6.2 Modulation accuracy
3GPP51.021Base Station System (BSS) equipment specificationRadio aspectsRelease 17TS
6.2.1 Test purpose
1) To verify the correct implementation of the pulse shaping filtering.
2) To verify that at GMSK modulation the phase error during the active part of the time slot does not exceed the specified limits under normal and extreme test conditions and when subjected to vibration.
3) To verify that the frequency error during the active part of the time slot does not exceed the specified limits under normal and extreme test conditions and when subjected to vibration.
4) To verify that at supported modulations 8-PSK, QPSK, AQPSK, 16-QAM and 32-QAM the Error Vector Magnitude (EVM) and the origin offset during the active part of the time slot do not exceed the specified limits under normal and extreme test conditions and when subjected to vibration.
6.2.2 Test case
All TRXs in the configuration shall be switched on transmitting full power in all time slots for at least 1 hour before starting the test.
In case of a multicarrier BTS, the tests shall be performed with one carrier active and with the declared maximum number of carriers active at declared maximum output power equally distributed.
If the Manufacturer declares that Synthesizer Slow Frequency Hopping is supported by the BSS, the BSS shall be configured with the maximum number of TRXs with ARFCNs which shall be distributed over the entire declared bandwidth of operation for the BSS under test, and including B, M and T, and three tests shall be performed. These tests may either use a test apparatus which employs the same hopping sequence as the BSS, or a fixed frequency apparatus on the radio frequency channels B, M and T. If only Baseband SFH is supported or SFH is not supported, one test shall be performed for each of the radio frequency channels B, M and T, using different TRXs to the extent possible for the configuration. As a minimum, one time slot shall be tested on each TRX specified to be tested.
GMSK modulation
The transmitted GMSK modulated signal from the TRX under test shall be extracted in the BSSTE for a pseudo‑random known bit stream of encrypted bits into the TRX modulator (the BSSTE is defined in annex B.1). The pseudo‑random bit stream shall be any 148 bit sub‑sequence of the 511 bit pseudo‑random bit stream defined in recommendation CCITT Q.153 fascicle IV.4. This pseudo‑random bit stream may be generated by another pseudo‑random bit stream inserted before channel encoding in the TRX and shall generate at least 200 different bursts. The phase trajectory (phase versus time) for the useful part of the time slots (147 bits in the centre of the burst ‑ see 3GPP TS 45.004 and 3GPP TS 45.010 for further information) shall be extracted with a resolution of at least 2 samples per modulating bit. The RF receiver parts of the BSSTE shall not limit the measurement.
The theoretical phase trajectory from the known pseudo‑random bit stream shall be calculated in the BSSTE.
The phase difference trajectory shall be calculated as the difference between the measured and the theoretical phase trajectory. The mean frequency error across the burst shall then be calculated as the derivative of the regression line of the phase difference trajectory. The regression line shall be calculated using the Mean Square Error (MSE) method.
The phase error is then finally the difference between the phase difference trajectory and its linear regression line.
8-PSK, QPSK, AQPSK, 16-QAM and 32-QAM modulation
The transmitted 8-PSK, QPSK, AQPSK, 16-QAM or 32-QAM modulated signal from the TRX under test shall be extracted in the BSSTE for a pseudo‑random known bit stream of encrypted bits into the TRX modulator (the BSSTE is defined in annex B.1). The pseudo‑random bit stream shall be any bit sub‑sequence of the 32767-bit pseudo‑random bit stream defined in recommendation CCITT O.151 10/1997.
The error vector between the vector representing the transmitted signal and the vector representing the error-free modulated signal defines modulation accuracy. The magnitude of the error vector is called Error Vector Magnitude (EVM). Origin suppression is defined to be the ratio of the carrier leakage to the modulated signal. For definition and calculation of EVM, see 3GPP TS 45.005 Annex G.
The following steps 1) to 5) shall be performed according to 3GPP TS 45.005 subclause 4.6.2 and annex G.
