3 G Questions

8/13/2019 3 G Questions

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1. What is a typical NodeB sensitivity level?

The service and load determines the NodeB sensitivity; in general, in a no-loadcondition, the sensitivity is between -115dBm to -125dBm. For Ericsson, the NodeB

sensitivity level is calclated at arond!"#12.2! -12$ dBm%#-&$! -11' dBm%#-12(! -115 dBm%#-)($! -115 dBm2. What is a typical UE sensitivity level?

The service and load determines the *E sensitivity; in general, in no-load condition, thesensitivity is between -1+5dBm and -12+dBm. For Ericsson, the *E sensitivity level iscalclated at arond!"#12.2! -11' dBm%#-&$! -112 dBm%#-12(! -11+ dBm

%#-)($! -1+5 dBm#%! -'5 dBm3. What is a typical NodeB maximum output power?The ma/imm NodeB ot0t 0ower is sally 2+ or $+, that is, $)dBm or $&dBm.4. What is UE maximum transmit power in your lin !ud"et?21dBm.#. What is a typical antenna "ain?The antenna gain de0ends on antenna model; in lin bdget we se arond 13dBi.$. What is a typical maximum path loss?


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The ma/imm 0ath loss is de0endent on the service and vendor recommendations;ty0ically it is in between 1)5 to 1$+dB 4or rban areas and between 15+ to 1&+dB 4orrral areas.%. What is di&&erence !etween dBi and dBd?

dBi is the gain in dB 4rom isotro0ic sorce; dBd is the gain 4rom a di0ole sorce.dBd 2.15 6 dBi.'. What is the di&&erence !etween dB and dBm?dBm is a nit o4 0ower level, measred in milli-watts in logarithm scale, that is,dBm 6 1+ 7 log871+++9 where is the 0ower in atts

dB is not a nit, it is the di44erence in dBm.(. What is )dBm?+dBm 6 1 milli-watt.1). *ow does +,- wor?

T: redces system noise, im0roves 0lin sensitivity and leads to longer *E batteryli4e.

#ensitivity is the minimm in0t 0ower needed to get a sitable signal-to-noise ratio8#N9 at the ot0t o4 the receiver. ?1 8NF)-19>8?17?29 @ 8NFi-19>8?17?27@7?i9

s the e=ation shows, the 4irst bloc im0oses the minimm and the most 0rominentnoise 4igre on the system, and the 4ollowing blocs im0oses less and less im0act to thesystem 0rovided the gains are 0ositive. Ainear 0assive devices have noise 4igre e=alto their loss. T: ty0ically has a gain o4 12dB.There are ty0ically to0 m0er, main 4eeder and a bottom m0er between antenna andBT#. T: 0laced near antenna with a short m0er 4rom antenna 0rovides the bestnoise 4igre im0rovement C the noise 4igre will be restricted to the to0 m0er loss 8NF 19


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and T: 88NF2-19>?19, and the remaining blocs 8main 4eeder and bottom m0er9 havelittle e44ect.To smmariDe, a T: has a gain thats close to 4eeder loss.

11. What are the pros and cons advanta"es and disadvanta"es/ o& +,-?n the 0side, a T: redces system noise, im0roves 0lin sensitivity and leads tolonger *E battery li4e. n the downside, T: im0oses an additional insertion loss8ty0ically +.5dB9 on the downlin and increases site installation and maintenancecom0le/ity.12. What is typical +,- "ain?T: ty0ically has a 12 dB gain; however, the e44ective gain comes 4rom noise 4igreredction and the gain is close or e=ivalent to the 4eeder loss.

13. Why +,- are installed at the top near the antenna and not the !ottom near theNodeB?Based on Friis E=ation, having a T: near the BT# will have the to0 m0er and main4eeder losses 8noise 4igres9 cascaded in and a T: will not be able to hel0 s00ressthe losses.14. What is U,+0 chip rate?).($:D.

1#. What is processin" "ain?%rocessing gain is the ratio o4 chi0 rate over data bit rate, sally re0resented in decibel8dB9 scale. For e/am0le, with ).($:D chi0 rate and 12.2 data rate, the 0rocessinggain is!%?12.26 1+ 7 log 8),($+,+++ > 12,2++9 6 25dB1$. What are the processin" "ains &or 0 and 0 services?"#12.2! 25dB%#-&$! 1(dB%#-12(! 15dB%#-)($! 1+dB


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#%! 2dB1%. *ow to calculate maximum num!er o& users on a cell?To calclate the ma/imm nmber o4 sers 8M9 on a cell, we need to now!

