Drive test interview questions Part-2

8/4/2019 Drive test interview questions Part-2

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PART _______2

HAND OVERHAND OVER IS THE PROCESS IN WHICH, THE SERVICE TO THE

SUBSCRIBER IS TRANSFERRED FROM THE SERVING CELL TO

THE ANOTHER CELL DURING ACTIVE MODE OF MS AND THE

CALL WILL CONTINUE TILL MS DISCONNECT THE CALL.

WHY HAND OVER?

A] IN ORDER TO PROVIDE THE BETTER LINK QUALITY TO THESUBSCRIBERS.

B] MANAGE THE TRAFFIC DISTRIBUTION AMOUNG THE CELLS

OF THE NETWORK.

OR1 TO MAINTAIN QUQLITY AND CONTINUETY OF CALLS.2 CELL SIZE CONTROL IN ORDER TO MINIMIZE TOTAL

INTERFERENCE IN THE NETWORK.NOTE: HO IS THE EFFECT OF FREQUENCY HOPPING

GIVE THE SPECIFIC REASON FOR HANDOVER (H.O.)?

REASONS:

RECIEVER(RX) SIGNAL QUALITY

RECEIVER SIGNAL LEVEL

INTERFERANCE

POWER BUDGET

CONGESTION

RX QUAL.: IF THE RX LEVEL BAD AND RX QUAL.IS ALSO BAD

THEN H.O. IS DUE TO RX QUAL.

RX.LEVEL: IF THE RX LEVEL IS BAD RX QUAL. IS GOOD THEN

HO IS DUE TO RX.LEVEL.


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INTERFERANCE: IF THE RECIEVER LEVEL IS GOOD AND THE

RX QUAL. IS BAD THEN H.O. IS DUE TO INTERFERENCE.

(Receiver level is nothing but how much amount the signal

strength you get.)

(Receiver quality is nothing but the voice quality which we get

during call.)

(Interference is nothing but the disturbance or unwanted signal)

LEVEL QUALITY H.O

GOOD BAD INTERFERENCE

BAD BAD RX QUAL.

BAD GOOD RX LEVEL

WHAT ARE THE SHORT COMING IN HAND OVER?

1. CALL DROP

2. FAR AWAY CELL EFFECT

3. PING PONG H.O

WHAT IS PING PONG HO?PING HO IN WHICH (UNNECSESARY) NETWORK TAKING

CONTINIOSLY H.O.

LET US SUPPOSE 4 SITES. ARE SERVING IN ANY ONE AREA

THEN THEIR WOULD BE SUCH TYPE OF POINT AT THEIR ALL 4

SITES ARE GIVING THEIR OWN SIGNALS .SO WHEN U ENTER ON

THAT SPOT FIRST HO IS GIVEN TO 2ND NO. SITE SIGNALS

,AFTER IMMEDIATELY RECIVEING THE 2ND NO.SITE 3,RD NO

WILL TAKE HO ,AFTER 4THAFTER 1ST ..2,ND SO

ONSECOND REASON OF PING PONG IS PARTIAL CABLE SWAP. (SEE

AT CABLE SWAP FOR DETAIL)

HOW IT CAN BE AVOID?


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SO ALWAYS GIVE THRESHOLD VALUEACCORDING TOPLANNER OR FIX THE THRESHOLD VALUE.

Or

Adjust the mechanical and electrical tilt.

(Choose one of the above solution because its depends on theclutter)

If clutter is dense then choose tilt solution because if we adjust

threshold then our QUALITY would be decrease.

WHAT IS THE BAD EFFECT OF PING PONG HO?

NETWORK QUALITY IS BAD.

WHAT IS INTELLIGENT HO?

1 NEAURAL NETWORK2 FUZZY LOGIC

WHAT IS INTERNAL & EXTERNAL HO?

INTERNAL HO:

INTER BTS:CALLS TRANSFER BETWEEEN TWO CHANNELS (TIME SLOT) IN

SAME CELL.

INTRA BSC:CALLS TRANSFER BETWEEN BTS UNDER THE CONTROL OF

SAME BSC.

EXTERNAL HO:

INTER BSC (BSC - BSC):

1 CALL TRANSFER BETWEEN THE BTS UNDER THE

CONTROL OF DIFF. BSC.

INTER MSC (MSC - MSC):

CALL TRANSFER BETWEEN CELLS UNDER THE

CONTROL OF DIFF. MSC.W H A T I S I N T R A C E L L H O ?I T IS B A S E D O N T H E U P L I N K I D L E C H A N N E LI N T E R F R E N C E M E A R S U R M E N T C A N E F F I C I E N T L Y A V O I DU P L I N K IN T E R F E R A N C E W H E N T H E N E T W O R K L O A D I SR E A S O N A B L E .


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W H E N T H E L O A D I S H I G H I N T H E N E T W O R K , T H E G A I NO F I N T R A C E L L H O I S L O W .W H E N T H E L O A D I S L O W T H E N T H E G A I N I S G O O D .

