Engineering level college report on GSM done at Vodafone Essar Ltd.

2. 2

3. CHAPTER – 1
INTRODUCTION
1.1 ORGANISATIONAL HISTORY
• Vodafone is a British mobile network operator with its headquarters in Newbury,
Berkshire, England, UK. It is the largest mobile telecommunications network
company in the world by turnover and has a market value of about £75 billion
(August 2008). Vodafone currently has operations in 25 countries and partner
networks in a further 42 countries.
• The name Vodafone comes from Voice data fone, chosen by the company to
"reflect the provision of voice and data services over mobile phones."
• As of 2009 Vodafone had an estimated 303 million customers in 25 markets
across 5 continents. On this measure, it is the second largest mobile telecom
group in the world behind China Mobile.
• In the United States, Vodafone owns 45% of Verizon Wireless, the largest
wireless telecommunications network in the United States, based on number of
subscribers.
1.2 ABOUT THE ORGANIZATION
• Largest telecommunication company in terms of turnover.
• Second Largest company in terms of Subscribers which is around 260 million in
25 markets in 5 continents.
• On 21st September 2007 Hutch is rebranded to Vodafone in India
3

4. 1.3 About Mumbai Network
• Mumbai is having one of the widest and busiest network in India.
• It is divided into Five Zone according to geographical distinctiveness.
• The five zones are :
– Zone 1 (Lower Parel)
– Zone 2 (Santa Cruz)
– Zone 3 (Borivali)
– Zone 4 (Thane)
– Zone 5 (Vashi )
1.4 Sites Description
• The number of MSC’s – 13
• Total number of BSC’s – 73
• The total number of cell site – 2370
• The total number of cell’s – 5900
• Total Airtime (Million minutes) – 1253
• Total Subscribers – 28 Million
• Hardware used – Ericsson
1.5 Advantages of Ericsson (Hardware)
• Less number hardware to handle
• More traffic handling capacity
– More number of TRX’s
– High Erlang capacity
• Total ownership cost is low
• Compatible to forthcoming technologies
• IP supports for all Interface
4

5. 5

6. CHAPTER – 2
6

7. LITRATURE REVIEW
2.0 BASIC OF GSM
GSM: The Global System for Mobile communications (GSM) is a huge, rapidly
expanding and successful technology. Less than five years ago, there were a few 10's of
companies working on GSM. Each of these companies had a few GSM experts who
brought knowledge back from the European Telecommunications Standards Institute
(ETSI) committees designing the GSM specification. Now there are 100's of companies
working on GSM and 1000's of GSM experts. GSM is no longer state-of-the-art. It is
everyday-technology, as likely to be understood by the service technician as the ETSI
committee member.
GSM evolved as a mobile communications standard when there were too many standards
floating around in Europe. Analog cellular was in use for several years in different parts
of world. Even today there are few networks of Analog cellular. The experience of analog
cellular helped in developing specifications for a Digital Cellular standard. The work on
GSM specs took a complete decade before practical systems were implemented using
these specs.
GSM is quickly moving out of Europe and is becoming a world standard. Agilent has
become expert in GSM through our involvement in Europe. With excellent internal
communications, Agilent is in an excellent position to help our customers, in other
regions of the world, benefit from our GSM knowledge.
7

8. In this presentation we will understand the basic GSM network elements and some of the
important features. Since this is a very complex system, we have to develop the
knowledge in a step by step approach.
2.0.1 ADVANTAGES OF GSM
Due to the requirements set for the GSM system, many advantages will be achieved.
These advantages can be summarized as follows:
• GSM uses radio frequencies efficiently, and due to the digital radio path, the
system tolerates more intercell disturbances.
• The average quality of speech achieved is better than in analog cellular systems.
• Data transmission is supported throughout the GSM system.
• Speech is encrypted and subscriber information security is guaranteed.
• International roaming is technically possible within all countries using the GSM
system.
• The large market increases competition and lowers the prices both for investments
and usage.
2.1 GSM Network Overview
The diagram opposite shows a simplified GSM network. Each network component is
Illustrated only once, however, many of the components will occur several times
throughout a network.
Each network component is designed to communicate over an interface specified by the
GSM standards. This provides flexibility and enables a network provider to utilize system
components from different manufacturers. For example Motorola Base Station System
8

9. (BSS) equipment may be coupled with an Ericsson Network Switching System.
The principle component groups of a GSM network are:
2.1.1 The Mobile Station (MS)
This consists of the mobile telephone, fax machine etc. This is the part of the
network that the subscriber will see.
2.1.2 The Base Station System (BSS)
This is the part of the network which provides the radio interconnection from the
MS to the land-based switching equipment.
2.1.3 The Network Switching System
This consists of the Mobile services Switching Centre (MSC) and its associated
system-control databases and processors together with the required interfaces.
This is the part which provides for interconnection between the GSM network and
the Public Switched Telephone Network (PSTN).
2.1.4 The Operations and Maintenance System
This enables the network provider to configure and maintain the network from a
central location.
9

10. Fig 1.0 : GSM Network Components
2.2 Mobile Station (MS)
The MS consists of two parts, the Mobile Equipment (ME) and an electronic ‘smart card’
called a Subscriber Identity module (SIM).The ME is the hardware used by the subscriber
to access the network. The hardware has an identity number associated with it, which is
unique for that particular device and permanently stored in it. This identity number is
called the International Mobile Equipment Identity (IMEI) and enables the network
operator to identify mobile equipment which may be causing problems on the system.
The SIM is a card which plugs into the ME. This card identifies the MS subscriber and
also provides other information regarding the service that subscriber should receive. The
subscriber is identified by an identity number called the International Mobile Subscriber
10

11. Identity (IMSI).
Mobile Equipment may be purchased from any store but the SIM must be obtained from
the GSM network provider. Without the SIM inserted, the ME will only be able to make
emergency calls.By making a distinction between the subscriber identity and the ME
identity, GSM can route calls and perform billing based on the identity of the ‘subscriber’
rather than the equipment or its location.
2.3 Mobile Equipment (ME)
The ME is the only part of the GSM network which the subscriber will really see. There
are three main types of ME, these are listed below:
2.3.1 Vehicle Mounted
These devices are mounted in a vehicle and the antenna is physically mounted on
the outside of the vehicle.
2.3.2 Portable Mobile Unit
This equipment can be handheld when in operation, but the antenna is not
connected to the handset of the unit.
2.3.3 Hand portable Unit
This equipment comprises of a small telephone handset not much bigger than a
calculator. The antenna is be connected to the handset. The ME is capable of operating at
a certain maximum power output dependent on its type and use.
These mobile types have distinct features which must be known by the network, for
example their maximum transmission power and the services they support. The ME is
therefore identified by means of a classmark. The classmark is sent by the ME in its
initial message.
11

