Content
Preface…………………………………………………………………………………………….5
Acknowledgement…………………………………………………………………………..6
Certificate………………………………………………………………………………………...7
NOKIA
SEIMENS NETWORKS PROFILE…………………………………..8
1
Introduction to GSM……………………………………………………………………
10
1.1
CELLULAR TELEPHONY………………………………………………………………….10
1.2
Extended GSM (EGSM)…………………………………………………………………11
1.3 DCS1800
FREQUENCIES…………………………………………………………………….11
1.4
INCREASED CAPACITY……………………………………………………………………….12
1.5 AUDIO
QUALITY……………………………………………………………………………..13
1.6 USE OF
STANDARDISED OPEN INTERFACES……………………………………13
1.7
IMPROVED SECURITY AND CONFIDENTIALITY…………………………………13
1.8
ENHANCED RANGE OF SERVICES………………………………………………………..14
1.9
Frequency reuse………………………………………………………………………………15
2 NETWORK COMPONENTS…………………………………………………………………..16
2.1 Mobile
Switching Centre (MSC)……………………………………………………….16
2.2 Mobile
Station (MS)…………………………………………………………………………18
2.3 Mobile
Equipment…………………………………………………………………………..18
2.4 SIM………………………………………………………………………………………………..19
2.4.1
Mobile Station International Subscribers Dialling Number ( MSISDN ) 20
2.4.2
International Mobile Subscribers Identity ( IMSI ) ………………………….21
2.4.3
Temporary Mobile Subscribers Identity ( TMSI ) :……………………………….21
2.4.4
Equipment Identity Register ( EIR )………………………………………………………..22
2.4.5
International Mobile Equipment Identity ( IMEI ) :………………………………….23
2.5 HOME
LOCATION REGISTER( HLR )…………………………………………………………….24
2.6 VISITOR
LOCATION REGISTER ( VLR )……………………………………………………….25
2.7
Authentication Centre ( AUC )……………………………………………………………..26
2.8 Base
Station Sub-System ( BSS ) :…………………………………………………………….27
2.9
Transcoder( XCDR )………………………………………………………………………………….28
2.10 Base
Station Controller (BSC)………………………………………………………………….29
2.11 Base
Transceiver Station (BTS) …………………………………………………………….30
3 MULTIPLE
ACCESS TECHNIQUES…………………………………………………………………32
3.1
INTERFACE NAMES……………………………………………………………………………….32
4 CHANNEL
CONCEPT………………………………………………………………………………..34
4.1
Physical channel…………………………………………………………………………………….34
4.2 Logical
channel……………………………………………………………………………………..34
4.3 BCH
Channels………………………………………………………………………………………..36
4.3.1 BCCH(
Broadcast Control Channel )…………………………………………………………36
4.3.2 SCH(
Synchronization Channel )……………………………………………………………..36
4.3.3 FCCH(
Frequency Correction Channel )…………………………………………………36
4.4 CCCH
Channels……………………………………………………………………………………37
4.4.1 RACH(
Random Access Channel )…………………………………………………37
4.4.2 AGCH(
Access Grant Channel )………………………………………………………….37
4.4.3 PCH(
Paging Channel )……………………………………………………………………….37
4.5 DCCH
Channels………………………………………………………………………………..37
4.5.1
SDCCH( Standalone Dedicated Control Channel )…………………………..37
4.5.2
SACCH( Slow Associated Control Channel )……………………………………38
4.5.3
FACCH( Fast Associated Control Channel )…………………………………..38
5 CALL FLOW …………………………………………………………………………..39
6 Handover …………………………………………………………………………………..40
6.1 MS END…………………………………………………………………………………41
6.2 BTS END………………………………………………………………………………………….42
6.3 MS IDLE
TIME REPORTING……………………………………………………………….42
7 HANDOVER CONDITIONS…………………………………………………………………….44
7.1.1Interference……………………………………………………………………………………44
7.1.2 RXQUAL…………………………………………………………………………………………44
7.1.3RXLEV…………………………………………………………………………………………44
7.1.4Distance
or Timing Advance……………………………………………………………44
7.1.5Power
Budget…………………………………………………………………………………..44
7.2
HANDOVER TYPES……………………………………………………………………………….45
7.2.1
Intra-Cell Handover………………………………………………………………………….45
7.2.2
Intra-BSC Handover………………………………………………………………………….46
7.2.3 Inter-BSC
Handover……………………………………………………………………………46
7.2.4
Inter-MSC Handover…………………………………………………………………………..47
7.3
LOCATION UPDATE……………………………………………………………………………47
7.4
LOCATION UPDATE TYPES……………………………………………………………………….48
7.4.1
Normal location update……………………………………………………………………….48
7.4.2
Periodic location update…………………………………………………………………………49
7.4.3 IMSI attach……………………………………………………………………………………..49
8
SIGNALLING SYSTEM………………………………………………………………………………….50
8.1 GENERAL
INTRODUCTION……………………………………………………………………..50
8.2 Access
Signaling……………………………………………………………………………………52
8.3 Trunk
Signaling……………………………………………………………………………………..53
8.4 Channel
Associated Signaling (CAS)……………………………………………………….54
8.5 Common
Channel Signaling (CCS)…………………………………………………………..54
8.6 CHANNEL
ASSOCIATED SIGNALING (CAS)……………………………………………….54
8.7 COMMON
CHANNEL SIGNALING (CCS)……………………………………………………55
9 SYS
INFORMATION MESSAGES………………………………………………………………….56
9.1
BROADCAST MESSAGES…………………………………………………………………………56
9.1.1
SYSTEM INFORMATION 1……………………………………………………………………….57
9.1.2 SYSTEM
INFORMATION 2…………………………………………………………………..59
9.1.3
SYSTEM INFORMATION 3……………………………………………………………………60
9.2 PAGING…………………………………………………………………………………………….62
Preface
The six weeks industrial/vocational
training is a part of my academic curriculum of Bachelors of Technology degree
in Instrumentation and Control engineering. from National Institute of Technology
Jalandhar (Punjab). Practical Industrial training mainly aims at making one
aware of industrial environment; which means that one get to know the limitation,
constraint and dimensions under which the theoretical knowledge can be applied
by an Engineer.
