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CHAPTER – 1                     INTRODUCTION1.1       ORGANISATIONAL HISTORY      •   Vodafone is a British mobile network...
1.3       About Mumbai Network      •   Mumbai is having one of the widest and busiest network in India.      •   It is di...
5
CHAPTER – 2         6
LITRATURE REVIEW2.0    BASIC OF GSMGSM: The Global System for Mobile communications (GSM) is a huge, rapidlyexpanding and ...
In this presentation we will understand the basic GSM network elements and some of theimportant features. Since this is a ...
(BSS) equipment may be coupled with an Ericsson Network Switching System.The principle component groups of a GSM network a...
Fig 1.0 :   GSM Network Components2.2    Mobile Station (MS)The MS consists of two parts, the Mobile Equipment (ME) and an...
Identity (IMSI).Mobile Equipment may be purchased from any store but the SIM must be obtained fromthe GSM network provider...
2.4     Subscriber Identity Module (SIM)The SIM as mentioned previously is a “smart card” which plugs into the ME and cont...
unauthorized use of the card. The SIM is capable of storing additional information suchas accumulated call charges. This i...
2.6    Base Station Controller (BSC)As previously mentioned, the BSC provides the control for the BSS. The functions ofthe...
2.7     Network Switching SystemThe Network Switching System includes the main switching functions of the GSMnetwork. It a...
The MSC/VLR is based on AXE technology. In Ericsson’s GSM system the AXE in SSis structured in a new way according to a co...
The HLR also stores and updates dynamic data about each “home” subscriber includingsubscriber location (VLR-address),servi...
2.8      Frequency Spectrum2.8.1   IntroductionThe frequency spectrum is very congested, with only narrow slots of bandwid...
that all the MS subscribers would want to make a call at the same time. Therefore,without knowing it, MSs share the same p...
transmitted between the BTS and the MS. The information is grouped into differentlogical channels. Each logical channel is...
Synchronization CHannel (SCH)The MS needs to synchronize to the time-structure within this particular cell, and alsoensure...
To switch a call to a mobile subscriber, the right identities need to be involved. It istherefore important to address the...
2.10.2         CELL GLOBAL IDENTITY (CGI)The CGI is used for cell identification within a location area. This is done by a...
Fig : 4.0 : BSIC2.11     Calls2.11.1   CALL FROM MSProvided that the MS is listening to the system information in the cell...
assigns it to the call and tells the BTS to activate the channel. The BTS sends anacknowledgment when the activation is co...
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CHAPTER – 3                   PROJECT WORKDuring the Six months training, I had participated in various small projects, th...
3.0      OPTIMIZATION3.0.1    IntroductionEvery alive Network needs to be under continuous control to maintain/improve the...
3.0.3    Optimization ProcessOptimization process can be explained by below step by step description:   •    Problem Analy...
Network Optimization Cycle…                               Nominal Cell Design                                             ...
•    Each operator has a certain set of decided KPIs (Key Performance Indicators)        based on which the operator gauge...
3.1.2.1       Path balance problems – If the path balance is below 100 or above 120, it          indicates that there coul...
3.2.1.3           BSC/Transcoder ProblemsAlthough the occurrence is rare, there are instances where some part of Transcode...
a) Actual site locations are away from the nominal planned locations.             b) It is not practicable to build a grid...
3.3 Analysis and troubleshooting        Things which normally subscribers normally experience(common problems) –   •     N...
•       In case of rural/suburban cells where the concern is a weak uplink – TMA could           be installed.3.3.3       ...
•   Interference – Co BCCH/Co BSIC issue.       •   Faulty hardware on target cell.       •   Improper neighbourlist defin...
•   Neighbour list problems   •   Sometimes handover problems occur due to improper neighbour list definition.   •   Neigh...
4.1    DRIVE TEST4.1.0 Before Starting   •   Preparing Action Plan   •   Defining drive test routes   •   Collecting RSSI ...
4.1.2 After the Test   •    Post processing of data   •    Plotting RX Level and Quality Information for overall picture o...
4.2      DRIVE TESTINGDrive testing is the most common and maybe the best way to analyze Networkperformance by means of co...