I N C A S E O F H A N D O V E R D E F I N E B U T H A N D O V E R W O U L DN O T T A K E P L A C E ?C H E C K F O R :1 ) C H E C K N E I G H B O U R D E F I N E D O R N O T ?F I R S T S E E I N N E T M O N I T E R O R T E M S I F Y E S T H E NF O L L O W 2 N D S T E P IF N O T T H E N C A L L M S C A N D T E L LT H E M T O D E F I N E .2) IS F R E Q U E N C Y A N D B S I C S A M E ( S E E I N M C O M )3 ) C H E C K I S T H A T F R E Q . O N W H I C H H O W I L L T A K ED E F I N E D I N M B C C H F R E Q U E N C Y L I S T O R N O T ?( C A LL M S C A N D A S K )4 ) C H E C K N C C P A R A ( P A R A M E T E R ) I S S E T O R N O T ?( C A LL M S C A N D A S K )

2) IS F R E Q U E N C Y A N D B S I C S A M E ( S E E I N M C O M ) :A T B E L O W S E E 8 4 2 I S F R E Q . A N D ( 4 3 ) B S IC W H E R E 4 I SN C C 3 I S B C C . F R E Q . A N D B S I C I S S A M E D O E S N O T M E A NT O C H E C K 8 4 2 A N D 4 3 I S S A M E !I T M E A N S T H E S I T E W I T H S A M E F R E Q . A N D B S I C P A I RS H O U L D N O T B E I N T H E 1 5 K M O R 2 0 K M R A D I U S. B E C A U S E I F T H I S H A P P E N E D , T H E N T H E R E I SI N T E R F E R E N C E D U E T O F R E Q . H I T A N D W E C A N T F I N DI T , D U E T O S A M E P A I R W E C A N T F I N D W H I C H T W O F R E Q .A R E H I T T I N G .T H E R A D I U S I S A L S O D E P E N D O N T E R R I O N .


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W H A T I S B A S I C ?B A S E S T A T I O N I D E N T I T Y C O D E I S T H E C O D E W H E R E I NT H E F I R S T D I G IT I N D I C A T E S N C C A N D S E C O N D D I G I TI N D I C A T E S B C C .N C C : N E T W O R K C O L O U R C O D EB C C : B A S E S T A T I O N C O L O U R C O D E

T H E N C C A N D B C C H A V E V A L U E R A N G I N G F R O M O T O 7

N C C : T H E N C C I S F I X E D F O R A N O P E R A T O R , S I G N I F Y IN GA T A N Y G I V E N P O I N T T H ER E C A N B E M A X I M U M O F 8O P E R A T O R S I N A N A R E A .B C C : B C C D E F IN E S T H E C L U S T E R N O . W H I C H M E A N S AG R O U P O F 8 C L U S T E R S C A R R Y U N I Q E I D E N T I T Y W H I C HA R E U S E D F O R A N O T H E R G R O U P O F 8 A N D S O O N .

E X . I F B S IC I S 6 5 T H E N 6 I S N C C A N D 5 I S B C CI F B S I C IS 5 5 A N D F R E Q . I S 5 5 T H E N H O W O U L D N O TT A K E P L A C E .W H A T I S C L U S T E R ?G R O U P O F F R E Q . C A N B E P L A C E D T O G E T H E R I N T O

P A T T E R N S O F C E L L S C A L L E D C L U S T E R .C L U S T E R I S A G R O U P O F C E L L S I N W H I C H A L LA V A I L A B L E F R E Q . H A V E B E E N U S E D O N C E A N D O N L YO N C E .


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T H E P R I N C I P A L F O R A L L O C A T I O N O F T H E B S I C I S T H ES A M E A S T H E R F C A R R I E R B U T A T C L U S T E R L E V E LR A T H E R T H A N C E L L L E V E L .M B C C H F R E Q :MBCCH NO. IS THE BCCH ALLOCATION(BCCH Allocation (BA) List is alist of BCCH frequencies that every Idle mobile in a cell is supposed to

monitor. The list can be of two types - Idle BA List and Dedicated BA

List. Idle is used by Idle mobiles while Dedicated BA List is used byDedicated Mobiles. You always dont need to make two BA lists, it

depends on your planning process whether you will be using single BALor BAL rotation or Dual BAL. We can use one BAL for all the mobiles

(idle & dedicated).)i.e. IT INDICATES TO THE MS THE FREQ.MUST BE MONITERED AND

MEASURED IN IDLE .ACTIVE OR BOTH MODES.THIS NO. IS SENT TO MS

IN THE SYSTEM INFORMATION MESSAGES ON THE BCCH CHANNEL INIDLE MODE AND ON THE SACCH IN ACTIVE MODE.

U P T O 3 2 B C C H C A R R I E R S C A N B E D E F I N E D B YS P E C I F A Y I N G T H E I R A R F C N .

DEEP CONCEPT OF HO:THE MEASUREMENT REPORT FROM THEM S IS SENT TO THEB S C ON THE SACCH INDICATING THE SIGNAL STRENGTH ANDQUALITY OF THE SERVING LINK AND THE

S I G .S T R E N G T H , F R E Q . A N D B S I C F R O M T H ESIX BTSWITH STRONGEST SIGNAL STRENGTHS.ONLY MEASURMENTS FROM THE NEIGHBOURING CELLS THAT

FULLFILL THE REQUREMENT BY BCCH HAS A FREQ. AS

INDICATED BY MBCCH NO.

IT IS NECESSARY THAT THE MEASURED CELL IS DEFINED AS

THE NEIGHBOUR OF THE SERVING CELL .

U P T O 6 4 D I F F . C E L L S C A N B E D E F I N E D A S N E I G H B O U R .H O P R O C E S S M A Y B E T R I G G E R E D B Y Q U A L . , F I E L D

S T R E N G T H O R D I S T A N C E V A L U E S F A L L B E L O L W /E X C E E D T H E I R T H R E S H O L D P E R I O D I C C H A N G E S .

