High RTWP High call drop
High RTWP - High call drop
2014-06-12
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High RTWP High call drop
1. Issue Description Since the RTWP problem is one of the main causes of Call drop in UMTS system, RTWP check task had a huge impact on The network performance by decreasing the Call drop rate, decreasing signaling caused by call drops, improving the UL capacity & throughput & improving overall network performance & Quality of Service. .
2. RNC/ Node-B software version RNC 6900 V900R012ENGC01SPH510 Node-B: 3900 /3900A/3900L/3900DBS V200R012ENGC00SPC420
3. Issue analysis & related Solutions:
Common causes of RTWP: A. Load: Sites with High load usually suffer from high RTWP, UMTS System is affected by intrasystem interference by UMTS users themselves (Specially HSUPA users), and it becomes very clear when many users are located in the same area (power competition). Example:
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B. Hardware Installation problems: • This is common problem especially in new launched networks, • This may be caused by Antenna, Feeder, Connector, Triplexer or any element between the RF unit and the antenna. • For Networks which already have multi carriers, these hardware problems will be easier to detect. • Usually if one sector has a hardware problem, so all the cells using any frequency band will suffer from the same problem. For example: Cell ID 30001/30006/ 3009 are co-sector cells using deferent frequency bands (F1, F2, F3), If all these cells suffers from the same RTWP problem, so it’s very clear and important indicator for hardware problem in that sector because usually it’s not common to have external interference on Three frequency bands in the same time for the whole monitoring period. One of the most common problems is the connector connection point as shown below:
This kind of HW faults can be detected directly by using “Site Master” which show the exact hardware fault point
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After arranging the Site engineer to check and fix the hardware problem, the performance immediately showed a great improvement. In L country, T operator, we did this check & corrective action for 96 cells, the improvements where beyond the expectation as shown below: RTWP-Batch-X Task had a clear impact on 96 Cells in Touch Network, the total performance of all these cells have been remarkably improved which affected overall 3G network performance.
Total Number of daily Drops on target cells decreased from 118,000 to 37000 Dropped calls PS Call drops decreased 68.64%. PS Call Drop Rate Decreased on target cells from 4.5% to 1.5%, PS Call Drops ratio decreased 66.667% 2014-06-12
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CS (AMR Voice) Call Drop Number Decreased on target cells from 1600 to 400 daily drops. CS Call drops number decreased 75%
CS (AMR Voice) Call Drop Rate Decreased on target cells from 2.05 % to 0.82% CS Call Drops ratio decreased 60.1% Top cases (all the cases show always the same problem for cells 1&6, 2&7, 3&8 which are cells for the same sector with different frequency band.
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Sector-3 for below sites (2 cells co-sector are affected because of the HW problem.
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C. External interference case: Some cells suffered from unacceptable RTWP values which was affecting the call drop rate, UL capacity, HSUPA throughput, & also HSDPA retransmission rate, The UL Frequency Scan function in the Node-B LMT shown below results on site “HOSS_ID02 Sector D):
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The neighbor site also showed the same interference behavior:
By checking the interfered sectors on map, it was clear that there is external interference source in below area on the map.
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This issue was reported to the operator, on Field scans detected two jammers related to one university in that area. The solution proposed is to dismantle the interference source.
Alarms & Major Problems: No alarms, but many complaints related network retain ability and HSUPA throughput.
Notes WCDMA system is self interference system, highly affected by RTWP, UL power resource is so critical and limited resource and should always be maintained and monitored. For new networks, installation quality will highly affect the RTWP. For on air networks, always PS drop & RTWP counters should be monitored to detect any abnormal behavior and solve any RTWP problem immediately since its very annoying problem to any WCDMA network.
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