The drive testing is basically collecting measurement data with a TEMS phone, but themain concern is the analysis and eval...
Fig 6.0 : TEMS informationBy connecting an additional TEMS phone to a vacant serial port of the PC, data from twonetworks ...
4.4     ANALYSIS of LOG FILES4.4.1     Coverage ProblemsLow signal level is one of the biggest problems in a Network. The ...
signal, there might be a lot of coverage holes or places with insufficient signal level. Payattention to the significant o...
the locating procedure to make decisions about handover. There are different types ofhandovers:   •   Intra BSC handover: ...
advance to the MS on the FACCH. The old MSC is informed (via, the new BSC and thenew MSC) about the detection of HO bursts...
4.4.3.3          Ping–Pong HandoverIf measurement analysis shows an inconsistency in the parameter setting, hysteresis and...
5.0ANTENNA OPTIMIZATION & SITE SURVEY5.1           Site Survey      •       Taking our perfect network we generate a Site ...
•           O and M engineer      •           Responsibility – To check for space and power requirements  5.1.2           ...
•   Floor layout drawing showing the location of network elements, other equipment          and cable ladder routes at the...
5.4.1   Antenna Types                  Fig 9.0 : Types of Antenna                              53
5.4.2    Down tilting of antennasNetwork planners often have the problem that the base station antenna provides an overcov...
5.4.2.2      Electrical down tiltIn general, the dipoles of an antenna are fed with the same phase via the distributionsys...
4   The grounding kit ensures that the Antenna line is DC grounded as a protection    against lightning.5   The RF-feeder ...
5.5          Antenna Installation•     Check frequency range of used material•     Approved connector types have to be use...
3.   Install the antennas on the antenna support exactly vertical or with a specified     offset.4. Use the data specified...
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Report on gsm vodafone

  1. 1. 2
  2. 2. CHAPTER – 1 INTRODUCTION1.1 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
  3. 3. 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 – Ericsson1.5 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
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  5. 5. CHAPTER – 2 6
  6. 6. LITRATURE REVIEW2.0 BASIC OF GSMGSM: The Global System for Mobile communications (GSM) is a huge, rapidlyexpanding and successful technology. Less than five years ago, there were a few 10s ofcompanies working on GSM. Each of these companies had a few GSM experts whobrought knowledge back from the European Telecommunications Standards Institute(ETSI) committees designing the GSM specification. Now there are 100s of companiesworking on GSM and 1000s of GSM experts. GSM is no longer state-of-the-art. It iseveryday-technology, as likely to be understood by the service technician as the ETSIcommittee member.GSM evolved as a mobile communications standard when there were too many standardsfloating around in Europe. Analog cellular was in use for several years in different partsof world. Even today there are few networks of Analog cellular. The experience of analogcellular helped in developing specifications for a Digital Cellular standard. The work onGSM specs took a complete decade before practical systems were implemented usingthese specs.GSM is quickly moving out of Europe and is becoming a world standard. Agilent hasbecome expert in GSM through our involvement in Europe. With excellent internalcommunications, Agilent is in an excellent position to help our customers, in otherregions of the world, benefit from our GSM knowledge. 7
  7. 7. In this presentation we will understand the basic GSM network elements and some of theimportant features. Since this is a very complex system, we have to develop theknowledge in a step by step approach.2.0.1 ADVANTAGES OF GSMDue 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 OverviewThe diagram opposite shows a simplified GSM network. Each network component isIllustrated only once, however, many of the components will occur several timesthroughout a network.Each network component is designed to communicate over an interface specified by theGSM standards. This provides flexibility and enables a network provider to utilize systemcomponents from different manufacturers. For example Motorola Base Station System 8
  8. 8. (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 thenetwork 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 theMS to the land-based switching equipment.2.1.3 The Network Switching SystemThis consists of the Mobile services Switching Centre (MSC) and its associatedsystem-control databases and processors together with the required interfaces.This is the part which provides for interconnection between the GSM network andthe Public Switched Telephone Network (PSTN).2.1.4 The Operations and Maintenance SystemThis enables the network provider to configure and maintain the network from acentral location. 9