12. 2.4 Subscriber Identity Module (SIM)
The SIM as mentioned previously is a “smart card” which plugs into the ME and contains
information about the MS subscriber hence the name Subscriber Identity Module.
The SIM contains several pieces of information:
2.4.1 International Mobile Subscriber Identity (IMSI)
This number identifies the MS subscriber. It is only transmitted over the air during
initialization.
2.4.2 Temporary Mobile Subscriber Identity (TMSI)
This number identifies the subscriber, it is periodically changed by the system
management to protect the subscriber from being identified by someone attempting to
monitor the radio interface.
2.4.3 Location Area Identity (LAI)
Identifies the current location of the subscriber.
2.4.4 Subscriber Authentication Key (Ki)
This is used to authenticate the SIM card.
2.4.5 Mobile Station International Services Digital Network (MSISDN)
This is the telephone number of the mobile subscriber. It is comprised of a country
code, a network code and a subscriber number. Most of the data contained within the
SIM is protected against reading (Ki) or alterations (IMSI). Some of the parameters (LAI)
will be continuously updated to reflect the current location of the subscriber.
The SIM card, and the high degree of inbuilt system security, provide protection of the
subscriber’s information and protection of networks against fraudulent access. SIM
cards are designed to be difficult to duplicate. The SIM can be protected by use of
Personal Identity Number (PIN) password, similar to bank/credit charge cards, to prevent
12

13. unauthorized use of the card. The SIM is capable of storing additional information such
as accumulated call charges. This information will be accessible to the customer via
handset/keyboard key entry. The SIM also executes the Authentication Algorithm.
2.5 Base Station System (BSS)
The GSM Base Station System is the equipment located at a cell site. It comprises a
combination of digital and RF equipment. The BSS provides the link between the MS
and the MSC. The BSS communicates with the MS over the digital air interface and with
the MSC via 2 Mbit/s links.
The BSS consists of three major hardware components:
2.5.1 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.
2.5.2 The Base Station Controller – BSC
The BSC as its name implies provides the control for the BSS. The BSC
communicates directly with the MSC. The BSC may control single or multiple
BTSs.
2.5.3 The Transcoder – XCDR
The Transcoder is used to compact the signals from the MS so that they are
more efficiently sent over the terrestrial interfaces. Although the transcoder is
considered to be a part of the BSS, it is very often located closer to the MSC.
The transcoder is used to reduce the rate at which the traffic (voice/data) is transmitted
over the air interface. Although the transcoder is part of the BSS, it is often found
physically closer to the NSS to allow more efficient use of the terrestrial links.
13

14. 2.6 Base Station Controller (BSC)
As previously mentioned, the BSC provides the control for the BSS. The functions of
the BSC are shown in the table opposite.
Any operational information required by the BTS will be received via the BSC. Likewise
any information required about the BTS (by the OMC for example) will be obtained by
the BSC. The BSC incorporates a digital switching matrix, which it uses to connect the
radio channels on the air interface with the terrestrial circuits from the MSC. The BSC
switching matrix also allows the BSC to perform “handovers” between radio channels on
BTSs, under its control, without involving the MSC.
Table 1.0 : Features of Base Station Controller (BSC) & The Base Transceiver
Station(BTS)
14

15. 2.7 Network Switching System
The Network Switching System includes the main switching functions of the GSM
network. It also contains the databases required for subscriber data and mobility
management. Its main function is to manage communications between the GSM
network and other telecommunications networks.
The components of the Network Switching System are listed below:
2.7.1 Mobile Services Switching Centre – MSC
2.7.2 Home Location Register – HLR
2.7.3 Visitor Location Register – VLR
2.7.4 Equipment Identity Register – EIR
2.7.5 Authentication Centre – AUC
2.7.6 Interworking Function – IWF
2.7.7 Echo Canceller – EC
In addition to the more traditional elements of a cellular telephone system, GSM has
Location Register network entities. These entities are the Home Location Register
(HLR), Visitor Location Register (VLR), and the Equipment Identity Register (EIR). The
location registers are database-oriented processing nodes which address the problems of
managing subscriber data and keeping track of a MSs location as it roams around the
network.
Functionally, the Interworking Function and the Echo Cancellers may be considered as
parts of the MSC, since their activities are inextricably linked with those of the switch as
it connects speech and data calls to and from the MSs.
2.7.1 Mobile Services Switching Center
The Mobile services Switching Center (MSC) performs the system telephony switching
functions. It also controls calls to and from other telephony and data systems, such as the
Public Switched Telephone Network (PSTN) and Public Land Mobile Network (PLMN).
In Ericsson’s GSM system, the VLR is always integrated with the MSC to form a
MSC/VLR.
15

16. The MSC/VLR is based on AXE technology. In Ericsson’s GSM system the AXE in SS
is structured in a new way according to a concept called Application Modularity (AM).
The MSC/VLR is responsible for:
• Functions for setting up and controlling calls, including supplementary services.
• Functions for handling speech path continuity for moving subscribers (handover).
• Functions for updating mobile subscribers’ location (location updating and
location canceling) in the different location registers.
• Functions for updating mobile subscriber data.
• provision of functions for signaling to and from:
– The BSCs and the MSs (using BSSAP, see chapter 10).
– Other GSM entities (using MAP, TUP or ISUP).
– Other networks such as PSTN or ISDN (using TUP or
ISUP).
• Administrative functions for defining data and handling of the mobile
subscribers.
• Security related functions that perform authentication or selective authentication,
ciphering, (re)allocation and analysis of the TMSI.
• Functions for IMEI check.
• Functions for receiving and delivering short messages to and from the MS.
• Charging and accounting.
2.7.2 Home Location Register
The Home Location Register (HLR) is a database that stores and manages subscriptions.
In a PLMN there is one or several HLRs. For each “home” subscriber, the HLR contains
permanent subscriber data such as:
• The associated numbers - MSISDN and IMSI
• A list of services - teleservices, bearer services and supplementary services,
which the subscriber is authorizedto use.
16

