Phase and Frequency Error Measurement Description

Last updated: May 8, 2002

How is a phase and frequency error (PFER) measurement made?

The PFER measurement performs a narrow-band (<200 kHz) measurement of the modulation quality and frequency accuracy of the mobile station's transmitter. The test set measures frequency error, rms phase error and peak phase error over the useful part of the burst.

The PFER measurement demodulates the data and compares the measured wave form with the "ideal" waveform that was expected for the data received. The frequency error is the difference in frequency, after adjustment for the effect of the modulation and phase error, between the RF transmission from the mobile station and the test set. The phase error is the difference in phase, after adjustment for the effect of the frequency error, between the mobile station and the theoretical "ideal" transmission. This measurement conforms to ETSI GSM 05.05; and ETSI GSM 11.10, section 13.1.

For GPRS mobiles which support a single uplink timeslot or two adjacent uplink timeslots, this measurement conforms to ETSI GSM 05.05 (Ver 8.2.0, 7.2.0, 6.6.0), section 4.6.1. It also conforms with 3GPP 51.010 (formerly ETSI GSM 11.10) if used as part of a type approval system. You can measure one of the two adjacent uplink bursts of the multislot configuration at any one time. You specify the burst to measure using RFANalyzer:MSLot:MEASurement:BURSt . There are no limits on the relative powers of the two uplink bursts in the multislot configuration.

The PFER measurement is controlled by the DSP in the test set. No calibration is required by the user, the DSP gets calibration information during test set power up. PFER measurements can be initiated with any measurement made by the test set.

Single or Multi-Measurements

The DSP demodulates the data and compares the measured waveform with the "ideal" waveform created by the DSP.

A single burst for a PFER measurement calculates the following:

peak phase error
rms phase error
frequency error

A multiple burst PFER measurement is made when the multi-measurement state is on and calculates the maximum, minimum and average values for the following:

peak phase error
rms phase error
frequency error
worst frequency error (worst frequency error is the frequency furthest from zero.)

All of these results are available using the FETCh command. If the most positive and the most negative frequency error are the same value, the most positive frequency will be returned. Worst frequency error is only accessible through GPIB. The test set always has an integrity indicator available regardless of whether it is a single or multiple burst measurement.

Types of Signals PFER can Measure

PFER measurements can be made on these types of input signals.

Normal GSM TCH or GPRS PDTCH burst with mobile station in active cell mode.
Access (RACH) burst with mobile station in active cell mode (GSM only).
Normal GSM TCH or GPRS PDTCH burst with mobile station in test mode.
Access (RACH) burst with mobile station in test mode (GSM only).
Bursted signal with GMSK modulation without a valid midamble.

Input Signal Requirements

The PFER measurement will complete and meet its accuracy specification of:

Frequency error measurement accuracy of +/-12 Hz + timebase reference (+/-18 Hz for RACH bursts).
rms phase error measurement accuracy of less than +/-1 degree.
Peak phase error measurement accuracy of less than +/-4 degrees.

under these conditions:

Level is between -15 dBm and +43 dBm.
Level within +/-3 dB of the expected input level.
Frequency is within +/-100 kHz of expected input frequency.

Trigger Source

Auto triggering is the recommended trigger source for each measurement allowing the test set to choose the preferred trigger source. However, you may want to select the trigger source. Immediate trigger source is not recommended for PFER measurements.

Recommended Trigger Source settings
Input Signal Type	Recommended Trigger Source
Normal GSM TCH or GPRS PDTCH burst with mobile station in active cell mode	Protocol or RF Rise
RACH burst with mobile station in active cell mode (GSM only)	Protocol or RF Rise
Normal GSM TCH or GPRS PDTCH burst with mobile station in test mode	RF Rise
RACH burst with mobile station in test mode (GSM only)	RF Rise
Bursted signal with GMSK modulation but no valid midamble	RF Rise
Non-bursted (CW) signal with a manual frequency offset of +/- 67.7083 kHz	Immediate

Burst Synchronization

The PFER measurement provides you with a choice for the time reference (burst synchronization). (See Burst Synchronization of Measurements ). For GPRS mobiles, you should note that only the Midamble synchronization method is available when you set the multislot configuration to D2U2 (2 downlink timeslots, 2 uplink timeslots). For more details on setting the multislot configuration, see CALL:PDTCH:MSLot:CONFiguration .


Burst Synchronization	Description
Midamble	References measurement timing to the midamble transmitted within a timeslot.
RF Amplitude	The amplitude rise and fall of a transmitted burst determines the measurement time reference.
None	No edge of the burst is detected, the measurement is made using the first 87 or 147 bits of data found centered around the middle of the expected burst position. Can be used when measuring non-bursted signals