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Generation of wireless Network
Technologies used in 1G/2G/2.5G/3G/4G
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Analog and Digital Signals
Analog Signals
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Advantage of Analog Signals
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Digital Signals
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Advantage of Digital Signals
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Analog and Digital Clocks
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Analog to digital Transmission
Digital transmission involves sending a series of symbols, ones and
zeros; from one point to another. Because speech is analogue, that
is, a continuous wave form; it must be converted to digital signals
before it can be transmitted. This process is called analogue to
digital conversion (A/D conversion).
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The A/D conversion is performed by using a process called Pulse
Code Modulation (PCM). PCM is a common method used in
telecommunication systems. It involves the three main steps
described below:
Sampling
Quantization
Coding
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SAMPLING
Sampling involves measuring the analogue signal at specific time
intervals. Each measurement is called a sample and the sampling
time interval is defined as Ts [s]. The accuracy of describing the
analogue signal in digital terms depends on how often the analogue
signal is sampled, among other things. This is expressed as thesampling frequency: fs=1/Ts [Hz].
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According to the Sampling principle:
Normal speech mainly contains frequency components lower than
3000 Hz. Higher components have quite low energy and may be
omitted without affecting the speech quality very much. Applying
the sampling principle when sampling analogue speech signals, the
sampling frequency,fs, should be at least 2 x 3 kHz = 6 kHz.Telecommunication systems use a sampling frequency of 8 kHz,
which is acceptable based on the Sampling principle.
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QUANTIZATION
In order to limit the number of values transmitted, the amplitude
level is divided into a finite set of levels. Each sample within a
certain interval is represented by one of these levels. Figure 6.6
shows the principle of quantization applied to the analogue signal -
the actual sample and the quantified value. The figure shows the
principle ofUniform Quantization used in the GSM system. In
uniform quantization, the distance between two levels is constant.
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CODING
Every quantified value is represented by a binary code. In order to
obtain the 256 levels, 8 bits are used (2^8 = 256). In GSM, 13 bits
are used to obtain the 8192 levels (2^13 = 8192). The process of
PCM, including sampling at 8 kHz and performing quantization and
coding using 8 bits; produces a bit rate of 8000 x 8 = 64 kbit/s. Adigital link used to transmit these bits is called a PCM link.
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In order to use the link more efficiently several channels are
multiplexed onto the same link. The technique used is called Time
Division Multiple Access (TDMA) and it means that several channels
share the same link. Each channel uses the link during a certain
amount of time called a time slot. Figure 6.7 shows how 32
channels are multiplexed onto one PCM link, forming a first order
PCM system. The bit rate on such a link is 32 x 8 x 8000 = 2048
kbit/s called as E1 Link
Multiplexing 32 channels into one PCM link.
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There is also a solution where 24 channels are multiplexed ontoone PCM link. The bit rate for this solution is 24 x 8 x 8000 = 1544
kbit/s. This type of link is preferable in the US Called as T1 Link.
The result from the process of A/D conversion is 8,000 samples per
second of 13 bits each. This is a bit rate of 104 kbits/s. When it isconsidered that 8 subscribers use one radio channel, the overall bit
rate would be 8 x 104 kbits/s = 832 kbits/s. Recalling the general
rule of 1 bit per Hertz, this bit rate would not fit into the 200 kHz
available for all 8 subscribers. The bit rate must be reduced
somehow - this is achieved using segmentation and speech coding.
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Modulation
Modulation is the Process of Varying the Characteristics of high
Signal(Carrier) in accordance with instantaneous Value of low
signal(modulating Signal).
Signals are of low amplitude Strength with low frequency (20 Hz to
20 KHz).
To send signal up to longer distance Modulation is Required
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Types of Modulation
Three types of Digital Modulation Technique
Amplitude Shift Keying Modulation
Frequency Shift Keying Modulation
Phase Shift Keying Modulation
The Modulation used in GSM is Gaussian Minimum Shift
Keying(GMSK), a kind of Phase frequency Shift Keying.
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GMSK(Gaussian Minimum Shift Keying )
In GSM, the carrier bandwidth is 200 kHz. As a general rule, usingsimpler modulation techniques, 1 bit/s can be transmitted within1 Hz. Using this method, only 200 kbits/s could be transmittedwithin 200 kHz. However, more advanced modulation techniquesare available which can transmit more bits/s within 1 Hz. The
modulation technique used in GSM is Gaussian Minimum ShiftKeying (GMSK).
