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PRACH Preamble Analysis Troubleshooting
Last updated: January 16, 2009
This section is only applicable to the lab application.
Possible Setup Issues
-
Before performing a PRACH preamble analysis measurement, turn the UE on and wait for it to camp to the test set's signal. When the PRACH preamble analysis 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 preamble analysis measurement.
-
Recommended
PRACH Preambles
and
PRACH Ramping Cycles (MMAX)
settings
The measurement requires a minimum of 3 PRACH preambles, so
PRACH Preambles
must be no less than 3. It is also recommended that you set
PRACH Preambles
to no greater than 3 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 preamble analysis measurement is performed. If any measurements are running when a PRACH preamble analysis measurement is initiated, they are closed and a message is displayed to indicate that they were closed.
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.
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
).
-
The measurement will execute fastest if you only specify one available signature using the
PRACH Signature
setting.
-
The PRACH preamble analysis measurement reports the PRACH signature used by the UE for the preamble burst being analyzed. This result may differ from the
Detected PRACH Signature
result if more than one signature is specified as available by the
PRACH Signature
setting.
-
While on a faded channel (see
Digital Bus Information
), the measurement will only return valid results if
Trigger Source
is set to
RF Rise
or
External
.
-
Timing error is not reported when
Trigger Source
is set to
RF Rise
.
-
FDD Test Operating Mode Considerations
-
When operating in
FDD Test Operating Mode
, you do not have access to the
PRACH Signature
setting, as the test set does not send this type of signalling to the UE in FDD test operating mode. However, when you initiate the measurement in FDD test operating mode, the measurement uses the value last set in the PRACH signature setting to determine which signatures to try to correlate to the PRACH preamble burst. Thus, you must switch to
Active Cell Operating Mode
and ensure that the
PRACH Signature
setting includes the signature that your UE will transmit before running this measurement in FDD test operating mode.
-
If the PRACH preamble analysis measurement timeout is not on, the PRACH preamble analysis measurement will hang until it is triggered by a PRACH burst. You can reset the measurement by pressing the
MEASUREMENT RESET
key.
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
.
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