  9. 9. Fig 1.0 : GSM Network Components2.2 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 subscriberto access the network. The hardware has an identity number associated with it, which isunique for that particular device and permanently stored in it. This identity number iscalled the International Mobile Equipment Identity (IMEI) and enables the networkoperator 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 andalso provides other information regarding the service that subscriber should receive. Thesubscriber is identified by an identity number called the International Mobile Subscriber 10
  10. 10. Identity (IMSI).Mobile Equipment may be purchased from any store but the SIM must be obtained fromthe GSM network provider. Without the SIM inserted, the ME will only be able to makeemergency calls.By making a distinction between the subscriber identity and the MEidentity, 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. Thereare three main types of ME, these are listed below:2.3.1 Vehicle MountedThese devices are mounted in a vehicle and the antenna is physically mounted onthe outside of the vehicle.2.3.2 Portable Mobile UnitThis equipment can be handheld when in operation, but the antenna is notconnected to the handset of the unit.2.3.3 Hand portable UnitThis equipment comprises of a small telephone handset not much bigger than acalculator. The antenna is be connected to the handset. The ME is capable of operating ata certain maximum power output dependent on its type and use.These mobile types have distinct features which must be known by the network, forexample their maximum transmission power and the services they support. The ME istherefore identified by means of a classmark. The classmark is sent by the ME in itsinitial message. 11
  11. 11. 2.4 Subscriber Identity Module (SIM)The SIM as mentioned previously is a “smart card” which plugs into the ME and containsinformation 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 duringinitialization.2.4.2 Temporary Mobile Subscriber Identity (TMSI)This number identifies the subscriber, it is periodically changed by the systemmanagement to protect the subscriber from being identified by someone attempting tomonitor 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 countrycode, a network code and a subscriber number. Most of the data contained within theSIM 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 thesubscriber’s information and protection of networks against fraudulent access. SIMcards are designed to be difficult to duplicate. The SIM can be protected by use ofPersonal Identity Number (PIN) password, similar to bank/credit charge cards, to prevent 12
  12. 12. unauthorized use of the card. The SIM is capable of storing additional information suchas accumulated call charges. This information will be accessible to the customer viahandset/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 acombination of digital and RF equipment. The BSS provides the link between the MSand the MSC. The BSS communicates with the MS over the digital air interface and withthe MSC via 2 Mbit/s links.The BSS consists of three major hardware components:2.5.1 The Base Transceiver Station – BTSThe BTS contains the RF components that provide the air interface for a particularcell. This is the part of the GSM network which communicates with the MS. Theantenna is included as part of the BTS.2.5.2 The Base Station Controller – BSCThe BSC as its name implies provides the control for the BSS. The BSCcommunicates directly with the MSC. The BSC may control single or multipleBTSs.2.5.3 The Transcoder – XCDRThe Transcoder is used to compact the signals from the MS so that they aremore efficiently sent over the terrestrial interfaces. Although the transcoder isconsidered 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 transmittedover the air interface. Although the transcoder is part of the BSS, it is often foundphysically closer to the NSS to allow more efficient use of the terrestrial links. 13
  13. 13. 2.6 Base Station Controller (BSC)As previously mentioned, the BSC provides the control for the BSS. The functions ofthe BSC are shown in the table opposite.Any operational information required by the BTS will be received via the BSC. Likewiseany information required about the BTS (by the OMC for example) will be obtained bythe BSC. The BSC incorporates a digital switching matrix, which it uses to connect theradio channels on the air interface with the terrestrial circuits from the MSC. The BSCswitching matrix also allows the BSC to perform “handovers” between radio channels onBTSs, under its control, without involving the MSC.Table 1.0 : Features of Base Station Controller (BSC) & The Base TransceiverStation(BTS) 14
