Confirm the call drop due to missing neighbor cell by 3G cell information displayed on M testing cell. You must check whether the neighbor cells are missing in the following situations:
The signals of 3G cell are weak. Ec is smaller than –110 dBm. Ec/Io is smaller than –10 dB.
A 2G testing UE detects that the 2G signals of indoor DAS are strong The UE starts compression mode for measurement
The UE does not sent the measurement report of 2G neighbor cells.
The following are two examples.
Example 1:
14:24:17(12): According to RB Setup, the UE accesses the network by PSC 417. 14:25:36(02): The UE does not report 2D measurement report until call drop. The RNC does not send measurement control report.
Conform that no inter-RAT neighbor cells are configured by examining parameters. If the cells are added, call drop problems are solved.
Example 2:
16:38:18(18): The UE reports 1D event of cell 273, and cell 273 becomes the best cell. However, the BCCH 538 indoor 2G cell is not configured as an inter-RAT neighbor cell of cell 273.
16:38:40(20): The UE keeps sending measurement reports, but detects that the signals of other GSM neighbor cells are weak. Therefore the RNC does not start handover, and then call drop occurs.
The cell of PSC273 and PSC 264 alternate to be the best server. Indoor GSM neighbor cells are configured as the inter-RAT neighbor cells of the cell of PSC264, but the cell of PSC273 is not configured with any neighbor cells. When the UE enters indoor, the cell of PSC273 becomes the best server, so call drop occurs. After indoor GSM neighbor cells are configured as the inter-RAT neighbor cells of the cell of PSC273, no call drop occurs.
Abundant Inter-RAT Neighbor Cells
According to the signaling, the phenomena of excessive inter-RAT neighbor cells are as follows: After the RNC sends Physical channel reconfiguration and inter-RAT measurement control
messages, the UE keeps sending the measurement report of Nonverified until call drop.
In S subject, for convenient configuration of parameters, the original 2G neighbor cell information is used to configure inter-RAT neighbor cells. All the inter-RAT cells are configured as the neighbor cells of 3G cells. Inter-RAT cell offset is configured to enable the UE to hand over to the target cell and to disable the UE to hand over to the undesired cell.
If excessive neighbor cells are configured, the UE must spend more time on inter-RAT measurement. The measurement internal of UE is limited, excessive neighbor cells delay UE to measure available neighbor cells, so call drop occurs.
Example :
11:30:11(92): The RNC sends measurement control messages (23 inter-RAT neighbor cells)
11:32:22(61): The UE keeps reporting to BSIC Nonverified cell until 2 minutes before call drop.
Configure the inter-RAT neighbor cells to the needed four neighbor cells, the MotoA835 hands over successfully.
Improper Configuration of LAC
Confirm improper configuration of LAC by signaling. The CN replies the No Resource Available messages, so examining data configuration before test is necessary. In addition, if the mobile switching center (MSC) fails in assigning related resources, such as inter-MSC trunk resources, the T resource to MGW, control table resource, the CN might reply the No Resource Available messages.
Example :
10:53:23(29): The RNC sends the Relocation Require message due to the No Resource Available message.
10:53:23(71): The CN replies the Relocation Failure message due to the No Resource Available message.
The RNC keeps sending Relocation Require message due to No Resource Available message until call drop, and is rejected. The actual LAC is 21000. After adjustment, the UE succeeds in handover.
No Measurement Report by UE
If the UE does not send measurement report, the UE performs the same as when the neighbor cells are missing. The phenomena are as follows:
The signals of 3G cell is weak Ec is smaller than –110 dBm. Ec/Io smaller than –10 dB.
A 2G testing UE detects that the 2G signals of indoor DAS are strong The UE does not hand over.
Check the signaling to confirm whether the UE send measurement report messages. If you compare it with terminals of other types, confirming the problem is easier and more accurate. Example :
Moto A835 handset:
16:38:05(99): The UE sends 2D measurement reports.
16:38:06(06): The RNC sends Physical channel reconfiguration (active sets contains PSC46, PSC492, and PSC36)
16:38:07(19): The RNC receives Physical channel reconfiguration completion, and then sends measurement control messages.
16:38:08(75): The cell of PSC 492 reports 1D and becomes the best server. It sends new measurement control messages after 1.5s.