I got the opportunity to perform
summer training at Nokia seimens networks Pvt. Ltd., Meerut. I was assigned GSM
technology project under the RF team. I
witnessed the related on-desk operations and tried to be familiar with the
process and technology used. I visited the circle warehouse and some sites in
and around Meerut zone of the UP-West Telecom circle to have a closer look at
the physical processes required for the GSM technology.
This report is intended to provide an
introduction to GSM technology, its importance to the organizations, the
concept of GSM system and its part, methods for better signal , less noise , better
place of providing site, which implementation of all these concepts in the
organizations by a case study of Nokia seimens networks Pvt. Ltd.
Acknowledgement
First of all, I want to
thank Nokia seimens networks Pvt. Ltd., the telecomm giant for providing me the
opportunity to work with them. However, the project would not have been
possible without the kind support and help of many individuals in the
organization. I would like to extend my sincere thanks to all of them.
I wish to express my deep
gratitude to Mr. RAJ KUMAR YADAV (PLANNING MANAGER, UP-W) for his guidance and
supervision as well as for providing necessary information regarding the
project & also for his support in completing the project.
I owe special thanks and
gratitude to Mr. RAHUL BHARGAVA (COMPLAIN LISTNER REGARDING NETWORK) for their guidance and constant supervision,
for providing me the necessary information about the project, for insightful
evaluation at each stage and for giving me support to complete the project in
an inspiring environment.
Furthermore, I want to
thank all the individuals who have willingly helped me out with their knowledge
and experience in completing the project. Without their support this project
would not have been completed.
CERTIFICATE
This is to certify that Mr. Atul kumar uttam,
student of Final Year, Bachelor of Technology, in Instrumentation
and Control Engineering at NIT Jalandhar, has successfully completed the
project given to him during the course of Industrial Training at NOKIA SEIMENS
NETWORKS PVT. LTD., Meerut, during the period of 25th May 2012 to 10th July
2012. He was assigned the Project of Inventory Management. His performance was
praiseworthy throughout the training period. The project assigned to him was
successfully completed within the specified time period.
This report accounts his experience and
knowledge of the field he had worked in. I have verified and sanctioned the
report. His overall performance during the project was excellent.
I wish him success in his
life and believe that this training will stand him in good stead in future.
Mr. Raj Kumar Yadav
Planning Manager
Vodafone Account, UP West
NOKIA SEIMENS
NETWORKING Pvt. Ltd.
NOKIA SEIMENS NETWORKS PROFILE…………
Nokia
Siemens Networks is one of the largest telecommunications hardware, software
and professional services companies in the world. The company is a 50-50 joint venture
combining the Nokia Networks Business Group and the carrier related businesses
of Siemens Communications which began its operations on 01 April 2007.
Around the world, Nokia
Siemens Networks expects a 100-fold growth in network traffic at ever lower
cost over the coming years, and the majority of this growth is expected to come
from emerging markets like India. For Nokia Siemens Networks, India is not just
a high-growth market but also an innovation hub. The manufacturing operations,
global delivery centers and research and development setups in India reflect
Nokia Siemens Networks’ unwavering focus on the country and enhanced proximity
to its customers. Nokia Siemens Networks is making strategic investments in
India to further strengthen its local market position and tap the tremendous
local growth opportunities in mobile, fixed and broadband segments.