17. The HLR also stores and updates dynamic data about each “home” subscriber including
subscriber location (VLR-address),services registered to/activated by the subscriber or
the operator such as call forwarded numbers and call barring for certain types of calls.
The HLR can be integrated in the same node as the MSC/VLR, or can be implemented as
a separate node. The AXE technology is used.
2.7.3 Visitor Location Register
The Visitor Location Register (VLR) is a database containing information about all MSs
that currently are located in the MSC service area. The VLR contains temporary
subscriber information needed by the MSC to provide service for visiting subscribers.
The VLR can be seen as a distributed HLR. When a Mobile Station (MS) roams into a
new MSC service area, the VLR connected to that MSC requests data about the MS from
the HLR and stores it. When the MS makes a call, the VLR already has the information
needed for call set-up. In Ericsson’s GSM system, the VLR is always integrated with the
MSC so that internal signaling can be used. This setup eliminates signaling between the
two nodes over the network unnecessary thus decreasing the network signaling load.
2.7.4 Equipment Identity Register
The Equipment Identity Register (EIR) is a database that stores the International Mobile
station Equipment Identity (IMEI) for each MS equipment. Each IMEI is unique. During
any MS access (except in the case of IMSI-detach), the MSC/VLR may verify the IMEI.
When necessary, the EIR is requested by the MSC/VLR to check the IMEI. The main
objective is to ensure that the equipment is not stolen or faulty
2.7.5 Authentication Center
The AUthentication Center (AUC) is a database that stores the
following data:
• a RANDom number (RAND)
• a Signed RESponse (SRES)
• a Ciphering Key (Kc)
17

18. 2.8 Frequency Spectrum
2.8.1 Introduction
The frequency spectrum is very congested, with only narrow slots of bandwidth allocated
for cellular communications. The list opposite shows the number of frequencies and
spectrum allocated for GSM, Extended GSM 900 (EGSM), GSM 1800 (DCS1800) and
PCS1900. A single Absolute Radio Frequency Channel Number (ARFCN) or RF carrier
is actually a pair of frequencies, one used in each direction (transmit and receive). This
allows information to be passed in both directions. For GSM900 and EGSM900 the
paired frequencies are separated by 45 MHz, for DCS1800 the separation is 95 MHz and
for PCS1900 separation is 80 MHz. For each cell in a GSM network at least one ARFCN
must be allocated, and more may be allocated to provide greater capacity.
The RF carrier in GSM can support up to eight Time Division Multiple Access (TDMA)
timeslots. That is, in theory, each RF carrier is capable of supporting up to eight
simultaneous telephone calls, but as we will see later in this course although this is
possible, network signalling and messaging may reduce the overall number from eight
timeslots per RF carrier to six or seven timeslots per RF carrier, therefore reducing the
.
number of mobiles that can be supported.
Unlike a PSTN network, where every telephone is linked to the land network by a pair of
fixed wires, each MS only connects to the network over the radio interface when
required. Therefore, it is possible for a single RF carrier to support many more mobile
stations than its eight TDMA timeslots would lead us to believe. Using statistics, it has
been found that a typical RF carrier can support up to 15, 20 or even 25 MSs. Obviously,
not all of these MS subscribers could make a call at the same time, but it is also unlikely
18

19. that all the MS subscribers would want to make a call at the same time. Therefore,
without knowing it, MSs share the same physical resources, but at different times.
2.8.2 Frequency Re-use
Standard GSM has a total of 124 frequencies available for use in a network. Most
network providers are unlikely to be able to use all of these frequencies and are generally
allocated a small subset of the 124.
Example:
A network provider has been allocated 48 frequencies to provide coverage over a large
area, let us take for example Great Britain. As we have already seen, the maximum cell
size is approximately 70 km in diameter, thus our 48 frequencies would not be able to
cover the whole of Britain. To overcome this limitation the network provider must re-use
the same frequencies over and over again, in what is termed a “frequency re-use pattern”.
2.8.3 RADIO FREQUENCY CARRIERS
Table 2-0 shows the frequency bands allocated to each system.
GSM 900 GSM 1800 GSM 1900
Uplink 890 - 915 MHz 1710 - 1785 MHz 1850 - 1910 MHz
Downlink 935 - 960 MHz 1805 - 1880 MHz 1930 - 1990 MHz
Carrier separation is 200 kHz, which provides:
• 124 pairs of carriers in the GSM 900 band
• 374 pairs of carriers in the GSM 1800 band
• 299 pairs of carriers in the GSM 1900 band
Using Time Division Multiple Access (TDMA) each of these carriers is divided into
eight Time Slots (TS). One TS on a TDMA frame is called a physical channel, i.e. on
each duplex pair of carriers there are eight physical channels. A variety of information is
19

20. transmitted between the BTS and the MS. The information is grouped into different
logical channels. Each logical channel is used for a specific purpose such As paging, call
set-up and speech. For example, speech is sent on the logical channel Traffic CHannel
(TCH). The logical channels are mapped onto the physical channels. The information in
this chapter does not include channels specific for GPRS (General Packet Radio Service).
2.9 LOGICAL CHANNELS
The logical channels can be separated into two categories. They are traffic channels and
signaling channels.
There are two forms of TCHs:
• Bm or full rate TCH (TCH/F) - this channel carries information at a gross rate of 22.8
kbit/s.
• Lm or half rate TCH (TCH/H) - this channel carries information at a gross rate of 11.4
kbit/s.
Signaling channels are subdivided into three categories:
• Broadcast CHannels (BCH)
• Common Control CHannels (CCCH)
• Dedicated Control CHannels (DCCH)
The following sections describe specific channels within these
categories.
2.9.1 BROADCAST CHANNELS (BCH)
Frequency Correction CHannel (FCCH)
On FCCH, bursts only containing zeroes are transmitted. This serves two purposes. First
to make sure that this is the BCCH carrier, and second to allow the MS to synchronize to
the frequency. FCCH is transmitted downlink only.
20

21. Synchronization CHannel (SCH)
The MS needs to synchronize to the time-structure within this particular cell, and also
ensure that the chosen BTS is a GSM base station. By listening to the SCH, the MS
receives information about the frame number in this cell and about BSIC of the chosen
BTS. BSIC can only be decoded if the base station belongs to the GSM network. SCH is
transmitted downlink only.
Broadcast Control CHannel (BCCH)
The MS must receive some general information concerning the cell in order to start
roaming, waiting for calls to arrive or making calls. The needed information is broadcast
on the Broadcast Control CHannel (BCCH) and includes the Location Area Identity
(LAI), maximum output power allowed in the cell and the BCCH carriers for the
neighboring cells on which the MS performs measurements. BCCH is transmitted on the
downlink only. Using FCCH, SCH, and BCCH the MS tunes to a BTS and synchronized
with the frame structure in that cell. The BTSs are not synchronized to each other.
Therefore, every time the MS camps on another cell, it must listen to FCCH, SCH and
BCCH in the new cell.
2.9.2 Half Rate channels
So far, this chapter has described full rate TCH and SACCH/T that uses all of the
allocated resources (all 26 timeslots in a multiframe). When half rate traffic channels are
implemented in the system, traffic capacity will double. Two users share the same
physical channel when channel combinations (ii) and (iii) are used. Using half rate
channels, the Idle frame from the full rate channel will be used for SACCH signaling for
the second MS. Since the MSs only use every other time slot for the call, the
multiframe will contain 13 idle frames for each MS. Using channel combination (iii), one
mobile can also be allocated two traffic channels, for example, one for speech and the
other for data.
2.10 GSM IDENTITIES
21

