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3G Dropped & Blocked Call Specifications

Nov 28, 2014

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RANT Dropped and Blocked Calls Classification Summary (WCDMA Network MTN South Africa)

1 2 2.1 2.2 2.3 2.4 2.5 2.6 3 3.1 3.2 3.3 3.3.1 3.3.2 3.4 3.4.1 3.4.2 3.4.3 3.5 3.5.1 3.5.2 3.5.3

Introduction ................................ ................................ ....................... 2 Dropped Calls Classification ................................ .............................. 2 Missing Neighbours ................................ ................................ ........... 3 Poor Coverage ................................ ................................ .................. 3 Bad Radio Environment ................................ ................................ .... 4 Congestion ................................ ................................ ........................ 5 Not Radio ................................ ................................ .......................... 6 Equipment Fault ................................ ................................ ................ 7 Blocked Calls Classification ................................ ............................... 9 Missing Neighbour ................................ ................................ ............ 9 Poor RF (Bad Coverage and Radio Environment) ........................... 10 Equipment Fault (UE) ................................ ................................ ...... 11 Security and Authentication Mode Failure ................................ ....... 11 UE Freeze ................................ ................................ ....................... 12 Not Radio ................................ ................................ ........................ 13 Disconnect on RAB Setup ................................ ............................... 13 Resources Unavailable (Congestion) ................................ .............. 14 UE Sensitivity Fault ................................ ................................ ......... 15 Abnormal blocked calls ................................ ................................ ... 16 Unclassified - Unanswered RRC requests ................................ ....... 16 Faulty Block Recording - Barred Network ................................ ........ 17 Call Initialisation during L.U. signalling ................................ ............ 18

1

IntroductionThis document describes some of the typical dropped/blocked call classifications encountered during several RAN Tuning Projects for WCDMA networks. The purpose of the document is for RAN Consultants to understand some of the problems to make the UE analysis and classifi cation easier. The analysis has been based on limited data (for example no UETR data or data based on similar tool, no usage of RBS and RNC tracers) and for this result there could be a deviation in the results. Some of these classifications are only a guideline and should be viewed merely as documenting the typical problem until the correct reason behind the dropped call is established. All these dropped/blocked calls categories are adapted to the radio environment evaluation thresholds set up for the MTN 3G RAN Tuning project in the post-processing tool TEMS Deskcat 5.6. In the table below are listed the main causes that must be considered during the analysis, with the explanation for each cause.

CLASSIFICATION CRITERIA The Drop occurs in regions where conditions CPICH RSCP and/or CPICH Ec/No are measured in critical values not suitable for a proper connection. Every drop that occurs when Best Server is Missing (Mostly in good CPICH RSCP conditions). The UE active set update cannot follow the quick coverage changes. In this case Pilot Pollution situations are included as well (3 cells in AS and more than 1 strong SCs is interfering the connection within a range of 5 dB - Ec/No basis evaluation). Every drop that occurs when there are no more available radio resources for the connection. The network sends an RRC Connection Release when the RBS reaches the maximum available Power in DL.

Poor Coverage

Bad Radio Environment

Congestion

Not Radio

Every drop that occurs when the radio conditions are good, the logging equipment is working properly and the RRC connection release cause (marked usually as "Unspecified") could be attributed to a RBS/Network fault, (including UL UE power going to maximum even if the CPICH RSCP is measured at good values, crossed feeders causing false missing neighbours, crossed ULDL feeders, wrong parameter settings that can affect accessibility/SHOs in the cell).

Equipment Fault

Every drop that occurs when TEMS Investigation/UE are Blocking or Freezing and/or SW is crashing, so that it's not possible to maintain the connection.

Missing Neighbours

Every drop that occurs when there are poor RSCP and/or Ec/No levels/quality on the Best Server/AS, with the contemporary possibility for the UE to perform a SHO on a better cell that is not declared as a Neighbour for the AS cells themselves.

2

Dropped Calls ClassificationThe main cases and dropped call causes are listed below.

