Network optimisation is necessary for the betterment of public presentation and for best use of resources.It is a manner in which web can be modify on the footing of roll uping informations, normally done by Drive Test.Network optimisation can be analyse by different stairss like 1 roll uping basic data,2 thrust trial,3 OMCR data statistical Reports.1 Collecting Basic Data, Basic information from web be aftering like tower tallness, antenna tallness and type, AZ, BSC and location country codification ( Lac ) , antenna joust, frequence band.2 Drive Test This trial is done to look into whether the demand of site is fulfilled or non. It is a method of finding about web public presentation by agencies of handiness, capacity, and congestion rate. If the consequences of this trial do non fit with demand than some alterations are suggested in order to acquire desire end. 3 OMCR informations statistical Reports It includes the traffic studies about call bead, call failure, handover failure and so on.
RF OPTIMIZATION OF GSM
Procedure of GSM web optimisation is as shown in figure
Optimization of BTS in good manner is truly a challenge.if the optimisation is successfully done than we will be achieve best quality of services
2. Optimization equipment
All the parametric quantities are analyse on particular type of package installed in laptop
2.2 TEMS Software
TEMS package by Ericsson, package which is used for optimisation, this is installed in laptop and all RF parametric quantities can be analyse. The package is besides connected with TEMS Mobile
2.3 Global Positing System ( GPS )
GPS is connected with laptop.its basic map is to turn up place of drive trial way.
It is used to look into the joust of aerial on the tower
3 Drive Test Procedure
3.1 Basic Information about Network
Before gazing optimisation, we need to acquire basic information to do optimisation program.Different information like frequence planning, technology parametric quantities.These information are helpful in optimisation procedure. After obtaining complete information of site, RF engineer range on site by utilizing MapInfo package ( package used to see the location of site with latitude and longitude of site. In first measure, DT applied scientist look into the aerial tallness, AZ and joust in order to corroborate that all these equipment installing is harmonizing to planning. After linking equipment, engineer start recording of log files and set up call from TEMS Mobile to look into intra site handovers, both clock wise and anticlockwise. In TRX ( Transceiver ) trial, he makes 10 calls for 15 unsweet continuance from each TRX to look into the TRX public presentation. Now engineer do long log files to look into INTER site handover between neighboring BTS in idle and dedicated manner, besides analyse a Numberss of parametric quantities like RX degree, RX signal quality, Co channel interface, next channel interface, coverage of BTs in each sector. GPRS services are besides checked from each sector from different location. If RX signal degree is drop due to obstacle like mountain, edifice, wood, RF applied scientist must enter the latitude and longitude and demo the ground of weak signal at peculiar topographic point. The Drive Test procedure from TEMS can be shown in figure
3.1 TEMS Software Information
It provides different information in separate Windowss like cell individuality, base station individuality codification, ARFCN for up to seven neighbors, Mobile state codification ( MCC ) , Mobile web, codification ( MNC ) , .code ( LAC ) . This information are displayed in inactive Windowss, information about RX degree, Quality, C/I, handover are displayed in graphical window.Layer 2 and layer 3 messages can besides be displayed in different Windowss.
3.2 Cardinal Factors of Network Performance
To look into handiness, RF engineer do short call.The handiness is measured in following manner
Accessibility=SDCCH-serviceability*TCH service ability
3.2.2 Retain ability
For look intoing retain-ability, long calls are set up during drive trial. Retain-ability is required 100 per cent. The expression for retain-ability is
Retain-ability=1-TCH call bead rate
TCH call bead rate= ( figure of bead call ) / ( entire figure of TCH effort )
Numbers of bead call consists of all beads due to Abis mistake, A interface losingss or BTS failure
3.2.3 Idle Mode Behaviour
When no dedicated channel is assigned to mobile, the Mobile is said to be in idle manner. In idle manner Mobile is able to entree web at any clip. The idle manner behavior of Mobile is controlled by base station. Parameters which are necessary to command idle manners are transmitted on BCCH bearer. The Mobile is able to entree the system after power on.it is besides able to update its location so that the web will be able to send on a call to specific user Mobile. Idle mode behavior of Mobile in TEMS is shown in diagram.
In idle manner, Mobile is sent message to web about its alteration in place and visitant location registry update new location of Mobile.
