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TELECOM 2G,3G,4G,R F,IPv6 Study M ater i al s: GSM Inter vi ew Questi on - Answer Share
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TELECOM 2G,3G 2G,3G,4G,RF,IPv6 Study Materials Mobile Communication,Question related to GSM SM,CDMA,WCDMA ,CDMA,WCDMA & LTE,Short description about RF Deive Test,RF Planning,RF Optimization, Optimization,IP IP v4 & IPv6
Friday, January 18, 2013
About Me
GSM Interview Interview Question -Answer 1.
Wh at is t he fu ncti on of SDCCH & SAC CH?
Dharmendra singh An s. (a) SDCCH-- -- Sl ow Dedicate d Contr ol Cha nne l.
Function----
(b)
a)
Location updates
b)
SMS
c)
Ciphering Initiation
d)
Equipment Validation
e)
Subscriber Subsc riber auth entat ion
f)
Call set up signaling
SACCH---Slow Associated Control Channel. Function: (a)
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Presently 2G / 3G / WCDMA RF/Telecom Consultant Consultant in United Unite d Telecom Limited since July 2012 to T ill Date.Extensive Date.Extensive knowledge of TEMS, NEMO, PROBE, MAPINFO PROFESSIONAL, MCOM, ACTIX & SCANNER (PCTEL, R&S TSMO). View my complete profile
Timing advance data
(b) Transmit power control (c) transmission of signaling signaling data (d) radio link supervision measurements 2. What are ar e the reasons r easons for for Hand Ov ers?
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(Ans) . (a) Signal Strength (RX LEVEL) (b) Signal Quality (RX Qual) (c) Power Budget (d)Timing (d) Timing Advance. (e) Interference 2.
Wha t a re t he sh ortcomi ngs in ha ndover s?
a)
Call Dro Dropping. pping.
b)
Ping- Pong handover
c)
Far- Away cell effect
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4. What is intelligent h and over?
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Ans)Fu zzy logic a)
ARTS Neutral netwo networks rks
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5. What are internal & external hand over?
(1)INTERNAL (1)I NTERNAL HANDOVER
2013 (53) (53) ▼ 2013 ► 10/20 10/27 (2) 10/27 (2)
► 10/06 10/13 (1) 10/13 (1)
( INTER BTS) ---- Transfer between two
channels (time slo slot) t) in same cell. b)
2014 (6) (6) ► 2014
► 10/13 10/20 (1) 10/20 (1)
Ans
a)
POST
► 08/25 09/01 (2) 09/01 (2)
( INTRA INTRA BSC ( BTS –BTS)-----1 . tr ansfer bet ween BTS under
contr co ntr ol of same Bsc Bsc 2
Measuring the quality of radio connection
3
Power Po wer level s
► 07/07 07/14 (1) 07/14 (1) 12 have us View 12 have in circles all
2. EXTERNAL HANDOVER.
( a) INTER BSC (BSC_ BSC)---- 1. Tra nsfer between BTS under
► 05/26 06/02 (3) 06/02 (3) ► 05/19 05/26 (1) 05/26 (1)
th e co contr ntr ol of diff
► 05/12 05/19 (1) 05/19 (1)
2.
► 04/21 04/28 (6) 04/28 (6)
BSC BSC TO BSC
3 . NSS to att ends the hand over 4. MSC co contr ntr ols.
http://r ftel ecomm.bl og spot.i n/2013/01/g sm- i nter vi ew- q uesti on- answer .html
► 04/14 -
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TELECOM 2G,3G,4G,RF,IPv6 Study Materials: GSM Interview Question -Answer 04/21 (4) ( b) INTER MSC ( MSC- MSC) ----1. tra nsfer between cell under
► 04/07 04/14 (2)
th e contr ol of diff MSC
► 03/24 03/31 (1)
.What is the frequency Hopping its imp? (Ans)
► 03/17 03/24 (3)
It is defined as sequential change of carrier frequency on
·
the ra dio link between mobile & base stat ion.
► 03/10 03/17 (4)
Two types of freq hopping----- 1. Base band fr eq hopping.
·
2. synt hesized frequency hopping.
► 03/03 03/10 (2)
7. Explain the major diff between BBH & SFH?
► 02/24 03/03 (2)
Ans ·
In BBH the no of hopping freq is same as n o of TRX.
