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Introduction into Communication
Eng./Mohamed Tarek
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2006-01-24 Lecture 1 2
Communication Introduction
Multiple Access Technique
GSM Network Architecture
Contents
Call scenario and call set up ,Hand over ,Location update
Radio planning and GSM coverage
GSM Network Interferences and Signaling
Access to 3G and New communication systems
Communication Companies and Different positions
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2006-01-24 Lecture 1 3
Introduction
Any Communication system consists of :-
source DestinationTransmission medium
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2006-01-24 Lecture 1 4
Introduction
The kinds of transmission medium :
Wired
Wireless
Wired transmission medium :
1- Twisted-pair
2- Coaxial cable
3-optical fibers
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2006-01-24 Lecture 1 5
Introduction
Communication Channels types:-
ApplicationsPropertiesChannel Type
FM radio, televisionOne-way onlySimplex
Police radio, push-to-talkTwo-way, only one at a timeHalf duplex
PSTN, Mobile systemsTwo-way, both at the same timeFull duplex
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2006-01-24 Lecture 1 6
Introduction
Communication system consists of :-
SourceSource
encoder
Channel
encoderModulator
DestinationSource
decoder
Channel
decoderDemodulator
Transmitter
Receiver
SOURCE
Info.Transmitter
Transmitted
signal
Received
signalReceiver
Received
info.
Noise
Channel
Source User
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2006-01-24 Lecture 1 7
Introduction
Encoding:-
Encoding is the process of transforming information from one format
into another. The opposite operation is called decoding.
Encoding is the process of putting a sequence of characters (letters,numbers, punctuation, and certain symbols)
into a specialized format for efficient transmission or storage.
Decoding is the opposite process Source Encoding
conversion from analog to digital is Encoding
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2006-01-24 Lecture 1 8
Introduction
Channel encoding deals with error control during the transmission
through the communication channel.
Error detection Codes
Parity check codes (Odd parity Even parity)
(Frame Protocols )??
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2006-01-24 Lecture 1 9
Introduction
Data Compressionis an important subject as more digital
information is required to be stored and transmitted.
Compression methods:
There are two main types of compression.
Lossless compression
Lossy compression
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2006-01-24 Lecture 1 10
Classification of signals
Periodic and non-periodic signals
Analog and discrete signals
A discrete signalAnalog signals
A non-periodic signalA periodic signal
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2006-01-24 Lecture 1 11
Classification of signals
Deterministic and random signals Deterministic signal: No uncertainty with
respect to the signal value at any time.
Random signal: Some degree of uncertainty in
signal values before it actually occurs.
Thermal noise in electronic circuits due to the
random movement of electrons
Reflection of radio waves from different layers of
ionosphere
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2006-01-24 Lecture 1 12
Noise
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2006-01-24 Lecture 1 13
Digital versus analog
Advantages of digital communications:
Regenerator receiver
Different kinds of digital signal are treated
identically.
Data
Voice
Media
Propagation distance
Original
pulse
Regenerated
pulse
A bit is a bit!
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2006-01-24 Lecture 1 14
Analog VS Digital
Digital Communication:-Advantages of Digital :-
Less noise effect
More reliable
Easy to manipulateFlexibleCompatibility with other digital systemsOnly digitized information can be transported
through a noisy channel without degradationIntegrated networks
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2006-01-24 Lecture 1 15
Introduction
Disadvantages of Digital -
Sampling Error
Digital communications require greater bandwidth than
analogue to transmit the same information.
We loss some of information due to sampling process
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2006-01-24 Lecture 1 16
Introduction
Definition of Analogue :-
Analogue is a transmission standard that uses electrical impulses to
emulate the audio waveform of sound. When you use a phone, the
variations in your voice are transformed by a microphone into similar
variations in an electrical signal and carried down the line to the
exchange
Advantages of Analogue -
Uses less bandwidth
More accurate
Disadvantages of Analogue -
The effects of random noise can make signal loss and distortion
impossible to recover and more effect by noise
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2006-01-24 Lecture 1 17
Circuit Switching VS Packet SwitchingCircuit Switching
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2006-01-24 Lecture 1 18
Circuit Switching VS Packet Switching
Packet Switching
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2006-01-24 Lecture 1 19
Circuit Switching VS Packet Switching
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2006-01-24 Lecture 1 20
Circuit Switching VS Packet Switching
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2006-01-24 Lecture 1 21
Multiple Acess TechniqeIt is used because the limitation of transmission resources comparing with the
number of users
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2006-01-24 Lecture 1 22
Multiple Acess Techniqe
Three types of Multiple Access Technique are available:
Frequency Division Multiple Access (FDMA)
Time Division Multiple Access (TDMA)
Code Division Multiple Access (CDMA)
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2006-01-24 Lecture 1 23
Frequency Division Multiple Access (FDMA)
Each FDMA user is assigned a specific frequency channel. No one else in the samecell or a neighboring cell can use the frequency channel while it is assigned to a
user. Although this technology will reduce signal interference, it also severely limits
the number of users able to transmit at a time.
Strength
f1 f2 f3
Frequency
User 1 User 2 User 3
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2006-01-24 Lecture 1 24
Time Division Multiple Access (TDMA)
TDMA users share a common frequency channel, but use the channel foronly a very short amount of time. They are each given a time slot and
only allowed to transmit during that particular time slot. When all
available time slots in a given frequency are used, the next user must be
assigned a time slot on another frequency. The time slices are so small
that the human ear cannot perceive the time slicing, and thereforeassumes that they have the entire channel to transmit their signal.