Nokia
Siemens Networks India has fully indigenized operations and workforce with
13,000 people (direct & indirect) at 50 principle offices and present in
177 locations. Nokia Siemens Networks’ operations in India include marketing
and sales to HQ offices in Delhi NCR and Mumbai; two of out five Global Network
Solutions Centers (GNSC) in Noida (Delhi NCR) and Chennai; two manufacturing
facilities (2G/3G) in Chennai and Kolkata (for fixed line); and a research and
development center in Bangalore. Our global services headquarters, GSM-Edge
product management and a Centralized Solution Support Center (CSSC) are also
based in India strengthening our local presence further.
With an
installed base of close to 150,000 base station sites, which is increasing at
the rate of more than 5,000 per month, Nokia Siemens Networks is a leading
provider of telecommunication network solutions in India. It is the vendor of
choice for all major operators and has the top market share in Managed
Services, Packet Core and GSM-Railways. 10 Indian operators rely on us,
including Aircel, Bharti, BSNL, Defense, Idea, Railways, Tata, Uninor, Videocon
and Vodafone
As a
responsible corporate citizen, Nokia Siemens Networks India is focused on
making a difference in a variety of areas key to the growth and development of
India – these include education, women’s role in society, the environment, and
community work (volunteering). Due to the size of our company’s deployments in
India, the country is at the forefront of our efforts for greater energy
efficiency not only to focus on reduction of carbon emissions but also to help
operators improve their business performance through savings in energy costs.
•
The Global System for Mobile Communications (GSM) is a
set of recommendations and specifications for a digital cellular telephone
network (known as a Public Land Mobile Network, or PLMN).
•
These recommendations ensure the compatibility of equipment from different GSM manufacturers,
and interconnectivity between different administrations, including operation
across international boundaries.
•
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
Digital Network (ISDN), using a digital radio interface between the cellular
network and the mobile subscriber equipment.
1.1
CELLULAR 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.
1.2
Extended GSM (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.
1.3 DCS1800 FREQUENCIES
•
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.
1.4
INCREASED CAPACITY
•
The GSM system provides a greater subscriber capacity
than analogue systems.
•
GSM allows 25 kHz per user, that is, eight
conversations per 200 kHz channel pair (a pair comprising one transmit channel
and one receive channel).
•
Digital channel coding and the modulation used makes
the signal resistant to interference from cells where the same frequencies are
re-used (co-channel interference); a Carrier to Interference Ratio (C/I) level
of 12 dB is achieved, as opposed to the 18 dB typical with analogue cellular.
This allows increased geographic reuse
by permitting a reduction in the number of cells in the reuse pattern.
1.5
AUDIO QUALITY
•
Digital transmission of speech and high performance
digital signal processors provide good quality speech transmission.
•
Since GSM is a digital technology, the signals passed
over a digital air interface can be protected against errors by using better
error detection and correction techniques.
•
In regions of interference or noise-limited operation
the speech quality is noticeably better than analogue.
1.6
USE OF STANDARDISED OPEN INTERFACES
•
Standard interfaces such as C7 and X25 are used
throughout the system. Hence different manufacturers can be selected for
different parts of the PLMN.
•
There is a high flexibility in where the Network
components are situated.
1.7
IMPROVED SECURITY AND CONFIDENTIALITY
•
GSM offers high speech and data confidentiality.
•
Subscriber authentication can be performed by the
system to check if a subscriber is a valid subscriber or not.
•
The GSM system provides for high degree of
confidentiality for the subscriber. Calls are encoded and ciphered when sent
over air.
•
The mobile equipment can
be identified independently from the mobile subscriber. The mobile has a
identity number hard coded into it when it is manufactured. This number is
stored in a standard database and whenever a call is made the equipment can be
checked to see if it has been reported stolen.
CLEANER
HANDOVERS
•
GSM uses Mobile assisted handover technique.
•
The mobile itself carries out the signal strength and
quality measurement of its server and signal strength measurement of its
neighbors.
•
This data is passed on the Network which then uses
sophisticated algorithms to determine the need of handover.
SUBSCRIBER
IDENTIFICATION
•
In a GSM system the mobile station and the subscriber
are identified separately.
•
The subscriber is identified by means of a smart card
known as a SIM.
•
This enables the subscriber to use different mobile
equipment while retaining the same subscriber number.
1.8
ENHANCED RANGE OF SERVICES
•
Speech services for normal telephony.
•
Short Message Service for point to point transmission
of text message.
•
Cell broadcast for transmission of text message from
the cell to all MS in its coverage area. Message like traffic information or
advertising can be transmitted.
•
Fax and data services are provided. Data rates
available are 2.4 Kb/s, 4.8 Kb/s and 9.6 Kb/s.
•
Supplementary services like number identification ,
call barring, call forwarding, charging display etc can be provided.
1.9
FREQUENCY REUSE
•
There are total 124 carriers in GSM ( additional 50
carriers are available if EGSM band is used).
•
Each carrier has 8 timeslots and if 7 can be used for
traffic then a maximum of 868 ( 124 X 7 ) calls can be made. This is not enough
and hence frequencies have to be reused.