22. To switch a call to a mobile subscriber, the right identities need to be involved. It is
therefore important to address them correctly. The numbers used to identify the identities
in a GSM network are described in this chapter. Numbering plans are used to identify
different networks. For a telephone number in the PSTN/ISDN network, numbering plan
E.164 is used.
2.10.1 INTERNATIONAL MOBILE EQUIPMENT IDENTITY
(IMEI)
The IMEI is used for equipment identification and uniquely identifies a MS as a piece or
assembly of equipment. The IMEI (see Figure) consists of the following:
IMEI = TAC + FAC + SNR + spare
TAC = Type Approval Code, determined by a central GSM body.
FAC = Final Assembly Code, identifies the manufacturer.
SNR = Serial Number, an individual serial number of six digits uniquely identifies all
equipment within each TAC and FAC.
Spare = A spare bit for future use. When transmitted by the MS
this digit should always be zero. IMEI has the total length of 15 digits.
Fig 2.0 : IMEI
22

23. 2.10.2 CELL GLOBAL IDENTITY (CGI)
The CGI is used for cell identification within a location area. This is done by adding a
Cell Identity (CI) to the components of a LAI. CI has a length of 16 bits.
CGI (see Figure) consists of:
CGI = MCC + MNC + LAC + CI
Fig 3.0 : CGI
2.10.3 BASE STATION IDENTITY CODE (BSIC)
BSIC allows a mobile station to distinguish between different neighboring base stations.
BSIC (see Figure) consists of:
BSIC = NCC + BCC
NCC = Network Color Code (3 bits), identifies the PLMN. Note that it does not uniquely
identify the operator. NCC is primarily used to distinguish between operators on each
side of a border.
BCC = Base Station Color Code (3 bits), identifies the Base
Station to help distinguish between BTS using the same BCCH
frequencies.
23

24. Fig : 4.0 : BSIC
2.11 Calls
2.11.1 CALL FROM MS
Provided that the MS is listening to the system information in the cell and that it is
registered in the MSC/VLR handling this cell, the MS can attempt to make a call. The
procedures are shown in Figure.
1. a)The MS requests a dedicated channel using the RACH.
b)The MS gets information about the dedicated resource on the AGCH.
2. The MS indicates that it wants to set up a call. The identity of the MS, IMSI, is
analyzed and the MS is marked as busy in the VLR.
3. Authentication is performed as described for location updating.
4. Ciphering may be initiated.
5. The MSC receives a setup message from the MS. This information includes the kind of
service the MS wants and the number (called the B number) dialed by the mobile
subscriber. MSC checks that the MS does not have services like barring of outgoing calls
activated. Barring can be activated either by the subscriber or by the operator. If the
MS is not barred, the setup of the call proceeds.
6. Between the MSC and the BSC a link is established and a PCM TS is seized. The MSC
sends a request to the BSC to assign a TCH. The BSC checks if there is an idle TCH,
24

25. assigns it to the call and tells the BTS to activate the channel. The BTS sends an
acknowledgment when the activation is complete and then the BSC orders the MS to
transfer to the TCH. The BSC informs the MSC when the assignment is complete. The
traffic control subsystem analyses the digits and sets up the connection to the called
subscriber. The call is connected through in the group switch.
7. An alert message is sent to the MS indicating that a ringing tone has been generated on
the other side. The ringing tone generated in the exchange on the B subscriber side is sent
to the MS via the group switch in MSC. The ringing tone is sent over the air, not
generated in the MS.
8. When the B subscriber answers, the network sends a connect message to the MS
indicating that the call is accepted. The MS returns a connect acknowledgment, which
completes the call setup.
Fig 5.0 : Mobile originating call establishment.
25

26. 26

27. 27

28. CHAPTER – 3
PROJECT WORK
During the Six months training, I had participated in various small projects, this help me
a lot in gaining and enhancing my knowledge in the field of Telecommunication. During
this six months I have participated in many projects or targets, which I have completed
successfully. I worked at “Network Optimization” department under experts of the field.
The following are those key skills which I have learnt in these six months :
• BASIC OF GSM
• OPTIMIZATION
 Network KPIs and Quality
 Daily Analysis of Statistics and Performance Reports
 Alarm monitoring & solving
 Neighbour Deletion
 Co BCCH sites
• DRIVE TEST
 Frequency change
 Swap
 GPRS & Voice call check
 Software upgrade
 LAC change & BSC change
• ANTENNA OPTIMIZATION & SITE SURVEY
 Measurement of Angle of Sectors
 Calculation of VSWR
 Installing/Swapping Hardware
• VARIOUS REPORT ANALYSIS
 Daily Cell hourly & HOSR Report
 Daily POP UP Report & GPRS Report
28

29. 3.0 OPTIMIZATION
3.0.1 Introduction
Every alive Network needs to be under continuous control to maintain/improve the
performance. Optimization is basically the only way to keep track of the network by
looking deep into statistics and collecting/analyzing drive test data. It is keeping an eye
on its growth and modifying it for the future capacity enhancements. It also helps
operation and maintenance for troubleshooting purposes.
Successful Optimization requires:
• Recognition and understanding of common reasons for call failure
• Capture of RF and digital parameters of the call prior to drop
• Analysis of call flow, checking messages on both forward and reverse links to establish
“what happened”, where, and why. Optimization will be more effective and successful if
you are aware of what you are doing. The point is that you should know where to start,
what to do and how to do.
3.0.2 Purpose and Scope of Optimization
The optimization is to intend providing the best network quality using available
spectrum as efficiently as possible. The scope will consist all below;
• Finding and correcting any existing problems after site implementation and
integration.
• Meeting the network quality criteria agreed in the contract.
• Optimization will be continuous and iterative process of improving overall
network quality.
• Optimization can not reduce the performance of the rest of the network.
• Area of interest is divided in smaller areas called clusters to make optimization
and follow up processes easier to handle.
29

30. 3.0.3 Optimization Process
Optimization process can be explained by below step by step description:
• Problem Analysis
Analyzing performance retrieve tool reports and statistics for the worst performing BSCs
and/or Sites Viewing ARQ Reports for BSC/Site performance trends Examining Planning
tool Coverage predictions. Analyzing previous drive test data. Discussions with local
engineers to prioritize problems. Checking Customer Complaints reported to local
engineers
• Checks Prior to Action
Cluster definitions by investigating BSC borders, main cities, freeways, major roads
Investigating customer distribution, customer habits (voice/data usage) Running specific
traces on Network to categorize problems. Checking trouble ticket history for previous
problems. Checking any fault reports to limit possible hardware problems prior to
Test.
The process of Optimization is explained with a process a cycle known as Network
Optimization Cycle
30