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2006-01-24 Lecture 1 25
Time Division Multiple Access (TDMA)
Frequency
Strength
User 1, time=0
User 2, time=t0
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2006-01-24 Lecture 1 26
TDMA VS FDMA
Strength
User 7User 2
User 1
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2006-01-24 Lecture 1 27
Code Division Multiple Access (CDMA)
CDMA users share a common frequency channel. All users are on the same
frequency at the same time. However, each pair of users is assigned a
special code that reduces interferences while increasing privacy.
Frequency
Strength
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2006-01-24 Lecture 1 28
TDMA VS FDMA VS CDMA
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2006-01-24 Lecture 1 29
What is the GSM?
GSM is the Global System for Mobile telecommunications.
It is the European standard for the Mobile telecommunications and it
is considered as one of the most popular standard worldwide.
It is known as the second generation mobile telecommunicationssystem 2G system.
It is used in Egypt by the two existing operators; Mobinil and Vodafone;
also it used as a part of the third operator in Egypt Etisalat.
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2006-01-24 Lecture 1 30
GSM Worldwide (darker areas)
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2006-01-24 Lecture 1 31
What is the GPRS?
GPRS is the General Packet Radio Service.
Within the GSM network it shares the network databases and radio access
network.
It is known as the 2.5generation mobile telecommunications system 2Gsystem.
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2006-01-24 Lecture 1 32
3G Systems
Universal Mobile Telecommunication Service (UMTS) is the marketing
name for the 3G has two standardization bodies:
1- 3GPP which uses the W-CDMA technology.
2- 3GPP2 which uses the CDMA2000 technology.
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2006-01-24 Lecture 1 33
Basic GSM Network Structure
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2006-01-24 Lecture 1 34
Basic GSM Network Structure
Mobile Station (MS) The Mobile Station (MS) is the interface between the user and the
network. The MS consists of two independent parts:
Subscriber Identity Module (SIM) card
Mobile Equipment (ME)
+
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2006-01-24 Lecture 1 35
Basic GSM Network Structure
Mobile Equipment (ME)
The ME is the only part of the GSM network which the subscriber will
really see.
Vehicle Mounted
These devices are mounted in a vehicle and the antenna is physically
mounted on the outside of the vehicle. Portable Mobile Unit
This equipment can be handheld when in operation, but the antenna is
not connected to the handset of the unit.
Handportable Unit
This equipment comprises of a small telephone handset not much bigger
than a calculator. The antenna is be connected to the handset.
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2006-01-24 Lecture 1 36
Basic GSM Network Structure
Mobile Equipment Capabilities:
RF power capability
Encryption capability
Frequency capability
Short message service capability
The ME is the hardware used by the subscriber to access the network. Thehardware has an identity number associated with it, which is unique forthat particular device and
permanently stored in it. This identity number is called The
International Mobile Equipment Identity (IMEI)
To guarantee that the mobile not to be stolen
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2006-01-24 Lecture 1 37
Basic GSM Network Structure
IMEI
6 Digits
TAC
2 Digits
FAC
6 Digits
SN
TAC: Type Approval Code,
The first two digits are the
code for the country approval
FAC: Final Assembly Code
SN: Serial Number
International Mobile Equipment Identity (IMEI)
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2006-01-24 Lecture 1 38
Basic GSM Network Structure
IMEI
Short for International Mobile Equipment Identity, a unique number given
to every single mobile phone, typically found behind the battery.
IMEI numbers of cellular phones connected to a GSM network are stored
in a database (EIR - Equipment Identity Register) containing all validmobile phone equipment.
When a phone is reported stolen or is not type approved, the number is
marked invalid.
The number consists of four groups that looks this:
nnnnnn--nn-nnnnnn-n
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2006-01-24 Lecture 1 39
Basic GSM Network Structure
The first set of numbers is the type approval code (TAC). The first two
digits represent the country code. The rest make up the final assembly
code. The second group of numbers identifies the manufacturer:
01 and 02 = AEG
07 and 40 = Motorola
10 and 20 = Nokia 41and 44 = Siemens
51= Sony, Siemens, Ericsson
The third set is the serial number and the last single digit is an
additional number (usually 0).
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2006-01-24 Lecture 1 40
Basic GSM Network Structure
Subscriber Identity Module (SIM)
The SIM as mentioned previously is a smart card which plugs into the
ME Mobile Equipment.
It contains a memory that contain information about the MSsubscriber hence the name Subscriber Identity Module.
This memory can store data by the user.
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2006-01-24 Lecture 1 41
Basic GSM Network Structure
The SIM contains several pieces of information:
International Mobile Subscriber Identity (IMSI)
This number identifies the MS subscriber. It is only transmitted over the
air during initialization.
Temporary Mobile Subscriber Identity (TMSI)
This number identifies the subscriber, it is periodically changed by thesystem.
Location Area Identity (LAI)
Identifies the current location of the subscriber.
Subscriber Authentication Key (Ki) This is used to authenticate the SIM card.
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2006-01-24 Lecture 1 42
Basic GSM Network Structure
Mobile Station International Services Digital Network (MSISDN)
CC : Country Code
NDC : National Destination Code
SN : Subscriber Number
Vodafone Egypt MSISDN
20
CC
10
NDC
1100477
SN
Vodafone UK MSISDN
44
CC
385
NDC
196099
SN
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2006-01-24 Lecture 1 43
Basic GSM Network Structure
Base Station Subsystem (BSS)
MS
BTS BSC
BSS
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2006-01-24 Lecture 1 44
Basic GSM Network Structure
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2006-01-24 Lecture 1 45
Basic GSM Network Structure
The Base Transceiver Station BTS The BTS contains the RF components that provide the air interface for a
particular cell. This is the part of the GSM network which
communicates with the MS. The antenna is included as part of the BTS.