  14. 14. 2.7 Network Switching SystemThe Network Switching System includes the main switching functions of the GSMnetwork. It also contains the databases required for subscriber data and mobilitymanagement. Its main function is to manage communications between the GSMnetwork and other telecommunications networks.The components of the Network Switching System are listed below:2.7.1 Mobile Services Switching Centre – MSC2.7.2 Home Location Register – HLR2.7.3 Visitor Location Register – VLR2.7.4 Equipment Identity Register – EIR2.7.5 Authentication Centre – AUC2.7.6 Interworking Function – IWF2.7.7 Echo Canceller – ECIn addition to the more traditional elements of a cellular telephone system, GSM hasLocation Register network entities. These entities are the Home Location Register(HLR), Visitor Location Register (VLR), and the Equipment Identity Register (EIR). Thelocation registers are database-oriented processing nodes which address the problems ofmanaging subscriber data and keeping track of a MSs location as it roams around thenetwork.Functionally, the Interworking Function and the Echo Cancellers may be considered asparts of the MSC, since their activities are inextricably linked with those of the switch asit connects speech and data calls to and from the MSs.2.7.1 Mobile Services Switching CenterThe Mobile services Switching Center (MSC) performs the system telephony switchingfunctions. It also controls calls to and from other telephony and data systems, such as thePublic 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 aMSC/VLR. 15
  15. 15. The MSC/VLR is based on AXE technology. In Ericsson’s GSM system the AXE in SSis 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 orISUP). • 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 RegisterThe 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 containspermanent 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
  16. 16. The HLR also stores and updates dynamic data about each “home” subscriber includingsubscriber location (VLR-address),services registered to/activated by the subscriber orthe 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 asa separate node. The AXE technology is used.2.7.3 Visitor Location RegisterThe Visitor Location Register (VLR) is a database containing information about all MSsthat currently are located in the MSC service area. The VLR contains temporarysubscriber 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 anew MSC service area, the VLR connected to that MSC requests data about the MS fromthe HLR and stores it. When the MS makes a call, the VLR already has the informationneeded for call set-up. In Ericsson’s GSM system, the VLR is always integrated with theMSC so that internal signaling can be used. This setup eliminates signaling between thetwo nodes over the network unnecessary thus decreasing the network signaling load.2.7.4 Equipment Identity RegisterThe Equipment Identity Register (EIR) is a database that stores the International Mobilestation Equipment Identity (IMEI) for each MS equipment. Each IMEI is unique. Duringany 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 mainobjective is to ensure that the equipment is not stolen or faulty2.7.5 Authentication CenterThe AUthentication Center (AUC) is a database that stores thefollowing data: • a RANDom number (RAND) • a Signed RESponse (SRES) • a Ciphering Key (Kc) 17
  17. 17. 2.8 Frequency Spectrum2.8.1 IntroductionThe frequency spectrum is very congested, with only narrow slots of bandwidth allocatedfor cellular communications. The list opposite shows the number of frequencies andspectrum allocated for GSM, Extended GSM 900 (EGSM), GSM 1800 (DCS1800) andPCS1900. A single Absolute Radio Frequency Channel Number (ARFCN) or RF carrieris actually a pair of frequencies, one used in each direction (transmit and receive). Thisallows information to be passed in both directions. For GSM900 and EGSM900 thepaired frequencies are separated by 45 MHz, for DCS1800 the separation is 95 MHz andfor PCS1900 separation is 80 MHz. For each cell in a GSM network at least one ARFCNmust 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 eightsimultaneous telephone calls, but as we will see later in this course although this ispossible, network signalling and messaging may reduce the overall number from eighttimeslots 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 offixed wires, each MS only connects to the network over the radio interface whenrequired. Therefore, it is possible for a single RF carrier to support many more mobilestations than its eight TDMA timeslots would lead us to believe. Using statistics, it hasbeen 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
  18. 18. 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-useStandard GSM has a total of 124 frequencies available for use in a network. Mostnetwork providers are unlikely to be able to use all of these frequencies and are generallyallocated a small subset of the 124.Example:A network provider has been allocated 48 frequencies to provide coverage over a largearea, let us take for example Great Britain. As we have already seen, the maximum cellsize is approximately 70 km in diameter, thus our 48 frequencies would not be able tocover the whole of Britain. To overcome this limitation the network provider must re-usethe 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 MHzCarrier 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 bandUsing Time Division Multiple Access (TDMA) each of these carriers is divided intoeight Time Slots (TS). One TS on a TDMA frame is called a physical channel, i.e. oneach duplex pair of carriers there are eight physical channels. A variety of information is 19