•
The same RF carrier can be used for many conversations
in several different cells at the same time.
•
The radio carriers available are allocated according
to a regular pattern which repeats over the whole coverage area.
•
The pattern to be used depends on traffic requirement
and spectrum availability.
2.1
Mobile Switching Centre (MSC)
•
The Mobile services Switching Centre (MSC)
co-ordinates the setting up of calls to and from GSM users.
•
It is the telephone switching office for MS originated
or terminated traffic and provides the appropriate bearer services,
teleservices and supplementary services.
•
It controls a number of Base Station Sites (BSSs)
within a specified geographical coverage area and gives the radio subsystem
access to the subscriber and equipment databases.
•
The MSC carries out several different functions
depending on its position in the network.
•
When the MSC provides the interface between PSTN and
the BSS in the GSM network it is called the Gateway MSC.
Some important
functions carried out by MSC are Call processing including control of data/voice call setup,
inter BSS & inter MSC handovers, control of mobility management, Operation
& maintenance support including database management, traffic metering and
man machine interface & managing the interface between GSM & PSTN N/W
2.2
Mobile Station (MS)
•
The Mobile Station consists of the Mobile Equipment
(ME) and the Subscriber Identity Module (SIM).
2.3
Mobile Equipment
•
The Mobile Equipment is the hardware used by the
subscriber to access the network.
•
The mobile equipment can be Vehicle mounted, with the
antenna physically mounted on the outside of the vehicle or portable mobile
unit, which can be handheld.
•
Mobiles are classified into five classes according to
their power rating.
2.4 SIM
·
The SIM is a removable card that plugs into the ME.
·
It identifies the mobile subscriber and provides information about the
service that the subscriber should receive.
·
The SIM contains several pieces of information
·
International Mobile Subscribers Identity ( IMSI ) - This number
identifies the mobile subscriber. It is only transmitted over the air during
initializing.
·
Temporary Mobile Subscriber Identity ( TMSI ) - This number also
identifies the subscriber. It can be alternatively used by the system. It is
periodically changed by the system to protect the subscriber from being
identified by someone attempting to monitor the radio interface.
·
Location Area Identity ( LAI ) - Identifies the current location of the
subscriber.
·
Subscribers Authentication Key ( Ki ) - This is used to authenticate
the SIM card.
·
Mobile Station International Standard Data Number ( MSISDN ) - This is
the telephone number of the mobile.
·
Most of the data contained within the SIM is protected against reading (eg
Ki ) or alterations after the SIM is issued.
·
Some of the parameters ( eg. LAI ) will be continously updated to
reflect the current location of the subscriber.
·
The SIM card can be protected by use of Personal Identity Number ( PIN
) password.
·
The SIM is capable of storing additional information such as
accumulated call charges.
2.4.1
Mobile Station International Subscribers Dialling Number ( MSISDN ) :
•
Human identity used to call a MS
•
The Mobile Subscriber ISDN (MSISDN) number is the
telephone number 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.
2.4.2
International Mobile Subscribers Identity ( IMSI )
•
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.
2.4.3
Temporary Mobile Subscribers Identity ( TMSI )
•
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.
2.4.4
Equipment Identity Register ( EIR )
•
The Equipment Identity Register (EIR) contains a
centralized database for validating the international mobile station equipment
identity, the IMEI.
•
The database contains three lists:
The
white list contains the number series of equipment identities that have been
allocated in the different participating countries. This list does not contain
individual numbers but a range of
numbers by identifying the beginning and end of the series.
– The grey
list contains IMEIs of equipment to be monitored and observed for location and
correct function.
– The black
list contains IMEIs of MSs which have been reported stolen or are to be denied
service.
•
The EIR
database is remotely accessed by the MSC’s in the Network and can also be
accessed by an MSC in a different PLMN.
2.4.5
International Mobile Equipment Identity ( IMEI )
•
IMEI is a serial number unique to each mobile
•
Each MS is identified by an International Mobile
station Equipment Identity (IMEI) number which is permanently stored in the
Mobile Equipment.
•
On request, the MS sends this number over the
signalling channel to the MSC.
•
The IMEI can be used to identify MSs that are reported
stolen or operating incorrectly.
.
2.5
HOME LOCATION REGISTER( HLR )
•
The HLR contains the master database of all
subscribers in the PLMN.
•
This data is remotely accessed by the MSC´s and VLR’s in the network. The data can also be
accessed by an MSC or a VLR in a different PLMN to allow inter-system and
inter-country roaming.
•
A PLMN may contain more than one HLR, in which case
each HLR contains a portion of the total subscriber database. There is only one
database record per subscriber.
•
The subscribers data may be accessed by the IMSI or
the MSISDN.
•
The parameters stored in HLR are
– Subscribers
ID (IMSI and MSISDN )
– Current
subscriber VLR.
– Supplementary
services subscribed to.
– Supplementary
services information (eg. Current forwarding address ).
– Authentication
key and AUC functionality.