Converts the GSM radio signals into a format that can be recognized by
the BSC.
Channel coding and interleaving.
Records and passes to the BSC the Signal strength measurements.
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2006-01-24 Lecture 1 46
Basic GSM Network Structure
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2006-01-24 Lecture 1 47
Basic GSM Network Structure
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Basic GSM Network Structure
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2006-01-24 Lecture 1 49
Basic GSM Network Structure
The BSC is the central node within a BSS and co-ordinates the actions of
Base Stations. The BSC controls a major part of the radio network.
Its main functions can be divided into two types:
During Call Set Up:
Finding the called mobile station by paging.
Allocate the frequency for setting the call.During Call :
Monitoring the call quality.
Controlling the transmitted power to the MS depending
on the location of the MS.
Control the handover for the MS after receiving the
power measurements from the MS and from the BTS.
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2006-01-24 Lecture 1 50
Basic GSM Network Structure
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Basic GSM Network Structure
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Basic GSM Network Structure
One location area consists of more than one BTS.
One BSC controls more than one BTS.
One BTS covers 3 cells.
One cell is covered by one Antenna.
So, one Location Area consists of more than one cell.
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Basic GSM Network Structure
Transcoder (XCDR) The Transcoder (XCDR) is required to convert the speech or data output
from the MSC (64 kbit/s PCM), into the form specified by GSMspecifications for transmission over the air interface,
that is, between the BSS and MS
(64 kbit/s to 16 kbit/s and vice versa)
The 64 kbit/s Pulse Code Modulation (PCM) circuits from the MSC, iftransmitted on the air interface without modification, would occupy anexcessive amount of radio bandwidth.
This would use the available radio spectrum inefficiently. The requiredbandwidth is therefore reduced by processing the 64 kbit/s circuits sothat the amount of information
required to transmit digitized voice calls to a gross rate of 16 kbit/s. The transcoding function may be located at the
MSC, BSC, or BTS.
N t k S it hi S b t (NSS)
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Network Switching Subsystem (NSS)
MSC/VLR
HLR
AUC
BSC
NSS
BTS
BTS
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Basic GSM Network Structure
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The primary node in a GSM network is the MSC. It is the node
which controls calls establishment. The primary functions of anMSC include the following: Switching and call routing to or from MS. Charging. Service providing. Control of connected BSCs.
Access to PSTN. Provides the gateway functionality to other networks. One MSC controls more than one BSC.
Mobile Switching Center (MSC)
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Mobile Switching Center (MSC)
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58
Types of the MSC
VMSC: Visited MSC
There are three types of the MSC, the difference just in the function.
GMSC: Gateway MSC
TMSC: Transit MSC
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Visited Mobile Switching CenterIts function is to switch in the level of BSCs and it is combined with a VLR.
MSC/VLR
BSC BSC
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Transit Mobile Switching CenterIts function is to switch between the different
VMSC. It is not combined with a VLR.
TMSC
VMSC VMSC
Gateway Mobile Switching Center (GMSC)
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Its function is to connect the PLMN to the PSTN or to the
other PLMN existing in the country.
Gateway Mobile Switching Center (GMSC)
TMSC
VMSCVMSC
TMSC
VMSCVMSC
Mobinil GMSC
PSTNVodafone
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Home Location Register (HLR)
The HLR is a centralized network database that stores and manages allmobile subscriptions belonging to a specific operator.
It acts as a permanent store for a persons subscription informationuntil that subscription is cancelled.
The primary functions of the HLR include:
Stores for each mobile subscriber:
Basic subscriber categories.
Supplementary services.
Current location.
Allowed/barred services.
Authentication data.
Subscription database management
Controls the routing of mobile terminated calls and SMS
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Home Location Register (HLR)
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Visitor Location Register (VLR)
The role of a VLR in a GSM network is to act as a temporary storagelocation for subscription information for MSs, which are within a
particular MSC service area.
Thus, there is one VLR for each MSC service area. This means that theMSC does not have to contact the HLR (which may be located in
another country) every time the subscriber uses a service or changes
its status. The VLR is always integrated with the MSC.
Visitor Location Register (VLR)
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For the duration when the MS is within one MSC service area, then the VLRcontains a complete copy of the necessary subscription details, including
the following information:
Identity numbers for the subscriber
Supplementary service information (e.g. Does the subscriber has call
waiting activated or not)
Activity of MS (e.g. idle or busy)
Current Location Area of MS
Visitor Location Register (VLR)
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Visitor Location Register (VLR)
Authentication Center (AUC)
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To protect GSM systems, the following security functions have
been defined: Subscriber authentication: by performing authentication, the
network ensures that no unauthorized users can access thenetwork, including those that are attempting to impersonateothers.
Radio information ciphering: the information sent between thenetwork and an MS is ciphered. An MS can only decipherinformation intended for it.
Authentication Center (AUC)
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Equipment Identification Register(EIR) In order to block the stolen mobiles equipments; the EIR equipment
is used; also in case of the Mobile operator wants to block a certain
type of Mobile phones.
Example, In Turkey all the mobile phones bought from outside Turkeyare blocked and can not be used before paying fees.
The Mobile equipment is identified by a number called InternationalMobile Equipment Identity (IMEI). This number is uniquely identifiesthe MS worldwide.