HO ALGORITHUM:


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The locating algorithm: W o rk s o u t th e b a s i s f o rh a n d o ve r d e c is io n s . I t is im p le m e n te d i n th e b a sesta t ion cont ro l le r . I t i s the a lgor i thm fo r ce l l se lect ionf o r a c t i ve m o b i le s ta t io n s ( i . e . o n g o in g c o n n e c t io n ) a f te rim m e d ia te a ss ig n m e n t .I N P U T :T H E I /P T O T H E A L G O R I T H U M I S S I G N A L S T R E N G T H A N DQ U A L IT Y M E A S U R E M E N T F R O M T H E M S A N D F R O M T H EB A S E S T A T I O N C U R R E N T L Y S E R V I N G T H E C O N N E C T I O N .

O U T P U T :T H E O U T P U T I S T H E L I S T O F C E L L S T H A T T H EA L G O R I T H U M J U D G E S T O B E P O S S I B L E C A N D I D A T E SF O R H A N D O V E R . T H E C E L L S I N T H E L I S T IS R A N K E DA N D S T O R E D I N D E S C E N D IN G O R D E R O F P R E F E R E N C EF O R H A N D O V E R .

T H E A L G O R I T H U M W O R K S C O N T I N U E S L Y , C O M P L E T I N GA C A L C U L A T I O N C Y C L E I N G E N E R A L E V E R Y 4 8 0 m s .M O S T F R E Q U E N T L Y T H E A L G O R I T H U M W I LLR E C O M M E N D N O T T O P E R F O R M A H A N D O V E R .

H A N D O V E R C R I T E R IA A R E B A S E D O NT H R E E T Y P E S O F M E A S U R E M E N T

1 ] F IE L D S T R E N G T H ( S I G N A L S T R E N G T H A N D O R P A T HL O S S ) O F T H E C O N N E C T I O N A N D O F T H EB R O A D C A ST C O N T R O L C H A N N E L C A R R I E R SF O R N E I G H B O U R S .2 ] S IG N A L Q U A L I T Y O F T H E C O N N E C T I O N ( B I T E R R R O RR A T E E S T E M A T I O N M A P P E D O N A L G O R I TH U M S C A L E )3 ] T I M I N G A D V E N C E U S E D B Y T H E M S .W H A T I S T I M IN G A D V A N C E ?

I T IS A S O L U T I O N S P E C I A L Y D E S I G N E D T O C O U N T E R A C TT H E P R O B L M O F T I M E A L L I G N M E N T . IT S W O R K E D B Y


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I N S T R U C T I N G T H E M I S A L I G N E D M S T O T R A N S M I T IT SB U R S T E A R L IE R O R L A T E R T H A N I T N O R M A L L Y W O U L D .I N G S M T A I N F O R M A T I O N R E L A T E S T O B I T T I M E S. TH U S , A N M S M A Y B E I N S TR U C T E D T O C O M M E N C E I T ST R A N S M I S S IO N A C E R T A I N N O O F B IT T I M E S E A R L IE RO R L A T E R , R E L A T E D T O P R E V I O U S P O S I T I O N T O R E A C HI T S T IM E S L O T A T T H E BTSIN RIGHT TIME.

W H A T I S T H E D I F F . B E T W E E N C E L L R E S E L E C T I O N A N DH A N D O V E R ?H A N D O V E R H A P P E N E D I N D E D IC A T E D M O D E A N DC E L L R E S E L E C T I O N I N I D L E M O D E .

F R E Q U E N C Y H O P P I N GCa l l i s t ra n sm i t te d th ro u g h se ve ra l f r e q u e n c ie s i n o rd e rtoMin im iz ing the impa ct o f fad ing .Average the in te r fe rence ,O RI t i s de f ined a s seque nt ia l chan geo f ca r r ie r f requency o n the rad iol ink be t w een t he m o b i le and ba s estat ion .A dv an t age o f f r equency hopp i ng :Frequency diversity

Interference averaging


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How in frequency hopping there is enhancement of

network?

1F H i m p l e m e n t will enable more aggressive frequencyreuse pattern that leads to better spectrum efficiency.2 It can add more transceivers in the existing site, whilemaintains the network quality.3 freq. hopping compressing the available spectrum tomake room for extra freq.

Frequency reuses?FREQUENCY REUSE IMPLIES THAT IN A GIVEN COVERAGE AREA THERE ARE

SEVERAL CELLS THAT USES THE SAME SET OF FREQ.

THESE CELLS ARE CALLED COCHANNEL CELLS .AND THE INTERFERENCE

BETWEEN SIGNALS FROM THESE CELLS ARE CALLED CO CHANNEL

INTEREFERENCE.

Def ine a l l t he pa ramete r i n f requency ho pp ing? Fo l l ow ing a re the pa ramete r i n FHM O B I L E A L L O C A T I O N ( M A )

M O B I L E A L L O C A T I O N I N D E X ( M A I )M O B I L E A L L O C A T I O N I N D E X O F F S E T ( M A I O )H O P P I N G S E Q U E N C E N O . (H S N )

M O B I L E A L L O A T I O N :IT IS THE SET OF FREQ. The mobile allowed to hope over

.maximum of 63 freq. can be defined in MA list.

M O B I L E A L L O C A T I O N I N D E X ( M A I ) :I t i s the no . r ang ing f rom ze ro to the no . o f f r eq . i n the M Al ist sub t rac ted by one .

It is the output of hopping sequence algorithms.

H O P P I N G S E Q U E N C E N O . ( H S N ) :I t de te rmines the h opp ing o rde r use d i n the ce l l . it i s poss ib leto ass ign 6 4 d i f f .se t t i ng .when H SN = 0 prov ides cyc l i chopp ing (pa t te rn ) .H S N = 1 T O 6 3 p r o v id e s v a r i o u s p s e u d o r a n d o m h o p p i n g .