·
In SFH the no of Hoping freq can be i n t he ra nge of 1to 63.
► 02/03 02/10 (2) ► 01/20 01/27 (3)
8. what are the advantages of Frequency Hopping?
1.
Frequency Diversity
2.
Interference Averaging
3.
capacity
▼ 01/13 01/20 (5)
2G Spectru m SCAM in India
9. How in frequency hopping there is enhancement of network capacity?
·
INTERNS HIP PROGRA MME FOR FOREIG N CANDID AT ES IN IND...
Freq hopping implement will enable more aggressive freq
reuse pattern, th at l eads to better spectrum efficiency. ·
It can add more transceiver in the exi sting sites , while
maintaing the net work quality/ ·
Freq hopping compressing the avai lable spectrum t o
make room for extra capacity
WCDMA/3 G Question s& Answers
. 10. Define the freq. hopping parameters?
Frequency Hopping Parameters
GSM Intervie w Question -Answer
GSM defines th e following set of para meters:
Mobile Al location (MA): Set of frequencies the mobile is all owed to hop over. Maximum of 63 frequencies can be defined in the MA list.
RF Optimiza tion and Log File Analysis in GSM
Hopping Sequence Number (HSN): Determines the hopping order used in the cell. It is possible to assign 64 different HSNs. Sett ing HSN = 0 provides cyclic hopping sequence and HSN = 1 to 63 provide va rious pseudo-random hopping sequences.
Mobile Allocation Index Offset (MAIO): Determines inside the hopping
► 01/06 01/13 (7)
sequence, which frequency t he mobile starts do transmit on. The va lue of MAIO ranges between 0 to (N-1) where N is th e nu mber of frequ encies defin ed in th e MA li st.
► 2012 (7)
Presently MAIO is set on per carrier basis.
Motorola has defined an additional parameter, FHI. Hopping Indicator (FHI): Defines a hopping syst em, made up by an associat ed set of frequencies (MA) to hop over and sequence of hopping (HSN). The v alu e of FHI va ri es between 0 t o 3. It i s possible t o define a ll 4 FHIs in a singl e cell .
Motorola system a llows to define the hopping system on a per tim eslot basis. So different hopping configurat ions are all owed for different ti meslots. Thi s is very useful for int erference av eraging and to randomize th e distribution of errors.
11. What are the effects of freq hopping? (Ans)
1 Handovers:
2 Call setup:
3 Frame Erasure Rate (FER):
12 .Explain in brief what is FER. ·
An s
FER= Numb er of era sed blocks\ t ota l no of blocks *100
·
It is the right measure of voice quality.
·
FER is performed on speech& signaling frames
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TELECOM 2G,3G,4G,RF,IPv6 Study Materials: GSM Interview Question -Answer FER------- 0 to 4%,
·
4
GOOD.
to 15% , slightly degraded
Greater tha n 15%, useless
13. What happens when speech frames discarded in FER?
System will interpolate.
·
14. What happens when signaling frames discarded in FER?
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MS is instructed to resend.
·
15. What is TCH_ TCH Interference? How it is measur ed.
Whe n TC H carr ies a re re used t ha t l eads t o co-cha nnel
·
interference. Wh en T CH carr ier h av e cal l a cti vi ty .
·
This is measured by delta measurement. --- 1. BCCH carries are
·
diff
2. TCH carriers in both cell 1& cell2 are same A FRCN TCH
16. Define th e terms?
·
BER--- The number of erroneous bits received Total no of bits received.
·
RBER---1 Residual bit error rate 2
It is performed on demodulated speech frames that
are not ma rk corrupt
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.BFI -- Bad frame indicat ion.
17. Explain the parameters in TEMS POCKET mobile.
L L
BC TC C/I
BS TS RQ
RXLEV TX FE
TA
DSC
CHM
MCC
RH MNC
CiMd LAC
RA
CI
1. 2.
Llcell BCCH ARFCN
3.
4.
5. ·
L1. Logical chan nel.---- - BCCH
·
L2. Logical chan nel ----- TCH
·
BC-- serving cell BCCH AFRCN.
·
BS-- ba se stat ion identi ty code.
·
RXLEV- recieved signal strength
·
TC--
·
TS -
·
TX - transmit power
·
C/I -- Carrier to interference ratio in db
·
RQ -- Receive bit error rate
traffic channel
time slot number.
