WiMAX Interference

[ninoy_122184]

Hello experts,


Can anybody explain what kind of interference and how to solve the interference issue for the site with 30Mbps backhaul but it only reaches a maximum of 6Mbps throughput with the cinr=33 and rssi=-50 and modulation is 64qam5/6,what parameters needed to be check. here is the result of the rfi band scan but its source is coming from 70 kilometers is radius, all neighbor on sector 2 sites are also scanned having the same result.

Please advise this issue is already almost a year and it is still not solved.

Reputation will be added for those who shares their knowledge on this issue.:)

http://www.4shared.com/photo/H1wCTlno/BAND_SCAN2.html

(http://www.4shared.com/photo/H1wCTlno/BAND_SCAN2.html)

[dimooon11]

Do you have only one site with low throughput?
What throughput you able to reach on another cells?

[ninoy_122184]

Do you have only one site with low throughput?
What throughput you able to reach on another cells?

6 sites in all in 1 cluster ,all the has throughput problem.(same throughput)

[dimooon11]

I can't see interference in screenshot you provided. CINR is also not affected. How about Retransmission Rate?
Who is BS equipment vendor?
FDD or TDD? TDD split?
MIMO B enabled?
How many user equipment terminals do you use for testing? It is better to use 2-3 terminals simultaneously.

[BtwoG]

I dont have enough reputation to view the screenshot, but if the interference is coming from that far, you should increase the cell radius. What can happen is the DL part of the frame from the inteferer site is delayed in time and is received during the UL part of the frame at the victim site. This interferes with the feedback zone on the UL and does not usually affect CINR because it is not measured on this part of the frame.

[ninoy_122184]

can you please explain further sir,yes you are correct the interference does affect the cinr,can you please explain the DL frame issue?many thanks

[ninoy_122184]

samsung is the vendor sir,
MIMO
we have 6 terminals that we are testing on every site but the result is the same.


I can't see interference in screenshot you provided. CINR is also not affected. How about Retransmission Rate?
Who is BS equipment vendor?
FDD or TDD? TDD split?
MIMO B enabled?
How many user equipment terminals do you use for testing? It is better to use 2-3 terminals simultaneously.

[gurs_leoboy@yahoo.com]

If your Wimax is TDD, what is ratio DL and UL? What is spectrum frequency you using (MHz)? What is CIR, MIR, and QoS your setting?


BR//

[dimooon11]

,can you please explain the DL frame issue?many thanks

TDD system requires synchronization - all BS must start sending data (DL) and receive data (UL) at precise time, otherwise TDD interference occur - interfered BS is already in the receiving state when the DL sub-frame transmitted by a remote BS.
It can be true if:
- at different BS you use different TDD split (29:18 and 32:15)
- due to propagation delay - the distance is long enough so propagation delay of DL sub-frames is greater than TTG (Transmit transition gap).

One of the symptoms - high HARQ retransmission rate.
You can't see that kind of interference during common spectrum sweeping - you need to see power of symbols of wimax frame.

[dimooon11]

Follow these steps:
1) check retransmission rate (HARQ)
if you couldn't then compare throughput at PHY, MAC and IP layers - difference between PHY and IP should not exceed 10%
2) tell your results - I have one more idea but let's follow the procedure

[ninoy_122184]

i will update you sir,, i will ask our NOC engineer for your suggestion.. many thanks:)

Follow these steps:
1) check retransmission rate (HARQ)
if you couldn't then compare throughput at PHY, MAC and IP layers - difference between PHY and IP should not exceed 10%
2) tell your results - I have one more idea but let's follow the procedure

[BtwoG]

To put a bit of a finer point on dimooon's reply. The normal timing separation between the DL part of the frame and the UL part of the frame is the TTG, which is normally 105.7 microseconds. If the distance between cell sites is greater than 31.7 km, then the DL part of the frame of the interfering site will be received during the UL part of the frame of the victim site. Many vendors have a cell radius feature that blanks out the last DL symbols, which effectively allows for a greater TTG. Each symbol is 102.9 microseconds, which allows for an additional 30.9 km of delay to be tolerated. The first part of the UL is used for handshaking with the base station and is not data bearing. So CINR is usually not calculated on this part of the frame. Therefore you can have interference on this part of the frame and the CINR measurements look good. What you may see is high DL frame errors and high HARQ retransmissions, because the DL frame error reporting occurs in the early part of the UL frame. So even though there are not DL frame errors, the base station thinks there are because it cannot receive confirmation on the UL that there are not frame errors. Hence throughput suffers.

I would suggest the following
1) make sure all the base stations have the same TDD split ratio
2) during the maintenance window, turn down all but 1 site in the cluster. See what the throughput measurements are. If they look OK, then you are getting self interference from within the cluster. If Samsung has a cell radius feature, increase the cell radius.
3) if throughput is still poor, check for outside interference. If there is another WiMax network operating close by, see if you can coordinate TDD ratios. Or change your TDD ratio so the interference is on the DL part of the frame (make the DL part of the frame longer in duration), not the UL part. If you are receiving interference from a FDD system, it will be very difficult to mitigate.

Hope that helps.

[ninoy_122184]

Thanks for your explanation sir,this helps a lot on our side.