3.2.4 Location Update
The MS continuously analyse the system information received from the web and compare it with location country individuality ( LAI ) which is shop in nomadic station. If LAI is different from shops LAI than location update is performed. The MS send location update petition which include new LAI and older LAI and cell individuality. The hallmark parametric quantities are sent by MS to MSC/VLR, if the MS is registered in VLR Than no location update is performed but if the visitant location registry ( VLR ) is non same as shop in MSC/VLR than new MSC/VLR sent petition to older MSC/VLR in order to authenticate the MS.If the hallmark is successful new VLR is updated and older VLR is besides updated. New MSC order BTS to delegate SDDCH to MS. The MS so let go of SDCCH and goes to tick over manner. If MS is altering its location country quickly so every alteration in location demands to update location country individuality ( LAI )
3.2.5 Call Setup
In cell choice process, the MS tried to acquire cell. Once a cell is selected, nomadic station start to seek best RX degree cell from neighboring cells in order to do cell reselection. After constitution of wireless connexion between nomadic station and web, The MS send call apparatus petition ( including figure of finish ) . The cell individuality and IMSI are analysed, besides hallmark are requested from VLR.After this procedure, MSC receive a call apparatus petition from Mobile. MSC so analyse the services for MS like call blackball for calls. These services are activated by user or from web. If MS is non barred MSC direct a message to BSC for traffic channel petition. BSC cheque about free TCH and apportion it to name and inquire base station ( BTS ) to trip channel. The MS direct verification message and BSC assign a TCH to mobile and inform to MSC about TCH assignment. After that call is connected and a ringing message is sent to naming figure, When called figure choice up call, a message is send to bespeak that a call apparatus procedure in completed
Signing for call apparatus C/I for non- hopping
4 GSM Network Problems and Solutions
4.1 Coverage jobs
One of the of import parametric quantity in optimisation is coverage. There are several factors which effects on coverage, if there is any topographic point between two different BTS where signals can non make, that peculiar topographic point is known as blind zone. This job can be resolved by increasing transmittal power.Blind zone in tunnels can be removed with aid of repeaters. The top solution of coverage job is installing of new sites or repeater. If client is non willing to better the state of affairs by adding new sites or repeaters than RF applied scientist will hold to observe possible ground of fading by look intoing connections, jumpers or others equipment on site, after look intoing equipment on site, coverage can be improve by trading antenna type and tallness, replacing faulty equipment or taking fading.
4.2 Quality Problems
The gathered indexs those give information about the address quality are Calls bead, RX degree bead, let go of call because of hapless quality, handover bead.
4.2.1 Bit error rate ( BER ) and Frame erasure rate ( FER )
BER and FER have besides consequence on address quality. In order to cut down BER and FER, figure of factors is considered like co channel intervention and next channel intervention. A good cell planning is required to get the better of intervention jobs.
( RX Quality classes with BER )
( Bad Rx Level, Rx Quality and SQI )
As signal degree bead as shown in above TEMS graph, Rx quality and SQI are besides dropped
4.2.2 Speech Quality Index ( SQI )
SQI is another parametric quantity when quality is under consideration. Using TEMS package SQI can besides be estimated which depends on handover, BER and FER. The quality of address can besides depends on wireless channel, reverberation, and type of nomadic utilizing by subscriber. Different trial are made in order to look into which parametric quantity is impacting on quality.
4.2.3 CO-Channel Interference ( C/I )
Co channel intervention is produced due to the same bearer used in others cells. Harmonizing to the GSM criterions, C/I must hold larger than 9dB for skiping frequence. one e C/I & A ; gt ; 9dB and for non-hopping frequence C/I demand is greater than 12dB.Interference is present non merely in downlink frequence but besides on uplink frequence but intervention in downlink will make serious job as compared on uplink frequence intervention.
4.2.4 Adjacent channel Interference ( C/A )
Power of signal from an next channel causes intervention. The distance between uplink and downlink frequence in GSM is 200KHZ which is called channel separation. This is necessary to cut down intervention between frequences. Adjacent frequences are non used in same cell, these are used in different cells, GSM criterions shows that bearer to adjacent channel ratio must hold larger than -9dB. Adjacent channel intervention reduces C/I public presentation. During GSM cell be aftering C/A must hold larger than 3dB.i vitamin E C/A & A ; gt ; 3dB.
4.2.5 Inter System Interference
Erstwhile intervention is produced by other radio webs runing on same next frequence or military web are runing on the same frequence. This sort of intervention is really hard to avoid.If intervention from other beginnings are impacting on quality of services than a comparing thrust trial is made to analyze to acquire clear state of affairs. Spectrum analyzer is besides used to analyze inter system intervention.