– TMSI and MSRN
2.6
VISITOR LOCATION REGISTER ( VLR )
•
The Visited Location Register (VLR) is a local
subscriber database, holding details on those subscribers who enter the area of
the network that it covers.
•
The details are held in the VLR until the subscriber
moves into the area serviced by another VLR.
•
The data includes most of the information stored at
the HLR, as well as more precise location and status information.
•
The additional data stored in VLR are
– Mobile
status ( Busy / Free / No answer etc. )
– Location
Area Identity ( LAI )
– Temporary
Mobile Subscribers Identity ( TMSI )
– Mobile
Station Roaming Number ( MSRN )
•
The VLR provides the system elements local to the
subscriber, with basic information on that subscriber, thus removing the need
to access the HLR every time subscriber information is required.
2.7
Authentication Centre ( AUC )
•
The AUC is a processor system that perform
authentication function.
•
It is normally co-located with the HLR.
•
The authentication process usually takes place each
time the subscriber initializes on the system.
•
Each subscriber is assigned an authentication key (Ki)
which is stored in the SIM and at the AUC.
•
A random number of 128 bits is generated by the AUC
& sent to the MS.
•
The authentication algorithm A3 uses this random
number and authentication key Ki to produce a signed response SRES( Signed
Response ).
•
At the same time the AUC uses the random number and
Authentication algorithm A3 along with the Ki key to produce a SRES.
•
If the SRES produced by AUC matches the one produced
by MS is the same, the subscriber is permitted to use the network.
2.8
Base Station Sub-System ( BSS ) :
•
The BSS is the fixed end of the radio interface that
provides control and radio coverage functions for one or more cells and their
associated MSs.
•
It is the interface between the MS and the MSC.
•
The BSS comprises one or more Base Transceiver
Stations (BTSs), each containing the radio components that communicate with MSs
in a given area, and a Base Site Controller (BSC) which supports call
processing functions and the interfaces to the MSC.
•
Digital radio techniques are used for the radio communications
link, known as the Air Interface, between the BSS and the MS.
•
The BSS consists of three basic Network Elements
(NEs).
– Transcoder
(XCDR) or Remote transcoder (RXCDR) .
– Base
Station Controller (BSC).
– Base
Transceiver Stations (BTSs) assigned to the BSC. .
2.9
Transcoder( XCDR )
•
The speech transcoder is the interface between the 64
kbit/s PCM channel in the land network and the 13 kbit/s vocoder (actually 22.8
kbit/s after channel coding) channel used on the Air Interface.
•
This reduces the amount of information carried on the
Air Interface and hence, its bandwidth.
•
If the 64 kbits/s PCM is transmitted on the air
interface without occupation, it would occupy an excessive amount of radio
bandwidth. This would use the available radio spectrum inefficiently.
•
The required bandwidth is therefore reduced by
processing the 64 kbits/s PCM data so that the amount of information required
to transmit digitised voice falls to 13kb/s.
•
The XCDR can multiplex 4 traffic channels into a
single 64 kbit/s timeslot. Thus a E1/T1
serial link can carry 4 times as many channels.
•
This can reduce the number of E1/T1 leased lines
required to connect remotely located equipment.
•
When the transcoder is between the MSC and the BSC it
is called a remote transcoder (RXCDR).
2.10
Base Station Controller (BSC)
•
The BSC network element provides the control for the
BSS.
•
It controls and manages the associated BTSs, and
interfaces with the Operations and Maintenance Centre (OMC).
•
The purpose of the BSC is to perform a variety of
functions. The following comprise the functions provided by the BSC:
– Controls
the BTS components.-
– Performs
Call Processing.
– Performs
Operations and Maintenance (O & M).
– Provides
the O & M link (OML) between the BSS and the OMC.
– Provides
the A Interface between the BSS and the MSC.
– Manages the
radio channels.
– Transfers
signaling information to and from MSs.
2.11
Base Transceiver Station (BTS)
•
The BTS network element consists of the hardware
components, such as radios, interface modules and antenna systems that provide
the Air Interface between the BSS and the MSs.
•
The BTS provides radio channels (RF carriers) for a
specific RF coverage area.
•
The radio channel is the communication link between
the MSs within an RF coverage area and the BSS.
•
The BTS also has a limited amount of control
functionality which reduces the amount of traffic between the BTS and BSC.
Base Station Identity Code
3 MULTIPLE ACCESS TECHNIQUES
•
In order for several links to
be in progress simultaneously in the same geographical area without mutual
interference , multiple access techniques are deployed.
•
The commonly used multiple access techniques are
– Frequency
Division Multiple Access (FDMA )
– Time
Division Multiple Access (TDMA )
– Code
Division Multiple Access (CDMA )
3.1
INTERFACE NAMES
Each interface specified in GSM has
a name associated with it.
4.1 Physical channel - Each
timeslot on a carrier is referred to as a physical channel. Per carrier there
are 8 physical channels.