W! chi0 rate 84or *:T# ),($+,+++ chi0s 0er second9EbNo! Eb>No re=irement 8assming )dB 4or "#-12.29i! other-cell to in-cell inter4erence ratio 8assming &+G9R! ser data rate 8assming 12,2++ b0s 4or "#-12.29H! loading 4actor 8assming 5+G9

Tae 12.2b0s as e/am0le!: 6 > 8EnNo 7 81 i9 7 9 7 H 6 ),($+,+++ 8) 7 81 +.&9 7 12,2++9 7 +.5 6 )2.(The nmber o4 sers cold also be hard-limited by I#F code s0ace. Tae "#12.24or e/am0le! "#-12.2 bearer needs 1 #F12( code.

Total available codes 4or "#-12.2 6 12( C 2 81 #F&$9 C 2 8$ #F25&9 6 12$.

"onsider so4t-handover 4actor o4 1.( and loading 4actor o4 5+G! 12$ > 1.( 7.+5 6

)$ ers>cell.

1'. What is E!No?By de4inition Eb>No is energy bit over noise density, i.e. is the ratio o4 the energy 0erin4ormation bit to the 0ower s0ectral density 8o4 inter4erence and noise9 a4terdis0reading.Eb>No 6 %rocessing ?ain #No is 5dB and 0rocessing gain is 25dB then the #No targets are de0endent on the service! n the 0lin, ty0ically "# is 5 to &dB and %# is ) to $dB C %# is abot 2dB

lower.


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n the downlin, ty0ically "# has & to 3dB and %# is 5 to &dB C %# is abot 1dB

lower.

2). Why is E!No reuirement lower &or 0 than &or 0?%# has a better error correction ca0ability and can tiliDe retransmission, there4ore itcan a44ord to a lower Eb>No. "# is real-time and cannot tolerate delay so it needs ahigher Eb>No to maintain a stronger F lin.21. What is Ec5o?Ec>


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The 0lin noise increases with the loading e/0onentially. hen the 0lin noisea00roaches in4inity then no more sers can be added to a cell C and the cell loading isclose to 1++G and has reached its J0ole ca0acityK.:athematically, to calclate the 0lin 0ole ca0acity we need to now!

W! chi0 rate 84or *:T# ),($+,+++ chi0s 0er second9R! ser data rate 8assming 12,2++ b0s 4or "#-12.29f! other-cell to in-cell inter4erence ratio 8assming &5G9EbNo! Eb>No re=irement 8assming 5dB9

F! ctivity 4actor 8assming 5+G9

%ole "a0acity 6 8>9 > 881f9 7 F 7 1+L8EbNo>1+99 6 12+.&

To calclate the downlin 0ole ca0acity we also need to now!! downlin channels orthogonality 4actor 8assming 55G9%ole "a0acity 6 8>9 > 881-f9 7 1+L8EbNo>1+99 6 &$.+&2%. What is typical pole capacity &or 0912.26 09$46 0912' and 093'4?ith same assm0tions as above!

"#-12.2! 12+.& 8*A9, &$.1 8A9.

%#-&$! )$.( 8*A9, 12.(8A9.

%#-12(! 1&.2 8*A9, (.$ 8A9.

%#-)($! 1&.2 8*A9, 2.( 8A9.

%#-)($ has only 12( on the 0lin, there4ore the 0lin ca0acity is the same 4or both.2'. *ow many types o& handovers are there in U,+0?#o4t handover, so4ter handover, inter-4re=ency handover, inter-T handover, inter-T cell change 8*E moving ot o4 *:T# coverage into ?#:>?%#>E??Ecoverage9.2(. What is so&t handover and so&ter handover?


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#o4t handover! when a *E is connected to cells owned by di44erent NodeB.

#o4ter handover! when a *E is connected to cells owned by the same NodeB.

3). *ow does so&tso&ter handover wor?

#o4t>so4ter handover downlin! *E rae receiver 0er4orms ma/imm ratio

combining, i.e. *E combines mlti-0ath signals and 4orm a stronger signal. #o4t handover 0lin! N" 0er4orms selection combining, i.e. N" selects the

better signal coming 4rom mlti0le NodeB.