31. Network Optimization Cycle…
Nominal Cell Design
Traffic Optimization
RF Planning
RF Fine tuning
Network Rollout
/Build Phase Optimization Stages
Database
Network Pre –
parameter optimization
Optimization
Physical/
Hardware
Optimization
Company Confidential
78
9
Fig 6.0 : Network Optimization Cycle
3.1.1 Importance of Optimization
• RF Optimization is a continuous and iterative process.
• Main Goal – To achieve performance levels to a certain set standard.
• Network subscribers expect wire line/near wire line quality.
• Network subscribers also expect 100 % availability at all given times.
• Network optimization is a process to try and meet the expectation of subscribers
in terms of coverage, QoS, network availability.
• Optimization also aims to maximize the utility of the available network resources.
31

32. • Each operator has a certain set of decided KPIs (Key Performance Indicators)
based on which the operator gauges the performance of his network.
• RF/Access Network KPIs can be broadly classified into three types
– Access related KPI
– Traffic/Resource Usage related KPI
– Handover related KPI
• Examples of access KPI
a) SDCCH Drop rate b) Call setup success rate
c) SDCCH Blocking, etc.
• Examples of Traffic KPI
a) TCH Drop Rate b) Call success rate
c) TCH Blocking, etc.
• Examples of handover performance KPI
a) Handover Success rate b) Handover failure rate.
c) Handover per cause, per neighbor, etc.
• Apart from the KPIs mentioned earlier the operator may have his own set of
custom KPIs which the operator feels is critical to gauge the performance of his
network.
• RF optimization process drives the effort to achieve and maintain the network
performance KPI.
• Optimization can be broadly divided into 3 categories, as follows –
– Hardware Optimization
– Physical Optimization
– Database/Parameter Optimization
• Generally the activities mentioned above are done in parallel. In some cases one
may precede the other.
3.1.2 Hardware Optimization - Typical Hardware Problems
32

33. 3.1.2.1 Path balance problems – If the path balance is below 100 or above 120, it
indicates that there could be a problem in either downlink or uplink. PB value
above 120 represents a weaker uplink and stronger downlink, whereas PB value
below 100 would represent a weaker downlink.
If MHA/TMA is used or receive diversity is applicable, an additional 3 dB
gain is
introduced in the uplink. In such case a deviation of –20 is acceptable, i.e, a
PB of
95 would be normal in such case.
Path Balance – If the PB statistic indicates problem in the downlink/uplink – the
RF path should be traced for possible hardware faults. Possible things that could
go wrong are –
a) High VSWR due to faulty feeder cable
b) Improper connectorisation
c) Faulty combiner
d) Faulty antenna – improper impedance matching between
antenna and feeder cable (rare case)
3.2.1.2 Processor problems –
• The present BTS equipment architecture is quite robust and with the evolution of
VLSI techniques, the different hardware modules have been compacted into
single units.
• The current TRXs/TRUs are having inbuilt processing abilities apart from also
containing the RF physical channels.
• However in places where older equipment are still in use, problems with
processor, could be encountered.
• These problems are easily identifiable by drive test and usually also show up
degradation on OMCR statistics. However in the current scenario these problems
have rare occurences.
33

34. 3.2.1.3 BSC/Transcoder Problems
Although the occurrence is rare, there are instances where some part of Transcoder or
timeslot on the PCM link goes faulty. In such cases, the timeslot mapping needs to be
identified and appropriate troubleshooting steps need to be taken. These problems can
seldom be identified by drive testing.
• Steps for Hardware Optimization
a) Check from OMCR statistics for indications of hardware faults
b) Check event logs from OMCR to find out if any alarms were generated
c) Conduct call test on the site/cell in question – check for assignment
failures, handover failures, from layer 3 messages.
d) Isolate the problem to the specific TRX. This can be done by ‘locking’ the
suspicious TRX.
e) Check for downlink receive level on each TRX. In some cases the
downlink receive level on a particular TRX may be very low, due to faulty
radio.
f) Request VSWR test to be performed if the problem appears to be related
to poor path balance.
g) Check for improper connectorization, improper antenna installation. One
loose connector could skew the performance of the entire cell!!!
f) If the problem is not isolated to a bad TRX/ other BTS hardware – further
investigations needed to check other possible faulty hardware in the BSC/
XCDR.
3.2 Physical Optimization
• A well designed RF is key to good network performance.
• More often than not, the actual network built is deviated from the network
designed from the desktop. The variations are
34

35. a) Actual site locations are away from the nominal planned locations.
b) It is not practicable to build a grid-based network due to several
constraints.
c) Antenna heights may differ from the planned antenna heights.
• Physical RF optimization may be done at several stages of network rollout.
• Physical RF Optimization is an essential requirement during the network build/pre
optimization stages. In most cases the OEM vendor is responsible for the network
during this phase and he carries out the process to ensure that the actual network
is as near good as the desktop designed one.
• The process comprises of conducting a drive test for the entire cluster, which may
comprise of one or several BSC areas.
• The drive test results are plotted on a GIS map and deficiencies in
coverage/interference problems are identified by plotting Rxlev/Rxqual values.
• Most of the coverage deficiencies are fixed by making changes to antenna heights
(rare), bore and tilts.
• At later stages parametric optimization is done to bring the network performance
close to desktop design.
• RF optimization is also carried out during network expansion phase, i.e when new
site or group of sites are added into the network.
• In many networks RF optimization is also done as a regular process to maintain
good network performance.
• RF optimization is helpful in resolving specific coverage problems or interference
problems, cell overreach, no dominant server issues, etc.
• Typical thumb rule to follow while carrying out physical RF optimization for
resolving coverage or interference issues -
• Step 1:- Try tilting the antennas.
• Step 2:- Try changing the orientation.
• Step 3:- Increase or reduce the height if tilt/reorientation does not solve the
problem
• Step 4:- Change the antenna type as a last resort.
35

36. 3.3 Analysis and troubleshooting
Things which normally subscribers normally experience(common problems) –
• No coverage/poor coverage issues.
• Dropped calls.
• Failed handovers/Dominant server issues.
• Breaks in speech/crackling sound or bad voice quality.
• Access related problems – “Network Busy”. Often all the above problems are
addressed to the RF optimization team for resolution.
3.3.1 Poor Coverage Issues
• Coverage problems are one of the most concerning issues.
• Subscribers experience a “No network” or “Network Search” scenarios on the
fringe area of the cells.
• Mostly these problems are experienced in suburban areas and also in many cases
in building coverage problems occur.
• Analysis is simple
• TEMS equipment/test phone displays Rxlev of serving cell and neighbour cells –
Generally problem occurs when Rxlev drops below –95 dBm. When the Rxlev
drops to –100 dBm or lower the subscriber experiences a “fluctuating single bar”
or a “network search” scenario.
• When Rxlev (DL) drops below –95 dBm its very difficult to have successful call
setup, as typically the uplink Rxlev would be much lower.
3.3.2 Poor Coverage Issues (Steps to solve the problem)
• Analyze the extent of area which is experiencing a coverage problem
• Can this be solved by physical optimization??
• Possible steps would be to improve the existing serving cell strength by proper
antenna orientation or up-tilting the antenna.
• If it is an indoor coverage/limited area coverage issue, this could be resolved by
deploying a repeater/micro cell if the traffic requirement in the question area is
high.
36