2.1

Missing Neighbours Every drop that occurs when there are poor RSCP and/or Ec/No levels/quality on the Best Server/AS, with the contemporary possibility for the UE to perform a SHO on a better cell that is not declared as a Neighbour for the AS cells themselves. An example of dropped call for missing neighbour problem is shown in figure below.

Problem Description: The Active Set best server is cell 61888 (SC = 205). During the call sector 62096 (SC = 293) becomes the strongest sector but is not added to the active set, as the two cells are not defined neighbours. This can be seen in the Serving/Active Set window in TEMS. The cell 62096 act as an increasing interferer until eventually the call is released. The release cause is classified as unspecified. 2.2 Poor Coverage The Drop occurs in regions where conditions CPICH RSCP and/or CPICH Ec/No are measured in critical va lues not suitable for a proper connection. In the table below an example is shown.

Problem e cri tion: In t is c se t e environment s reported by t e E is very poor before t e c ll is dropped. he best server S P dBm nd Ec/No dB. he sc nner lso reports poor r dio conditions for the same S at the same instant i.e. S P . dBm and Ec/Io . dB. he Active Set omplete messa e sent by the E. last messa e sent is the he E then goes into idle mode.

.3

i E

i

m

ostly in good PICH Every drop that occurs hen Best Server is issing SCP conditions . he E active set update cannot follo the uick coverage changes. In this case Pilot Pollution situations are included as ell cells in AS and more than strong SCs is interfering the connection ithin a range of dB Ec/No basis evaluation).

Problem Description: The Active Set best servers are cells with SCs 49 and 303, and all MN (SCs 304, 179 and 180) are close to them on a RSCP basis (from 70dBm to 79 dBm). During the call UE is performing a continuous number of SHOs, affecting both the service continuity and the quality of the connection (low values of Ec/No on each cell). So, the Radio Environment is not suitable for a good connection and therefore the dro pped call occurs. Sometimes the TEMS Inv. doesnt show the event on the chart, like in this case, so its advisable to check the Events and Layer 3 messages: In the L3 table the RRC Connection Release DL corresponds (into the Event table) to an RRC Connection Abnormal Release with the specification Unspecified. 2.4 Congestion Every drop that occurs when there are no more available radio resources for the connection. The network sends an RRC Connection Release when the RBS reaches the maximum available Power i n DL. In the corresponding DL Layer 3 message RRC Connection Release when the drop happens, the release cause is clearly marked as Congestion. An example is shown in figure below.

Problem Description: In this case the radio environment doesnt show a ny critical issue: the AS is full, and there is a Best Server cell (SC 352) with two more cells that are carrying the service. Also the MN set is good, and the Layer 3 messages sequence is regular. The radio resource unavailability pops up suddenly after a certain number of fast SHOs, and an RRC Connection Release message from the network comes to interrupt the call. In the TEMS L3 messages window details the release cause is clearly marked as Congestion.

2.5

Not Radio Every drop that occurs when the radio conditions are good, the logging equipment is working properly and the RRC connection release cause (marked usually as "Unspecified") could be attributed to a RBS/Network fault, (including UL UE power going to maximum even if the CPICH RSCP is measured at good values, crossed feeders causing false missing neighbours, crossed UL-DL feeders, wrong parameter settings that can affect accessibility/SHOs in the cell). This case also includes the UE Sensitivity drop, as shown in figure below.

Problem Description: The radio environment as reported by the UE is very poor just before the call dropped i.e. Best server RSCP= -127dBm and Ec/No=-27dB. The scanner reports much better radio conditions for the same SC at the same instant i.e. RSCP = -93.57dBm and Ec/Io = -8.66dB. Although the drop is as a result of low RSCP as measured by the UE it should not be classified, as a poor coverage drop since the scanner indicates the radio conditions should be ok to maintain the call. 2.6 Equipment Fault Every drop that occurs when TEMS Investigation/UE are Blocking or Freezing and/or SW is crashing, so that it's not possible to maintain the connection. An example of UE freezing dropped call is shown in figure below.

Problem description: In the example the network sends a DL Measurement Control message and then the UE freezes. There are no further massages sent between the network a