Last updated: November 25, 2010
The Output RF Spectrum Measurement is applicable to GSM, GPRS, and EGPRS. This measurement description contains two sections:
The ORFS measurement is a narrow-band measurement that provides information about the distribution of the mobile station transmitter's out-of-channel spectral energy due to modulation and switching as defined in ETSI GSM 05.05, section 4.2, 3GPP 51.010 (formerly ETSI GSM 11.10), section 13.4 at offsets < 1800 kHz.
The test set provides two forms of the ORFS measurement filter types: analog and digital. The Digital ORFS measurement is optimized for speed. It allows all ORFS offset frequencies to be computed from a single acquisition rather than obtaining them individually, which is the process for the Analog ORFS measurement. For power levels greater than 2 dBm, the dynamic range of the Digital ORFS measurement is about 3 dB to 7 dB less than the dynamic range for the Analog ORFS measurement. However, at lower values of expected power, the dynamic range of the ORFS measurement is actually greater than the Analog ORFS measurement.
The measurement filter type can be configured either manually or remotely. The available settings for the measurement filter type are
Analog
,
Digital
, and
Auto
. The Auto setting allows the test set to determine which filter type to use based on the current hardware. The test set always chooses the filter type that returns the fastest measurement results. The command to set the filter type is
SETup:ORFSpectrum:FILTer:TYPE
. The manual setting for the filter type is in the
Measurement Setup
window of the
ORFS Setup
screen.
The analog and digital measurement filter types each include ORFS due to modulation and ORFS due to switching. Switching and modulation measurements may be performed from the same burst. If you request both modulation and switching results at the same frequency offsets, measurement throughput is improved.
ORFS due to modulation measures out of channel interference due to the GMSK, 8PSK or 16QAM modulating signal. The measurement returns relative results in (dB) using the power in a 30 kHz bandwidth centered on the carrier frequency as the reference. You can set 0 to 22 modulation offset frequencies.
ORFS due to switching measures out of channel interference due to the TDMA switching transients. The measurement returns absolute power results (dBm) for each offset frequency indicating the peak power value over the entire burst plus 10 additional bits on either side of the 147 bit wide normal burst. You can set 0 to 8 ORFS due to switching offset frequencies.
The number of measurements to be averaged for each offset may be different. The test set internally controls all other aspects of the measurement, including calibration.
TX power (average power), 30 kHz bandwidth power at zero offset, ORFS due to modulation average power, and ORFS due to switching maximum power are included in an ORFS measurement, when both modulation and switching measurements are made. (TX power is performed using the same method as described in the Transmit Power Measurement Description , which synchronizes the measurement with the burst amplitude).
When multiple offset frequencies for the ORFS due to modulation measurement are set, the DSP averages the power across the appropriate time segments (40 bits) of the burst with a 30 kHz resolution bandwidth, 5-pole, synchronously tuned filter placed at the center frequency of the burst and compares it to a time segment of the response of the same filter placed at some frequency offset. The result is a relative power measurement using the 30 kHz bandwidth power at zero offset as a reference. When the ORFS measurement filter type is
ANALog
, for each offset you specify, the DSP retunes the filter and measures the 30 kHz bandwidth power and compares it to the reference, the relative power measurement of signal power over the entire burst. The DSP processes the data and makes these results available to you.When the ORFS measurement filter type is
DIGital
, the test set captures the signal in the full 3.6 MHz ORFS bandwidth in a single acquisition, and does not need to retune the receiver for each offset which reduces the measurement time.
For offsets up to 1.799999 MHz, an ORFS due to modulation measurement uses the 30 kHz resolution bandwidth filter required in GSM 05.05. At the 1800 kHz offset frequency the ORFS due to modulation measurement is made using the 30 kHz resolution bandwidth filter, not the 100 kHz resolution bandwidth filter required by ETSI.
The ORFS due to modulation measurement measures both the front and back data portions of the burst. Measurements occur from bit 15 to 60 and from bit 87 to 132. GSM 11.10 recommends that this measurement is performed on only the back section of the burst. Measuring both the front and back of the burst has the speed advantage of providing two modulation measurements per burst.
When multiple offset frequencies for the ORFS due to switching measurement are set, the DSP looks at the signal through the 30 kHz resolution bandwidth, 5-pole, synchronously tuned to each offset frequency in turn. The result for the measurement is the maximum of these sampled values over the entire burst and is reported as an absolute power measurement. When the measurement filter type is set to ANALog, the DSP then retunes the filter, samples the signal, and processes the data for each requested offset. When the measurement filter type is set to
the DSP computes the result for all requested offset frequencies from the same sample acquisition.
To obtain statistical measurement results, the multi-measurement count must be set for both switching and modulation measurements. (See Statistical Measurement Results for more information.)