37. • In case of rural/suburban cells where the concern is a weak uplink – TMA could
be installed.
3.3.3 Dropped Calls
• Dropped calls may be attributed to several reasons.
• Usually categorized as –
– Drop during call setup – aka SDCCH Drop.
– Drop during call progress – aka TCH Drop.
– Drop due to failed handovers – with no recovery.
• Call drops may occur due to RF/non RF reasons.
• RF Reasons attributing to dropped calls
– Weak coverage – RL timer times out.
– Interference – low C/I – bad Rx Qual – RL timer times out.
– Faulty TRX – resulting in low C/I – call may drop during setup or after
TCH assignment – RL timer may/may not time out.
• Non RF Reasons
– Switch related – MS experiences a “Downlink Disconnect” – abnormal
release, usually with a Cause Value.
– CV 47 is a common example – Layer 3 message “DL Disconnect”.
– Non RF related call drops need to be escalated to isolate the fault which
could be related to the switch/transcoder or at any point in the Abis/A
Interface.
3.3.4 Handover Problems
• Handover failures may also be attributed to different reasons.
• Usually occur due to RF reasons.
Common RF reasons for handover failures
37

38. • Interference – Co BCCH/Co BSIC issue.
• Faulty hardware on target cell.
• Improper neighbourlist definition. Steps to identify and solve Handover issues.
• Use TEMS (layer 3 messages) to identify the cell to which the MS attempts
handover and results in a failure.
Steps to identify and solve Handover issues.
• The sequence of layer 3 messages –
• Handover Command
• Handover Access
• Handover Complete
• Handover Failure
• Sometimes the sequence of messages would be
• Handover Command
• Handover Access
• Handover Failure
Handover Failures/Problems
• Handover failures may also be attributed to different reasons.
• Usually occur due to RF reasons.Common RF reasons for handover failures
• Interference – Co BCCH/Co BSIC issue.
• Faulty hardware on target cell.
• Improper neighbor list definition
Steps to identify and solve Handover issues
• Use TEMS (layer 3 messages) to identify the cell to which the MS attempts
handover and results in a failure.
• The “Handover Command” message contains information about the BCCH and
BSIC of the target cell to which the handover was attempted. Check for any
possible Co BCCH/Co BSIC interferers.
• Check for possible hardware faults on the target cell.
38

39. • Neighbour list problems
• Sometimes handover problems occur due to improper neighbour list definition.
• Neighbour Rxlevel are reported to be strong, but “Handover Command” does not
get initiated.
• Call drags on the source cell and in some situation drops.
• Most common cause is improper definition of “neighbour BSIC/BCCH”
Neighbour list Problems
• Crosscheck with RF BSC dump to confirm the BCCH/BSIC and other parameters
of the target cell.
• Report any inconsistencies to the OMCR personnel.
39

40. 4.1 DRIVE TEST
4.1.0 Before Starting
• Preparing Action Plan
• Defining drive test routes
• Collecting RSSI Log files
• Scanning frequency spectrum for possible interference sources
• Re–driving questionable data
3.1.1 Subjects to Investigate
• Non–working sites/sectors or TRXs
• In–active Radio network features like frequency hopping
• Disabled GPRS
• Overshooting sites – coverage overlaps
• Coverage holes
• C/I, C/A analysis
• High Interference Spots
• Drop Calls
• Capacity Problems
• Other Interference Sources
• Missing Neighbors
• One–way neighbors
• Ping–Pong Handovers
• Not happening handovers
• Accessibility and Retainability of the Network
• Equipment Performance
• Faulty Installations
40

41. 4.1.2 After the Test
• Post processing of data
• Plotting RX Level and Quality Information for overall picture of the driven area
• Initial Discussions on drive test with Local engineers
• Reporting urgent problems for immediate action
• Analyzing Network feature performance after new implementations
• Transferring comments on parameter implementations after new changes
4.1.3 Recommendations
• Defining missing neighbor relations
• Proposing new sites or sector additions with Before & After coverage plots
• Proposing antenna azimuth changes
• Proposing antenna tilt changes
• Proposing antenna type changes
• BTS Equipment/Filter change
• Re–tuning of interfered frequencies
• BSIC changes
• Adjusting Handover margins (Power Budget, Level, Quality, Umbrella HOs)
• Adjusting accessibility parameters (RX Lev Acc Min, etc..)
• Changing power parameters
• Attenuation Adds/Removals
• MHA/TMA adds
3.1.4 Tracking
• Re–driving areas after implementing recommendations
• Create a tracking file to follow–up implementation of recommendations
41

42. 4.2 DRIVE TESTING
Drive testing is the most common and maybe the best way to analyze Network
performance by means of coverage evaluation, system availability, network capacity,
network retainibility and call quality. Although it gives idea only on downlink side of the
process, it provides huge perspective to the service provider about what’s happening with
a subscriber point of view.
Fig 5.0 : TEMs gives great presentation options to the user like displaying
multiple windows of different indicators on the map. Theme properties will make you
understand easier by showing the serving cell on the map.
42

43. The drive testing is basically collecting measurement data with a TEMS phone, but the
main concern is the analysis and evaluation part that is done after completition of the test.
Remember that you are always asked to perform a drive test for not only showing the
problems, but also explaining them and providing useful recommendations to correct
them. Please note that a successful analysis should be supported by handling of network
statistics from a statistics tool and careful evaluation of coverage predictions from a
cell planning tool (Planet, DB–Planner, TEMs Cell Planner, etc..). Please see Figure for a
usual view from TEMS.
4.2.1 TEMS Information
The information provided by TEMS is displayed in status windows. This information
includes cell identity, base station identity code, BCCH carrier ARFCN, mobile country
code, mobile network code and the location area code of the serving cell.
There is also information about RxLev, BSIC and ARFCN for up to six neighboring
cells; channel number(s), timeslot number, channel type and TDMA offset; channel
mode, sub channel number, hopping channel indication, mobile allocation index offset
and hopping sequence number of the dedicated channel; and RxLev, RxQual, FER, DTX
down link, TEMS Speech, Quality Index (SQI), timing advance (TA), TX Power, radio
link timeout counter and C/A parameters for the radio environment.
The signal strength, RxQual, C/A, TA, TX Power, TEMS SQI and FER of the serving
cell and signal strength for two of the neighboring cells can also be displayed graphically
in a window.
43