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Because the subscriber and equipment are separate in GSM, it is
necessary to have a separate authentication process for the MSequipment.
The equipment identification procedure uses the identity of theequipment itself (IMEI) to ensure that the MS terminal equipment isvalid.
EIR
1. IMEI Request
2. IMEI3. IMEI Check
4. Access/ Barring Data
MSC / VLR
Equipment Identification Register (EIR)
Equipment Identification Register (EIR)
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International Mobile Equipment Identity (IMEI)
IMEI
6 Digits
TAC
2 Digits
FAC
6 Digits
SN
TAC: Type Approval Code,
The first two digits are the
code for the countryapproval
FAC: Final Assembly Code
SN: Serial Number
Equipment Identification Register (EIR)
Equipment Identification Register (EIR)
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Equipment Identification Register (EIR)
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Interworking Function (IWF)
Interworking Function (IWF)The IWF provides the function to enable the GSM system to
interface with the various
forms of public and private data networks currently available.
The basic features of the IWF are listed below.
Data rate adaption.Protocol conversion.
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Echo Canceller (EC)
An EC is used on the PSTN side of the MSC for all voice circuits. Echocontrol is required at the switch because the incoherent GSM system
delay can cause an unacceptable echo condition, even on short
distance PSTN circuit connections.
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OSS
The operation and Maintenance center (OMC) is connected to all equipment(the GMSC, MSC, HLR, VLR, AUC, EIR and the BSC).
It can be viewed as a computerized monitoring center were staff canmonitor and control the network remotely.
MSC
SMSCBSC
HLR
OMC
LAN
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Operation and Support Subsystem (OSS)
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Operation and Support Subsystem (OSS)
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Operation and Support Subsystem (OSS)
Operations and maintenance center (OMC)
(OMC) is connected to all equipment in the switching system and to
the BSC. The implementation of OMC is called the operation and
support system (OSS). The OSS is the functional entity from which thenetwork operator monitors and controls the system. The purpose of
OSS is to offer the customer cost-effective support for centralized,
regional, and local operational and maintenance activities that are
required for a GSM network. An important function of OSS is to
provide a network overview and support the maintenance activities of
different operation and maintenance organizations.
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Operation and Support Subsystem (OSS)
Mobile Originated Call
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1. The MS ask for a signaling channel.
2. The BSC/TRC allocates a signaling channel.
3. The MS sends a call set-up request via MSC/VLR.all signaling preceding a call takes place. This
includes:
Marking the MS as active in the VLR
The authentication procedure
Equipment identification
Sending the B-subscribers number to the
network
Checking if the subscriber has the service
Barring of outgoing calls activated
4. The MSC/VLR instructs the BSC/TRC to allocate .
The BTS and MS.5. The MSC/VLR forwards the Bnumber to an
exchange in the PSTN, which establishes a
connection to the subscriber.
6. If the B-subscriber answers, the connection is
established.
PSTN
g
BSC
MSC
Mobile Terminating call
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PSTN
HLR
GMSC MSC
1
3
2
5
4
7
6
8
9
Mobile Terminating call
BSC
Roaming: Location Update
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82
g p
HLR
Attached
VLR ADD=
Egypt Airport
Roaming & Int.
Allowed
Detached
Roaming & Int.
Allowed
MSC/VLR
Is a roaming agreement present ?IMSI
60202..
Isroaming
andInt.
callsallowed?
Attached
VLR ADD=
Stock. Airport
Roaming & Int.
Allowed
Copy of the HLR Profile will
be stored in Stock. VLR
Roaming: Call to HPLMN
H P bli L ti M bil N t k
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HLR
Attached
VLR ADD=
xyz
GWMSC
MSC/VLR
MSISDN
+2010.
Home Public Location Mobile Network
Roaming: Call from HPLMN
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HLR
Attached
VLR ADD=Stock. Airport
Roaming & Int.
AllowedGWMSC
MSISDN
010
MSC/VLR
Roaming: Call from another Roamer
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HLR
GWMSC
MSC/VLR
A
MSC/VLR
B
Attached
VLR ADD=
Stock. B
Roaming & Int.
Allowed
MSISDN
+2010.
g
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Location Update
Why do we need to update our location data ?
Actually, the location update process is done in aim to exactlyidentify the location of the subscribers within the network so thatany incoming call goes directly to the called subscriber.
To fulfill this aim, one can say that we may update the system withthe cell ID each time the subscriber changes his serving cell. TheMSC/VLR will now know the exact cell you are roaming in. This willresult in a huge amount of location update messages.
An extreme is never to make a location update and to be paged inall the network. This will cause huge amount of paging messages.
Location Update
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Types of Location Update
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1. Normal Location update within same MSC/VLR service area
2. Normal Location update between 2 different MSC/VLR service areas
3. IMSI attach/detach
4. Periodic Location Update
Normal Location within the same MSC/VLR Service area
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BSC
1. The Mobile sends an allocation request
message to the BTS
2. The BTS responds with the allocation
message
3. The mobile sends a location update request
message with its IMSI to the MSC/VLR
4
4. The MSC/VLR updates the location
information and sends a Location Update
confirmation message
MSC/VLR
UpdatesLA Record
Normal Location Update between 2 different MSC/VLR service areas
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Old MSC/VLR New MSC/VLR
NEW BSCOld BSC
LA 1
LA 2
1. The mobile sends a location update
request to the MSC.2. The new MSC/VLR receives the IMSI and
conclude the its HLR address.