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TELECOM 2G,3G,4G,RF,IPv6 Study Materials: GSM Interview Question -Answer
·
FE –frame erasure rat e.
·
TA -- Timing advance
·
CHM --C hannel Mode
·
RH -- cell reselction Hystresis
·
CiMd—Ciphering mode
·
RAC – Routing area code.
·
LAC—Location area code.
18. Explain t he analy sis behind RX Qual.?
RX Qual i s the basic measure. It reflects th e average BER over
·
the certain period of time(0.5s)
·
RX QUAL done over 104 TDMA frames.
·
Limitation of RXQUAL---- 1. The distributions of bit error over
time.
2. Frame erasure 3. Hand over. 19. What are type of interference occur? 1.
Co- channel interference.
2.
Adj-ch an nel int erfer ence.
3.
Near end- Far end interference.
20.
Wha t i s ERLANG?
·
Unit of telephone traffic intensity is called Erla ng.
·
One ERLANG is one channel occupied continuously for one
·
1E = 64Kbps.
hour.
21. what do you mean by GOS?
·
It is the probabity of hav ing a call blocked during busiest h our.
·
Ex GOS=0.05 means one call in 20 will be blocked call during
busi est h our beca use of in suffi cient capaci ty .
22. What are th e technique GSM offers which combat Mult ipath fading?
·
Equalization
·
Diversity
·
Freq Hopping
·
Interleaving
·
Channel coding
23. What are control &t raffic channels?
·
CONTROL CHANNEL.----1 BCH 2. CCCH 3. DCCH.
·
TRAFFIC CHANNEL-- Hal f rat e
Full rate
EFR == Enha nced full rate.
24. Wha t are BCH, CCH, DCCH channel s?
·
BCH-- 1. BCCH
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TELECOM 2G,3G,4G,RF,IPv6 Study Materials: GSM Interview Question -Answer 2 .FCCH 3. SCH
·
CCCH. --- 1.PCH 2. AGCH 3. RACH
·
DCCH----
1.SDCCH.
2. SACCH 3. FACCH 25. What are ty pes of bursts?
·
Normal Burst
·
Frequency Correction Burst
·
Synchronization Burst.
·
Dummy Burst
·
Access Burst .
26. What is adjacent channel separat ion in GSM? ·
Urban Environment-------- 200khz
·
Sub Urban Environment ---- 400khz
·
Open environment ----- 800khz
27. Wha t is t he watt t o dBm conversions? ·
Power in dBm = 10 l og( watt s *100)
·
0 dBm= 1mili watt
·
1watt = 30dbm
·
28. What are the optimizations you have done during Drive
Test?
·
Wh at ar e sam ples i n gsm?
·
Wh ich m odula ti on ta ke pla ce in GSM
·
In one TRU how many fra mes are there?
·
Wh at is t he v al ue RX LEV of nei ghbori ng cell ?
·
Wh at do you m ean by V AD?
·
Wh at is BFI, where i t i s use?
2929. Define the h opping parameters in detail?
The MA is a list of hopping frequencies transmitt ed to a mobile every ti me it is assigned to a hopping physical channel. T he MA-list is a subset of the CA list. The MAlist is au tomatically generated if the baseband hopping is used. If the net work ut ilises the RF hopping, the MA-lists ha ve t o be generated for each cell by the n etwork planner. The MA-list is able t o point to 64 of the frequencies defined in the CA list. However, the BCCH frequency is al so included in th e CA list, so the practical m aximum number of frequencies in t he MA-list i s 63. The frequencies in the MA-list are required to be in increasing order because of the type of signaling used to transfer the MA-list. 1.1 Hopping Sequen ce Number The Hopping Sequence Numbe r (HSN) indicat es which hopping sequence of the 64 avail able is selected. The hopping sequence determines the order in which t he frequencies in the MA-list are to be used. The HSNs 1 - 63 are pseudo random sequences used in the random hopping while the HSN 0 is reserved for a sequential sequence used in the cyclic hopping. The hopping sequence algorithm takes HSN and FN as an input and the output of the hopping sequence generation is a Mobile Allocation Index (MAI) which i s a nu mber ra ngin g from 0 t o the n um ber of frequ encies i n t he MA -l ist subtracted by one. The HSN is a cell specific parameter. For the baseband hopping two HSNs exists. The zero time slots in a BB hopping cell use the HSN1 and the rest of the time slots follow the HSN2 as presented in Error! Reference source not found.. All the time slots in RF hopping cell follow the HSN1 as presented in Error! Reference source not found.. 1.2 Mobile Allocation Index Offset Whe n t her e is m ore th an one T RX in th e BTS u sing t he sa me MA- li st t he Mobile Allocation Index Offs et (MAIO) is used to ensure that each TRX uses always an unique frequency. Each hopping TRX is allocated a different MAIO. MAIO is added to MAI when the frequency to be used is determined from the MA-list. Example of the hopping sequence generati on is presented in E rror! Reference source not found.. MAIO and HSN are tra nsmitted t o a mobile together with t he MA-list. In Nokia solution the MAIO offset is a cell specific parameter defining the MAIO TRX for the first hopping TRX in a cell.
