PRACH Preamble Analysis Measurement Description

How is a PRACH Preamble Analysis Measurement Made?

3GPP TS 25.101, 6.8 states "Transmit modulation defines the modulation quality for expected in-channel RF transmissions from the UE. The requirements apply to all transmissions including the PRACH/PCPCH pre-amble and message parts and all other expected transmissions. In cases where the mean power of the RF signal is allowed to change versus time e.g. PRACH, DPCH in compressed mode, change of TFC and inner loop power control, the EVM and Peak Code Domain Error requirements do not apply during the 25 us period before and after the nominal time when the power is expected to change."

The PRACH preamble analysis measurement determines the modulation and timing errors between the transmitted signal of the UE and the ideal signal. The measurement algorithm is similar to that used in the waveform quality and IQ tuning measurements (see Waveform Quality Measurement Description and IQ Tuning Measurement Description ), except that the measurement is performed on a PRACH preamble burst, rather than over a timeslot of the DPCH transmission.

You can choose whether to include the "transient periods" of 96 chips (25 us) on either side of the PRACH preamble in the measurement using the Transient Period setting (for all measurement results except Relative Power (in dB) ). The measurement can thus be performed over the entire PRACH preamble burst, (4096 chips, or 1066.7 us), or only over 3904 chips (1016.7 us).

Before initiating a PRACH preamble analysis measurement, turn the UE on and wait for it to camp to the test set's signal. When you initiate the PRACH preamble measurement by pressing START SINGLE or sending the INITiate command, the test set sets Call Limit State to On to prevent successful call connection, then pages the UE (the test set returns Call Limit State to its prior setting after completion of the measurement). This forces the UE to transmit PRACH preamble bursts.

After the measurement is triggered by a burst (see Trigger Source ) it must determine which signature the UE used to transmit the PRACH preamble so that it can decode the burst data. To do this, it attempts to correlate the data to each of the signatures specified by the PRACH Signature setting. The measurement will execute fastest if you only specify one available signature.

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, before running this measurement in FDD test operating mode, you must switch to Active Cell Operating Mode and ensure that the PRACH Signature setting includes the signature that your UE will transmit.

To perform the PRACH preamble analysis measurement, you must set Available Subchannels (Bit Mask) to only allow one available subchannel.

You must also set PRACH Preambles to at least 3 before initiating this measurement. It is recommended that you set PRACH Preambles to 3 , PRACH Ramping Cycles (MMAX) to 1 , and Call Limit State to Off before initiating this measurement to minimize issues after the measurement has completed. See the following:

• Recommended PRACH Preambles and PRACH Ramping Cycles (MMAX) settings
• Importance of Setting Call Limit State to Off before Initiating a PRACH Measurement
• Test set may lock up if operations are attempted before the UE completes its PRACH sequence

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.

PRACH Preamble Analysis Measurement Parameters

• Trigger Source

  You can set Trigger Source as follows:

  • Protocol : If trigger source is set to protocol, the test set monitors every available access slot (as determined by the Available Subchannels (Bit Mask) setting) to see if a significant change in power occurs (which would indicate a PRACH preamble burst is present in that access slot). If a burst is present, the measurement is triggered on the access slot boundary.
  • External : see Trigger Source Description .
  • RF Rise : If trigger source is set to RF rise, the measurement is triggered when the UE's power rises to within 9 dB of the expected power (the expected power is equal to Initial PRACH TX Power if Power Control is set to Auto , or Manual Power if Power Control is set to Manual ; see Receiver Control ). When Trigger Source is set to RF Rise, you may specify a Trigger Delay . When trigger source is set to RF rise, the Timing Error (in chips) result is not available.

• Trigger Delay

  Trigger delay is only available when Trigger Source is set to RF Rise. The trigger delay setting specifies when to begin the measurement relative to the trigger event. If trigger delay is set to 0 chips, the measurement will begin immediately after the trigger event. See Trigger Delay Description for additional information about trigger delays.