  19. 19. transmitted between the BTS and the MS. The information is grouped into differentlogical channels. Each logical channel is used for a specific purpose such As paging, callset-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 inthis chapter does not include channels specific for GPRS (General Packet Radio Service).2.9 LOGICAL CHANNELSThe logical channels can be separated into two categories. They are traffic channels andsignaling channels.There are two forms of TCHs:• Bm or full rate TCH (TCH/F) - this channel carries information at a gross rate of 22.8kbit/s.• Lm or half rate TCH (TCH/H) - this channel carries information at a gross rate of 11.4kbit/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 thesecategories.2.9.1 BROADCAST CHANNELS (BCH)Frequency Correction CHannel (FCCH)On FCCH, bursts only containing zeroes are transmitted. This serves two purposes. Firstto make sure that this is the BCCH carrier, and second to allow the MS to synchronize tothe frequency. FCCH is transmitted downlink only. 20
  20. 20. Synchronization CHannel (SCH)The MS needs to synchronize to the time-structure within this particular cell, and alsoensure that the chosen BTS is a GSM base station. By listening to the SCH, the MSreceives information about the frame number in this cell and about BSIC of the chosenBTS. BSIC can only be decoded if the base station belongs to the GSM network. SCH istransmitted downlink only.Broadcast Control CHannel (BCCH)The MS must receive some general information concerning the cell in order to startroaming, waiting for calls to arrive or making calls. The needed information is broadcaston the Broadcast Control CHannel (BCCH) and includes the Location Area Identity(LAI), maximum output power allowed in the cell and the BCCH carriers for theneighboring cells on which the MS performs measurements. BCCH is transmitted on thedownlink only. Using FCCH, SCH, and BCCH the MS tunes to a BTS and synchronizedwith 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 andBCCH in the new cell.2.9.2 Half Rate channelsSo far, this chapter has described full rate TCH and SACCH/T that uses all of theallocated resources (all 26 timeslots in a multiframe). When half rate traffic channels areimplemented in the system, traffic capacity will double. Two users share the samephysical channel when channel combinations (ii) and (iii) are used. Using half ratechannels, the Idle frame from the full rate channel will be used for SACCH signaling forthe second MS. Since the MSs only use every other time slot for the call, themultiframe will contain 13 idle frames for each MS. Using channel combination (iii), onemobile can also be allocated two traffic channels, for example, one for speech and theother for data.2.10 GSM IDENTITIES 21
  21. 21. To switch a call to a mobile subscriber, the right identities need to be involved. It istherefore important to address them correctly. The numbers used to identify the identitiesin a GSM network are described in this chapter. Numbering plans are used to identifydifferent networks. For a telephone number in the PSTN/ISDN network, numbering planE.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 orassembly of equipment. The IMEI (see Figure) consists of the following:IMEI = TAC + FAC + SNR + spareTAC = 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 allequipment within each TAC and FAC.Spare = A spare bit for future use. When transmitted by the MSthis digit should always be zero. IMEI has the total length of 15 digits. Fig 2.0 : IMEI 22
  22. 22. 2.10.2 CELL GLOBAL IDENTITY (CGI)The CGI is used for cell identification within a location area. This is done by adding aCell 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 : CGI2.10.3 BASE STATION IDENTITY CODE (BSIC)BSIC allows a mobile station to distinguish between different neighboring base stations.BSIC (see Figure) consists of:BSIC = NCC + BCCNCC = Network Color Code (3 bits), identifies the PLMN. Note that it does not uniquelyidentify the operator. NCC is primarily used to distinguish between operators on eachside of a border.BCC = Base Station Color Code (3 bits), identifies the BaseStation to help distinguish between BTS using the same BCCHfrequencies. 23
  23. 23. Fig : 4.0 : BSIC2.11 Calls2.11.1 CALL FROM MSProvided that the MS is listening to the system information in the cell and that it isregistered in the MSC/VLR handling this cell, the MS can attempt to make a call. Theprocedures 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, isanalyzed 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 ofservice the MS wants and the number (called the B number) dialed by the mobilesubscriber. MSC checks that the MS does not have services like barring of outgoing callsactivated. Barring can be activated either by the subscriber or by the operator. If theMS 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 MSCsends a request to the BSC to assign a TCH. The BSC checks if there is an idle TCH, 24