10/24

In G S M the re a re 64 d i f f . pa t te rns o f FH .One o f them i s a s imp le cyc l i c o r sequent ia l pa t te rn .

The rema in ing 63 a re known as pseudo random p at te rnswh ich an opera to r can choose f rom the MA l i s t .

W H E R E W E U S E C Y C L I C A N D R A N D O M P A T T E R N ?C Y C L I C : IT I S U S E D I N T H E A R E A W H E R E T H E I T E R F E R E N C EI S N O T A P R O B L E M .R A N D O M : IT I S U S E D IN T H E A R E A W H E R E I N T E R F E R E N C E I SA P R O B L E M . ( H I G H T R A F F I C A R E A ) .

M O B I L E A L L O C A T I O N I N D E X O F F S E T ( M A I O ) :Dete rmines i ns ide the FH sequence w h ich f req . t he mob i l es ta r t s do t ransmi t on .The va lue o f MAIO ranges be tw een ze ros to N -1 .Where N i s the no .o f f r eq .de fi ned i n the M A l i s t .

Present l y MA IO i s se t on per ca r r ie r bas is .

What a re the t ypes o f F H and? Wh at i s d if . be tween them?Two types o f f r eq . hopp ing .B a s e b a n d F H ( B B H )Synthes i zed FH (SFH)Di f f . :BBH: IN BBH no . o f hopp ing f req . same as no .o f TRX . (TRU)

SFH : No . o f hopp ing freq . can be in the range o f 1 to 63 .- here the ARFCN wud be more than the no. Of TRX/TRU in bts.also

we have better hopping gain here.& also we need not to go for new

frequency scheme when we add new trxs to the site as this is to be

do done in Base band hopping.Definition of SFH AND AMR:

SFH & AMR IS different terms


11/24

SFH is synthesizer freq hopping and AMR is adaptive multirate. Thesetwo terms are in all different from each other. One defines the way of

using fewer frequencies more efficiently and other defines the way ofcontrolling the quality of call in FULL RATE as well as HALF Rate so as

to increase capacity indirectly with controlled quality.

Wh at i s the e f fec t o f fr eq . hopp ing?1 H a n d o v e r2 Ca l l se t up3 F r a m e e r a s e r r a te ( F E R )These a re the e f f . o f FH .W hat i s FE R?I T I S TH E R A T IO O F D I S C A R D E D S PE A C C H F R A M E S C O M P A R E D T OA L L T H E R E C E I V E D S P E E C H F R A M E S .It is the right measure of voice quality.

It is performed on speech and signaling frame.

FFR 0 to 4 % good

4 to 15 % slightly degrade

Greater than 15 %

F O R M U L A :% O F F E R = ( N O .E R A S E D B L O C K S T O T . N O .O F B L O C K S ) 1 0 O

D e e p c o n c e p t :M A I O :

It is a parameter that will allow the operator to specify a list of

up to 32 MAIO values in order in which they are to be allocated to

a channel group. This parameter set to default whichremoves the manual MAIO list in favor for the default MAIO list.

The no. of MAIO values in list stretches from zero up to one less

than no. of freq. in the HFS.

Ex. 9(0 to 8) freq. their than maio list will be 0 to 7.

The actual MAIO values to be used for a channel group

depend on the no. of TRX in the channel group.


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Default list:

In order of the MAIO values in the default list is arranged in a

first even then odd. MAIO values manner.

This means that the beginning of the list will consist of all theeven values in ascending order.

After the even values all the odd values are arranged an

ascending order.

Ex.

For hopping group with 9 freq. the default list will be 0, 2, 4, 6, 1,

3, 5 and 7.

MA: MA LIST IS A LIST OF HOPPING FREQ. TRANSMITTEED TO

A MOBILE EVERY TIME .IT IS ASSIGNIED TO HOPPING

PHYSICAL CHANNEL.

THE MA LIST IS A SUBSET OF CA LIST.

#WHAT IS CA LIST?

THE MA LIST IS AUTOMATICALLY GENERATED

IF THE BASEBAND HOPPING IS USED.

IF THE NETWORK UTILISES THE RF HOPPING

THE MA LIST HAVE TO BE GENERATED FOREACH CELL BY THE PLANNER.

The MA list is able to point the 64 of freq. defined in the CA

list .However the BCCH freq. is also included In the CA list ,so

the practically max.no. Of freq. in the MA list is 63.


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The freq. in the MA list is required to be in increased order

because of the type of signaling used to transfer

the MA list.

HOPPING sequence algo?Input: The hopping seq. algo. Takes HSN &

FN (freq.no.) as an input.

Output: Mobile allocation index (MAI) is the

O/P.

MAIO:WHERE THERE ARE MORE THAN ONE TRX IN THE BTS USING THE SAME LIST

THE MOBILE ALLOCATION INDEX OFFSET IS USED TO ENSURE THAT EACH

TRX USES ALWAYS AN UNIQUE FREQ.

EACH HOPPING TRX IS ALLOCATED A DIFF. MAIO.

MAIO IS ADDED TO MAI WHEN THE FREQ. TO BE USED DETERMINED FROM

THE MA LIST.

MAIO AND HSN ARE TRANSMITTED TO

A MOBILE STATION TOGETHER WITH

MAIO LIST.

HSN DEFINES WHICH HOPPING SEQUENCE TO BE USED.

MAIO DECIDES STARTING POINT OF HOPPING.