#o4ter handover 0lin! NodeB 0er4orms ma/imm ratio combining, i.e. NodeBrae receiver combines signals 4rom di44erent 0aths and 4orms a stronger signal.

31. Why is there :so&t handover "ain;?#o4t handover gain comes 4rom the 4ollowing! :acro diversity gain over slow 4ading.

:icro diversity gain over 4ast 4ading.

ownlin load sharing over mlti0le F lins. By maintaining mlti0le lins eachlin cold transmit at a lower 0ower, reslting in lower inter4erence there4ore a gain.

32. Brie& descri!e the advanta"es and disadvanta"es o& so&t handover?

dvantages! vercome 4ading throgh macro diversity.

edced Node B 0ower which in trn decreases inter4erence and increases

ca0acity.

edced *E 0ower 80 $dB9, decreasing inter4erence and increasing battery li4e.

isadvantages!

*E sing several radio lins re=ires more channeliDation codes, and more

resorces on the


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Fast 4ading is also called mlti-0ath 4ading, as a reslt o4 mlti-0ath 0ro0agation. henmlti-0ath signals arriving at a *E, the constrctive and destrctive 0hases create avariation in signal strength.#low 4ading is also called shadowing. hen a *E moves away 4rom a cell the signal

strength dro0s down slowly.34. What are &ast &adin" mar"in and slow &adin" mar"in?To 4actor in the 4ast 4ading and slow 4ading, we need to have a margin in the lin bdgetand they are called 4ast 4ading margin and slow 4ading margin.


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"% with a 3)dBm 5* and a 91))dBm UE sensitivity6i"norin" anythin" in !etween6 what is the maximum path loss?)+ C 8C1++9 6 )+ 1++ 6 1)+dB.44. 0uppose 5 have a maximum path9loss o& 13)dBm6 what is the new path9loss i&a #dB !ody loss is added?125dB.


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4#. What is channeliation code?"hanneliDation codes are orthogonal codes sed to s0read the signal and hence0rovides channel se0aration, that is, channeliDation codes are sed to se0arate

channels 4rom a cell.4$. *ow many channeliation codes are availa!le?The nmber o4 channeliDation codes available is de0endent on the length o4 code.


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#1. Which service usually needs hi"her power6 0 or 0?"onsider downlin and tae "#-12.2 and %#-)($ 4or e/am0le. The 0rocessing gain is25 4or "#-12.2 and 1+ 4or %#-)($. The Eb>No re=irement is 3 4or "#-12.2 and 5 4or%#-)($. There4ore the 0ower re=irement is higher 4or "#-12.2 than %#-)($.

#2. What is E!No reuirement &or *0No re=irement 4or #% varies with ser bit rate 8data rate9, ty0ically 2 4or3&(b0s and 5 4or 2:b0s.#3. What is :noise rise;? What does a hi"her noise rise mean in terms o& networloadin"?For every new ser added to the service, additional noise is added to the networ. Thatis, each new ser cases a Jnoise riseK.


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#%.


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T)++ C time to wait between " retries 81++ms to (+++ ms, ty0ical 15++ms9 "losed oter loo0! 1++ times a second.

"losed inner loo0! 1,5++ times a second.

$4. Brie&ly descri!e why open loop power control is needed and how it wors? hen a *E needs to access to the networ it ses " to begin the 0rocess. " is a shared channel on the 0lin sed by all *E, there4ore may enconter

contention 8collision9 dring mlti0le ser access attem0ts and inter4ere with eachother.

Each *E mst estimate the amont o4 0ower to se on the access attem0t since

no 4eedbac 4rom the NodeB e/ists as it does on the dedicated channel.

The 0r0ose o4 o0en loo0 0ower control is to minimiDe the chance o4 collisionand minimiDe the initial *E transmit 0ower to redce inter4erence to other *E.


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$%. 0uppose two UE are served !y the same cell6 the UE with weaer lin poor 7Acondition/ uses more :capacity;6 why does this mean?The *E with weaer F lin will re=ire NodeB to transmit higher tra44ic 0ower in orderto reach the *E, reslting in less 0ower 4or other *E C there4ore consmes more

Jca0acityK.$'. Under what circumstances can a NodeB reach its capacity? What are thecapacity limitations?NodeB reaches its ma/imm transmit 0ower, rns ot o4 its channel elements, 0linnoise rise reaches its design target, etc.$(. What is :cell !reathin"; and why?The cell coverage shrins as the loading increases, this is called cell breathing.

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3 G Questions