PRACH Transmit On/Off Power Troubleshooting

Possible Setup Issues

• Before performing a PRACH transmit on/off measurement, turn the UE on and wait for it to camp to the test set's signal. When the PRACH transmit on/off power measurement is initiated, the test set pages the UE. The UE must be camped to the test set and in idle mode before performing the PRACH Transmit On/Off Power measurement.
• Recommended PRACH Preambles and PRACH Ramping Cycles (MMAX) settings

  The measurement requires a minimum of 3 PRACH preambles, but it is recommended that you set PRACH Preambles to 4 to ensure that the test set is able to capture two PRACH bursts for analysis. It is also recommended that you set PRACH Preambles to no greater than 4 and set PRACH Ramping Cycles (MMAX) to 1 to allow the UE's PRACH sequence to end as soon as possible. This helps avoid the following issue: Test set may lock up if operations are attempted before the UE completes its PRACH sequence .

• Importance of Setting Call Limit State to Off before Initiating a PRACH Measurement

  It is recommended that you set Call Limit State to Off before initiating this measurement. Then, when the measurement completes, if the UE is still sending PRACH preambles to the test set, the test set will acknowledge the UE. Note, when the test set acknowledges the UE, the call is not completed because the UE is attempting to establish a test set-originated call, whereas the test set acknowledges the UE expecting a UE-originated call. Acknowledging the UE helps prevent the UE from placing the test set into its cell barred list (see Test Set in Cell Barred List ). When the test set acknowledges the UE, you will see the call status move from Paging to Idle , to Setup , to Releasing and then back to Idle . Do not attempt to stop or re-initiate the measurement, or to start any new measurements until the test set has reached Idle state (see Test set may lock up if operations are attempted before the UE completes its PRACH sequence ).

  Setting call limit mode to off before initiating the measurement also avoids another issue: When the measurement completes, if you try to send signalling to the UE while it is still sending PRACH preambles to the test set, the UE will ignore the incoming messages and the signalling will fail. If call limit mode is set to off, the test set will acknowledge the UE and cause it to stop sending PRACH preambles, and then send the signalling you have requested to the UE.

• Available Subchannels (Bit Mask) must be set to only one available subchannel.
• During front panel operation of this measurement, you must press the START SINGLE key to initiate the measurement.
• No other measurements can be running when a PRACH transmit on/off power measurement is performed. If any measurements are running when a PRACH transmit On/Off power measurement is initiated, they are closed and a message is displayed to indicate that they were closed.
• An RF rise to a level within 9 dB of the expected power ( Initial PRACH TX Power if Power Control is set to Auto, or Manual Power if Power Control is set to Manual, see Receiver Control ) is required to allow the measurement to then trigger based on protocol. If your UE is not transmitting at the expected Initial PRACH Tx Power level, you may need to set expected power manually.
• Absolute measurement results are affected by any amplitude offsets that are entered (relative measurement results are not). See Amplitude Offset .

Other Considerations

• Test set may lock up if operations are attempted before the UE completes its PRACH sequence

  When the measurement completes, you must wait until the UE has finished its PRACH sequence before turning off or re-initiating the measurement, or before starting any new measurements. Otherwise, the test set may lock up. If you are controlling the test set via remote program, you must include a wait period after the measurement completes (see Programming a PRACH Transmit On/Off Power Measurement ).

  If you set Call Limit Mode to Off before initiating the measurement, you will know that the UE's PRACH sequence is complete when you see the call status move from Paging to Idle , to Setup , to Releasing and then back to Idle (see Importance of Setting Call Limit State to Off before Initiating a PRACH Measurement ). Do not attempt any of the above listed operations until the test set has reached Idle state.

  To allow the UE to complete its PRACH sequence as quickly as possible, it is recommended that you set PRACH Preambles to 4 and PRACH Ramping Cycles (MMAX) to 1 (see Recommended PRACH Preambles and PRACH Ramping Cycles (MMAX) settings ).

• To change the UE's Initial PRACH TX Power level (which is reported by the Burst On Power result), you can change Primary CPICH TX Power , Uplink Interference , Constant Value , Cell Power and/or CPICH RSCP (Received Signal Code Power) . If you change Primary CPICH TX Power , Uplink Interference , or Constant Value , you must force the UE to re-read the BCCH before initiating the measurement (so that it will use the same values for these settings as the test set when calculating the power of its initial PRACH preamble). If your UE supports the Broadcast Channel (BCCH) Update Procedure (SIB Contents) , set BCCH Update Page to Auto to force the UE to re-read the BCCH. If your UE does not support the BCCH Update procedure, see BCCH Update Page for suggestions on forcing the UE to re-read the BCCH.
• If the UE registers after the measurement has completed, the measurement results will no longer be viewable from the front panel or accessible via the FETCh:WOOPower commands. This will occur if the UE expects integrity protection to be enabled. See UE Registers Continuously Due to Integrity Protection Expectation .
• If the PRACH transmit on/off power measurement timeout is not on, the PRACH transmit on/off measurement will hang until it is triggered by a PRACH burst. You can reset the measurement by pressing the MEASUREMENT RESET key.
• This measurement does not provide valid results while on a faded channel (see Digital Bus Information ).

Interpreting Integrity Indicator Values

If Over Range (5) is returned, the measured signal exceeds the expected input level or exceeds the maximum allowed input power for the test set.

If Under Range (6) is returned, the measured signal is below the expected input level.

If Uncalibrated Due to Temperature (19) is returned, the temperature in the test set has changed by ± 10° C or more since the last calibration and should be calibrated again. Calibrating the Test Set

See Integrity Indicator .

Related Topics

• PRACH Transmit On/Off Power Measurement Description
• Amplitude Offset
• Integrity Indicator