WHAT IS SLOW FREQ.HOPPING AND WHAT IS FAST

FREQ.HOPPING?THE PRINCIPAL OF FREQUENCY HOPPING USED

WITHIN GSM IS THAT:

SUCESSIVE TDMA BURST OF CONNECTION IS

TRANSMITTED VIA. DIFF. FREQ.


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THAT FREQ. BELONGING TO A RESPECTIVE CELL

ACCORDING TO NETWORK PLANNING. THIS METHOD

IS CALLED SLOW FREQ. HOPPING.

SINCE TRANSMISSIOMN FREQ. REMAIN CONSTENT

DURING ONE BURST.

IN CONTRAST FAST FRFEQ. HOPPING WHERE THE

TRANSMISSION FREQ. CHANGES WITHIN THE ONE

BURST.

DETAILS OF FRAME ERASER RATIO:

IT IS THE RATIO OF DISCARDED SPEACH FRAMES COMPARED TO ALL THE

RECEIVED SPEECH FRAMES.

A SPEECH FRAME IS GENERALLY DISCARDED IF AFTER THE DECODING AND

ERROR CONNECTION PROCESS ANY OF THE CATEGORY A BIT IS FOUND TO

BE CHANGED BASED ON THE THREE PARITY BITS FOLLOWING THEM IN A

SPEECH FRAME.

FER IS MEASURE OF HOW SUCESSFUL THE SPEECH FRAME WAS RECIVED

AFTER THE ERROR CORRECTION PROCESS AND IT IS THUS A BETTERINDICATION OF THE SUBJECTIVE SPEECH QUALITY COMPARED TO THE LINK

QUALITY IN TERMS OF BER .THE RECIEVER QUALITY DOES NOT INDICATE

HOW THE BIT ERRORS WERE DISTRIBUTED IN A SPEECH FRAME.

THE BIT ERROR DISTRIBUTION AFFECTS

THE ABILITY OF THE CHANNEL DECODING

TO CORRECT THE ERRORS.A BLOCK IS ERASED WHEN PARITY CHECK FAILED.

BIT ERROR RATE:IT IS THE RATIO OF THE NO. OF ERRORNEOUS BIT RECIEVIED TO THE TOTAL

NO.OF BITS RECEIVED.

RESIDUAL BIT ERROR RATE:


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IT IS PERFORMED ON DEMODULATED SPEECH FRAMES THAT

ARE NOT MARKING CORRECT.

WHAT HAPPENS WHEN SPEECH FRAMES DISCARDED IN FER?

ANS: SYSTEM WILLS INTERPOLUTE.

SPEECH QUQLITY INDEX DEPENDS ON FER AND

BER.

SPECCH QUALITY IS DEPENDING ON BER.

TROUBLSHOOTINGWHAT IS CABLE SWAP AND PARTIAL CABLE SWAP?

THERE ARE TWO TYPES OF CABLE SWAP/SECTOR SWAP.

FIRST CABLE SWAP/SECTOR SWAP AND ANOTHER IS PARTIAL

SWAWP.

CABLE SWAP IS NOTHING BUT WHEN TWO WIRES WHICH IS COMING

FROM GSM AND CONNECTED IN TRX/TRU IN BTS WIL CONNECTWRONGLY. MEANS FIRST SECTOR TWO CABLE (POSITIVE AND

NEGATIVE) CONNNECTED IN SECOND SECTOR TRU/TRX OR SECOND

SECTOR TWO CABLE CONNNECTED IN THIRD OR THIRD SECTOR IN

FIRST .

WHAT IS THE SOLUTION OF TCH OR CALL

DROP?BOTH PROBLEMS WOULD BE OCCURRED DUE TO THE POSSIBILITY OF CABLE

SWAP OR FREQUENCY HIT.

CABLE SWAP : TWO WIRES CAME FROM THE GSM AND JOIN AT THE TRX IN

BTS ROOM. WHILE CONNCTING THESE WIRE THEIR COULD BE MISMATCH OR

SWAPPING.BECAUSE FROM THESE TWO WIRES ONE WIRE IS OF

TRANSMETER SECTION (+ SIGN ON THAT CABLE ) AND ANOTHER SIGN IS OF

RECIEVER ( - SIGN IS ON THAT CABLE).SO THERE SHOULD BE CHANCES

THAT + WIRE WOULD BE ATTACHED TO - AND VICE VERSA.

TWO SOLVE THE PROBLEM OF CABLE SWAP WE WANT TO SEE WHETHER

THESE CONNECTION IS EXACT OR NOT.

DUE TO CABLE SWAP THERE WOULD BE CHANCES OF CALL DROP.

SECOND CASE:

FREQUENCY HIT: THIS MEANS ADJUCENT FREQUENCY WOULD BE HIT

TOWARDS AREA.

SOLUTION OF THIS CASE GIVES DOWN TILT TO OUR GSM.

WHAT IS PARTIAL CABLE SWAP?

THERE ARE TWO TYPES OF CABLE SWAP ONE IS ABOVE AND SECOND IS

PARTIAL CABLE SWAP.


16/24

IN FIRST CABLE SWAP TWO WIRES ARE FROM ANY ONE SECTOR IS

CONNECTED IN ANOTHER SECTOR TRX/TRU .BUT IN PARTIAL CABLE SWAP

ONLY ONE WIRE WOULD BE SWAP MEANS ONE WIRE FROM ANY ONE SECTOR

AND ANOTHER WIRE FROM ANY OTHER SECTOR IS CONNECTED AT ONE

TRX/TRU.

WHAT IS THE SOLUTION FOR PROBLEM OF UPLINK?