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TELECOM 2G,3G,4G,RF,IPv6 Study Materials: GSM Interview Question -Answer The MAIOs for t he other hopping TRXs are aut omatically allocated according to th e MAIOstep -parameter introduced in the following section. 30. What is the effect of frequency hopping in RXQual? Frequency hopping causes some changes in the RXQUAL distribution. Also, there ar e some differences in a way th e RXQUAL distribut ion should be int erpreted. The Frame Erasure Ratio (FER) is a rat io of discarded speech fram es compared t o all the r eceived speech frames. A speech frame is generally discarded if after the decoding and error correction process any of the category 1a bits is found to be changed based on t he t hre e par it y bi ts foll owing th em i n a spe ech fra me. FER is a measur e of how successfull y the speech frame was received after the error correction process and it is thus a better indication of the subjective speech qualit y compared to the RXQUAL which gives an estimate of the link qua lity in terms of BER. The RXQUAL doesn’t indicate how the bit errors were distributed in a speech frame. The bit error distribution affects t he abilit y of th e channel decoding to correct the errors.
The following table gives an idea of the correlation between RXQUAL and FER and between subjective speech quality and different FER classes.
31. What i s the relat ion link between RXQUAL& FER?
Table 1. RXQUAL vs. FER comparison according to the laboratory tests.
The rela tion of downlink FER and RXQUAL was measured during a FH tria l. Th e relation is clearly different in the hopping case compared to the non-hopping case. The distributions of FER in each RXQUAL class are presented in Error! Reference source not found. and Error! Reference source not found.. One clear observation can be made; in the non-hopping case there are significant amount of samples indicating deteriorated qualit y (FER>10%) in RXQUAL class 5 while in t he hopping case the significant quality deterioration (FER>10%) happens in RXQUAL class 6. Thus, it may be concluded that in the frequency hopping networks significant qualit y deterioration start s at RXQUAL class 6 while in non-hopping network this happens at RXQUAL class 5. This improvement of FER means that the higher RXQUAL values may be allowed in a frequency hopping network. RXQUAL thresholds are used in the handover and power control decisions. Because of the improvement in the relative reception performance on the RXQUAL classes 4-6, the RXQUAL thresholds affecting handover and power control decisions should be set higher in a network using frequency hopping network. In a frequency hopping network RXQUAL classes 0-5 are indicating good quality.
Typically , the share of the RXQUAL classes 6 and 7 may increase after FH is switched on, even if no other changes have been made. This may seem to be surprising since it is expected that frequency h opping improves the network quality . However, in most cases the quality is actually improved, but t he improvement is more visible in the call success rati o. The improved tolerance against interference and low field strength in FH network means th at i t is l ess likely tha t t he decoding of SACCH frames fails causing increment in t he radio link timeout counter. Thus, it is less likely tha t a call is dropped because of th e radio link t imeout. Instead, the calls generating high RXQUAL samples tend t o stay on. This m ay lead to increase in t he share of RXQUAL 67. However, at the same t ime th e call success rate is significantly im proved.
In the Error! Reference source not found., there are presented some trial results of a DL RXQUAL distribution with different frequency allocation reuse patterns. A s can be seen fr om th e figu res, t he t igh ter th e reu se becomes, th e less sa mpl es fal l i n qua li ty class 0 and more samples fall in quality classes 1-6. There’s bigger difference in downlink than in uplink direction.