4.2.6 Possible Way to cut down intervention
Change the aerial tallness, adjust the joust of aerial, change AZ of aerial, by altering transmittal power of BTS, intervention can besides be overcome by seting discontinuous transmittal and response, by altering distance between two BTS, both utilizing same frequence
4.2.7 Signal Propagation
Many factors effects on extension like contemplation, diffraction, and soaking up.Usually, the tallness of nomadic aerial is low as comparison to edifice or trees, so signal comes across nomadic aerial through different ways with holds. Amplitude and stages, sometime the signals are wholly out of stage and the natural each other. Rayleigh attenuation besides effects on signal quality. Different diverseness techniques are used to get the better of these jobs depending on the state of affairs.
4.2.8 Time Dispersion
Due to different terrain like mountain, high edifice, hilly small towns, clip scattering jobs are produced. If the clip hold is less than 15ms than equaliser manages the job.In hapless quality, clip scattering is considered in order to look into the existent cause of job. There are several factors which kept in head when covering with clip scattering. Some contemplation is utile and some are harmful, merely those contemplation are harmful which causes hold in signal more than equaliser capacity. To avoid clip scattering, site must be suggested to turn up near contemplation object.
Rx degree of break uping and neighboring cell are continuously measured by web, whenever signal degree of functioning cell is low and neighbour cell is high, a handover is attempt from weak signal degree site to stronger signal degree site. There are different types of handovers in GSM system.
1 INTER BSC HANDOVER
VLR is same but cells belong to different BSC. In this type of handover MSC/VLR aid BSC to take handover
2 INTRA BSC HANDOVER
In this type of handover, endorser remains in the same BSC and handover take topographic point in different cell of same BSC.
3 INETR CELL HANDOVER
Handover between different sectors of same cell
4 INTER MSC HANDOVER
The handover between cell of different MSC, In this instance functioning MSC/VLR helps to new MSC/VLR in order to handover take topographic point.
During call, functioning BSC make up one’s mind about handover depending on RX degree and place of endorser. The handover process follows some basic regulations like, BSc sends a handover petition to MSC including cell individuality ( CI ) of mark cell, The functioning MSC and new MSC communicate with each other for handover petition than new MSC assign a handover figure and send message to BSC. The new BSC release a TCH to aim cell in order to do handover, the new MSC receive message about handover with mention figure.
4.2.10 Particular types of Handover
220.127.116.11 Power Budget Handover
In handover parametric quantities, power budget handover are defined, if the signal degree between functioning and neighbour cell is transcending to a specific degree ( define in power budget handover which is set to be 3 to 6dB ) , the call is transportation to neighbor cell by handover procedure. If there is Ping-Pong handover, than the job can be solve by increasing power budget handover border.
18.104.22.168 Quality Handover
An immediate quality handover is happen when down link quality is worse than threshold quality degree.
22.214.171.124 Rapid field Handover
When the endorser is going, RX degree will alter with the place of user, at some topographic points, signal degree will sudden lessening so quickly that BSC will non able to execute handover and name will be bead. This type of call bead is known as rapid field bead. The job can be solved by specifying signal degree border i.e. if signal degree bead up to -110dbm in certain countries than call will be handed over to following best Rx degree cell.
126.96.36.199 Pinging Pong Handover
In some topographic points subscriber gets same signal degree from different base station and consequence is rapid handover from one BTS to another BTS.The solution of Ping-Pong handover is to alter the aerial joust, azimuth angle or cut down transmittal power of one BTS.
188.8.131.52 Solution of Handover jobs
Change the handover parametric quantities. Add all possible neighbouring cells for handover.
4.2.11 call Drops
In GSM web, call beads is one of the chief factor.Basic factors due to which call is bead are call bead due to associate failure and SACCH multi-frames. Drop may be when subscriber enters in blind zone due to associate failure.Interference consequence on SACCH decrypting failure. If user ranges at boundary line of cell, it will bespeak for handover to following helping cell but due to congestion, no channel will be available and consequence is drop call. If the wireless nexus is fail than call is bead. These sorts of bead depend on different grounds like bead due to clocking progress ( TA ) .User is at a long distance from tower. The possible solution is put ining a new BTS. Call may besides be bead due to interference, which may be co channel or next channel. To take intervention, Optimizer should happen ground for intervention.
This paper describe the optimisation of GSM web.It is of import for every web to be proctor on regular footing in order to observe the jobs. This is the lone manner in which we can increase client satisfaction by bettering the public presentation of web. One of the inexpensive and most popular methods is drive trial.By observing the job ; we can easy happen the solution to better quality of services.