  24. 24. assigns it to the call and tells the BTS to activate the channel. The BTS sends anacknowledgment when the activation is complete and then the BSC orders the MS totransfer to the TCH. The BSC informs the MSC when the assignment is complete. Thetraffic control subsystem analyses the digits and sets up the connection to the calledsubscriber. 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 onthe other side. The ringing tone generated in the exchange on the B subscriber side is sentto the MS via the group switch in MSC. The ringing tone is sent over the air, notgenerated in the MS.8. When the B subscriber answers, the network sends a connect message to the MSindicating that the call is accepted. The MS returns a connect acknowledgment, whichcompletes the call setup. Fig 5.0 : Mobile originating call establishment. 25
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  27. 27. CHAPTER – 3 PROJECT WORKDuring the Six months training, I had participated in various small projects, this help mea lot in gaining and enhancing my knowledge in the field of Telecommunication. Duringthis six months I have participated in many projects or targets, which I have completedsuccessfully. 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
  28. 28. 3.0 OPTIMIZATION3.0.1 IntroductionEvery alive Network needs to be under continuous control to maintain/improve theperformance. Optimization is basically the only way to keep track of the network bylooking deep into statistics and collecting/analyzing drive test data. It is keeping an eyeon its growth and modifying it for the future capacity enhancements. It also helpsoperation 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 ifyou 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 OptimizationThe optimization is to intend providing the best network quality using availablespectrum as efficiently as possible. The scope will consist all below;• Finding and correcting any existing problems after site implementation andintegration.• Meeting the network quality criteria agreed in the contract.• Optimization will be continuous and iterative process of improving overallnetwork 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
  29. 29. 3.0.3 Optimization ProcessOptimization process can be explained by below step by step description: • Problem AnalysisAnalyzing performance retrieve tool reports and statistics for the worst performing BSCsand/or Sites Viewing ARQ Reports for BSC/Site performance trends Examining Planningtool Coverage predictions. Analyzing previous drive test data. Discussions with localengineers to prioritize problems. Checking Customer Complaints reported to localengineers • Checks Prior to ActionCluster definitions by investigating BSC borders, main cities, freeways, major roadsInvestigating customer distribution, customer habits (voice/data usage) Running specifictraces on Network to categorize problems. Checking trouble ticket history for previousproblems. Checking any fault reports to limit possible hardware problems prior toTest.The process of Optimization is explained with a process a cycle known as NetworkOptimization Cycle 30
  30. 30. 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 789 Fig 6.0 : Network Optimization Cycle3.1.1 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
  31. 31. • 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
  32. 32. 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 dBgain is introduced in the uplink. In such case a deviation of –20 is acceptable, i.e, aPB 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
  33. 33. 3.2.1.3 BSC/Transcoder ProblemsAlthough the occurrence is rare, there are instances where some part of Transcoder ortimeslot on the PCM link goes faulty. In such cases, the timeslot mapping needs to beidentified and appropriate troubleshooting steps need to be taken. These problems canseldom 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
  34. 34. 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
  35. 35. 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
  36. 36. • 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
  37. 37. • 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 FailureHandover 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 definitionSteps 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
  38. 38. • 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
  39. 39. 4.1 DRIVE TEST4.1.0 Before Starting • Preparing Action Plan • Defining drive test routes • Collecting RSSI Log files • Scanning frequency spectrum for possible interference sources • Re–driving questionable data3.1.1 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
  40. 40. 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 changes4.1.3 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 adds3.1.4 Tracking • Re–driving areas after implementing recommendations • Create a tracking file to follow–up implementation of recommendations 41
  41. 41. 4.2 DRIVE TESTINGDrive testing is the most common and maybe the best way to analyze Networkperformance by means of coverage evaluation, system availability, network capacity,network retainibility and call quality. Although it gives idea only on downlink side of theprocess, it provides huge perspective to the service provider about what’s happening witha subscriber point of view.Fig 5.0 : TEMs gives great presentation options to the user like displayingmultiple windows of different indicators on the map. Theme properties will make youunderstand easier by showing the serving cell on the map. 42
