Security Level:
2008-11-3
How to Analyze Quality Issue by DT www.huawei.com
HUAWEI TECHNOLOGIES CO., LTD.
Huawei Confidential
Outline • Downlink RxQuality Issue
What is RxQuality Issue
The problems raised by RxQuality issue
• How to detect quality issue by DT
Bad Quality due to Signal Strength – FER is Bad
Bad Quality due to Signal Strength – FER is OK
Bad Quality due to C/A Interference
Bad Quality due to Time Dispersion
• The solution to RxQuality issue
What is RxQuality Issue
Bad RxQuality is one of the biggest problems in a Network. The RxQuality that a network operator can offer to customers mostly depends on the RxLevel and the interference of the network.
There are two types of RxQuality problems, uplink RxQuality and downlink RxQuality. We can only detect downlink RxQuality problem by DT, however, if the downlink RxQuality is bad in one cell, there is a risk that there would be problems on the uplink as well.
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What is RxQuality Issue
Good RxQualit y
Bad RxQualit y
RxQuality is divided into eight levels which are from 0 to 7, the level 0 is the best and the level 7 is the worst.
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The problems raised by RxQuality issue
Bad RxQuality may raise many problems, such as:
Difficulty in accessing the network
Dropped calls due to bad quality
Poor handover success rate
Low MOS value
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Bad Quality due to Signal Strength – FER is Bad As the signal strength drops down, the quality of the call becomes worse being effected by interference and/ or fading. Consequently the system becomes weaker to handle the interference. Drop calls and ping pong handovers usually happen in such environments. RxLev (Serving Cell and Neighbors) is not high enough (about less than -95dbm). Maybe there are interferences in this region for bad FER.
Bad RxLev Bad RxQual Bad FER
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Bad Quality due to Signal Strength – FER is OK This case is similar with the previous except for FER. Signal strength is also bad in this, but FER is still fine. FER is ok, it means that there is no obvious interference in the area. The coverage is usually the problem in this situation.
Bad RxLev Bad RxQual Fine FER
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Bad Quality due to C/A Interference There is adjacent channel interference in this case and the RxQuality is not good. Bad Quality due to Adjacent Interference. Adjacent BCCH between best server and best neighbor.
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Bad Quality due to Time Dispersion
Site Reflecting object
MS Time dispersion is caused by the reflections. The MS uses all or most of the received power, instead of only the direct signal, there is a larger probability to decode the information. So the RxQuality will be very bad perhaps.
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Bad Quality due to Time Dispersion The MS is near the cell, it is less than 1 mile far away. The RxQuality is very bad for the bad C/R, in which, R stands for reflected signal and C stands for original signal. The TA is too high. It is because that TA stands for the reflected signal but the original signal.
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The solution to RxQuality issue (1) RxQuality Issue
Solution Find out the interference source or /and
Bad Quality due to Signal Strength – FER is Bad
adjust the azimuth or downtilt of the antenna or /and adjust the power of the transmitter(s). There is no obvious interference in this
Bad Quality due to Signal Strength – FER is OK
situation. Adjust the azimuth or downtilt of the antenna or /and adjust the power of the transmitter(s).
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The solution to RxQuality issue (2) RxQuality Issue
Solution
Bad Quality due to C/A Interference
Avoided adjacent frequencies in the same cell and preferably in neighboring cells as well.
Move the site to be placed near the reflecting Bad Quality due to Time Dispersion object to prevent time dispersion. Another efficient solution is to modify the antenna arrangement, either in azimuth (horizontally) or by tilt (vertically).
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Thank you www.huawei.com