GMSK enables the transmission of 270kbit/s within a 200 kHzchannel. The channel capacity in GSM does not compare favorablywith other digital mobile standards, which can fit more bits/s into
a channel. In this way the capacity of other mobile standards ishigher. However, GSMs GMSK offers more tolerance ofinterference. This in turn enables the tighter re-use of frequencies,which leads to an overall gain in capacity which out-performs thatof other systems.
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GMSK Diagram
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Multiple Access Technology
Multiple Access Technique is achieved by dividing the available radio
frequency spectrum, So that multiple users can be given at the
same time.
Frequency division multiple access (FDMA)( eg.GSM each user frequency channel is 200Hz )
Time division multiple access (TDMA)( eg.GSM each frequency channel is divided into 8 time slots )
Code division multiple access (CDMA)( eg.IS 95- Each user data is coded with unique code)
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Frequency division multiple access (FDMA)
Frequency division multiplexing is used to allow multiple user to share aphysical communication channel , It is called frequency division multiple
access (FDMA)
Time division multiple access (TDMA)TDMA is a channel access method for shared medium network . It allowsseveral user to share the same frequency channel by dividing the signal intodifferent time slots . he user transmit in rapid success in ,one after the other ,
each using his own time slot.
Code division multiple access (CDMA)
CDMA is a channel access method used by various radio communication
technologies .
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Duplex Technology
Types of Duplexing Technology
Frequency division duplex (FDD)( eg; In GSM the up link and down link of a user is separated by 45
MHz)
Time division duplex (TDD)
( eg; In GSM the up link and down link of a user will be the
same frequency but at different Time)
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Duplex Technology
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FREQUENCY CONCEPTS
The following table summarizes the frequency-related specifications ofeach of the GSM systems. The terms used in the table are explained in the
remainder of this section.
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FREQUENCY
An MS (Mobile Station) communicates with a BTS by transmitting orreceiving radio waves, which consist of electromagnetic energy. Thefrequency of a radio wave is the number of times that the waveoscillates per second. Frequency is measured in Hertz (Hz), where 1
Hz indicates one oscillation per second. Radio frequencies are usedfor many applications in the world today. Some common usesinclude:
Television: 300 MHz approx.
FM Radio: 100 MHz approx.
Mobile networks: 300 - 2000 MHz approx.
The frequencies used by mobile networks vary according to thestandard being used. An operator applies for the availablefrequencies
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UPLINK AND DOWNLINK
The MS to the network is referred to as uplink. The direction from thenetwork to the MS is referred to as downlink.
Logic question
Why uplink band consists of lower range of frequency?
Because it requires less power to transmit a lower frequency overa given distance , uplink frequency in mobile system are always the
lower band of frequency- this saves a valuable battery power of theMS
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Wave Length
There are many different types of electromagnetic waves. These
electromagnetic waves can be described by a sinusoidal function,which is characterized by wavelength. Wavelength is the length ofone complete oscillation and is measured in meters (m). Frequencyand wavelength are related via the speed of propagation, which forradio waves is the speed of light (3 x108 m/s).
The wavelength of a frequency can be determined by using the
following formula:
Wavelength = Speed/Frequency
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Thus, for GSM 900 the wavelength is:
Wavelength = 3 x 108m/s/900 MHz
Wavelength = 300,000,000 m/s/900,000,000
Wavelength = 0.33 m (or 33 cm)
From this formula it can be determined that the higher thefrequency, the shorter the wavelength. Lower frequencies, with
longer wavelengths, are better suited to transmission over large
distances, because they bounce on the surface of the earth and in
the atmosphere. Television and FM radio are examples of
applications, which use lower frequencies.
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Higher frequencies, with shorter wavelengths, are bettersuited to transmission over small distances, because they are
sensitive to such problems as obstacles in the line of the
transmission path. Higher frequencies are suited to small areas of
coverage, where the receiver is relatively close to the transmitter.
The frequencies used by mobile systems compromise between the
large-coverage advantages offered by lower frequencies and the
closeness-to-the-receiver advantages offered by use of higher
frequencies.
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Module B;Overview of GSM
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What is GSM?
Global System for Mobile (GSM) is a second
generation cellular standard developed to
cater voice services and data delivery using
digital modulation
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Evolution of GSM
GSM in world
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GSM in INDIA
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Fundamentals of GSM
The Global System for Mobile Communications (GSM) is a set ofrecommendations and specifications for a digital cellulartelephone network (known as a Public Land Mobile Network, orPLMN).
