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qaqa
2011-03-17, 05:09 AM
Hello Friends

I am having a training the upcoming week with Award Solution for LTE/EPC.
I got this aucasion to ask all the guys who are working on/studying or curious about LTE to provide their most difficult questions they still confused about.
I will collect all your questions and expose it to the lecture for answer.
kindly do it as quickly as possible. tyhe training starting from this Monday to Friday.

Waiting for all your questions :D

I wanna give them hard time hehhe:cool:

raednoor
2011-03-17, 05:52 AM
the most obvious and difficult question should be asked is :

What is LTE in the first place !!!! :D

good for you my friend.

BR

raednoor

dk2000
2011-03-17, 11:33 AM
Hi guy,

Thank you so much for your opinion!

I have question:
- Which is the range of RSRP and SIRN? Which is the good value, acceptable value and the target for driving test?

qaqa
2011-03-17, 11:51 AM
thanls,it is noted.

More questions please guys....:D

edinburgh
2011-03-17, 11:59 AM
Ask them how to calculate the pathloss in LTE.:D

Normally we submit the SNR Vs. THroughout, RSRP Vs. Throughput and Pathloss Vs. Throughput in DT.

Do they have any idea on DM RS guideline and PDCCH Capacity?

And also Zadoff–Chu (ZC) sequences??

Thanks.

BR,
Edin

s.sunilpal123
2011-03-17, 01:21 PM
Hello qaqa..

Thnx for ur initiative.

Pls provide the following questions from my side.

1. How does SC-FDMA reduce the PAR (Crest factor)? In almost all books, this is just stated, not explained. It will be better if a subcarrier level expalanation (with figures) can be provided for this!

2. What are the latency differences between TDD & FDD LTE and why is one less than the other? Some source for the answer will also be helpful.

3. Simplistic explanation of working of cyclic prefix...Almost all treatments are either too mathematical or too vague. Something intuitive (like a story) will be of great help!

4. For 20 MHz there are 2048 FFT. So why only 1200 Subcarriers? Why not some value nearer to 2048???

5. The formulae for Interference Margin in Downlink as well as Uplink?

6. SFR vs FFR differences and similarities pointwise?

7. Why is LTE said to have soft capacity?

8. Consider 2T2R MIMO. Consider cell I,II,III at enodeB1. The RE's for the RS of 1st antenna port in cell I are not used for the 2nd antenna port in cell I , correct? My question is can the REs used for RS in the 1st antenna port in cell I be used for RS in cell II/III or another cell I of enodeB2?

Pls provide answers if you know already! Help will be appreciated!!!!

Thanks very much!!

s52d
2011-03-17, 02:27 PM
Hello!

We have nice, working W-CDMA 2.1 GHz network. Decent KPIs, so we are quite happy.
We know how to tune it (RET, changing antennas, setting pilot power etc).

One day we will get LTE frequencies. And some pocket money to buy equipment.

Question:
What are main differencies in planning LTE and 5 MHz W-CDMA/HSPA+ (beside coverage)?
If we just overlay LTE with same antenna pattern/tilt/sites as working W-CDMA:
- what is main problem for LTE? Works for W-CDMA, does not for OFDMA?
- what is very bad in W-CDMA, but works fine in LTE?
looking at pure layer1; parametrization comes later.

BR
s52d

hexium
2011-03-17, 05:37 PM
Here is my question:

In Section 7.1.7.2.1 of TS 36.213 where the Table of Transport Block Sizes is given, why isn't the value for Nprb = 1 and Itbs = 6 in line with the remaining entries of this table? Is that a mistake or is this TBS used for "special" transport blocks (eg VoIP).

Thanks :-)

qaqa
2011-03-17, 08:20 PM
waw guys that is grate.
lot of question means more understanding of this new technology.

Keep posting.... Bring up your most headache questions :D
I am starting answering your questions from next week.

cheers

s.sunilpal123
2011-03-17, 08:48 PM
Thanks Qaqa...