• Measurement Timeout: (see Measurement Timeouts )
• Transient Period

  The transient period setting determines whether to include the "transient periods" of 96 chips (25 us) on either side of the PRACH preamble in the measurement. If Transient Period is set to Include , the measurement is performed over the entire PRACH preamble, 4096 chips (1066.7 us). If Transient Period is set to Exclude , the measurement is performed over only 3904 chips (1016.7 us).

     

  NOTE

  The transient period affects the measurement interval for all measurement results except Relative Power (in dB) . Relative Power is always measured over 4096 chips.

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PRACH Preamble Analysis Measurement Results

• EVM (rms) (in %)

  This result is the rms EVM for the entire PRACH preamble burst (either 4096 or 3904 chips, depending upon the Transient Period setting).

  The EVM for each chip measured in the burst is also available (see EVM (in %) ).

• EVM (peak) (in %)

  This result is the worst EVM reported for any chip in the burst (either 3904 or 4096 chips are compared, depending upon the Transient Period setting). See EVM (in %) .

• Frequency Error (in Hz)
• Origin Offset (in dB)
• Phase Error (rms) (in degrees)
• Magnitude Error (in %)
• Timing Error (in chips)

  This result is the difference in time of the PRACH data relative to the expected timing for the given subchannel setting (see Available Subchannels (Bit Mask) ). See 3GPP TS 25.211, 5.2.2 and 7.3 and 3GPP TS 25.214, 6.1.

  Timing error is not available when Trigger Source is set to RF Rise .

• IQ Gain Imbalance (in dB)
• IQ Phase Imbalance (in degrees)
• Signature: The test set 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.

Results Returned for Each Chip Measured

• Relative Power (in dB)

  The measurement always measures the power in all 4096 chips of the PRACH preamble (regardless of the Transient Period setting), and also measures the power in up to 100 chips before and after the PRACH preamble (if there is a substantial amount of timing error, then fewer than 100 chips before or after the PRACH preamble will be measured and reported). The measurement reports the power in each chip relative to the greatest power measured in any of the chips.

• EVM (in %)

  This result is the EVM for each measured chip (either 3904 or 4096 chips, depending upon the Transient Period setting).

  The rms EVM (see EVM (rms) (in %) ) and the peak EVM (see EVM (peak) (in %) ) for the entire PRACH preamble burst is also available.

• Phase Error (in degrees): The measurement calculates the phase difference between each measured chip (either 3904 or 4096 chips, depending upon the Transient Period setting) and its corresponding chip in the ideal signal.
• IQ Constellation: The measurement plots the I-Q coordinates for each measured chip (either 3904 or 4096 chips, depending upon the Transient Period setting).

A typical measurement result is shown below:

Key 3GPP Tests Performed Using the PRACH Preamble Analysis Measurement

3GPP TS 34.121 5.13.4 PRACH Preamble Quality.

PRACH Preamble Analysis Measurement Input Signal Requirements

• This measurement does not autorange, therefore the expected power level from the mobile station (UE) is set using the current MS Target Power setting, or by using manual receiver power control and specifying the manual power level. See Receiver Control .
• The frequency of the signal being measured must be in the range of 800 MHz to 1000 MHz, 1700 MHz to 1990 MHz, or 2480 MHz to 2580 MHz.
• The level into the test set's RF IN/OUT connector must be in the range of -25 dBm to +28 dBm, in a 3.84 MHz bandwidth.
• Maximum measurable EVM = 35%.
• Maximum measurable frequency error = +/- 1 kHz.
• Maximum measurable timing error = +/- 96 chips (25 us).

PRACH Preamble Analysis Measurement Calibration

This measurement should be calibrated using the Calibrate Measurements function ( CALibration:MEASurements? ) when the temperature has changed by more than ± 10° C since the last calibration. If this situation exists, the integrity indicator value becomes 19 and a message is displayed indicating "Uncalibrated Due to Temperature".

Related Topics

Manual Operation: How Do I Make a PRACH Preamble Analysis Measurement?

Programming the PRACH Preamble Analysis Measurement

PRACH Preamble Analysis Troubleshooting

What 3GPP W-CDMA/HSPA Conformance Tests Are Supported?

Triggering of Measurements

Integrity Indicator