3. The MSC/VLR sends a subscriber
information request with the IMSI
to the proper HLR
4. The HLR stores the address of
the new MSC/VLR
VLR Address
=
Old MSC
VLR Address
=
New VLR
5. The HLR sends the data to the
new MSC/VLR and it is kept there
6. The HLR sends a location
cancellation message to the old
MSC/VLR to remove the data
HLR
7. The new MSC/VLR sends a location
updating confirmation message to
the mobile
IMSI Attach
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IMSI attach is a complement to the IMSI detach procedure. It is used by the
mobile subscriber to inform the network that it has re-entered an active state
and is still in the same location area. If the MS changes location area while
being switched off, a normal location update takes place.
1. The MS requests a signaling channel.
2. The MSC/VLR receives the IMSI attach message from the MS.
3. The MSC/VLR sets the IMSI attach in the VLR. The mobile is now ready for
normal call handling.
4. The VLR returns an acknowledgment to the MS.
MSC/VLRBSC
1
2 3
4
Periodic Location Update
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92
Periodic location update is a routine task performed by the network if
the MS doesnt make any network action (sets a call, sends
SMS, location update, receives a call,. etc)
If the MS doesnt respond to this periodic location update, it will be
marked
as implicitly detached. ( Temporarily out of service )
Handover
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93
Handover is to keep continuity of the call when the subscriber is roaming
along the network moving from one cell to another and moving betweendifferent nodes in the network.
During call, the MS is continuously measuring transmission quality ofneighboring cells and reports this results to the BSC through the BTS.
The BSC, being responsible on supervising the cells, is responsible ofhandover initiation.
Good neighbor relations between cells is an important factor in keepingthe network performance in the accepted level.
Types of Handover
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94
1. Intra BSC Handover:
When the cell to which the call will be handed over belongs to the same BSC of theserving cell.
2. Inter BSC / Intra MSC Handover:
When the cell to which the call will be handed over belongs to the different BSCs butto the same serving MSC.
3. Inter MSC
When the cell to which the call will be handed over belongs to the different BSC anddifferent MSC.
Intra BSC Handover
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BSC
Serving Cell New Cell
1. The BSC decides from the power measurement reports
that the call must be handed over to another cell
2
2. The BSC checks the new cell and ordersthis cell to activate the TCH
3
3. The BSC orders the serving cell to senda message to the MS telling the information
of new TCH4. The MS tunes to the new frequency andSends handover access burst
45. The new cell detects the handover burstand sends information about the suitable
timing advance to the MS56. The MS sends complete message to the new cell
6
7. The new cell sends a message to the BSC that thehandover is successful
7
8.The BSC orders the old Cell to release the TCH
8
Inter BSC /Intra MSC Handover
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96
Old BSC New BSC
MSC/VLR
Inter MSC Handover
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Old MSC
Old BSC
New MSC
New BSC
Air Interface Layers
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Air Interface Layers
RadioTransmission
Logical
Channels
Messages
RadioTransmission
Logical
Channels
Messages
Terminal BaseStation
Layer 1Bits
Layer 2
Packets
Layer 3
Messages
Frequency Allocation
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99
GSM 1900GSM 1800GSM 900
1850-1910 MHz710-1785MHz890-915 MHzUplinkFrequency
1930-1990 MHz1805-1880 MHz935-960 MHzDownlink
60 MHz75 MHz25 MHzBandwidth
80 MHz95 MHz45 MHzDuplex Distance
200 KHz200 KHz200 KHzCarrier Separation299374124Radio Channels
system
space
Spectrum Allocation (GSM 900)
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GSM 900 Frequency Allocation
F (MHz)915890
Uplink1 2 3 4 121 122 123 124
F (MHz)
Downlink
960935
1 2 3 4 121 122 123 124
890.2
890.4
890.6
935.2
935.4
935.6
200 KHz
1
1
121
121
Downlink 935 960 MHz
Uplink 890 915 MHz
FDMA in GSM
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101
FDMA in GSM
Separation between carriers Frequency gap must be sufficient to eliminateinterference between adjacent channels.
Where The more the separation the less the co-channel interference but the lessthe available channels suited in the bandwidth.
It is found that a 200 kHz channel separation is suitable for all systems.
TDMA in GSM
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102
TDMA in GSM
With TDMA, one carrier is used to carry a number of calls, each call using that
carrier at designated periods in time .
These periods of time are referred to as time slots .
Each MS on a call is assigned one time slot on the uplink frequency and one on thedownlink frequency, and both the same.
It is found that a 8 Time Slots per carrier, called physical channels is suitable forall systems.
Information sent during one time slot is called a burst, and depending on
information sent we named what called logical Channels
Channel Type
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Traffic ChannelTransmit voice and data
Signaling Channel
transmit the signaling and synchronous data between
BTS and MS.
Channels
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Channels
Physical Channels Traffic Associated with frequency bands, time slots, codes
Physical channels transfer bits from one network element to another
Logical Channels Control
Distinguished by the nature of carried information and the way to assemblebits into data units
Three types
one-to-one: traffic channels between a BTS and a MS
one-to-many: synchronization signals from BTS to MSs in a cell
many-to-one: from MSs to the same BTS
Physical Channels
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GSM band is divided into 124 RF channels, and each channel is
divided into 8 time slots using TDMA. Thesetime slots are called physical channels.
CH 1 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
CH 2 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
CH 3 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
CH 1240 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
Traffic Channel
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106
Carries either encoded speech or user data up and down link
between a single mobile and a single BTS.
Types of traffic channel:
Full rate (TCH)
Transmits full rate speech (13 Kbits/s). A full rate TCHoccupies one physical channel.