SEE AROUND YOUR SITE ANY CDMA SITE IS PRESENT IF YES THEN USE

CDMA FILTER.

IF NOT THEN SEE IS THEIR SECTOR EXPANTION PRESENT THEN CHECK FOR

THE ORIENTATION OF BOTH EXPANSION ANTENA AND MAIN ANTENA IS

DIFF. OR SAME.

WHAT IS THE SOLUTION FOR DOWNLINK PROBLEM?

THE SOLUTION FOR THE DOWNLINK IS SAME FOR THE TCH /CALL DROP.

WHAT IS TH E SOLUTION FOR SD DROP?

IF SD DROP INCREASED THEN ASSIGN ONE MORE TIME SLOT BY USING

PLANNER.

WHAT IS THE REASON FOR SDCCH DROP?1>high interference of freq., like co-channel

2>sdcch time slot faulty3>poor TRX DL quality

4>hardware fault like antenna or duplexer malfunction5>may be feeder cable and connectors are faulty.

6>site taking calls from a very far distance.

7>Bad Radio link quality (any sort of interference, if highly) Bad Radiolink quality (any sort of interference, if highly destructive)

8>Could be a problem at NSS endand may be some other reasons....

SD drop happens after SD is assigned, and if TCH is not free but SD is

assigned and there is no directed retry, then in that case what

happens? SD waits for a timer value and then also if it doesn't find aTCH it can't hold SD, so drops..

WHAT IS VSWR?VOLTAGE WAVE STAND RATIO:IT IS THE RATIO OF FORWARD POWER TO THE REFLECTED POWER.[(1-ROW)/

(1+ROW)]IT THE PROBLEM OF LOOSE CONNECTOR OR DUST OR SHARE

BENDING OR RAIN WATER . DUE TO THIS PROBLEM THERE IS LESS

COVERAGE IN THAT AREA.

WHENEVER THIS PROBLEM OCCURRED THERE IS ALARM FOR THIS IS IN

MSC.


17/24

THERE ARE LOTS OF TYPE OF ALARMS ANOTHER IS IF BTS DOOR IS OPEN

THEN THERE IS ALSO ALARM WILL OCCURD IN MSC.

TO SOLVE THE PROBLEM OF VSWR PROBLEM WE CONNECT TIGHTLY (LOOSE

CONNECTOR) ALL CONNECTOR/CABLE WHICH ARE LOOSE.


18/24

ABOVE TEMS 6.1 S/W IS COMPITABLE WITH INSTRUMENTS(MOBILE) T610.


19/24

WHAT IS TEMS?TEST EQIPEMENT MOBILE SYSTEM IS A TESTING TOOL USED TO READ AND

CONTROL THE INFORMATION SENT OVER AIR INTERFACES BETWEEN BASE

STATION AND THE MOBILE STATION .IT CAN BE USED FOR RADIO

COVERAGE MEASUREMENS.IN ADDITION TO FIELD

MEASUREMENT AND POST PROCESSING.ALL KIT CONSIST OF MOBILE STATION WITH SPECIAL SOFTWARE, A

PORTABLE PC AND OPTIONALLY A GLOBAL POSITONING SYSTEM

RECIEVER.THE PC IS USED FOR PRESENTATION ,CONTROL AND

MEASUREMENT STORAGE .

MS IS USED IN ACTIVE OR IDLE MODE.

WHICH WINDOW WE NEED TO CHECK IN DRIVE TEST?

1] CURRENT CHANNEL

2]SERVING NEIGHBOUR

3]RADIO PARAMETER

4]C/I

5] C/A

TELL US ABOUT DETAILS?

1] CURRENT CHANNEL:

CELL NAME

CGI (MCC NCC LAC (BSC) CI)

BAND 900/1800/1900

CHANNEL TYPE

CHANNEL MODE

SPEECH CODEC

CIPHERING ALGORITHUM

SUB CHANNEL NO.

HOPPING CHANNEL

MAIO

HSN

2]SEERVING NEIGHBOUR: FULL SUB

HERE THE DEFINED NEIGHBOUR WILL APPEAR.

3]RADIO PARAMETER : FULL SUB

A] RX LEVEL RANGE -10 TO -120

-10 TO -70 BEST

- 71 TO -80 GOOD


20/24

-91 TO -120 BAD PURPOSE NEW SITE AT THIS AREA.

B] RX QUALITY (ITS DEPEND ON INTERFERENCE ) RANGE 0 TO 7

0 TO 3 GOOD

4 TO 5 AVG.6 TO 7 BAD

C] FER ACTUAL

D] BER ACTUAL

E] SQI

21 TO 30 OK

ABOUT SQI :IF BSIC AND FREQ ARE SAME THEN SQI GOES NEGATIVE.

4]C/I (WORST /BEST) RANGE 5 TO 25

15 AVG.

10 TO 15

5 TO 10 BAD

MS POWER CONTROL LEVELDTX

TA

1 TA = 500m

(RECEIVING LEVEL)RL TIME OUT COUNTER (MIN)

RL TIME OUT COUNTER (MAX)

MS BEHEVIOR MODIFIED

5] C/A

ANOTHER NETWORK PROBLEM:

C/I:CARRIER TO INTERFERENCE RATIO

IT IS DEFINED AS THE RATIO BETWEEN THE LEVEL OF THE RECIVED

DESIRED SIGNAL TO THE LEVEL OF RECIVED UNDESIRED SIGNAL.

C/I IS DEPENDENT ON THE INSTANTANEOUS POSITION OF THE MOBILE

STATION AND IS AFFECTED BY TERREIN DETAILS AND VARIOUS

SHAPES,TYPES AND NO.OF LOCAL SCATTERS.

