Transistor Safe Operating Area Protection

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CHAPTER----6

ABOUT THE CIRCUIT

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ABOUT THE CIRCUIT

The output from the transformer secondary is applied to the

full wave rectifier circuit, which converts the sinusoidal

into full wave rectified output. The filter capacitor at the

out put of the full wave rectifier is charged to the peak

value of the rectified output voltage whenever diodes are

forward biased.

For the filter circuit V(t)=V0(1-exp(-t/RC) for RC circuit

charging V(t)=V0exp(-t/rc) for RC circuit discharging

R= Very small Since the diodes are not forward biased

during the entire positive and negative half cycles of he

input waveform, the voltage across the filter capacitor is a

pulsating dc that is a combination of dc and a ripple

voltage. From the pulsating dc voltage, a regulated +5 dc

voltage is obtained by a regulator IC 7805.The output of IC

7805 is taken through a capacitor of 1 F

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CIRCUIT DIAGRAM

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PCB LAUOUT

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GENERATION OF CLOCK

Here IC 7555 is used for generating the clock pulses.Its IC

configuration is same as that of IC 555.The circuit diagram

for generating he clock pulses is given below

Vcc

GND

LM555/NE555/SA555

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Single Timer

Features :

High Current Drive Capability (200mA)

Adjustable Duty Cycle

Temperature Stability of 0.005%/C

Timing From Sec to Hours

Turn off Time Less Than 2Sec

Applications :

Precision Timing

Pulse Generation

Time Delay Generation

Sequential Timing

Internal Block Diagram :

GND

Trigger

Output

Reset

Description :

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The LM555/NE555/SA555 is a highly stable controller

capable of producing accurate timing pulses. With

monostable operation, the time delay is controlled by one

external resistor and one capacitor. With astable operation,

the frequency and duty cycle are accurately controlled with

two external resistors and one capacitor

COMPONENT USED

POWER SUPPLY UNIT

A 9-0-9 step down transformer-200ma

Electrolytic capacitor of 1000F

Regulator IC 7805

4 diode IN 4007

ASTABLE PULSE GENERATOR

CIRCUIT

2 , 10 K resistor

1 M resistor

Capacitor of .01 F

Capacitor of .1 FCapacitor of 1000 F

diode IN 4007

IC 7555

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CHAPTER ----7

PCB Designing

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PCB Designing

The heart of any electronic project is the PCB.

Without a proper PCB the design may end up in total

failure. A perfect PCB gives a facelift to the appearance

and performance of the circuit and what is of great

importance is its neatness. An easy way to make the PCB is

described below:

Materials Required:

Copper clay boardEnamel Paint or Marker

Hand Drill

Ferric Chloride Solution

In design of PCB, firstly we design the circuit with actual

size of components on graph in design of PCB; firstly we

design the circuit with actual size of components on a graph

paper. Then we make the PCB layout by using the PCB

Designing/Express PCB software. This finally designed

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layout is now screen printed or drawn by hand using

marker on the Copper clay board and is required to remove

extra copper from the clay board. The screen-printed plate

is dipped in the solution of FeCl3 +HCl. The plate is stirred

for 1 or 2 hour or till the unpainted copper area is totally

dissolved. The unwanted copper is dissolved and finally we

get PCB fabricated. This is popularly known as

ETCHING. The etched plate is washed with water and

soap to remove marker ink.

PCB Testing:

The tracks made are checked to be continuous. It is carried

with the help of multimeter to get zero resistance.

Circuit Testing:

1. All individual components should be checked previously

with multimeter.

2. IC base continuity should be checked after soldering.

3. All the components are soldered and check for the

continuity.

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Precautions:

1-While using the PCB designer/Express PCB software we

must be careful about the proper track selection and also try

to reduce the size as much as we can.

2-While etching we must be very careful otherwise the.

Tracks can also be etched. The HCL should be used for

reducing the speed of etching if needed.

3-While soldering we should avoid dry soldering.

4-After soldering the continuity should be checked.

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EXPERIMENT

OBJECT:

To design a convolutional encoder 1\3rate when data bit is 101

OBSERVATION:

Let us assume the generator polynomials :

U1(x)=

U2(x)=

U3(x)=

We assume that initial contents of the shift register zero. By pressing

the clear switch the contents of all flip flops becomes zero. The input data

stream is applied tat serial input port. The clock switch is pressed at

different timings and the register contents shifts one block to right

direction. The output encoded message is obtained as-

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Timing

message

Register contents

Encoded output

S1 S2 S3 S4 U1 U2 U3

T0

T1

T2

T3

T4

T5

T6

T7

T8

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CHAPTER----8

DISCUSSION

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DISCUSSION

During commencement of any work A man has to face many

problems and if he has faced these problems patiently then it is true he will

be successful in his object. In my design I have faced many problems and

tried to remove them, the result of that is now before us.

For hardware implementation of convolutional encoder we have

used shift registers. In shift register, the contents of flip flops are shifted to

the next flip flop when a clock is applied. The shifting in contents of flip

flops is observed when negative edge of clock begins. At a particular instant

the output of flip flops are X-ORed and encoded message is displayed by

LEDs.

If there is any discrepancy in results then this may be due to

presence of noise.

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CHAPTER----9

References

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References

[1] Simon Haykin,Digital Communications (Wiley, 2000)

[2] Bernard Sklar,Digital Communications :

Fundamentals and Applications (Pearson Education Asia,

2001)

[3] John G. Proakis,Digital Communications (McGraw-

Hill, Inc., 1995)

[4] Hwei Hsu,Schaums Outlines : Analog and Digital

Communications (Tata Mc Graw-Hill Publishing

Company Limited, 2004)

[5]William C. Y. Lee Mobile Cellular Telecommunications

,analog and digital systems

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APPENDIX