GPRS Data Connection Troubleshooting

Problems Getting the Mobile to Perform a GPRS Attach

If you have problems getting the mobile to perform a GPRS Attach, try working through some or all of the following troubleshooting hints:

• Ensure that a GSM Test SIM card, or a standard GSM SIM card is installed correctly and is working properly.
• Some mobiles may not perform a GPRS attach automatically. You may have to instruct the mobile to go into a data mode. The method for doing this varies from one mobile to another. For example, you may have to press a key on the mobile's keypad, or make a selection from the mobile's on-screen menu system.
• Ensure that any cable loss or gain between the test set's RF IN/OUT front panel connector and the mobile's RF connector is correctly specified in the RF IN/OUT Amplitude Offset table (see Amplitude Offset or How Do I Configure the Test Set for My Test System? ).
• Check that the cell power is set to a level that is sufficient to overcome any interference (for example,
  -35 dBm), especially if an indirect RF connection is being used between the test set and the mobile (see CALL:POWer ).
• Try using coding scheme CS-1 which has the highest degree of error correction (see CALL:(PDTCH|PDTChannel):CSCHeme:UPLink ). To set the coding scheme manually, press the More key to access the Call Parms menu ( 2 of 3 ), then press the Coding Scheme ( F11 ) key.
• Ensure that you have selected a multislot configuration that your GPRS mobile supports (see CALL:(PDTCH|PDTChannel):MSLot:CONFig ). Try starting with a multislot configuration of 1 down, 1 up (D1U1) because all GPRS mobiles support this configuration. Initially, you should avoid using a multislot configuration with two uplinks because fewer mobiles support more than one uplink. To set the multislot configuration manually, press the More key to access the Call Parms menu ( 3 of 3 ), then press the Multislot Config ( F7 ) key.
• Verify that your mobile supports the test set's default frame numbering scheme (starting position) setting. The default is RELative which your mobile may not support. Try the ABSolute or IMMediate settings (see CALL:FUNCtion:DATA:FRAMe:STARt ). To set the frame numbering scheme manually, press the More key to access the Control menu ( 2 of 2 ), press Protocol Control ( F4 ), RLC/MAC ( F1 ), then press the Frame Start Pos ( F5 ) key.

Problems Establishing a BLER Data Connection

If you have problems establishing a data connection using the BLER Data Connection Type specifically, you may want to change the setting of the LLC Frame Check Sequence (see CALL:FUNCtion:DATA:BLER:LLC:FCSequence ) or the BLER Block Polling Interval (see CALL:FUNCtion:DATA:BLER:POLLing:INTerval ).

For example, if your mobile is not capable of a high level of GMM_INFORMATION messaging (the type of messaging used to stimulate the mobile to send ACK/NACK responses to the test set), then the data connection will timeout. One possible solution to this is to set the LLC Frame Check Sequence to CORRupt preventing the messaging while still forcing the mobile to send ACK/NACK responses. The BLER Block Polling Interval is the rate at which the RLC/MAC blocks have the MAC header poll bit set, forcing a response (Packet Downlink ACK/NACK) from the mobile.

To change the LLC Frame Check Sequence or BLER Block Polling Interval settings manually, press the More key to access the Control menu ( 2 of 2 ), then press the Protocol Control ( F4 ) key. Block Poll Rate is available under the RLC/MAC ( F1 ) key and BLER FCS is available under the LLC ( F2 ) key. Select a parameter and change its setting.

Problems with BLER Measurements in GPRS/EGPRS

If you have problems in BLER testing, such as dropped call connections, this may be the cause: when you test receiver sensitivity using the BLER measurement by lowering the Cell Power, both the BCH and TCH/PDTCH power levels are lowered the same amount. The test set does not implement a default offset between those two channels. Typically, the test set sends a protocol message setting Network Control Order = 0 (NCO=0), so the mobile decides which cell it will select. Thus, when the BCH signal level decreases, the mobile tries to select a different non-existent neighbor cell. Thus, the call is often dropped before a valid BLER sensitivity test can be completed.

Possible solutions:

• Try changing the Downlink TX Power levels to keep the BCH 10 to 20 dB above the TCH/PDTCH using the following steps: Press the PDTCH Parameters (F9), then press the Downlink Traffic Power (F7), scroll to "P0 (Power Reduction Reference)" or "Power Reduction Level (PRL One/Two)", set corresponding value.
• Alternatively, you can try changing the maximum transmit power level using the following steps:Press the Operating Mode (F1) key, set Operating Mode to Cell Off, then press the Cell Info ( F6 ) key, then press Cell Parameters (F2); in the Cell Parameters table, scroll to "MS TX Power Max CCH (GSM)", set thedesired value, return to Call Setup screen, and set Operating Mode (F1) back to Active Cell mode.

Problems with Measurements in ETSI Test Mode A or B

In order to perform measurements in Active Cell operating mode with the Data Connection Type set to ETSI Type A or ETSI Type B test modes, your mobile must fully support these connection types as defined in the standards. ETSI Type B is required if you want to perform BER measurements in active cell mode.

You can specify the first downlink burst to be looped back in the first uplink burst using the command CALL:(PDTCH|PDTChannel):MSLot[:FIRSt]:DOWNlink:LOOPback[:BURSt] .

In ETSI Type B test mode, the BLER measurement is performed using a different method from that used when the test set's data connection type is set to BLER. For more details on the BLER measurement see Block Error Measurement .