OTHER FACTORS SUCH AS ANTENNA TYPE DIRECTIONALITY AND HEIGHT

,SITE ELEVATIONS ,POSITIONS AND THE NO. OF LOCAL SOURCE OF

INTERFERENCE ALSO EFFEECT THE DISTRIBUTION OF THE C/I RATIO IN A

SYSTEM .

C/A: CARRIER TO ADJUCENT RATIO

IT IS DEFINED AS THE RELATION IN DB IN SIGNAL STRENGTH BETWEEN THE

SERVING AND AN ADJUCENT FREQ.


21/24

COCHANNEL INTERFERENCE:

FREQUENCY REUSE IMPLIES THAT IN A GIVEN COVERAGE AREA THERE ARE

SEVERAL CELLS THAT USES THE SAME SET OF FREQ.

THESE CELLS ARE CALLED COCHANNEL CELLS .AND THE INTERFERENCE

BETWEEN SIGNALS FROM THESE CELLS ARE CALLED CO CHANNEL

INTEREFERENCE.SOLUTION:TO REDUCE CO CHANNEL INTERFERENCE CO CHANNEL CELLS

MUST BE PHYSICALLY SEPERATED BY A MINIMUM DISTANCE IN ORDER TO

PROVIDE SUFFIECIENT ISOLATION.

W H AT I S BAS I C?B A S E S T A T I O N I D E N T IT Y C O D E I S T H E C O D E W H E R E I N T H E F I R S TD I G IT I N D I C A T E S N C C A N D S E C O N D D I G I T I N D IC A T E S B C C .N C C : N E T W O R K C O L O U R C O D EB C C : B A S E S T A T I O N C O L O U R C O D E

T H E N C C A N D B C C H A V E V A L U E R A N G I N G F R O M A N O T O 7

N C C : T H E N C C I S F IX E D F O R A N O P E R A T O R , S IG N I F Y I N G A T A N YG I V E N PO I N T TH E R E C A N B E M A X IM U M O F 8 O P E R A T O R S I N A NA R E A .

B C C : B C C D E F I N E S T H E C L U S T E R N O .W H I C H M E A N S A G R O U P O F 8C L U S T E R C A R R Y U N I Q E ID E N T I T Y W H I C H A R E U S E D F O R A N O T H E RG R O U P O F 8 A N D SO O N .

E X . I F BS I C I S 65 T H E N 6 I S N CC AN D 5 I S BCCI F B S IC I S 5 5 A N D F R E Q . I S 5 5 T H E N H O W O U L D N O T T A K E P L A C E .W H A T I S C L U S T E R ?G R O P U O F F R E Q . C A N B E P L A C E D T O G E T H E R I N T O P A T T E R N S

O F C E L L S C A L L E D C L U S T E R .C L U S T E R I S A G R O U P O F C E L L S I N W H I C H A L L A V A I L A B L E F R E Q .H A V E B E E N U S E D O N C E A N D O N L Y O N C E .T H E P R IN C I P A L F O R A L L O C A TI O N O F T H E B S IC I S TH E S A M E A S

T H E R F C A R R I E R B U T A T C L U S T E R L E V E L R A T H E R T H A N C E L LLE VE L .

Transmission problem:Path loss: Path loss occurs when the received signal becomes weaker andweaker due to increasing distance between MS and BTS ,even if there are no

obstacles between the transmitting and receiving antenna .

The path loss problem seldom leads to a dropped call because before the

problem becomes extreme a new transmission path is established via another

BTS .


22/24

Shadowing: Shadowing occurs when there are physical obstaclesincluding hills and building between the BTS and MS .The obstacles create a

shadowing effect which can decreases the received signal strength .

when the MS moves the signal strength fluctuates depending on the

obstacles between the MS and BTS .

FADING DIPS: A signal influenced by fading varies in

signal strength .

Drops in strength are called fading dips.

Multipath fading : It occurs when there is more than

one transmission path to the MS or BTS .This may be

due to building or mountains either close to or far from

the recdBi, dBd,dBm

dB itself is a measure of power on logarithmic scale.....when we talk

abt dBi (one more thing i want add here is dBd ), these indicate gain ofa given antenna with respect to isotropic and Lambda/2 dipole antenna

respectively....isotropic antenna is a non existent ideal antenna and

Lambda/2 as it indicates is half-wavelength antenna., here iso.. is anomni directional antenna while Lambda...is a directional antenna ..

When we measure gain wrt iso..Antenna,.gain is more bcoz it radiates

lesser in distance ..bt its less with Lambda/2 antenna ... bcoz itsradiation is directional hence more. Here is the relation...

dBi (gain of the given antenna wrt Isotropic antenna)=dBd(Gain wrtLambda/2 antenna +2.15 dB).

READ THIS AFTER LEARN THE DT FOR 10 DAYS!

ANALYASING THE LOG FILES?

AFTER HAVING THE ENTIRE NETWOR OR A GIVEN PART OF THE NETWORK,

THE LOG FILES SHOULD BRE ANAYLIESD .WHEN ANALYISING THE LOG FILES

,THE MAIN THINGS TO LOOK FOR :

1. INTERFERENCE

2. LOW SIGNAL STRENGTH

3. MISSING NEIGHBOUR

OFTEN, THESE PROBLEMS CAN BE SPOOTEED BY LOOKING AT THE RXQUAL

LEVELS AND /OR DROPPED CALLS.HOWEVER DUE TO LITTLE OR NO TRAFFIC

IN THE SYSTEM, IT IS NOT POSSIBLE TO SPOT ALL THE PROBLEMS THAT

MIGHT OCCUR WHEN THERE IS MORE TRAFFIC IN THE SYSTEM.FOR EX.