To put a bit of a finer point on dimooon's reply. The normal timing separation between the DL part of the frame and the UL part of the frame is the TTG, which is normally 105.7 microseconds. If the distance between cell sites is greater than 31.7 km, then the DL part of the frame of the interfering site will be received during the UL part of the frame of the victim site. Many vendors have a cell radius feature that blanks out the last DL symbols, which effectively allows for a greater TTG. Each symbol is 102.9 microseconds, which allows for an additional 30.9 km of delay to be tolerated. The first part of the UL is used for handshaking with the base station and is not data bearing. So CINR is usually not calculated on this part of the frame. Therefore you can have interference on this part of the frame and the CINR measurements look good. What you may see is high DL frame errors and high HARQ retransmissions, because the DL frame error reporting occurs in the early part of the UL frame. So even though there are not DL frame errors, the base station thinks there are because it cannot receive confirmation on the UL that there are not frame errors. Hence throughput suffers.

I would suggest the following
1) make sure all the base stations have the same TDD split ratio
2) during the maintenance window, turn down all but 1 site in the cluster. See what the throughput measurements are. If they look OK, then you are getting self interference from within the cluster. If Samsung has a cell radius feature, increase the cell radius.
3) if throughput is still poor, check for outside interference. If there is another WiMax network operating close by, see if you can coordinate TDD ratios. Or change your TDD ratio so the interference is on the DL part of the frame (make the DL part of the frame longer in duration), not the UL part. If you are receiving interference from a FDD system, it will be very difficult to mitigate.

Hope that helps.

[ninoy_122184]

http://www.4shared.com/office/sZsoFzxQ/DIS-STAT-DL-HARQ-THR.html

here is the stat exported by our NOc sir,please take a look.thanks


Follow these steps:
1) check retransmission rate (HARQ)
if you couldn't then compare throughput at PHY, MAC and IP layers - difference between PHY and IP should not exceed 10%
2) tell your results - I have one more idea but let's follow the procedure

[ninoy_122184]

TDD ratio, 35/15. we are using 23375-23575(Mhz) we are using best effort and UGS CPe,s during testing.


If your Wimax is TDD, what is ratio DL and UL? What is spectrum frequency you using (MHz)? What is CIR, MIR, and QoS your setting?


BR//

[dimooon11]

BtwoG (http://www.finetopix.com/member.php?73326-BtwoG), I meant the same but you elaborate. thank you!

ninoy_122184 (http://www.finetopix.com/member.php?29685-ninoy_122184), your data it is parameter settings or thresholds but we need performance statistics data. on monday I'll show example what we are looking for.

[ninoy_122184]

ok sir,, i will wait for your example on monday, many thanks for your support.:)


BtwoG (http://www.finetopix.com/member.php?73326-BtwoG), I meant the same but you elaborate. thank you!

ninoy_122184 (http://www.finetopix.com/member.php?29685-ninoy_122184), your data it is parameter settings or thresholds but we need performance statistics data. on monday I'll show example what we are looking for.

[ninoy_122184]

@ dimooon11 (http://www.finetopix.com/member.php?48800-dimooon11) samsung network in my country uses 35:12 TDD ratio, what should be the TDD ratio of the nearby WiMAX network? should it be 35:12 also for them to be synchronize at the same time?please reply asap..thanks


TDD system requires synchronization - all BS must start sending data (DL) and receive data (UL) at precise time, otherwise TDD interference occur - interfered BS is already in the receiving state when the DL sub-frame transmitted by a remote BS.
It can be true if:
- at different BS you use different TDD split (29:18 and 32:12)
- due to propagation delay - the distance is long enough so propagation delay of DL sub-frames is greater than TTG (Transmit transition gap).

One of the symptoms - high HARQ retransmission rate.
You can't see that kind of interference during common spectrum sweeping - you need to see power of symbols of wimax frame.

[dimooon11]

All networks operating on the same frequency should use the same TDD ratio.
If networks has separate spectrum there should be no problems.
(Let's omit here adjacent frequency interference and intermodulation interfence)

[ninoy_122184]

noted sir,yes the other network (i mean other service provider network)here uses higher frequency than ours..thanks again.


All networks operating on the same frequency should use the same TDD ratio.
If networks has separate spectrum there should be no problems.
(Let's omit here adjacent frequency interference and intermodulation interfence)

[dimooon11]

Hello,

As promised let's consider few examples on retransmission symptom. You'll need performance statistics data.

First piece is from Huawei statistics data:

Second from from ZTE system:

There raw counters but it's easy to calculate rate.
I don't know how it looks in Samsung but I hope you've got the idea.

If you can't find anything similar then try this:
compare throughput at PHY layer and IP layer:

As you can see at some sectors throughput differs a lot. So there is problem.

Hope this helps. Waiting for your discoveries.

[ninoy_122184]

Hello bro,i already send your screenshot to our NOC engineers for them to find and extract the raw data.


noted sir,yes the other network (i mean other service provider network)here uses higher frequency than ours..thanks again.

[ninoy_122184]

Dear experts,

Our network already ask the other vendors, we are all using the same TDD ratio for the whole country,what else is the problem bro?

[dimooon11]

Hello, have you got retransmission rate results?

[ninoy_122184]

i send you private message bro,, please check


Hello, have you got retransmission rate results?