Changing the multi-measurement modulation or switching count number or setting multi-measurement to ON allows the test set to make multiple measurements at each frequency offset. If you set Multi-measurement count state to OFF only one ORFS measurement is completed at each offset frequency (that is, one ORFS due to modulation, and one ORFS due to switching measurement).
If you want to make multiple ORFS due to modulation measurements and no ORFS due to switching measurements, a number must be entered in the multi-measurement modulation count, and all the switching offset frequencies must be off.
In order to make multiple ORFS due to switching measurements and no ORFS due to modulation measurements, a number must be entered in the multi-measurement switching count, and all modulation offset frequencies must be off.
For modulation measurements, the average and standard deviation of the relative power values at each offset frequency are returned.
For switching measurements, the maximum, average and standard deviation of the absolute power values at each offset frequency are returned.
The ORFS measurement will complete and meet its accuracy specification under the following conditions:
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.
| Recommended Trigger Source | |
|---|---|
|
Normal GSM TCH burst with mobile station in active cell mode |
Protocol |
| RF Rise | |
| CW signal | Immediate |
How Do I Make an Output RF Spectrum Measurement?
The ORFS measurement is a narrow-band measurement that provides information about the distribution of the mobile station transmitter's out-of-channel spectral energy due to modulation and switching as defined in ETSI GSM 05.05, section 4.2, 3GPP 51.010 (formerly ETSI GSM 11.10), section 13.4 at offsets < 1800 kHz.
The test set provides two forms of the ORFS measurements: analog and digital. The Digital ORFS measurement is optimized for speed. It allows all ORFS offset frequencies to be computed from a single acquisition rather than obtaining them individually, which is the process for the Analog ORFS measurement. For power levels greater than 2 dBm, the dynamic range of the Digital ORFS measurement is about 3 dB to 7 dB less than the dynamic range for the Analog ORFS measurement. However, at lower values of expected power, the dynamic range of the ORFS measurement is actually greater than the Analog ORFS measurement.
The measurement filter type can be configured either manually or remotely. The available settings for the measurement filter type are
Analog
,
Digital
, and
Auto
. The Auto setting allows the test set to determine which filter type to use based on the current hardware. The test set always chooses the filter type that returns the fastest measurement results. The command to set the filter type is
SETup:ORFSpectrum:FILTer:TYPE
. The manual setting for the filter type is in the
Measurement Setup
window of the
ORFS Setup
screen.
For analog ORFS measurement, You can measure one of the two adjacent uplink bursts of the multislot configuration at one time. You can specify the burst to measure using CALL:(PDTCH|PDTChannel):MSLot:MEASurement:BURSt . The relative power level is within 30dB according to the data sheet. Initiating analog ORFS with more than 2 uplink bursts will result in Unsupported Configuration error.
For digital ORFS measurement, You can measure one of the six adjacent uplink bursts of the multislot configuration at one time. You can specify the burst to measure using CALL:(PDTCH|PDTChannel):MSLot:MEASurement:BURSt . The relative power level is within 30dB according to the data sheet of the four uplink bursts in the multislot configuration.
For GPRS and EGPRS mobiles, the measurement conforms to 3GPP 51.010 (formerly ETSI GSM 11.10), section 13.16.3 at offsets < 1800 kHz (when the Multi-Measurement Count - Modulation parameter is set to Off using SETup:ORFSpectrum:COUNt:STATe ).
The analog and digital measurement each include ORFS due to modulation and ORFS due to switching.
ORFS due to modulation measures out of channel interference due to the GMSK or 8PSK modulating signal. The measurement returns relative results in (dB) using the power in a 30 kHz bandwidth centered on the carrier frequency as the reference. You can set 0 to 22 modulation offset frequencies.
ORFS due to switching measures out of channel interference due to the TDMA switching transients. The measurement returns absolute power results (dBm) for each offset frequency indicating the peak power value over the entire burst plus 10 additional bits on either side of the 147 bit wide normal burst (or 147 symbol wide normal burst for 8PSK modulation). You can set 0 to 8 ORFS due to switching offset frequencies.
When measuring a single uplink timeslot, switching and modulation measurements can be performed from the same burst (provided that the overshoot in the burst is less than 1 dB). If you request both modulation and switching results at the same frequency offsets, measurement throughput is improved. Measurements are made using a 30 kHz IF bandwidth, 5-pole synchronously tuned filter.
When measuring more than one uplink timeslots, the modulation measurement is performed for only one burst at a time in the multislot configuration, which you specify using CALL:(PDTCH|PDTChannel):MSLot:MEASurement:BURSt . The switching measurement is performed over all consecutive bursts irrespective of which burst you have currently selected to measure.
The number of measurements to be averaged for each offset may be different. The test set internally controls all other aspects of the measurement, including calibration.