Half rate (TCH/2)
Transmits half rate speech (6.5 Kbits/s).
Two half rate TCHs can share one physical channel, thus doubling
the capacity of a cell.
Traffic Channel
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Traffic Channel
Control Channels
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Control Channels
These are used to carry signaling or synchronization data. They are divided
into three types:-
Broadcast CHannels (BCH)
Common Control CHannels (CCCH)
Dedicated Control CHannels (DCCH)
1.Broadcast Channels
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109
From Single BTS to all the mobiles in the area
Frequency Correction Control CHannel (FCCH) Carries information for frequency correction of the mobile
Synchronization CHannel (SCH) Carries 2 important pieces of information
TDMA frame number (max = 2715684 ) Base station identity Code (BSIC)
Broadcast Control CHannel (BCCH) Broadcasts some general cell information such as:
Location Area Identity (LAI), maximum output power allowed in the cell and the identity of BCCH carriers for neighboring cells.
2.Common Control Channels
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110
2.Common Control Channels
To or from a certain BTS to a single mobile
Paging CHannel (PCH)
BTS Transmits a paging message to indicate an incoming call or short message.The paging message contains the identity number of the mobile subscriberthat the network wishes to contact.
Random Access CHannel (RACH)
MS Answers paging message on the RACH by requesting a signaling channel ofSDCCH.
Access Grant CHannel (AGCH)
Assigns a signaling channel (SDCCH) to the MS.
3.Dedicated Control Channels
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111
3.Dedicated Control Channels
Stand alone Dedicated Control Channel (SDCCH) The BTS switches to the assigned SDCCH. The call set-up procedure is
performed in idle mode. The BSC assigns a TCH (carrier and time slot) and theMS switches to the assigned SDCCH.
SDCCH is also used to Registration & Authentication
Slow Associated Control Channel (SACCH)
BTS Instructs the MS the transmitting power to use and gives instructions ontiming advance (TA).
MS Sends averaged measurements on its own BTS (signal strength and quality)and neighboring BTSs (signal strength). The MS continues to use SACCH forthis purpose during a call.
Fast Associated Control Channel (FACCH) Transmits handover information.
Transmits necessary handover information
Control Channels
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Control Channels
Channel Type-Summary
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channel
TCH
CCH
Voice CH
Data CH
FR Voice Traffic Channel (TCH/FS)
HR Traffic Channel (TCH/HS)
4.8Kbit/s HR TCH (TCH/H4.8)
9.6Kbit/s FR TCH(TCH/F9.6)
4.8Kbit/s FR TCH (TCH/F4.8)
BCH
FCCH (down)SCH (down)
BCCH (down)
CCCH
RACH (up)
AGCH (down)
PCH (down)
DCCH
SDCCH
FACCH
SACCH
14.4Kbit/s FR TCH (TCH/F14.4)
Enhanced FR Traffic Channel (TCH/EFR)
Power Measurements Performed by the Mobile
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114
Power measurements represent one of the important functions carried out by
a mobile station in both of its modes: idle mode
active mode
in order for the mobile to tune to the best cell.
Power Measurements in Active Mode
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1. To enable the mobile from making power measurements during a call,the uplink time slot will be delayed by an offset of three time slots fromthe down link time slot. (The mobile will try to measure the signalstrength of these carriers one by one during the time betweentransmission and reception of the allocated traffic channel)
2. The mobile is informed on the SACCH channel which BCCH frequenciesto be measured.
3. To make sure that the measured carriers do not belong to co-channel
cells, the mobile will have to check the identity of the adjacent cells byreading the BSIC value sent on the SCH of each cell. This will take placeduring the idle frame number 26.
(Note) The signal strength of the serving cell is measured duringreception of the allocated traffic channel.
4. The mobile will make a list of the strongest six carriers and their BSICvalues along with the signal strength of its cell, and reports this list tothe BSC via the uplink SACCH channel which is repeated once every 26frame.
GSM Coverage Plan
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116
g
To provide coverage for a large service area of a mobile networkwe have two Options:
(A) Install one transceiver with high radio power at the center of
the service area
Drawbacks:
The mobile equipments used in this network should have
high output power in order to be able to transmit signals
across the coverage area.
The usage of the radio resources would be limited.
GSM Coverage Plan
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117
g
(B) Divide the service area into smaller areas (cells) Advantages:
Each cell as well as the mobile handsets will have relatively
small power transceivers.
The frequency spectrum might be reused in two far
separated cells. This yields:1- Unlimited capacity of the system.
2- Good interference characteristics
Cell Geometry
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118
y
Problem of omni directional antennas
Dead Spots
Cell Geometrical Shape
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Differentiation between these three shapes will be in order tooptimize the number of cells required to cover a given service area
against the cell transceiver power. By some calculations, you will find
that using hexagonal shaped cells achieves the optimum.
R R R
Cell Geometrical Shape
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p
Umbrella Cell
Normal Cell Normal Cell
Macro Cell
Cell Geometrical Shape
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p
Umbrella cell
Macro cell
Slow moving subscribers
Fast moving subscribers
Pico cell
In building
coverage
Clusters
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122
Clusters
Cluster is a set of cells where the
frequency is not being reusedwithin this cluster.
Cluster can be 3, 4, 7 and 9 cells.