4.2 Logical channel - 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
4.3
BCH Channels
4.3.1 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.
4.3.2 SCH( Synchronisation Channel
)
•
Downlink only
•
Carries information for frame synchronization. Contains TDMA frame number and BSIC.
4.3.3 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.
4.4
CCCH Channels
4.4.1 RACH( Random Access Channel )
•
Uplink only
•
Used by the MS to access the Network.
4.4.2 AGCH( Access Grant Channel )
•
Downlink only
•
Used by the network to assign a signaling channel upon
successfull decoding of access bursts.
4.4.3 PCH( Paging Channel )
•
Downlink only.
•
Used by the Network to contact the MS.
4.5 DCCH Channels
4.5.1 SDCCH( Standalone Dedicated
Control Channel )
•
Uplink and Downlink
•
Used for call setup, location update and SMS.
4.5.2 SACCH( Slow Associated
Control Channel )
•
Used on Uplink and Downlink only in dedicated mode.
•
Uplink SACCH messages - Measurement reports.
•
Downlink SACCH messages - control info.
4.5.3 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.
5 CALL FLOW
•
The GSM handover process uses a mobile assisted
technique for accurate and fast handovers, in order to:
– Maintain
the user connection link quality.
– Manage
traffic distribution
•
The overall handover process is implemented in the
MS,BSS & MSC.
•
Measurement of radio subsystem downlink performance
and signal strengths received from surrounding cells, is made in the MS.
•
These measurements are sent to the BSS for assessment.
•
The BSS measures the uplink performance for the MS
being served and also assesses the signal strength of interference on its idle
traffic channels.
•
Initial assessment of the measurements in conjunction
with defined thresholds and handover strategy may be performed in the BSS.
Assessment requiring measurement results from other BSS or other information
resident in the MSC, may be perform. in the MSC.
•
The MS assists the handover decision process by
performing certain measurements.
•
When the MS is engaged in a speech conversation, a
portion of the TDMA frame is idle while the rest of the frame is used for
uplink (BTS receive) and downlink (BTS transmit) timeslots.
•
During the idle time period of the frame, the MS
changes radio channel frequency and monitors and measures the signal level of
the six best neighbor cells.
Measurements which feed the
handover decision algorithm are made at
both ends of the radio link
6.1 MS END
•
At the MS end, measurements are continuously signaled,
via the associated control channel, to the BSS where the decision for handover
is ultimately made.
•
MS measurements include:
– Serving
cell downlink quality (bit error rate (BER) estimate).
– Serving
cell downlink received signal level, and six best neighbor cells downlink
received signal level.
•
The MS also decodes the Base Station ID Code (BSIC)
from the six best neighbor cells, and reports the BSICs and the measurement
information to the BSS.
6.2
BTS END
•
The BTS measures the uplink link quality, received
signal level, and MS to BTS site distance.
•
The MS RF transmit output power budget is also
considered in the handover decision.
•
If the MS can be served by a neighbor cell at a lower
power, the handover is recommended.
•
From a system perspective, handover may be considered
due to loading or congestion conditions. In this case, the MSC or BSC tries to
balance channel usage among cells.
6.3
MS IDLE TIME REPORTING
•
During the conversation, the MS only transmits and
receives for one eighth of the time, that is during one timeslot in each frame.
•
During its idle time (the remaining seven timeslots),
the MS switches to the BCCH of the surrounding cells and measures its signal
strength.
•
The signal strength measurements of the surrounding
cells, and the signal strength and quality measurements of the serving cell,
are reported back to the serving cell via the SACCH once in every SACCH
multiframe.
•
This information is evaluated by the BSS for use in
deciding when the MS should be handed over to another traffic channel.
•
This reporting is the basis for MS assisted handovers.
Handover is done on five conditions
– Interference
– RXQUAL
– RXLEV
– Distance or
Timing Advance
– Power
Budget
7.1.1 Interference
- If signal level is high and still there is RXQUAL problem,
then the RXQUAL problem is because of interference.
7.1.2 RXQUAL
- It is the receive quality. It ranges from 0 to 7 , 0 being
the best and 7 the worst
7.1.3 RXLEV
- It is the receive level. It varies from -47dBm to -110dBm.
7.1.4 Timing
Advance - Ranges from 0 to 63.
7.1.5 Power
budget - It is used to save the power of the MS.
7.2
HANDOVER TYPES
7.2.1
Intra-Cell Handover
•
Handover takes place in the same cell from one
timeslot to another timeslot of the same carrier or different carriers( but the
same cell).
•
Intra-cell handover is triggered only if the cause is
interference.
•
Intra-cell handover can be enabled or disabled in a
cell.
7.2.2
Intra-BSC Handover
7.2.3
Inter-BSC Handover
7.2.4
Inter-MSC Handover
7.3
LOCATION UPDATE
•
MSC should always know the location of the MS so that
it can contact it by sending pages whenever required.