TX power (average power), 30 kHz bandwidth power at zero offset, ORFS due to modulation average power, and ORFS due to switching maximum power are included in an ORFS measurement, when both modulation and switching measurements are made. (TX power is performed using the same method as described in the Transmit Power Measurement Description , which synchronizes the measurement with the burst amplitude).
When multiple offset frequencies for the ORFS due to modulation measurement are set, the DSP averages the power across the appropriate time segments (40 bits) of the burst with a 30 kHz resolution bandwidth, 5-pole, synchronously tuned filter placed at the center frequency of the burst and compares it to a time segment of the response of the same filter placed at some frequency offset. The result is a relative power measurement using the 30 kHz bandwidth power at zero offset as a reference. When the ORFS measurement filter type is
ANALog
, for each offset you specify, the DSP retunes the filter and measures the 30 kHz bandwidth power and compares it to the reference, the relative power measurement of signal power over the entire burst. The DSP processes the data and makes these results available to you.When the ORFS measurement filter type is
DIGital
, the test set captures the signal in the full 3.6 MHz ORFS bandwidth in a single acquisition, and does not need to retune the receiver for each offset which reduces the measurement time.
For offsets up to 1.799999 MHz, an ORFS due to modulation measurement uses the 30 kHz resolution bandwidth filter required in GSM 05.05. At the 1800 kHz offset frequency the ORFS due to modulation measurement is made using the 30 kHz resolution bandwidth filter, not the 100 kHz resolution bandwidth filter required by ETSI.
The ORFS due to modulation measurement measures both the front and back data portions of the burst. Measurements occur from bit 15 to 60 and from bit 87 to 132. GSM 11.10 recommends that this measurement is performed on only the back section of the burst. Measuring both the front and back of the burst has the speed advantage of providing two modulation measurements per burst.
When multiple offset frequencies for the ORFS due to switching measurement are set, the DSP looks at the signal through the 30 kHz resolution bandwidth, 5-pole, synchronously tuned to each offset frequency in turn. The result for the measurement is the maximum of these sampled values over the entire burst and is reported as an absolute power measurement. When the measurement filter type is set to ANALog, the DSP then retunes the filter, samples the signal, and processes the data for each requested offset. When the measurement filter type is set to
DIGital
the DSP computes the result for all requested offset frequencies from the same sample acquisition.
To obtain statistical measurement results, the multi-measurement count must be set for both switching and modulation measurements. (See Statistical Measurement Results for more information.)
Changing the multi-measurement modulation or switching count number or setting multi-measurement to ON allows the test set to make multiple measurements at each frequency offset. For modulation measurements the offset values returned are the average power at each offset. For switching measurements the offset values returned are the maximum power at each offset. If you set Multi-measurement count state to OFF only one ORFS measurement is completed at each offset (that is, one ORFS due to modulation, and one ORFS due to switching measurement).
If you want to make multiple ORFS due to modulation measurements and no ORFS due to switching measurements, a number must be entered in the multi-measurement modulation count, and all the switching offset frequencies must be off.
In order to make multiple ORFS due to switching measurements and no ORFS due to modulation measurements, a number must be entered in the multi-measurement switching count, and all modulation offset frequencies must be off.
For modulation measurements, the average and standard deviation of the relative power values at each offset frequency are returned.
For switching measurements, the maximum, average and standard deviation of the absolute power values at each offset frequency are returned.
The result of the Output RF Spectrum measurement relies on pseudo random data being present in the data field of the RF burst. When using the BLER data connection type, these data fields do not contain pseudo random data, therefore the results may not be representative.
The following list summarizes the input signal attributes and mobile station operating modes for making PvT measurements.
Class 1 to 12 GPRS PDTCH multislot configurations with the mobile station in active cell mode.
Class 1 to 12 GPRS PDTCH multislot configurations with the mobile station in GPRS BCH or GPRS BCH+PDTCH test mode (no protocol).
Class 1 to 12 EGPRS PDTCH multislot configurations when the operating mode is active cell and the serving cell is EGPRS.
Class 1 to 12 EGPRS PDTCH multislot configurations with the mobile station in EGPRS BCH or EGPRS BCH+PDTCH test mode (no protocol).
Non-bursted signal including GMSK modulation with mobile station in test mode.
For a non-bursted signal, an ORFS due to switching measurement result is not useful.
The ORFS measurement will complete and meet its accuracy specification under the following conditions:
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.
For more information on measurement triggering, refer to Triggering of Measurements .
As the uplink burst number increases, the measurement speed is expected to decrease.
The test set also provides the result of ORFS due to Switching in time domain. However, Turning on the Time Domain Trace will slow down the measurement speed significantly. You can use SETup:ORFSpectrum:SWITching:TIME:DOMain:STATe to turn on/off the Time Domain Trace.
How Do I Make an Output RF Spectrum Measurement?