This difference is a consequence of interference and frequency diversities that
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TELECOM 2G,3G,4G,RF,IPv6 Study Materials: GSM Interview Question -Answer affect the frequency hopping network. Because of these effects, the interference or low signal strength tend to occur ra ndomly, while in a non-hopping network it is probable that interference or low field strength will affect several consecutive bursts makin g it harder for the error correction to actually correct errors. The successful error correction leads to less erased frames and thus improves the FER. 32. What do you understand by idle channel measurement?
·
Wh en a n ew call is est abl ishe d or a h an dover i s perform ed, t he
BSC selects the TRX and t he tim e slot for th e traffic channel based on the idle channel int erference measurements. The frequency hopping ha s a significant effect on the idle channel int erference measurement result s.
Whe n t he fr equen cy h opping i s used, t he fr equen cy of a h opping l ogical chan nel is changed about 217 times in a second. The frequency of the idle time slots changes according to the same sequence.
In a case of the random hopping , this means that the measured idle channel interference is likely t o be the same for all t he TRXs that use the same MA-list. If the interference is averaged over more than one SACCH frame, th e averaging effect is even stronger. However, normally the interferers are mobiles located in interfering cells. In this case, there ar e probably differences in the measured idle channel interferences between differ ent ti me sl ots in th e cell . Th is ha ppens, beca use t he i nt erfer ing m obiles are only transmit ting during the ti me slot th at ha s been allocated to them. This is illustra ted in Figure Error! No text of specified style i n document. -1. If the cyclic hopping sequence is used, there might occur differences on the measured idle channel interference levels between the TRXs on the same t ime slot as explained in the following section.
Figure Error! No text of specified style in document. -1. Idle channel interference in a case of the random RF hopping
33 .what a re ty pes of handover? There are four different types of handover in the GSM system, which involve transferring a call between: ·
Channels (time slots) in the same cell
·
Cells (Base Transceiver Stations) under the control of the same
Base Station Controller (BSC), ·
Cells under t he control of different BSCs, but belonging to th e
same Mobile services Switching Center (MSC), and ·
Cells under the control of different MSCs.
34. what a re important parameter of power saving in GSM Discontinuous transmission Minimizing co-channel interference is a goal in any cellular system, since it allows better service for a given cell size, or the use of small er cells, thus increasing the overall capacity of the system. Discontinuous tra nsmission (DTX) is a m ethod that takes advant age of the fact th at a person speaks less that 40 percent of the time in normal conversation [22], by tu rning the transmit ter off during silence periods. An added benefit of DTX is th at power is conserved at t he mobile unit. The most important component of DTX is, of course, Voice Activity Detection. It must distinguish between voice and noise inputs, a task tha t is not as triv ial a s it appears, considering background noise. If a voice signal is misinterpreted as noise, the transmit ter is turn ed off and a very a nnoying effect called clipping is heard at t he receiving end. If, on the other hand, noise is misinterpreted as a voice signal too often, the efficiency of DTX is dramatically decreased. Another factor to consider is that when the tr ansmitt er is turned off, there is total silence heard at t he receiving end, due to the digita l nat ure of GSM. To assure the receiver that the connection is not dead, comfort noise is created at the receiving end by try ing to match th e characteristics of the transmit ting end's background noise.
Disconti nuous reception Anot her met hod used t o conserv e power at th e mobil e sta ti on is discont inu ous reception. The paging channel, used by the base stat ion to signal an incoming call, is structured into sub-channels. Each mobile station needs to listen only t o its own subchannel. In the time between successive paging sub-channels, the mobile can go into sleep mode, when al most no power is u sed. Al l of t his i ncrea ses bat ter y l ife consider abl y whe n compar ed to a na log : What is Tri-band and Dual-band?
A: A tri-band phone operates at three supported frequencies, such as 900/1800/1900 MHz or 850/1800/1900
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TELECOM 2G,3G,4G,RF,IPv6 Study Materials: GSM Interview Question -Answer MHz. A dual-band phone operates at two frequencies, such as 850/1900 MHz or 900/1800
Posted by Dharmendra singh at Friday, January 18, 2013 +2 Recommend this on Google
3 comments: swetank aginhotri said... these are very helpful. thanks May 9, 2014 at 1:37 PM
swetank aginhotri said... these are very helpful. thanks May 9, 2014 at 1:38 PM
swetank aginhotri said... these are very helpful. thanks May 9, 2014 at 1:39 PM Post a Comment
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