These recommendations ensure the compatibility of equipmentfrom different GSM manufacturers, and interconnectivity betweendifferent administrations, including operation across internationalboundaries.
GSM networks are digital and can cater for high system capacities.
They are consistent with the world-wide digitization of the telephone
network, and are an extension of the Integrated Services DigitalNetwork (ISDN), using a digital radio interface between the cellularnetwork and the mobile subscriber equipment.
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CELLULAR TELEPHONYCELLULAR TELEPHONY
A cellular telephone system links mobile subscribers into the public
telephone system or to another cellular subscriber.
Information between the mobile unit and the cellular network
uses radio communication. Hence the subscriber is able to move
around and become fully mobile.
The service area in which mobile communication is to be provided
is divided into regions called cells. Each cell has the equipment to transmit and receive calls from any
subscriber located within the borders of its radio coverage area.
Mobile subscriber
RadioCell
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GSMGSM FREQUENCIESFREQUENCIES
GSM systems use radio frequencies between 890-915 MHz for receive and
between 935-960 MHz for transmit.
RF carriers are spaced every 200 kHz, allowing a total of 124 carriers for
use.
An RF carrier is a pair of radio frequencies, one used in each direction.
Transmit and receive frequencies are always separated by 45 MHz.
960935890 915
UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 45MHZ
UPLINK FREQUENCIES DOWNLINK FREQUENCIES
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ExtendedExtended GSMGSM (EGSM)(EGSM)
EGSM has 10MHz of bandwidth on both transmit and receive.Receive bandwidth is from 880 MHz to 890 MHz.
Transmit bandwidth is from 925 MHz to 935 MHz.
Total RF carriers in EGSM is 50.
UPLINK FREQUENCIES DOWNLINK FREQUENCIES
880 880 925 935 960
UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 45MHZ
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DCSDCS18001800 FreqencyFreqency
DCS1800 systems use radio frequencies between 1710-1785 MHz for receive
and between 1805-1880 MHz for transmit.RF carriers are spaced every 200 kHz, allowing a total of 373 carriers.
There is a 100 kHz guard band between 1710.0 MHz and 1710.1 MHz and
between 1784.9 MHz and 1785.0 MHz for receive, and between 1805.0
MHz and 1805.1 MHz and between 1879.9 MHz and 1880.0 MHz for
transmit.
Transmit and receive frequencies are always separated by 95 MHz.
1805 MHz1710 MHz 1785 MHz
UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 95MHZ
UPLINK FREQUENCIES DOWNLINK FREQUENCIES
1880 MHz1805 MHz
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GSM STRUCTURE
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GSM Architecture
OMC
Home Location Register
AuC
Equipment ID
Network
Management
Center
BT
S
BT
S
BT
S
ME
ME
ME
Subscriber
Identity
Module
SubscriberIdentity
Module
Subscriber
Identity
Module
Base stationcontroller
PSTN
Mobile
switching
center
Data
communication
network
BTS = Base Transceiver Station
AuC = Authentication Center
OMC = Operation and Maintenance Center
PSTN = Public Switched Telephone Network
ME = Mobile Equipment
Source: Stallings, 313
Source: Mehrotra, 27
Visitor LocationRegister
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INTERFACE NAMESINTERFACE NAMES
Each interface specified in GSM has a name associated with it
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GSM System Architecture
Mobile Station (MS)Mobile Equipment (ME)
Subscriber Identity Module (SIM)
Base Station Subsystem (BSS)
Base Transceiver Station (BTS)Base Station Controller (BSC)
Network Switching Subsystem(NSS)
Mobile Switching Center (MSC)
Home Location Register (HLR)Visitor Location Register (VLR)
Authentication Center (AUC)
Equipment Identity Register (EIR)
Operational support Subsystem(OSS)
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Mobile Station(MS)
The Mobile Station is made up of two entities:
1. Mobile Equipment (ME)2. Subscriber Identity Module (SIM)
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Mobile Equipment
Portable, vehicle mounted, hand held device
Uniquely identified by an IMEI (International Mobile EquipmentIdentity)
Voice and data transmission
Monitoring power and signal quality of surrounding cells foroptimum handover
Power level : 0.8W 20 W
160 character long SMS.