16:39:19(73): The system does not receive the UE inter-RAT measurement report before call drop.
Qualcomm 6250 handset
16:38:42(16): The UE sends 2D measurement reports.
16:38:42(49): The RNC sends Physical channel reconfiguration (active set contains PSC46 and PSC492)
16:38:43(43): The RNC receives Physical channel reconfiguration completion message, and it sends measurement control messages.
16:38:47(74): The UE report BCCH 847 BSIC Verified, and the level is –67 dBm. 16:38:48(88): The RNC sends HO CMD message, so the handover succeeds.
In the test of handover between outdoor 3G to indoor 2G DAS, the Moto A835 handset does not send inter-RAT the measurement report for multiple times. The IOT engineers think that the version of out handset is not updated, and they recommend updating handset version.
Delayed Handover
According to signaling of the RNC, a normal inter-RAT handover takes 5s. The following are the time needed by the RNC, longer than that on UE. If the walking speed is 3 km/h, it takes 4–5 meters. The time depends on different scenes.
16:21:06(30): The UE sends the 2D measurement report.
16:21:06(37): The RNC sends the Physical channel reconfiguration message.
16:21:07(46): The UE sends the Physical channel reconfiguration completion message. 16:21:09(72): The UE sends the inter-RAT measurement reports.
16:21:10(48): The system sends the UE HO FROM UTRAN CMD GSM message. 16:21:11(11): The RNC sends the Iu interface Release Command message.
When the UE moves outdoor to indoor with the 3G signals fluctuating sharply, call drop occurs due to delayed handover. According to the signaling, the phenomena of delayed handover are as follows:
During the handover process, the RNC originates lu Release because: − The NodeB reports RL Failure.
− The NodeB does not report RL failure, but SRB reset occurs.
Other situations: 3G signaling is normal, but actually the call drops. You can
only know whether the UE confronts call drop problems by checking the UE call drop recorded in test.
Example 1:
Moto handset:
15:26:27(87): The RNC sends Physical channel reconfiguration (active set contains PSC201 and PSC16).
15:26:30(30): The UE report BCCH 844 BSIC Nonverified, and the level is –87 dBm. 15:26:31(26): The UE report BCCH 844 BSIC verified, and the level is –88 dBm. 15:26:32(13): The RNC sends the HO CMD message.
15:26:34(25): The UE sends inter-RAT measurement reports, but does not hand over. This is because the UE does not receive HO CMD sent by the RNC, or the UE fails in accessing the 2G network. The CN sends lu Release due to treloccomplete expire (normally successful relocation causes lu Release, and the UE succeeds in accessing the 2G network).
Qualcomm handset in the same test period:
15:26:27(43): The RNC sends Physical channel reconfiguration (active set contains PSC201 and PSC16).
15:26:30(90): The UE report BCCH 844 BSIC verified, and the level is –79 dBm. 15:26:32(13): The RNC sends HO CMD, and the handover succeeds.
Here is the entrance to parking yard of Taigu Shopping Hall. Before call drop, the Moto handset indexes as follows:
Ec is smaller than –110 dBm. Ec/Io is small than –15 dB.
In addition, according to comparison of two terminals, they are different in measuring GSM level (Qualcomm 6250 uses an external antenna, while Moto A835 uses a built-in camera). This affects the inter-RAT measurement.
Example 2:
Moto handset:
17:08:59(61): The UE sends 2D measurement reports, and the RNC sends Physical channel reconfiguration.
17:09:00(78): The RNC receives Physical channel reconfiguration completion, and sends measurement control messages.
17:09:04(35): The NodeB is out of synchronization, so call drop occurs, and no inter- RAT the measurement report is sent.
17:09:20(89): The RNC originates Iu Release due to Radio Connection with UE lost.
Qualcomm handset in the same test period:
17:08:59(29): The UE sends 2D measurement reports, and the RNC sends Physical channel reconfiguration.
measurement control messages.
17:07:58(81): The RNC receives the measurement report from UE, BCCH 853, and the level is –61dBm.
17:08:00(25): The RNC sends HO CMD.
17:08:00(90): The CN sends Iu Release Command (successful relocation). Actually, call drop occurs during handover.
Now the starting threshold of compression mode is as high as –95 dBm. Do not change it to avoid impact on other parts of the network so that the handover occurs earlier.