My next question (they keep coming and coming!) :

9. In the special subframe configuration in TD-LTE, DwPTS, GP & UpPTS are present in a subframe after DL slots and then after this special subframe UL slots are present .

That is when switching from DL to UL, the above special subframe is present but when switching from UL to DL , the special subframe is not required/ present.

Why is this so?

auto_art
2011-03-17, 08:59 PM
what is the difference between LTE & 4G.? are they synonym..?:confused::confused::confused:

scorpion
2011-03-17, 09:11 PM
Current LTE is only 3.9G. LTE-Advanced is still under 3GPP development which will be 4G. The difference will be in Data rates.

As per 4G 1G Down and 100M uplink to be there.

But as of now, only 350M Doenling and 50M Uplink with max resources.

qaqa
2011-03-18, 12:34 PM
keep it active guys
squeeze your mind and bring up other question

I am felling very starving for knowledge nowww :D

qaqa
2011-03-21, 08:05 AM
Thanks guys.

Tomorrow we are starting the training. if you still have more questions please throw them in this thread.

More over, I have a webbased CBT training from the same tutor for the same subject and I want to record it "voice and Video" to my computer.
Any body can suggest a good softwafre to do that?
Thank you. :D

edinburgh
2011-03-21, 02:16 PM
use snagit...define video format...you may need enough HDD space..

nitailor
2011-03-21, 04:36 PM
Is 1 time slot = 1 RB?
If not, then what are the max nos of RB in 1 time slot?

s.sunilpal123
2011-03-21, 07:35 PM
Any answers yet?

qaqa
2011-03-22, 11:34 AM
Answers will come soon.
definitely all questions will be answered by the end of this week.

Thank Edin for the SW I am traying it now. I ll see:D

Mctest
2011-03-22, 01:06 PM
Is 1 time slot = 1 RB?
If not, then what are the max nos of RB in 1 time slot?


1RB it is time-frequency block which consists of 12 subcarriers in frequency domain and 0.5 ms in time domain(one time slot).In 20 MHZ it has 100 RBs per time slot.

nitailor
2011-03-22, 02:00 PM
1RB it is time-frequency block which consists of 12 subcarriers in frequency domain and 0.5 ms in time domain(one time slot).In 20 MHZ it has 100 RBs per time slot.

Then what are the nos. of RBs in 1 time slot for a system bandwidth of 1.4, 3, 5 and 10 MHz ?

MINTO
2011-03-22, 04:02 PM
will post more answers soon
Q:How does SC-FDMA reduce the PAR (Crest factor)? In almost all books, this is just stated, not explained. It will be better if a subcarrier level expalanation (with figures) can be provided for this!
A: Peak-to-Average Power Ratio in OFDMA
OFDMA transmits data in parallel across multiple subcarriers
The transmitted power is the sum of the powers of all the subcarriers, Due to large number of subcarriers, the peak to average power ratio (PAPR) tends to have a large range,
15140


Peak-to-Average Power Ratio in SC-FDMA
SC-FDMA transmits data in series employing multiple subcarriers
The parallel transmission of multiple symbols in OFDMA creates high PAR
SC-FDMA avoids this by additional processing before the IFFT: modulation symbols are presented to FFT. The output represents the frequency components of the modulation symbols.
Subcarriers created by this process have a set amplitude that should remain nearly constant between one SC-FDMA symbol and the next for a given modulation scheme which results in little difference between the peak power and the average power radiated on a channel
Or in simple words
SC-FDMA spreads the energy of one subcarrier over all subcarriers before theI FFT. This way spectral nulls in the channel is reduced with averaging. Hence, PAPR is reduced. This subtle idea is performed by introducing additional FFT block before the IFFT block of the transmitter
15141



Q: Simplistic explanation of working of cyclic prefix...Almost all treatments are either too mathematical or too vague. Something intuitive (like a story) will be of great help
A: first we go through TIME DISPERSION