Sectorization
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123
sectroized CellsOmni-Directional Cell
3/9 Cluster
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A3
A2
A1
B3
B2
B1
C3
C2
C1
A3
A2
A1
B3
B2
B1
C3
C2
C1
A3
A2
A1
B3
B2
B1
C3
C2
C1
A3
A2
A1
B3
B2
B1
C3
C2
C1
A3
A2
A1
B3
B2
B1
C3
C2
C1
A3
A2
A1
B3
B2
B1
C3
C2
C1
A3
A2
A1
B3
B2
B1
C3
C2
C1
A3
A2
A1
B3
B2
B1
C3
C2
C1
A3
A2
A1
B3
B2
B1
C3
C2
C1
4 / 12 Cluster
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A3
A2
A1
B3
B2
B1
C3
C2
C1
D3
D2
D1
A3
A2
A1
B3
B2
B1
C3
C2
C1
D3
D2
D1
A3
A2
A1
B3
B2
B1
C3
C2
C1
D3
D2
D1
A3
A2
A1
B3
B2
B1
C3
C2
C1
D3
D2
D1
A3
A2
A1
B3
B2
B1
C3
C2
C1
D3
D2
D1
A3
A2
A1
B3
B2
B1
C3
C2
C1
D3
D2
D1
A3
A2
A1
B3
B2
B1
C3
C2
C1
D3
D2
D1
A3
A2A1
B3
B2B1
C3
C2
C1
D3
D2
D1
A3
A2
A1
B3
B2
B1
C3
C2
C1
D3
D2
D1
A3
A2
A1
B3
B2
B1
C3
C2
C1
D3
D2
D1
A3
A2
A1
B3
B2
B1
C3
C2
C1
D3
D2
D1
A3
A2
E3
E2
7 / 21 Cluster
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A3
A2
A1
C3
C2
C1
D3
D2
D1
B3
B2
B1
E3
E2
E1
F3
F2
F1
G3
G2
G1
A3
A2
A1
C3
C2
C1
D3
D2
D1
B3
B2
B1
E3
E2
E1
F3
F2
F1
G3
G2
G1
A3
A2
A1
C3
C2
C1
D3
D2
D1
B3
B2
B1
E3
E2
E1
F3
F2
F1
G3
G2
G1
A3
A2
A1
C3
C2
C1
D3
D2
D1
B3
B2
B1
E3
E2
E1
F3
F2
F1
G3
G2
G1
A1
C3
C2
C1
D3
D2
D1
B3
B2
B1
E1
F3
F2
F1
G3
G2
G1
Frequency Reuse
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127
If the GSM900 system has 124 Absolute Radio Frequency TrafficChannels, and if we are using only in our network 60 of them, thenwe can only serve 8 x 60 = 480 Calls if we only use the frequencyonce.
However, a cellular network overcome this constraint andmaximizes the number of subscribers that it can serve by usingfrequency re-use.
The frequency reuse is performed by dividing the whole availablefrequencies between a group of neighboring cells which is calledfrequency reuse patternor a Cluster, and then repeat this cluster
over the whole network
Frequency Reuse
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128
3/9 cluster in which the available frequencies are divided into 9groups and distributed between 3 sites
4/12 cluster in which the available frequencies are divided into 12groups and distributed between 4 sites
7 / 21 cluster in which the available frequencies are divided into 21groups and distributed between 7 sites
But we must take into consideration two types of interference:
1- Co- Channel Interference
2- Adjacent Channel Interference
Co- Channel Interference
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129
Co-channel interference is caused by short distance between the cell and other cell thatuse the same frequency.
To overcome this type of interference. Each frequency is reused after the same distanceD
Reuse Plan = (D/R)2 = 3N. Where N is the number of cells per cluster
Adjacent Channel Interference
d f h f h f d k f h
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130
Adjacent frequencies, that are frequencies shifted 200kHz from the carrierfrequency, must be avoided in the same cell and preferably in neighboring cellsalso .
To overcome this type we must make good planning for the frequencies in thecluster
Frequency Planning
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131
A3A2
A1
B3B2
B1C3
C2C1
A3A2
A1
B3B2
B1C3
C2C1
B3
B2B1
C3 C2C1
A3A2
A1
B3B2
B1C3
C2C1
A3A2
A1
C3B3A3C2B2A2C1B1A1Frequency
group
727170696867666564
Channels818079787776757473
878685848382
Frequency Planning
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132
In a real network the allocation of channels to cells will not be asuniform as in table, as some cells will require more channels and
some will require less.
In this case, a channel may be taken from a cell with low traffic
load and moved to one with a higher traffic load.
However, if doing so, it is important to ensure that interference is
still minimized.
Which Cluster Size to use?
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133
Carrier to interference ratio Its the difference in power level between the carrier in a given cell and the same
carrier received from the nearest cell that reuses the same frequency.
Number of frequenciesper site
Traffic ChannelsC/I Ratio
3/9 High High Low
4/12 Medium Medium Medium
7/21 Low Low High
Introduction to Cell Planning
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134
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2006-01-24 Lecture 1 135
Radio Transmission problems
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1
As it was stated before that the mobile telecommunications will use
radio transmission as the transmission technique; the radio transmissionis suffering from many problems which causing unacceptable degradation
of the service quality.
We will discuss these problems in details during our course.
Radio Transmission problems
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2
1. Path Loss
2. Multipath Fading
a. Rayleigh Fading
b. Time Dispersion
3. Time Alignment
Radio Transmission problems
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3
1. Path Loss
Cause
Due to Increasing distance between MS, and BTS.
Solution
Handover
p
Radio Transmission problems
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5
2. Multipath Fading
Cause
Due to different paths of signals between MS, and BTS.