Change of Best Cell in Physical Channel Reconfiguration
According to the test result, if the best cell changes, the handover is delayed, so call drop occurs in the following situations:
Between RNC sending Physical channel reconfiguration and receiving
Physical channel reconfiguration completion sent by UE (about 1s).
After Physical channel reconfiguration process is complete.
Example 1:
14:06:18(75): The best server PSC201 report 2D event (meanwhile, PSC16 is in the active set).
14:06:18(82): The RNC sends Physical channel reconfiguration. 14:06:18(95): The UE reports 1D event of PSC16 cell.
14:06:19(95): The RNC receives Physical channel reconfiguration completion from UE, and it sends inter-RAT measurement control message of PSC201 cell, and inter-
frequency and intra-frequency measurement control of PSC16 cell. 14:06:20(94): The UTRAN sends 1B event to the UE to delete PSC 201.
14:06:21(45): The RNC sends inter-RAT measurement control to the cell of PSC16 (3s delay compared with 1D event).
14:06:22(83): The UE reports the GSM cell 852 (BSIC Verify) according to the new measurement control, and the RSSI is –79 dBm. The RNC does not process the report (to prevent UE from handing over to incorrect cell, the RNC must process UE measurement report 3s after sending new measurement control)
14:06:28(94): NodeB is out of synchronization, so call drop occurs. Example 2: Qualcomm handset:
14:53:08(63): The UE sends 2D measurement reports, and the RNC sends Physical channel reconfiguration (the cell 144 is the best server)
14:53:09(67): The RNC receives Physical channel reconfiguration completion, and sends measurement control messages.
14:53:16(58): The UE sends 1D measurement reports, and cell 137 becomes the best server. Therefore the RNC sends the measurement control messages of best server 137, including inter-RAT neighbor cells (the neighbor cell list is different from that of cell 144)
14:53:16(62): The RNC does not receive the measurement report from UE, and ensures that the cell ID is in the list of neighbor cells of cell 144. The RNC does not process the reports
14:53:19(99): The RNC originates Iu Release.
If different interRATCellID is used in inter-RAT measurement control, will the RNC avoid this problem?
UE Hand Back Failure
Other abnormalities in handover might cause handover failure. Example :
14:07:37(38): The UE reports BCCH the measurement report of cell 852, Nonverified BSIC.
14:07:38(38): The TimeToTrigger of Nonverified is 1s, and after 1s, the RNC sends Relocation to CN.
14:07:38(38): The UE sends BCCH the measurement reports of cell 852, verified BSIC. 14:07:38(74): The CN replies that Relocation Prepare fails (no radio resources).
14:07:38(78): The UE sends the measurement report before failure, so the RNC again originates Relocation to CN.
14:07:40(12): The CN replies Relocation to RNC, and RNC sends HO CMD to UE. 14:07:40(79): However, the UE replies HO FAIL.
Late, the UE keeps deleting cell 201 which is the best server, so the RNC does not process the request. The 3G signals are weak, so call drop occurs.
Delayed Starting of Compression Mode
Description:
The UE cannot hand over from the 3G network to the 2G network smoothly. In details, the UE originates a call in 3G coverage areas or uses PS services, and then enters 2G coverage areas. However, it fails in handing over to 2G networks, so call drop occurs. Analyze the signaling process at RNC side, and check the causes to handover failure. The causes include:
− The network side fails in receiving 2D report from UE, so compression mode is not
started. Consequently 2G cells are not measured, and then asynchronization or SRB/TRB reset cause call drop.
− The network side receives 2D report, but compression mode is not started. The reason
is that the network side sends a PHY_CH_RECFG message, but the UE fails in sending ACK message or PHY_CH_RECFG_CMP, so SRB is reset, and call drop occurs.
− The network side receives Verified measurement reports. After it sends UE the
handover messages, the UE fails in receiving it, so call drop occurs (also for other reasons).
signals of the original cell becomes weak. Therefore subsequent starting compression mode and handover process cannot proceed normally.
Analysis:
Starting compression mode is affected by 2D event configuration of ID2 measurement control sent by the network side. You can enable 2D event to be reported more quickly by the following methods:
− Increasing the threshold of 2D event − Reducing hysteresis
− Reducing delayed triggering time
Now the back system can configure different starting threshold of inter-RAT compression mode for signaling, CS and PS services.