15142

IN LTE, an advantage with 15 kHz tones is that we get very long symbol time; this means it is robust against multipath propagation & in other words very good at handling time dispersion.
Explained in above figure we do not only receive direct data streams at the terminal, but also reflected ones, if we now have the situation as seen in this slide the terminal data both from the correct direct path with some data from another OFDMA symbol .bot how do we solve this
We do his by introducing a cyclic prefix. We take a small part from the end of the OFDM Symbol & insert it at the beginning. That is why we get the name Prefix.
15143

As a result, the OFDM symbol will be a little longer & the terminal will have the possibility to combine both direct path data & reflected data, as long as the delay of the reflected signal is shorter than the cyclic prefix time
Q: For 20 MHz there are 2048 FFT. So why only 1200 Subcarriers? Why not some value nearer to 2048???
A: FIRST CHECK THE Sampling Frequency
The rate at which sampling of signals is carried out. Its origin is the WCDMA chip rate: 3.84 Mcps. The same clock that generates 3.84 Mcps chip rate in WCDMA can be used to generate various sampling frequencies in LTE:
1.92 MHz = 0.5 x 3.84 Mcps( Used in LTE 1.4 Mhz)
3.84 MHz = 1 x 3.84 Mcps (Used in LTE 3 Mhz)
7.68 MHz = 2 x 3.84 Mcps (Used in LTE 5 Mhz)
15.36 MHz = 4 x 3.84 Mcps (Used in LTE 10 Mhz)
23.04 MHz = 6 x 3.84 Mcps (Used in LTE 15 Mhz)
30.72 MHz = 8 x 3.84 Mcps (Used in LTE 20 Mhz)
The subcarrier spacing is linked with the sampling frequency as follows:
FFT Size x Subcarrier Spacing = Sampling Frequency
So FFT SIZE = Sampling Frequency/ Subcarrier Spacing
Means for 20 mhz it will be = 30.72 * 1000/15= 2048
The following table gives the numbers of ―used‖ subcarriers corresponding to each FFT size:
FFT Size Used Subcarriers
128 72
256 180
512 300
1024 600
1536 900
2048 1200
Used Subcarriers Transmission Bandwidth
72 72 x 15000 = 1.08 MHz
180 180 x 15000 = 2.7 MHz
300 300 x 15000 = 4.5 MHz
600 600 x 15000 = 9 MHz
900 900 x 15000 = 13.5 MHz
1200 1200 x 15000 = 18 MHz
Nominal carrier bandwidths corresponding to each used bandwidth have been defined by the 3GPP and the mapping is as shown below:
Transmission Bandwidth Nominal Carrier Bandwidth
1.08 MHz 1.4 MHz
2.7 MHz 3 MHz
4.5 MHz 5 MHz
9 MHz 10 MHz
13.5 MHz 15 MHz
18 MHz 20 MHz
The difference between the used and the nominal bandwidth is considered to serve as guard bands on the upper and lower sides of the spectrum
Q: The formulae for Interference Margin in Downlink as well as Uplink?
A : Downlink we use formula or manual values. Below is the formula ( values as example)
B1....Required SINR at Cell Edge (dB)--- 0.6
B2....Maximum SINR at Cell Edge (dB)----- -0.03
B3....Cell Load…. in % 50%
Interfarance margin =IF(1-(10^((B1)/10)*B3*(1/10^(B2/10)))<0,"ERROR!",ROUND(-10*LOG(1-(10^((B1)/10)*B3*(1/10^(B2/10)))),2))


Uplink
In uplink we use either based on simulation or manual value
Below is some simulation values & IM (Interference margin)
UL Interference Margin
Cell Load IM (dB)
35% 1
40% 1.3
50% 1.8
60% 2.4
70% 2.9
80% 3.3
90% 3.7
100% 4.2



Q: Why is LTE said to have soft capacity?
A: means the capacity of the Interference Pool, that’s why the increase in interference and noise by increasing the number of users will decrease the cell coverage forcing the cell radius to become smaller.