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Subscriber Identity Module (SIM)
Smart card contains the International Mobile SubscriberIdentity (IMSI)
Allows user to send and receive calls and receive other
subscribed services Encoded network identification details
- Key Ki,Kc and A3,A5 and A8 algorithms
Protected by a password or PIN
Can be moved from phone to phone contains key informationto activate the phone
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International Mobile Subscribers IdentityInternational Mobile Subscribers Identity -- IMSIIMSI
Network Identity Unique to a MS
The International Mobile Subscriber Identity (IMSI) is the
primary identity of the subscriber within the mobile network
and is permanently assigned to that subscriber.
The IMSI can be maximum of 15 digits.
404 XX 12345..10
MCC MNC MSIN
MCC
MNC
MSIN
= Mobile Country Code ( 3 Digits )
= Mobile Network Code ( 2 Digits )
= Mobile Subscriber Identity Number
Mobile Station International SubscribersMobile Station International Subscribers DiallingDialling
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Mobile Station International SubscribersMobile Station International Subscribers DiallingDiallingNumberNumber (MSISDN ) :(MSISDN ) :
Human identity used to call a MS
The Mobile Subscriber ISDN (MSISDN) number is the telephonenumber of the MS.
This is the number a calling party dials to reach the subscriber.
It is used by the land network to route calls toward the MSC.
CC= Country codeNDC= National Destination CodeSN= Subscriber Number
98 XXX 12345
CC NDC SN
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TemporaryTemporary MobileMobile SubscribersSubscribers IdentityIdentity (( TMSITMSI )) ::
The GSM system can also assign a Temporary Mobile Subscriber Identity
(TMSI).
After the subscriber's IMSI has been initialized on the system, the TMSI
can be used for sending messages backwards and forwards across the
network to identify the subscriber.The system automatically changes the TMSI at regular intervals, thus
protecting the subscriber from being identified by someone attempting
to monitor the radio channels.
The TMSI is a local number and is always allocated by the VLR.
The TMSI is maximum of 4 octets.
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Base Station Subsystem (BSS)
Base Station Subsystem is composed of two parts that
communicate across the standardized Abis interface allowing
operation between components made by different suppliers
1. Base Transceiver Station (BTS)
2. Base Station Controller (BSC)
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Base Station Controller (BSC)
Manages Radio resources for BTS
Assigns Frequency and time slots for all MSs in its area
Handles call set up
Transcoding and rate adaptation functionality
Handover for each MS Radio Power control
It communicates with MSC and BTS
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Structure of Base Station Controller(BSC)
BBase Station Controller (Base Station Controller (BSCSC)) Siemens BSCSiemens BSC
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Network Switching Subsystem(NSS)
Mobile Switching Center (MSC)
Heart of the networkManages communication between GSM and other networksCall setup function and basic switchingCall routingBilling information and collectionMobility management
- Registration- Location Updating- Inter BSS and inter MSC call handoff
MSC does gateway function while its customer roams to othernetwork by using HLR/VLR.
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Structure ofMobile Switching Centre(MSC)
MMobileobile SSwitchingwitching CCentre (MSC)entre (MSC) Lucent MSCLucent MSC
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Home Location Registers (HLR)
- permanent database about mobile subscribers in a largeservice area(generally one per GSM network operator)
database contains IMSI ,MSISDN ,prepaid/postpaid ,roamingrestrictions ,supplementary services.
Visitor Location Registers (VLR)
Temporary database which updates whenever new MS entersits area, by HLR database
Controls those mobiles roaming in its area
Reduces number of queries to HLR
Database contains IMSI ,TMSI ,MSISDN ,MSRN ,Location Area ,authentication key
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Authentication Center (AUC)
Protects against intruders in air interface
Maintains authentication keys and algorithms and providessecurity triplets ( RAND ,SRES ,Kc)
Generally associated with HLR
Equipment Identity Register (EIR)
- Database that is used to track handsets using the IMEI(International Mobile Equipment Identity)
Made up of three sub-classes: The White List, The Black Listand the Gray List
Only one EIR per PLMN
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Operational support Subsystem(OSS) OROR
Operation And Maintenance Centre For RadioOperation And Maintenance Centre For Radio
((OMCOMC--RR))The OMC controls and monitors the Network elements within a
region.