  42. 42. The drive testing is basically collecting measurement data with a TEMS phone, but themain 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 theproblems, but also explaining them and providing useful recommendations to correctthem. Please note that a successful analysis should be supported by handling of networkstatistics from a statistics tool and careful evaluation of coverage predictions from acell planning tool (Planet, DB–Planner, TEMs Cell Planner, etc..). Please see Figure for ausual view from TEMS.4.2.1 TEMS InformationThe information provided by TEMS is displayed in status windows. This informationincludes cell identity, base station identity code, BCCH carrier ARFCN, mobile countrycode, 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 neighboringcells; channel number(s), timeslot number, channel type and TDMA offset; channelmode, sub channel number, hopping channel indication, mobile allocation index offsetand hopping sequence number of the dedicated channel; and RxLev, RxQual, FER, DTXdown link, TEMS Speech, Quality Index (SQI), timing advance (TA), TX Power, radiolink 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 servingcell and signal strength for two of the neighboring cells can also be displayed graphicallyin a window. 43
  43. 43. Fig 6.0 : TEMS informationBy connecting an additional TEMS phone to a vacant serial port of the PC, data from twonetworks can be monitored and logged at the same time. In this case, the data from thesecond mobile phone is serving cell and neighboring cell data and radio environmentparameters.TEMS Investigation also can perform frequency scanning of all significant carrierfrequencies. The information presented is ARFCN, RxLev and, if successfully decoded,BSIC. 44
  44. 44. 4.4 ANALYSIS of LOG FILES4.4.1 Coverage ProblemsLow signal level is one of the biggest problems in a Network. The coverage that anetwork operator can offer to customers mostly depends on efficiency of network designand investment plans. This problem usually pops up when building a new Network or asthe 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 networkperformance. Poor coverage problems are such problems that are really hard to solve,because it is impossible to increase coverage by optimizing network parameters. Anyhardware 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 ofterrain structures like hills or obstacles those stopping the line of sight to the broadcasting 45
  45. 45. signal, there might be a lot of coverage holes or places with insufficient signal level. Payattention to the significant oscillation on the C/I affected by the drop of signal level.4.4.2 Solutions to Low Level ProblemsPossible 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 siteadditions. A prediction tool with correct and detailed height and clutter data supportedwith a reasonable propagation model could be used to identify the best locations to putnew sites. If client is not eager to put new sites because of high costs to the budget orfinds it unnecessary because of low demand on traffic, then appropriate repeaters couldbe used to repeat signals and improve the coverage. Adding repeaters always needs extraattention because they can bring extra interference load to the network. The receivedlevel in the repeater should be above –80dBm (or desiredlimits) so that it can be amplified and transmitted again. The mobile should not receiveboth theoriginal and the repeated signals at the same area, cause signal from the repeater isalwaysdelayed and it will interfere with the original signal. A repeater should not amplifyfrequenciesoutside the wanted band.4.4.3 HandoverMobiles in communication with the network will continuously perform measurements onserving and neighboring cells. The measurement results are sent to the BSC and used in 46
  46. 46. the locating procedure to make decisions about handover. There are different types ofhandovers: • 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, tothe MSC.• The old MSC asks the new MSC for help.• The new MSC allocates a handover number (ordinary telephone number) in order toreroute 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 BTSto 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 withthe 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 MSwith information about which frequency and time slot to use in the new cell and whathandover reference to use in the HO access burst.• The MS tunes to the new frequency and sends HO access bursts on the FACCH. Whenthe new BTS detects the HO access burst it sends physical information containing timing 47