Q: Consider 2T2R MIMO. Consider cell I,II,III at enodeB1. The RE's for the RS of 1st antenna port in cell I are not used for the 2nd antenna port in cell I , correct? My question is can the REs used for RS in the 1st antenna port in cell I be used for RS in cell II/III or another cell I of enodeB2?

A: yes, RS are cell specific but you should have different Physical cell id for nearby or neighbour cell because the sequence used to generate the RS is dependent upon the physical cell id.

Q: SFR vs FFR differences and similarities pointwise?
A: plz check my post at http://www.finetopix.com/live-optimization/16210-sfr-vs-ffr.html (http://www.finetopix.com/live-optimization/16210-sfr-vs-ffr.html)

Mctest
2011-03-23, 01:42 AM
Then what are the nos. of RBs in 1 time slot for a system bandwidth of 1.4, 3, 5 and 10 MHz ?

So, in 1.4MHz - 6 RB, in 3MHz - 15RB, 5MHz - 25 RB, 10MHz - 50 RB, 15 MHz - 75 RB, 20 MHz - 100 RB.

Also it should be noted that eNode B scheduler works with SB (Scheduled Block) which consists of two consequent RBs in time domain.

nitailor
2011-03-23, 03:10 PM
So, in 1.4MHz - 6 RB, in 3MHz - 15RB, 5MHz - 25 RB, 10MHz - 50 RB, 15 MHz - 75 RB, 20 MHz - 100 RB.

Also it should be noted that eNode B scheduler works with SB (Scheduled Block) which consists of two consequent RBs in time domain.

Dear McTest, I am asking for the RBs in 1 Time slot

Mctest
2011-03-23, 08:41 PM
Dear McTest, I am asking for the RBs in 1 Time slot

So,I suppose it's no correct to ask about Num of RBs in one time slot,because RB its time-frequency resource where 1 RB - 12 subcarriers in freq domain and 0.5ms=1 time slot in time domain.If you have range 20 MHhz it means you have 100 RB per 0.5 ms(per time slot) as I said it before.

nitailor
2011-03-24, 01:13 AM
So,I suppose it's no correct to ask about Num of RBs in one time slot,because RB its time-frequency resource where 1 RB - 12 subcarriers in freq domain and 0.5ms=1 time slot in time domain.If you have range 20 MHhz it means you have 100 RB per 0.5 ms(per time slot) as I said it before.

I got the answer fot 20MHz, now I want the ans for 1.4, 3, 5 and 10 MHz. :)

Mctest
2011-03-24, 04:09 AM
I got the answer fot 20MHz, now I want the ans for 1.4, 3, 5 and 10 MHz. :)

I have posted it already:
So, in 1.4MHz - 6 RB, in 3MHz - 15RB, 5MHz - 25 RB, 10MHz - 50 RB, 15 MHz - 75 RB, 20 MHz - 100 RB.

Also it should be noted that eNode B scheduler works with SB (Scheduled Block) which consists of two consequent RBs in time domain.

qaqa
2011-03-26, 11:41 AM
Hello Guys
first flavour from the LTE training.
this attached poster resumes all the LTE (RAN/EPC) components, Interfaces and protocols.
If you like it, hit the the Rep bottom.
use my default PWD

More to come....:cool: including Q&A

riyantoyadi
2011-03-27, 01:06 AM
Very very usefull for me to know more about LTE :D

snabeel03
2011-04-14, 10:35 AM
Well,what is the equivalent in LTE as GPEH in WCDMA?

Somebody asked me this question.I dont know the answer....

nitailor
2011-04-14, 12:50 PM
Hope the remaining questions shall be answered soon

s52d
2011-04-14, 01:50 PM
Well,what is the equivalent in LTE as GPEH in WCDMA?

Somebody asked me this question.I dont know the answer....

GPEH needs RNC, so ...
UETR and CTR in UTRAN can be parsed with same SW as GPEH.

CTR runs on eNode-B, so I guess we shall collect CTR there.
Are there any limitations, like number of simultanous users recorded?
Is OSS parser usable? Or we have to do our own like in UTRAN?

BR
s52d