The OMC also monitors the quality of service being provided by
the Network.The following are the main functions performed by the OMC-R
The OMC allows network devices to be manually removed for
or restored to service. The status of network devices can be
checked from the OMC and tests and diagnostics invoked.
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The alarms generated by the Network elements are reported
and logged at the OMC. The OMC-R Engineer can monitorand analyze these alarms and take appropriate action like
informing the maintenance personal.
The OMC keeps on collecting and accumulating traffic
statistics from the network elements for analysis.
Software loads can be downloaded to network elements oruploaded to the OMC.
Operation And Maintenance CentreOperation And Maintenance Centre
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Operation And Maintenance CentreOperation And Maintenance Centre
For Radio (For Radio (OMCOMC--RR))
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BBase Station Identity Codease Station Identity Code
BSIC allows a mobile station to distinguish between neighboringbase stations.
It is made up of 8 bits.
NCC = National Colour Code( Differs from operator to operator )
BCC = Base Station Colour Code, identifies the base station to help
distinguish between Cells using the same BCCH frequencies
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Cell Global Identity (CGI)Cell Global Identity (CGI)
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GSM CHANNELCONCEPTGSM CHANNELCONCEPT
PhysicalPhysical channelchannel - Each timeslot on a carrier is referred to as aphysical channel. Per carrier there are 8 physical channels.
LogicalLogical channelchannel - Variety of information is transmitted between the
MS and BTS. There are different logical channels depending on the
information sent. The logical channels are of two types Traffic channel
Control channel
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GSM Traffic ChannelsGSM Traffic Channels
GSM C t l Ch lGSM C t l Ch l
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GSMControl ChannelsGSMControl Channels
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BCHChannelsBCHChannels
BCCH( Broadcast Control Channel )BCCH( Broadcast Control Channel )
Downlink only Broadcasts general information of the serving cell called System
Information
BCCH is transmitted on timeslot zero of BCCH carrier
Read only by idle mobile at least once every 30 secs .
SCH( Synchronization Channel )SCH( Synchronization Channel ) Downlink only
Carries information for frame synchronization. Contains TDMA
frame number and BSIC.
FCCH( Frequency Correction Channel )FCCH( Frequency Correction Channel )
Downlink only.
Enables MS to synchronize to the frequency.
Also helps mobiles of the n cells to locate TS 0 of BCCH carrier.
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CCCHChannelsCCCHChannels
RACH( Random Access Channel)RACH( Random Access Channel)
Uplink only
Used by the MS to access the Network.
AGCH( Access Grant Channel )AGCH( Access Grant Channel ) Downlink only
Used by the network to assign a signaling channel upon
success full decoding of access bursts.
PCH( Paging Channel )PCH( Paging Channel )
Downlink only.
Used by the Network to contact the MS.
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DCCH ChannelsSDCCH( Standalone Dedicated Control Channel )SDCCH( Standalone Dedicated Control Channel )
Uplink and Downlink Used for call setup, location update and SMS.
SACCH(SACCH( Slow Associated Control Channel )Slow Associated Control Channel )
Used on Uplink and Downlink only in dedicated mode.
Uplink SACCH messages - Measurement reports. Downlink SACCH messages - control info.
FACCH( Fast Associated Control Channel )FACCH( Fast Associated Control Channel )
Uplink and Downlink.
Associated with TCH only. Is used to send fast messages like handover messages.
Works by stealing traffic bursts.
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Traffic Channel
TCH carries the Voice data
one TCH is allocated for every active call
Full Rate
used 22.8kbps/s
used for Speech at 13 kbps/sor Sending data at 9.6 kbps/s
Half rate
used for Speech at 6.5 kbps/s
or Sending data at 4.8 kbps/s
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TS 0 TS 1 TS 2 TS 3 TS 4 TS 5 TS 6 TS 7
FACCH
SCH
BCCH
PCH
RACH
AGCH
SDCCH
SACCH
CBCH
TCH
SACCH
FACCH
TCH
SACCH
FACCH
TCH
FACCH
SACCH
TCH
SACCH
FACCH
TCH
SACCH
FACCH
TCH
SACCH
FACCH
O.577 ms
1 TDMA FRAME
2OO kHZ
4.615 ms
TDMA Frame Structure in GSM
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Absolute Radio Frequency Channel
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Absolute Radio Frequency Channel
Number (ARFCN)
The ARFCN is a number that describes a pair of frequencies, one
uplink and one downlink. The uplink and downlink frequencies each
have a bandwidth of 200 kHz. The uplink and downlink have a
specific offsetthat varies for each band. The offset is the frequency
separation of the uplink from the downlink. Every time the ARFCN
increases, the uplink will increase by 200 khz and the downlink also
increases by 200 khz.