•
The mobile keeps on informing the MSC about its
current location area or whenever it changes from one LA to another.
•
This process of informing the MSC is known as location
updating.
•
The new LA is updated in the VLR.
LAI = MCC + MNC + LAC
MCC = Mobile country code.
MNC = Mobile Network Code.
LAC = Location area code.
Identifies a location area within a GSM PLMN network. The maximum length of LAC
is 16 bits. Thus 65536 different LA can be defined in one GSM PLMN
7.4
LOCATION UPDATE TYPES
•
Normal location update
•
Periodic location update
•
IMSI attach
7.4.1
Normal Location Update
•
Mobile powers on and is idle.
•
Reads the LAI broadcast on the BCCH.
Compares with the last stored LAI
and if it is different does a location update
7.4.2
IMSI ATTACH
•
Saves the network from paging a MS which is not active
in the system.
•
When MS is turned off or SIM is removed the MS sends a
detach signal to the Network. It is marked as detached.
•
When the MS is powered again it reads the current LAI
and if it is same does a location update type IMSI attach.
•
Attach/detach flag is broadcast on the BCCH sys info.
7.4.3
PERIODIC LOCATION UPDATE
•
Many times the MS enters non-coverage zone.
•
The MS will keep on paging the MS thus wasting
precious resources.
•
To avoid this the MS has to inform the MSC about its
current LAI in a set period of time.
•
This time ranges from 0 to 255 decihours.
Periodic location timer value is
broadcast on BCCH sys info messages
WHAT
IS SIGNALLING ?
•
The term signaling is used in many contexts.
•
In technical systems, it very often refers to the
control of different procedures.
•
With reference to telephony, signaling means the
transfer of information and the instructions relevant to control and monitor
telephony connections.
8.1 GENERAL INTRODUCTION
•
Today’s global telecom networks are included in very
complex technical systems.
•
Naturally, a system of this type requires extensive
signaling, both internally in different nodes (for example, exchanges) and
externally between different types of network nodes.
•
During this training we will focus on external
signaling.
•
Thus, the term signaling in the following slides always refers to external signaling traffic.
•
The main purpose of using signaling in modern telecom
networks – where different network nodes must cooperate and communicate with
each other – is to enable transfer of control information between nodes in
connection with:
– Traffic
control procedures as set-up, supervision, and release of telecommunication connections and services
•
Database communication, for example, database queries
concerning specific services, roaming in cellular networks, etc.
•
Network management procedures, for example, blocking
or de-blocking trunks.
•
Traditionally, external signaling has been divided
into two basic types
– Access
signaling (for example, Subscriber Loop Signaling) This means signaling between
a subscriber terminal (telephone) and the local exchange.
– Trunk
signaling (that is, Inter-Exchange Signaling) This is used for signaling
between exchanges.
8.2 Access Signaling
·
There are many types of access signaling, for example,
PSTN analogue subscriber line signaling, ISDN Digital Subscriber Signaling
System (DSS1), and signaling between the MS and the network in the GSM system.
·
Signaling on the analogue subscriber line between a
telephony subscriber and the Local Exchange (LE) is performed by means of
on/off hook signals, dialed digits, information tones (dial tone, busy tone,
etc.), recorded announcements, and ringing signals.
·
The dialed digits can be sent in two different ways:
as decadic pulses (used for old-type rotary-dial telephones), or as a
combination of two tones (used for modern pushbutton telephones). The latter
system is known as the Dual Tone Multi Frequency (DTMF).
·
The information tones (dial tone, ringing tone, busy
tone, etc.) are audio signals used to keep the calling party (the A-subscriber)
informed about what is going on in the network during the set-up of a call.
·
Digital Subscriber Signaling System No. 1 (DSS1) is
the standard access signaling system used in ISDN. It is also called a D-channel
signaling system
·
D-channel signaling is defined for digital access
lines only.
·
The signaling protocols are based on the OSI (Open
System Interconnection) reference model, layers 1 to 3.
·
Consequently, the signaling messages are transferred
as data packets between the user terminal and the local exchange.
·
Due to the much
more complex service environment at the ISDN user’s site, the amount of
signaling information and the number of variations
8.3
Trunk Signaling
The Inter-exchange Signaling information is usually
transported on one of the time slots in a PCM link, either in association with
the speech channel or independently.
There are two commonly used methods for Inter Exchange
Signaling.
8.4
Channel Associated Signaling (CAS)
In CAS, the speech channel (in-band), or a channel closely
associated with a speech channel (out-band), is used for signaling.
8.5
Common Channel Signaling (CCS)
In this case a dedicated channel, completely separate from
the speech channel, is used for signaling. Due to the high capacity, one
signaling channel in CCS can serve a large number of speech channels.
In a GSM network, CCITT Signaling System No. 7 is used.
Signaling System No. 7 is a Common Channel Signaling system.