23/24

INTERFERENCE FROM THE NON BCCH CARRIERS DOES NOT AFFECT THE

QUALITY .THEREFORE IT IS IMPORTANT THAT THE LOG FILES ARE

CAREFULLY ANYLYSED EVEN THOUGH THERE ARE NO SIGNS OF POOR

QUAL.

POOR QUAL:

THERE ARE THREE MAJOR REASONS FOR POOR QUALITY.

INTERFERENCR PROBLEM, LOW SIG. STRENGTH OR A MISSING NEIGHBOUR.

THE REASON FOR THE POOR QUAL.CAN BE:

1. MS DOES NOT ON BEST SERVER

2. INTERFERENCE

3. LOW SIGNAL STRENGTH

MAKE THE NECERRY CHANGES /ADJUSTMENTS DEPEPNDING ON THE

REASON FOR THE POOR QUAL.

MISSING NEIGHBOUR RELATIONS:

MISSING NEIGHBOUR RELATIONS DISABLES A HANDOVER AND MIGHTLEAD TO POOR QUALITY AND EVENTUALLY A DROPPED CALL.

INCLUDING ALL THE BCCH FREQ. IN THE MEASURING LIST DURING THE

INTIAL TUNING, MAKES MISSING REALATIONSHIP EASIER TO DETECT.

NEIGHBOUR THAT ARE NOT INCLUDED IN THE NEIGHBOUR LIST ARE NOT

NOT EVALUATED BY LOCATING.

IF HANDOVER IS NOT PERFORMED TO WHAT SEEMS TO BE THE BEST

SERVER, THERE IS A POSSIBILITY OF A MISSING NEIGHBOUR RELATION.

IF THAT IS NOT THE CASE AND TH EQUAL.IS POOR, HAND OVER HYSTERISIS,

OFFSET, L- CRITERION PARAMETERS (IF USED) AND HCS PARAMETER (IF

USED) SHOULD BE REVIEWED TO FIND THE REASON FOR THE MS NOT BEING

ON THE STRONGEST CANDIDATE.THERE IS SITUATION WE CAN IMPROVE THE COVERAGE, BY INCREASING

THE OUTPUT POWER AND/OR MAKING ANTENNA ADJUSTMENTS.

OUTPUT POWER:

BY INCREASING THE OUTPUT POWER,THE DOWNLINK SIGNAL STRENGTH

INCREASE .HOWEREVER ,IF THE O/P POWER IS TOO HIGH (APPROXIMATELY

-43 DBM OR MORE),A HIGHER O/P POWER WILL NOT GREATLY AFFECT THE

OVERALL PERFORMANCE DUE TO THE LACK OF POWER BALANCE BETWEEN

UPLINK AND DOWNLINK .

BUT AN INCREASE IN O/P POWER MAY LEAD TO HIGHER INTERFERENCE IN

COCHANNEL AND ADJUCENT CHANNEL CELLS.

THE CELL BORDERS ARE ALSO AFFECTED.ANTENNA ADJUSTMENTS: A HIGHER ANTENNA POSITION GENERALLY

INCREASE THE CELLS COVERAGE AREA .SOMETIMES THE RE DIRECTION OF

AN ANTENNA MAY HELP THE SITUATION. IF THE ANTENNA IS

DOWNTILTED ,A DECREASES OF THE TILT GENERALLY INCREASE THE

COVERAGE AREA.


24/24

JUST LIKE THE CHANGING THE O/P POWER ,AN ANTENNA ADJUSTMENTS

AFFECTS THE ENTIRE CELL PLAN REGARD TO CELL BOARDERS AND

INTERFERENCE.

INTERFERENCE PROBLEM

MAJOR IINTERFERNSE PROBLEMS REQUIRE A CHANGE OF FREQ. ON ONE OR

MORE CELLS.FOR A CELLS SEVERE PROBLEM ,ANATENNA DOWNTILTS CAN HELP

SITUATITIONS .

MINOR INTERFERENCE PROBLEM CAN SOMETIMES BE ELIMINATED OR

REDUSED BY PARAMETER CHANGES .MOVIING CELL BOARDER AND /OR

CHANGING THE HANDOVER (EX. SMALLER HANDOVER HYSTERIS AND

SHORTER FITER LENGTHS ) CAN TAKE CARE OF LOCAL INTERFERENCE

PROBLEMS.

ANTENNA ADJUSTMENTS:

ANTENNA ADJUSTMENTS SUCH AS ANTENNA TILT AND HEIGHT AFFECTS

THE SIGNAL STRENGTH AND THEREBY THE CELLS BOARDERS AND

INTERFERENCE LEVELS .BY DOENTILTING THE ANTENNAS ,A CALMER BEHAVIOR IS GENERALLY

ACHIEVED IN THE NETWORK .THE SIGANL STRENGTH BECOMES MORE

CONCENTRATED TO THE AREA CLOSE TO THE SITE .DOWNTILTING AN

ANTENNA CAN REDUCE IN INTERFERENCE IN CO- CHANNEL OR ADJUSTENT

CHANNEL CELLS AS WELL AS IN THECELL ITSELF.

THE MAJOR DRAWBACK OF HAVING TOO MUCH DOWNTILT IS THE RISK OF A

LOSS IN OVERALL COVERAGE.

Documents

Drive test interview questions Part-2