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Therefore 124 channels available for each UL and DL in GSM 900 and
374 channels available in GSM 1800
GSM 900= 1 to 124GSM 1800= 512 to 885
To calculate actual frequency;
For GSM 900 Band
UL freq-Fu(n)=890+0.2(1
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Call Flow in GSM
Mobile OriginatedCall
Mobile Terminated Call
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Mobile OriginatedCall
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Mobile TerminatedCall
RADIO INTERFACE
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RADIOINTERFACE
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INTERFERENCE
What is interference
Interference is the sum of the all signalscontributions that are neither noise not the wanted signal.
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Source of interference
Another mobile in the same cell.
A call in process in the neighbor cell.
Other base station operating on the same frequency.
Two types ofInterferenceCo Channel Interference
Adjacent Channel Interference
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Co Channel Interference
This type of Interference is due to frequency reuse, eg Several cellsuse the same set of frequency .
These cells are called Co Channel Interference
Co Channel Interference cannot be combated by increasing the power ofthe transmitter .This is because an increase in carrier transmit power
increases the Interference to neighbor co-channel cells.
To reduce Co Channel Interference , Co Channel cells must bephysically separated by a minimum distance to provide sufficientisolation due to propagation or reduce the foot print of cell .
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Adjacent Channel Interference
Interference resulting from signal which are adjacent in frequency
to the desired signal is called Adjacent Channel Interference.
Adjacent Channel Interference results from imperfect receiver filters
which are near by frequency to leak into the baseband.
Adjacent Channel Interference can be minimized through careful
filtering and channe3 assignments.By keeping the frequency separation between each channel in a given
cell as large as possible, the adjacent interference may be reduced
considerably.
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FREQUENCY HOPPING
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Frequency Hopping
Frequency Hopping is sequential change of carrier frequency on
the radio link between BS and MS.
Can be used to improve the quality of the network
Also can be used to increase the capacity of the Network therebyreducing the number of sites required for CAPACITY.
The way it works
Each burst is transmitted on a different frequency
Both mobile and base station follow the same hopping sequence
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TYPESTYPES OFOF HOPPINGHOPPING
BaseBase BandBand HoppingHopping (BBH)(BBH)
SynthesiserSynthesiser FrequencyFrequency HoppingHopping (SFH)(SFH)
HoppingHopping ParametersParameters
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pp gpp g
For frequency hopping operability, GSM defines the
following set of parameters: Mobile Allocation (MA): Set of frequencies the mobile is
allowed to hop over. MA is a subset of all the frequencies allocated
by the system operator to the cell (cell allocation) although it can
be the same. Eg:- If the operator has frequencies from 1 -32, then
he can use 1-15 for BCCH and 17-32 for hopping ( MA).
Hopping Sequence Number (HSN): Determines the hoppingorder used in the cell. 64 different HSNs can be assigned, where
HSN = 0 provides a cyclic hopping sequence and HSN = 1 to 63
provide various pseudorandom hopping sequences.
Mobile Allocation IndexOffset ( MAIO): Determines inside thehopping sequence which frequency the mobile starts to transmit
on.
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Short Message Services (SMS)
Short Message Services(SMS) is the text communication services
component of phone ,web or mobile communication system ,
using standardized communications protocols that allow the
exchange of short message between f5xed line 6r mobile phone
devices .
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SMS Applications
SMS up to 160 alphabets characters.
Alert services (MT-SMS)
voice message alert
FAX/Telex Message Alert
E-mail system Alert
Information Services
Financial Services (stock market queries and alerts)
Weather OR traffic information (eg; from TV/Radio station
data feeds)
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Concept of GPRS/EDGE
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GPRS(General Packet Radio Services )General Packet Radio Services (GPRS) is a packet based wireless
communication service that promises data rates from 56 up to 114 kbpsand continuous connection to the Internet for mobile phone and
computer users. The higher data rates allow users to take part in video
conferences and interact with multimedia Web sites and similar
applications using mobile handled devices as well as notebook
computers.GPRS is based on Global System for Mobile(GSM) communication and
complements existing services such circuit Switch cellular phone
connections and the Short Message Service (SMS).