8.6
CHANNEL ASSOCIATED SIGNALING (CAS)
·
Channel Associated Signaling (CAS) means that the
signaling is always sent on the same connection (PCM link) as the traffic.
·
The signaling is associated with the traffic channel.
·
In a 2 Mb/s PCM link, 30 time slots are used for
speech, whereas TS 0 is used for synchronization and TS 16 is used for the line
signaling.
·
All 30 traffic connections share TS 16 in a multiframe
consisting of 16 consecutive frames.
·
On TS 16, each traffic channel has a permanently
allocated recurring location for line signaling, where two traffic channels
share TS 16 in one frame.
8.7
COMMON CHANNEL SIGNALING (CCS)
·
In CCS, signaling messages (or data packets) are
transmitted over time slots in a PCM link reserved for the purpose of
signaling.
·
The system is designed to use a common data channel
(or signaling link) as the carrier of all signals, required by a large number
of traffic channels.
·
In 1968, CCITT specified a Common Channel Signaling
system called CCS System No. 6, which was designed especially for international
analogue telephony networks.
·
However, very few installations of this system remain
today. It has, as already mentioned, been replaced by Signaling System No. 7.
·
The first version of SS7 (1980) was designed for telephony and data.
·
In the 80’s the demand for new services dramatically
increased and the SS7 was therefore developed to meet the signaling
requirements, specified for all these new services.
·
Today SS7 is used in many different networks and
related services typically betn PSTN,
ISDN, PLMN & IN
services throughout the world.
9 SYS INFORMATION MESSAGES
9.1 BROADCAST MESSAGES
•
System information is data about the network which the
MS needs to be able to communicate with the network in a appropriate manner.
•
System information messages are sent on the BCCH and
SACCH.
•
There are six different types of system information
messages.
•
System information messages 1 to 4 are broadcast on
the BCCH and are read by the MS in idle mode.
•
System information message 5 and 6 are sent on the
SACCH to the MS in dedicated mode.
•
System information messages 1 to 4 are broadcast on
the BCCH in a cyclic mode over 8 BCCH multiframes, i.e. 8 * 51 frames.
•
Every message is sent at least after every 1.8 sec.
What is sent is optional on BCCH
Multiframe 4 and 5
•
System information 5 and 6 are sent on the SACCH
immediately after HO or whenever nothing else is being sent.
•
Downlink SACCH is used for system information messages
while Uplink SACCH is used for measurement reports.
9.1.1
SYSTEM INFORMATION 1
When
frequency hopping is used in cell MS needs to know which frequency band to use
and what frequency within the band it should use in hopping algorithm.
Cell Channel Description
Cell
allocation number :- Informs the band number of the frequency channels used.
00 - Band 0
( Current GSM band )
Cell
allocation ARFCN :- ARFCN’s used for hopping. It is coded in a bitmap of 124
bits.
RACH Control
Parameters
Access
Control Class :- Bitmap with 16 bits. All MS spread out on class 0 - 9.
Priority groups use class 11-15. A bit set to 1 barres access for that class.
Bit 10 is used to tell the MS if emergency call is allowed or not.
0 - All MS can
make emergency call.
1 - MS with
class 11-15 only can make emergency calls.
Cell barred
for access :-
0 - Yes
1 - No
RACH
Control Parameters
Re-establishment
allowed :-
0 – Yes
1 - No
max_retransmissions
:- Number of times the MS attempts to access the Network [ 1,2,4 or 7 ].
tx_integer
:- Number of slots to spread access retransmissions when a MS attempts to
access the system.
Emergency
Call Allowed :- Yes / No
9.1.2
SYSTEM INFORMATION 2
•
Contains list of BCCH frequencies used in neighbor
cells.
•
MS uses this list to measures the signal strength of
the neighbors.
Neighbor
Cell Description
BA
Indicator :- Allows to differentiate measurement results related to different
list of BCCH frequencies sent to the MS.
BCCH
Allocation number :- Band 0 is used.
BCCH ARFCN
number :- Bitmap 1 -124
1
= Set
0
= Not set
PLMN
permitted
RACH
Control Parameters
9.1.3
SYSTEM INFORMATION 3
Cell Options
dtx
pwrc :- Power control on the
downlink.
0
= Not used
1
= Used
Radio link timeout :- Sets the
timer T100 in the MS.
Cell Selection Parameters
Rxlev_access_min :- Minimum
received signal level at the MS for which it is permitted to access the system.
0-63
= -110 dBm to -47dBm
mx_txpwr_cch :- Maximum power the
MS will use when accessing the system.
Cell_reselect_hysteresis :- Used
for cell reselection.
RACH Control Parameters
9.2
PAGING
•
Whenever the Network wants to contact the MS, it sends
messages on the paging channel.
•
Paging is sent on the PCH and it occupies 4 bursts.
•
MS has to monitor the paging channel to receive paging
messages.
•
MS does not monitor all paging channel but only
specific paging channels.
