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LTE Throughput issue - cells high PDSCH BLER affecting DL throughput


#1

Hi, I need advice on an LTE throughput issue. I have got some cells that have high PDSCH BLER and it is affecting DL the throughput . How can we tackle high BLER issue?

This post is transcribed from the LTE Whatsapp group


#2

Are these remote looking cells ? In my understanding … high bler can be due to poor SINR … provided no alarms/availability issues etc … so SINR would have to be improved


#3

Thanks for your answer. The situation is like this. BLER I am getting is around 3%. SINR is above 27 all the time. CQI is above 13. The thruput is not that “low”, but then it is less than what is expected in KPI. it is lacking around 5mbps. the expected KPI is 72.4Mbps, I am only getting 67 Mbps.


#4

Is this all from Drive Test analysis ? Have u checked the count of connected users in the cell ?


#5

Yes. This is from the DT analysis.


#6

In my experience, I think this has to do with an interfering band.

So do frequency scanning to check if there is any nearby broadcasting tower or communication tower using an adjacent/similar frequency band without proper guarding.

I have observed such a case before on LTE 900 band


#7

Also. what is the load on the cell i.e. number of connected users at the time of testing ?


#8

This site is in rural, no users connected at the time of test. I am not really sure about interference.

But this site is in rural, most likely no other operator in this area. for your information, I am operating in 2.3G , with 20Mhz spectrum, using Configuration 1


#9

Throughput of 67 Mbps is being acheived!

Have u checked the phone category that what is the max that it can acheive ?

LTE TDD ?


#10

Good question. we are using Samsung S7. We have 3 sectors. One sector can achieve 74Mbps. while the other two not.

LTE TDD? Yes

Plus, if my calculation is correct the PRB I should be getting is around 40-60. Yet, on average I am getting around 56->58


#11

My other question is, what are the other factor (apart from CQI, SINR etc) that will determine the number of allocated PRB? Because looking from my case, RF condition is good but why there are variety in terms of PRB allocation? Could we relate backhaul issue to PRB allocation?


#12

Downloading from an internal server + no throttling ?


#13

I assume no, since one sector can pass the expected KPI (72.4 Mbps).


#14

Are you using Internet link for the throughput test or FTP?

Try performing test like UUDATA TEST or any form of the that will determine the capacity & capability of each cell through connected UE.

If the test pass then, there could be other forms of interference but certainly not RF issue if not then RF issue should be suspected.


#15

In my understanding … any possible bottleneck/constraint in the backhaul should not impact the allocation of PRBs …U said no connected users at the time of testing then 50-60 PRBs allocated out of 100 are less … can u check the stats again at the time of testing …


#16

I am afraid not 100, because we are using TDD, not FDD.


#17

Please perform capacity test on each of the cells.


#18

I am using FTP. Not really sure how to do UUDATA test. can you elaborate? And how can I perform capacity test on cells?


#19

In UUDATA TEST you load DL packets of high capacity from a remote server. In the case of test I have performed, we use UE IP, TMSI and other parameters to identify the UE on the connected eNB.

UU data test is a form of capacity test. It doesn’t go through FTP or IP.

U should be able to reach the max throughput configured for that cell e.g 72.4 Mbps as expected.if it failed then there other suspects like transmission issue or installation issues.