GPRS packet-based services cost users less than circuit-switched
services since communication channels are being used on a shared-use,
as-packets-are-needed basis rather than dedicated to only one user at a
time.
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GPRS Network
GPRS network provide the mobility management ,session
management , transport for internet protocol packet services in
GSM network
GPRS support node(GSN)-It is node which support use of GPRS in
GSM network .there are 2 key variant
GGSN(Gateway GPRS Support Node)SGSN(Serving GPRS Support Node)
Benefits of GPRS network;
High speed data rate 14.4-115 kbps.
Efficient use of BandwidthCircuit Switching and Pocket Switching are used in parallel.
Constant Connectivity
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Comparison of GSM and GPRS
EDGE (Enhanced Data GSM Environment)
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EDGE (Enhanced Data GSM Environment)
EDGE (Enhanced Data GSM Environment)EDGE (Enhanced Data GSM Environment) is a faster version
the Global System for Mobile (GSM) wireless service designed to deliver
data at rates up to 384 kbps and enable the delivery of multimedia and
other broad band applications to mobile phone and computer users.
The EDGE standard is built on the existing GSM standard, using thesame time-division multiple access (TDMA) frame structure and existing
cell arrangements.
EDGE is particular used as a GPRS solution for large data services ,Such
as Streaming Video and Video Conferencing.
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HANDOVERHANDOVER
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HAND OVER
The changing to a new traffic channel , During call setup or busy
state is called Handover. he network makes the decision about the
change .After receiving the information about the signal strength
and quality the BSC ranks the neighbour BTSs using through
information.
HANDOVERHANDOVER CONDITIONSCONDITIONS
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HANDOVERHANDOVER CONDITIONSCONDITIONS
HANDOVERHANDOVER CONDITIONSCONDITIONS
Handover is done on five conditions
Interference
RXQUAL
RXLEV
Distance or Timing Advance
Power Budget
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Interference - If signal level is high and still there is RXQUAL
problem, then the RXQUAL problem is because of interference.
RXQUAL - It is the receive quality. It ranges from 0 to 7 , 0 being thebest and 7 the worst
RXLEV - It is the receive level. It varies from -47dBm to -110dBm.
Timing Advance - Ranges from 0 to 63.
Power budget - It is used to save the power of the MS.
HANDOVERHANDOVER
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HANDOVERHANDOVERHANDOVER TYPESHANDOVER TYPES
IntraIntra--Cell HandoverCell Handover
Handover takes place in the same cell from one timeslot toanother timeslot of the same carrier or different carriers( but thesame cell).
Intra-cell handover is triggered only if the cause is interference.
Intra-cell handover can be enabled or disabled in a cell.
HANDOVERHANDOVER
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HANDOVERHANDOVER
HANDOVER TYPESHANDOVER TYPES
InterInter--BSCHandoverBSCHandover
Handover takes place between different cell which are controlled by
the different BSC.
HANDOVERHANDOVER
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HANDOVERHANDOVERHANDOVER TYPESHANDOVER TYPES
InterInter--MSCHandoverMSCHandover
Handover takes place between different cell which are controlled by the
different BSC and each BSC is controlled by different MSC
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Uses of Handover
To keep a continuous communication with a moving MS
To improve network service performance
To reduce the call drop rate
To reduce the congestion rate
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Cell Selection
When the mobile is turned on , it ill try to contact o public GSMPLMN , so the MS ill select a proper cell and extract from the cell
the control channel parameters and system message .This selection
process is called cell selection .the quality of radio channel is
important factor cell selection , GSM specification defines the path
loss rule C1.For the so- called proper cell,C1>0 must be ensured
ll l
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Cell Reselection
Cell Reselection (C2) is a process ,when MS change its service cell
idle mode.
When the MS selects a cell it will begin to measure the signal levels
of the BCCH TRX of its adjacent cells , record the Adjacent cells
whose signal levels are the strongest and extract from them varioustypes of strongest and extract from them various types of system
message and control message of each adjacent cell.
When given conditions are met ,the MS will move from the current
cell into another one . This process is called Cell reselection.
Pilot Pollution in Network
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Pilot Pollution in NetworkThe number of strong cells Exide more than then number of
active cells called Pilot Pollution .
Overshooting in Network
The another site signal strength is strong than the active cellsite is called Overshooting .
eg; Adjacent Site Signal is Stronger than our current site
signal