44. Fig 6.0 : TEMS information
By connecting an additional TEMS phone to a vacant serial port of the PC, data from two
networks can be monitored and logged at the same time. In this case, the data from the
second mobile phone is serving cell and neighboring cell data and radio environment
parameters.
TEMS Investigation also can perform frequency scanning of all significant carrier
frequencies. The information presented is ARFCN, RxLev and, if successfully decoded,
BSIC.
44

45. 4.4 ANALYSIS of LOG FILES
4.4.1 Coverage Problems
Low signal level is one of the biggest problems in a Network. The coverage that a
network operator can offer to customers mostly depends on efficiency of network design
and investment plans. This problem usually pops up when building a new Network or as
the number of subscribers increases by the time resulting in new coverage demands.
Low signal level can result in unwanted situations that could directly lower the network
performance. Poor coverage problems are such problems that are really hard to solve,
because it is impossible to increase coverage by optimizing network parameters. Any
hardware configuration changes might improve the coverage a little.
Let’s have a look at some different cases to poor coverage related problems.
Fig 7.0 : In areas where there are few sites and too many different types of
terrain structures like hills or obstacles those stopping the line of sight to the broadcasting
45

46. signal, there might be a lot of coverage holes or places with insufficient signal level. Pay
attention to the significant oscillation on the C/I affected by the drop of signal level.
4.4.2 Solutions to Low Level Problems
Possible solution ways can be listed as below:
–New Site Proposal
–Sector Addition
–Repeater
–Site Configuration Change (Antenna Type, height, azimuth, tilt changes)
–Loss or Attenuation Check ( Feeders, Connectors, Jumpers, etc..)
The best thing to do in case of low signal strength could be recommending new site
additions. A prediction tool with correct and detailed height and clutter data supported
with a reasonable propagation model could be used to identify the best locations to put
new sites. If client is not eager to put new sites because of high costs to the budget or
finds it unnecessary because of low demand on traffic, then appropriate repeaters could
be used to repeat signals and improve the coverage. Adding repeaters always needs extra
attention because they can bring extra interference load to the network. The received
level in the repeater should be above –80dBm (or desired
limits) so that it can be amplified and transmitted again. The mobile should not receive
both the
original and the repeated signals at the same area, cause signal from the repeater is
always
delayed and it will interfere with the original signal. A repeater should not amplify
frequencies
outside the wanted band.
4.4.3 Handover
Mobiles in communication with the network will continuously perform measurements on
serving and neighboring cells. The measurement results are sent to the BSC and used in
46

47. the locating procedure to make decisions about handover. There are different types of
handovers:
• Intra BSC handover: The new and old cells both belong to the same BSC. The
BSC can handle the handover on its own.
• Inter BSC handover: The new and old cells belong to different BSC but the same
MSC/VLR. In this case the MSC/VLR must help the BSC to carry out the
handover.
• Inter MSC handover: The new and old cells belong to different MSC/VLR. The
serving MSC/VLR must get help from the new MSC/VLR to carry out the
handover.
• Intra cell handover: No change of cell but of connection within the cell.
During a call, the serving BSC decides that a handover is necessary. The
handover procedure happens in this way:
• The serving BSC sends Handover Required, including the identity of the target cell, to
the MSC.
• The old MSC asks the new MSC for help.
• The new MSC allocates a handover number (ordinary telephone number) in order to
reroute the call. A handover request is sent to the new BSC.
• The new BSC, in cases where there is an idle TCH in the target cell, tells the new BTS
to activate a TCH.
• The new MSC receives the information about the new TCH and handover reference.
• The TCH description and handover reference is passed on to the old MSC together with
the handover number.
• A link is set up from the old MSC to the new MSC.
• A Handover Command message is sent on a signaling channel (FACCH) to the MS
with information about which frequency and time slot to use in the new cell and what
handover reference to use in the HO access burst.
• The MS tunes to the new frequency and sends HO access bursts on the FACCH. When
the new BTS detects the HO access burst it sends physical information containing timing
47

48. advance to the MS on the FACCH. The old MSC is informed (via, the new BSC and the
new MSC) about the detection of HO bursts. The new path through the group switch in
the old MSC is set–up.
• A handover complete message is sent from the MS. The new BSC and MSC inform the
old MSC. The old MSC informs the old BSC and the old TCH is released. The
originating MSC retains the main control of the call until it is cleared. This MSC is called
the anchor MSC. Because the call entered a new LA the MS is required to perform a
location updating when the call is released. During the location updating, the HLR is
updated and sends a Cancel Location message to the old VLR telling it to delete all stored
information about the subscriber.
Handover decision is given following order of priority :
– RXQUAL
– RXLEV
– DISTANCE
4.4.3.1 Handover Problems
Always keep in mind that all power related parameters need to be correctly set.
Otherwise the handover (HO) attempts will be done in a wrong place. There will always
be risk of a handover loop if handover parameters between two neighbors are not
correctly set.
4.4.3.2 Late Handover
There will be such cases that you will notice handover process taking place a little late.
There could be couple of reasons to that. First thing to check will be handover margins
between the neighbors. If margins for level, quality or power budget handovers are not
set correctly, handover will not take place at the right time. If margins are too much,
handover will happen late, vice versa. If umbrella handover is enabled between two
neighbors, you will notice that the small site will still keep the traffic although the level
of umbrella cell id too much higher. This is due to HO Level Umbrella RX Level which
is set to some definite level.
48

49. 4.4.3.3 Ping–Pong Handover
If measurement analysis shows an inconsistency in the parameter setting, hysteresis and
offset parameters can be tuned to improve network quality. A hysteresis is used to
prevent the ping–pong effect i.e., several consecutive handovers between two cells. The
ping–pong effect can be caused by fading, the MS moving in a zigzag pattern between
the cells, or by non–linearities in the receiver.
Incorrect handover margins will cause ping–pong handovers. You will have to adjust
these margins in such a way that handover will happen at the right time, not earlier or
late. Remember, lack of dominant server in an area or too many overlapping coverage
can also cause ping–pong effect.
4.4.3.4 Unnecessary Handover
Just like ping–pong handover effect, incorrect margins can cause unnecessary handovers
that will directly affect network performance. The more number of handovers, higher the
risk of facing quality problems or even drop calls. Unnecessary handovers or ping–pong
handovers will decrease the efficiency of data networks.
4.4.3.5 Handover Failure
Reasons for handover failure could be unavailable time slots because of high traffic,
congestion, low signal strength or bad quality on target cell. Handover can be failed
because of hardware problems in target cells –more likely TRX or time slot problems.
If handover attempt fails, MS tries to return to old channel. If it can not, call drops.
Handover attempt is repeated after a penalty time.
49