Which cause fading dips as a result of different in phase and amplitude
Solution
Diversity
a. Space Diversity
b. Polarization Diversity
c. Frequency Diversity ( Frequency Hopping)
Radio Transmission problems
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3. Time AlignmentCauseDue to different distance of different MSs from BTS (Near-Far)
Solution
Time Advance
7
Home Location Register (HLR)
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2006-01-24 Lecture 1 141
GSM Terrestrial Interfaces
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142
The standard interfaces used are as follows: 2 Mbit/s.
Signaling System ITU-TSS #7 (C7 or SS#7).
X.25 (packet switched data); (LAPB).
Abis using the LAPD protocol (Link Access Procedure D). Whatever the interfaces and whatever their function, they will often share a
common
physical bearer (cable) between two points, for example, the MSC and a
BSS.
GSM Terrestrial Interfaces
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GSM Terrestrial Interfaces
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GSM Terrestrial Interfaces
/
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145
2 Mbit/s Trunk 30-channel PCM
This diagram opposite shows the logical GSM system with the 2 Mbit/s interfaces
highlighted.
They carry traffic from the PSTN to the MSC, between MSCs, from an MSC to a BSC
and from a BSC to remotely sited BTSs.
These links are also used between the MSC and IWF. Each 2.048Mbit/s link provides thirty 64 kbit/s channels available to carry speech, data, or
control information.
The control information may contain C7, LAPD or X.25 formatted information.
These 2 Mbit/s links commonly act as the physical bearer for the interfaces used
between the GSM system entities.
GSM Terrestrial Interfaces
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146
X.25 Interfaces
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147
The X.25 packets provide the OMC with communications to all the entities over
which it has control and oversight.
Note that the X.25 connection from the OMC to the BSS may be nailed through
or (permanently connected by software) at the MSC, or may be supported by a
completely independent physical route.
X.25 Interfaces
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Signaling System #7
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C7 Interfaces SS7 Signaling System #7
The diagram opposite illustrates the use of C7 in the GSM system; carrying signalingand control information between most major entities, and to and from the PSTN.
Used to communicate between the different GSM network entities.
Between the MSC and the BSC, the Base Station System Management
Is used between the MSC and the VLR, EIR, and HLR.
Signaling System #7
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A-bis (LAPD) Interfaces
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151
a different type of interface is required. To Communicate between BTS and BSC
GSM has specified the use of LAPD A-bis.
The GSM specifications for this interface (termed A-bis) are not very specific and
therefore interpretations of the interface vary. This means that one manufacturers
BTS will not work with another manufacturers BSC.
As we have already mentioned, the functionality split between the BTS and BSC is
also largely in the hands of the manufacturer and therefore it is unlikely that they
would operate together, even if this interface were rigidly enforced by the
specifications.
A-bis (LAPD) Interfaces
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Interface Names
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The GSM System Interface Names
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154
GSM Transmission Process
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Segmentation
Speech Coding
Channel Coding
Interleaving
Encryption
A/D Conversion
Burst Formatting
Modulation and
Transmission
Analog to Digital Conversion
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Analog to digital conversion takesplace in 3 steps:
1. Sampling2. Quantization3. Coding
1. Sampling
Telecommunication systems use Sampling rate = 8 Ksample/s
Segmentation
Segmentation refers to the process of partitioning a digital information into
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1 2 3 4 5 6 7 8 9 10 11 12 13 0 1 2 3 4 5 6 7 8 9 10
1 2 3 4 . . . . . . . . . . . . . . . 160
160 sample in 20 ms = 1 Segment
Segmentation refers to the process of partitioning a digital information into
multiple regions . The goal of segmentation is to simplify and/or change the
representation of an image into something that is more meaningful and easierto analyze.
Interleaving
Interleaving in computer science is a way to arrange data in a non-contiguous way
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158
Interleaving in computer science is a way to arrange data in a non-contiguous way
in order to increase performance.
It is used in:
time-division multiplexing (TDM) in telecommunications .
computer memory.
disk storage.
Interleaving
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Second Level Interleaving
1 A T
2 A T
3 A T
4 A T
1 B T 5 A
2 B T 6 A
3 B T 7 A
4 B T 8 A
1 C T 5 B
2 C T 6 B
3 C T 7 B
4 C T 8 B
1 D T 5 C
2 D T 6 C
3 D T 7 C
4 D T 8 C
1
2
3
4
5
6
7
8
20 ms Block A
1
2
3
4
5
6
7
8
20 ms Block A
1
2
3
4
5
6
7
8
20 ms Block D1
2
3
4
5
6
7
8
20 ms Block D
1
2
3
4
5
6
7
8
20 ms Block c
1
2
3
4
5
6
7
8
20 ms Block c
1
2
3
4
56
7
8
20 ms Block B
1
2
3
4
56
7
8
20 ms Block B
Modulation / Demodulation in GSM
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GSM uses the Gaussian Minimum Shift Keying (GMSK)
Gaussian minimum-shift keying
Modulation / Demodulation in GSM
Gaussian minimum shift keying or GMSK is a continuous-phase frequency-shift
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keying modulation scheme. It is similar to standard minimum-shift keying (MSK);
however the digital data stream is first shaped with a Gaussian filter before beingapplied to a frequency modulator. This has the advantage of reducing sideband
power, which in turn reduces out-of-band interference between signal carriers in
adjacent frequency channels.
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Open
Discussion
Vendors :-
Communication Companies
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Communication Companies
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Services and subcontractors
CIVIL Telecom
Different kinds of engineers
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Telecom Civil
Power Mechanical
Target Job
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Good Luck
Eng / Mohamed [email protected]
01004758147