case analsyis handover

8/12/2019 Case Analsyis Handover

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The above flow include the counter for incoming of target cell and outgoing of original cell.

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Difference between "Internal inter cell handover success rate " and "Cell radio handover success rate " :

As viewed from formulas, both numerators are success times of handover, while thedenominators are different. While viewed from the measurement points of the counter,

Attempted inter cell handovers >= inter cell handovers, so intra BSC handover success rate


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Max resend time of physical information (value range: 1 ~ 255, 30 recommended, measuredin times)

Description: During asynchronous handover, MS keeps sending handover access Burst tonetwork. After detecting the handover access burst of MS, BTS reports the physicalinformation message to MS over FACCH, starts the timer T3105, and at the same time sendthe MSG_ABIS_HO_DETECT message to BSC. The physical information message containsrelevant information of different physical layers to ensure the proper transfer of MS. If thetimer fails before the SAMB frame from MS is received, BTS will re-send the physicalinformation message to MS. This parameter defines the maximum sending times Ny1 of thephysical information.

Radio link connection timer (value range: 0 ~ 255, measured in 10ms)

Description: This is the timer T3105. When the physical information is being sent, thenetwork starts the timer T3105. If the timer fails before an correct frame from MS is.received, the network will re-send the physical information message and re-start the timer,

and the maximum re-sending times is Ny1. Since the physical information is sent over FACCH, and FACCH sends the physical information every four TDMA frames (about 18ms).

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The key measurement points are as follows, same as those of intra BSC handover:

1. After sending "HO-REQUIRED", the original BSC measures "Attempted outgoing inter BSCinter cell handovers".

2. After receiving "HO-REQUEST", the target BSC measures "Attempted incoming inter BSC

handovers".

3. After sending "HO-REQUEST ACK", the target BSC measures "incoming inter BSC handovers".

4. After receiving "HO-Command" , the original BSC measures "outgoing inter BSC handovers".

5. After receiving "HO-Complete", the target BSC measures "Successful incoming inter BSChandover"

6. After receiving "Clear-COM" and the cause value is "HO-Successful", the original BSCmeasures "Successful outgoing inter BSC inter cell handover".

The difference between "handover times" and "handover request times":

Handover times - After "HO-COM" is received or "HO-REQ-ACK" is sent

Handover request times - After "HO-REQUIRED" is sent or "HO-REQUEST" is received

Therefore, inter BSC inter cell radio handover success rate >= inter BSC inter cell handover success rate.

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Note: Signaling flow of A interface and Abis interface of inter MSC handover is the same as that of -, .

As shown in above figure the signaling with "MAP" is of the MAP layer, and signaling of A and Abisinterfaces are omitted.

After receiving "HO-REQUIRED" of BSC-A (the request message includes CGI of the original cell

and target cell), if MSC-A finds that LAC of the target cell doesnt belong to this MSC, MSC-A willquery the "REMOT LAC Table (including the LAC and route of the adjacent MSC), and send"Pre are-HO" messa e to MSC-B accordin to the route. CGI of the tar et cell and the indicator of .whether to allocate the handover number are included in this Prepare-HO message.

According to the received "Prepare-HO" message, if the handover number needs allocating,MSC-B will request the local VLR to allocate the handover number. If VLR has the free handover number, the handover number will be sent to MSC-B through "Send-HO-Report". If no handover number is needed, proceed to the next step.

er n e ween - an - s es a s e , - sen s - oBSC-B. After that, BSC-B activates the target cells channel, and returns "HO-REQUEST ACK" toMSC-B after receiving the channel activation acknowledgement. According to this message, MSC-B sends "Prepare-HO ACK" to MSC-A.

MSC-A establishes the route to MSC-B according to the handover number, and sends "Initialize- Address" (IAI) to MSC-B to help the latter to identify which voice channel is reserved for MS. While

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- re urns ress- omp e e o - .


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After receiving the ACM message, MSC-A sends "HO-Command" to MS. After that MS. , -

will be received, and "HO-Complete" will be sent to MSC-B.

MSC-B sends "Send-End-Signal" to notify MSC-A to release the original channel. After receiving "Clear-Complete" from BSC-A, MSC-A returns "Sent-End-Signal ACK" to MSC-

B, thus finishing the inter MSC handover flow.

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1. Before receiving the measurement report and starting the basic cell ranking, BSC needsto determine the module No. and cell No. of all adjacent cells.

2. Adjacent Cell Relation Table: Once the adjacent cell has cells of the same frequency andBSIC, BSC will not be able to judge which is the target cell. This will easily result in wrong or failed sending of the handover command and thus the successful rate of handover must berather low.

. ,handover request message is sent through MPU board, so the connection between LAPDand MPU is the "Cell Module Information Table", and the index is CGI.

4. If the desired CGI is not in "Cell Module Information Table", MPU will consider the targetcell as an external cell, and send "HO-REQUIRED" to MSC, and count Attempted outgoinginter cell handover by 1 at the same time.

5. If the module number in "Cell Module Information Table" is wrong, the handover commandwill be sent to the wrong module, and the handover will fail. But BSC will still count Outgoinginternal inter cell handover" by 1.

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Frequent handover: Handover in GSM is hard handover, it is meaning, before handover tothe new channel, MS must release the original channel firstly. So frequent handover willresult in word-loss in handover and break-make of conversation, thus affecting theconversation quality.

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In isolated cell coverage area, when MS moves towards the cell edge, the signal becomesweaker and weaker, and since there is no adjacent cell available around, handover cannotbe triggered, thus call drop will occur.

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For BTS clock, BSC clock, and MSC clock, the following standards are used to judgewhether they are out of synchronization:

MSC: f/f (frequency deviation) 1E-8

BSC/BTS: f/f (frequency deviation) 5E-8

Inaccurate clock will cause that MS cannot decode BSIC of the adjacent cell correctly.

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The same frequency and the same BSIC will result in low value of both handover successrate and radio handover success rate.

For service cell: Outgoing inter cell handover will fail.

For illusory target cell: Incoming inter-cell handover will fail, and successful rate of handover

= successful rate of radio handover.

Notes:

CI can not configure as "FFFF".

"Transmitting BS/MS Power Level": If the measurement report preprocess isenabled, this parameter must be set to "Yes".

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The cause value of the handover failure message: Invalid message content.

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"Address Indicator" differs from the normal "HO-REQUEST".

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Signaling tracing is very helpful if there are problems in cooperation with other

manufacturers equipment.

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After BSC-HW sends "HO-REQUIRED" to MSC-HW, MSC-HW sends "Prepare-HO" to thepeer, however MSC-B directly returns abort message, causing that BSC-HW receives "HO-Reject" from MSC-HW.

The handover fails.

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Failure signaling:

MSC receives "HO-REQUEST-ACK" sent by Huawei BSC, and sends "HO-COMD" to Nvender BSC.

While MS doesnt perform "HO-ACCESS", so Huawei BSC do not send "HO-Detect" to

MSC, and MSC sends "Clear" command to N vender BSC, with the reason "Radio interfaceerror, return to the original channel".

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case analsyis handover

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