50. 5.0ANTENNA OPTIMIZATION & SITE SURVEY
5.1 Site Survey
• Taking our perfect network we generate a Site Survey Request for each nominal
• This is a request to the site survey engineer to go out and find candidates based on
specifications
• These specifications are:
– Location
– Height
– Area of interest
• It is a function in Network Planning for the identification of the best candidates
for a new site.
• To get all relevant information of the site
• In some cases, the Acquisition team also takes part in the site survey and helps in
getting civil and legal clarifications from site owners.
5.1.1 Site Survey Team
• The Site survey team should generally consists of;
• RF Site Survey Engineer :
– Responsibility :To decide on best location for the site,
– To decide the best location, height , type and orientation of Antenna
• Transmission Survey Engineer
• Responsibility – To check LOS with neighbouring sites and to decide on
connectivity
• Site Acquisition Representative
• Responsibility – To check for site survey permission and legal/civil
information.
50

51. • O and M engineer
• Responsibility – To check for space and power requirements
5.1.2 Tools used for Site Survey
• GPS
• Digital Camera
• Magnetic Compass
• Measuring Tape
• RF/Transmission Site Survey Form
• Accessories
5.1.3 Site candidate reports
• The site survey engineer will return a candidate report for each nominal
• Each candidate will have:
– A location in co-ordinates
– An address
– Building height
– Site photos
– Panoramic photos taken from the roof
– Any structural information
– Potential BTS locations
5.2 Installation Planning :
• Installation planning is based on the equipment requirements, observations and
agreed decisions during the site survey. Installation planning is used to achieve an
efficient usage of installation materials, and for fast and flexible installation for
every network element and site in the project. The task is to define drawings for
the construction works and installation purposes.
• Site specific documentation generated in installation planning include:
• Installation material list
51

52. • Floor layout drawing showing the location of network elements, other equipment
and cable ladder routes at the site
• Grounding, power, transmission and external cables related drawings
• Outdoor layout drawing for feeder, antenna and micro wave radio installations
5.4 Antenna
The antenna is a device which transforms guided electromagnetic signals into
electromagnetic waves propagating in free space. It can be used for reception and
transmission.
Fig 10.0 Relation between Antenna & MS
52

53. 5.4.1 Antenna Types
Fig 9.0 : Types of Antenna
53

54. 5.4.2 Down tilting of antennas
Network planners often have the problem that the base station antenna provides an over
coverage. If the overlapping area between two cells is too large, increased switching
between the base station (handover) occurs, which strains the system. There may even be
disturbances of a neighbouring cell with the same frequency. In general, the vertical
pattern of an antenna radiates the main energy towards the horizon. Only that part of the
energy which is radiated below the horizon can be used for the coverage of the sector.
Down tilting the antenna limits the range by reducing the field strength in the horizon
and increases the radiated power in the cell that is actually to be covered.
5.4.2.1 Mechanical Down Tilting
The simplest method of down tilting the vertical diagram of a directional antenna is a
mechanical tipping to achieve a certain angle while using an adjustable joint. But the
required down tilt is only valid for the main direction of the horizontal radiation pattern.
In the tilt axis direction (+/-90° from main beam) there is no down tilt at all. Between the
angles of 0° and 90° the down tilt angle varies according to the azimuth direction. This
results in a horizontal half-power beam width, which gets bigger with increasing downtilt
angles. The resulting gain reduction depends on the azimuth direction. This effect can
rarely be taken into consideration in the network planning
Fig 12 : Mechanical down tilt
54

55. 5.4.2.2 Electrical down tilt
In general, the dipoles of an antenna are fed with the same phase via the distribution
system. By altering the phases, the main direction of the vertical radiation pattern can be
adjusted. Figure shows dipoles that are fed from top to bottom with a rising phase of 70°.
The different phases are achieved by using feeder cables of different lengths for each
dipole. The electrical down tilt has the advantage, that the adjusted down tilt angle is
constant over the whole azimuth range. The horizontal half-power beam width remains
unaltered (see Figure). However, the down tilt angle is fixed and cannot be changed.
Fig 11 : Phase variations for a fixed down tilt
5.4.3 Item Description
1 The antennas can be either vertically polarised or cross polarised and directional
or omni-directional antenna.
2 The jumper cable is a flexible low loss cable (1/2"), which is used at the ends of
the feeder. It protects the connectors from the forces caused by the feeder cable.
3 7/16 connector are made of silver plated brass or a special grade of copper. All
connectors are IP68-classified.
55

56. 4 The grounding kit ensures that the Antenna line is DC grounded as a protection
against lightning.
5 The RF-feeder is corrugated coaxial cable. It can be of different sizes, i.e. 1/2”,
7/8” and 1 5/8”, depending on the length of the mast and the desired attenuation.
6 Cable clamps are made of stainless steel and plastic and they are easy and quick
to install. Design of the clamps prevents over tightening of a feeder cable.
7 A compact EMP protector protects the BTS against lightning and over voltage
that may occur down the antenna line.
Fig 12 Item description of Antenna
56

57. 5.5 Antenna Installation
• Check frequency range of used material
• Approved connector types have to be used
• Used connectors have to be suitable for used cable type
• All cables have to be labeled on both end of the cable
• Proper tools have to be used during antenna line installation
All cables have to be fixed properly
ANTENNA INSTALLATION SOLUTION
Antenna Type : Dual-band GSM1800 and 3G
1 SECTOR (X+0+0) 2 SECTOR (X+X+0) 3 SECTOR (X+X+X)
X= TRANSMISSION UNIT X= TRANSMISSION UNIT X= TRANSMISSION UNIT
28
Company Confidential
Fig 15 : Antenna connection with BTS
1. Verify that antenna support are installed and in right location.
2. Hoist the antenna up to the antenna support.
Note: when hoisting antenna in foul weather conditions, it is necessary to control
antenna movement to avoid damage. Use ropes etc.
57

58. 3. Install the antennas on the antenna support exactly vertical or with a specified
offset.
4. Use the data specified in the site installation documentation to set the antenna
heading, height, vertical and horizontal separation.
5. Connect one end of the antenna jumpers to the antennas, leaving the opposite ends
open
Note: the open ends should be protected from moisture.
6. Clamp the jumpers to the antenna support.
5.6 VSWR (Voltage Standing Wave Ratio):
“Voltage Standing Wave Ratio (VSWR) is another parameter used to describe an
antenna performance. It deals with the impedance match of the antenna feed point to
the feed or transmission line. The antenna input impedance establishes a load on the
transmission line as well as on the radio link transmitter and receiver. To have RF
energy produced by the transmitter radiated with minimum loss or the energy picked
up by the antenna passed to the receiver with minimum loss,the input or base
impedance of the antenna must be matched to the characteristics of the transmission
line.”
VSWR = Vmax/Vmin
58

59. 59

60. 60

61. 61