  47. 47. advance to the MS on the FACCH. The old MSC is informed (via, the new BSC and thenew MSC) about the detection of HO bursts. The new path through the group switch inthe old MSC is set–up.• A handover complete message is sent from the MS. The new BSC and MSC inform theold MSC. The old MSC informs the old BSC and the old TCH is released. Theoriginating MSC retains the main control of the call until it is cleared. This MSC is calledthe anchor MSC. Because the call entered a new LA the MS is required to perform alocation updating when the call is released. During the location updating, the HLR isupdated and sends a Cancel Location message to the old VLR telling it to delete all storedinformation about the subscriber.Handover decision is given following order of priority :– RXQUAL– RXLEV– DISTANCE4.4.3.1 Handover ProblemsAlways 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 alwaysbe risk of a handover loop if handover parameters between two neighbors are notcorrectly set.4.4.3.2 Late HandoverThere 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 marginsbetween the neighbors. If margins for level, quality or power budget handovers are notset 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 twoneighbors, you will notice that the small site will still keep the traffic although the levelof umbrella cell id too much higher. This is due to HO Level Umbrella RX Level whichis set to some definite level. 48
  48. 48. 4.4.3.3 Ping–Pong HandoverIf measurement analysis shows an inconsistency in the parameter setting, hysteresis andoffset parameters can be tuned to improve network quality. A hysteresis is used toprevent the ping–pong effect i.e., several consecutive handovers between two cells. Theping–pong effect can be caused by fading, the MS moving in a zigzag pattern betweenthe cells, or by non–linearities in the receiver.Incorrect handover margins will cause ping–pong handovers. You will have to adjustthese margins in such a way that handover will happen at the right time, not earlier orlate. Remember, lack of dominant server in an area or too many overlapping coveragecan also cause ping–pong effect.4.4.3.4 Unnecessary HandoverJust like ping–pong handover effect, incorrect margins can cause unnecessary handoversthat will directly affect network performance. The more number of handovers, higher therisk of facing quality problems or even drop calls. Unnecessary handovers or ping–ponghandovers will decrease the efficiency of data networks.4.4.3.5 Handover FailureReasons 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 failedbecause 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
  49. 49. 5.0ANTENNA OPTIMIZATION & SITE SURVEY5.1 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
  50. 50. • 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 locations5.2 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
  51. 51. • 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 installations5.4 AntennaThe antenna is a device which transforms guided electromagnetic signals intoelectromagnetic waves propagating in free space. It can be used for reception andtransmission. Fig 10.0 Relation between Antenna & MS 52
  52. 52. 5.4.1 Antenna Types Fig 9.0 : Types of Antenna 53
  53. 53. 5.4.2 Down tilting of antennasNetwork planners often have the problem that the base station antenna provides an overcoverage. If the overlapping area between two cells is too large, increased switchingbetween the base station (handover) occurs, which strains the system. There may even bedisturbances of a neighbouring cell with the same frequency. In general, the verticalpattern of an antenna radiates the main energy towards the horizon. Only that part of theenergy 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 horizonand increases the radiated power in the cell that is actually to be covered. 5.4.2.1 Mechanical Down TiltingThe simplest method of down tilting the vertical diagram of a directional antenna is amechanical tipping to achieve a certain angle while using an adjustable joint. But therequired 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 theangles of 0° and 90° the down tilt angle varies according to the azimuth direction. Thisresults in a horizontal half-power beam width, which gets bigger with increasing downtiltangles. The resulting gain reduction depends on the azimuth direction. This effect canrarely be taken into consideration in the network planning Fig 12 : Mechanical down tilt 54
  54. 54. 5.4.2.2 Electrical down tiltIn general, the dipoles of an antenna are fed with the same phase via the distributionsystem. By altering the phases, the main direction of the vertical radiation pattern can beadjusted. 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 eachdipole. The electrical down tilt has the advantage, that the adjusted down tilt angle isconstant over the whole azimuth range. The horizontal half-power beam width remainsunaltered (see Figure). However, the down tilt angle is fixed and cannot be changed. Fig 11 : Phase variations for a fixed down tilt5.4.3 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
  55. 55. 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
  56. 56. 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 BTS1. 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
  57. 57. 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
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