1) The RMS EVM shall be measured and calculated over the useful part of the burst (excluding tail bits) for at least 200 bursts.
2) The origin offset suppression shall be measured and calculated.
3) The frequency offset shall be measured and calculated.
4) The peak EVM shall be measured and calculated. The peak EVM is the peak error deviation within a burst, measured at each symbol interval, averaged over at least 200 bursts. The bursts shall have a minimum distance in time of 7 idle timeslots between them. The peak EVM values are acquired during the useful part of the burst, excluding tail bits.
5) The 95:th percentile EVM shall be measured and calculated. The 95:th percentile EVM is the point where 95% of the individual EVM, measured at each symbol interval, is below that point. That is, only 5% of the symbols are allowed to have an EVM exceeding the 95:th-percentile point. The EVM values are acquired during the useful part of the burst, excluding tail bits, over 200 bursts.
6.2.3 Void
6.2.4 Conformance requirement
Test Environment
Normal: The test shall be repeated until 3 TRXs or all TRXs (whichever is the less) have each been tested on B, M and T.
Extreme Power supply: One test shall be performed on each of B, M and T.
NOTE: tests under extreme power supply are carried out at extreme temperature limits.
Vibration : One test shall be performed on each of B, M and T.
In case of multicarrier BTS the test shall be performed for single carrier operation at B, M and T of the operating transmit band, and with declared maximum number of carriers distributed according to test case b) in subclause 6.12.2 throughout the maximum Base Station RF bandwidth, except in vibration conditions as stated in subclause 4.6.3 where only single active carrier operation need to be tested. For the test with maximum number of carriers, all carriers shall apply the same modulation type and operate at equal, maximum declared carrier power for this modulation type. The test shall be repeated for each modulation type supported by the multicarrier BTS.
Minimum requirement
GMSK modulation
The phase error shall not exceed:
5 degrees rms
20 degrees peak
For normal BTSs, micro BTSs, Wide Area and Medium Range multicarrier BTSs, the mean frequency error across the burst shall not exceed:
0,05 ppm
For pico BTSs and Local Area multicarrier BTSs, the mean frequency error across the burst shall not exceed:
0,1 ppm
Higher order modulation
The RMS EVM values, measured after any active element and excluding the effect of passive combining equipment, shall not exceed:
|
Normal symbol rate |
Higher symbol rate |
||||||
|
AQPSK |
8-PSK |
16-QAM |
32-QAM |
QPSK |
16-QAM |
32-QAM |
|
|
under normal conditions |
7,0 %1) 5,0 %2) |
7,0 % |
5,0 % |
5,0 % |
7,0 % |
4,0 % |
4,0 % |
|
under extreme conditions |
8,0 %1) 6,0 %2) |
8,0 % |
6,0 % |
6,0 % |
8,0 % |
5,0 % |
5,0 % |
|
Note 1: Applicable for absolute SCPIR_DL values ≤ 8,0 dB Note 2: Applicable for absolute SCPIR_DL values > 8,0 dB |
|||||||
The RMS EVM values, measured after any active element and including the effect of passive combining equipment, shall not exceed:
|
Normal symbol rate |
Higher symbol rate |
||||||
|
AQPSK |
8-PSK |
16-QAM |
32-QAM |
QPSK |
16-QAM |
32-QAM |
|
|
under normal conditions |
8,0 %1) 6,0 %2) |
8,0 % |
6,0 % |
6,0 % |
8,0 % |
5,5 % |
5,5 % |
|
under extreme conditions |
9,0 %1) 7,0 %2) |
9,0 % |
7,0 % |
7,0 % |
9,0 % |
6,5 % |
6,5 % |
|
Note 1: Applicable for absolute SCPIR_DL values ≤ 8,0 dB Note 2: Applicable for absolute SCPIR_DL values > 8,0 dB |
|||||||
The origin offset suppression shall exceed:
35 dB
For normal BTSs, micro BTSs, Wide Area and Medium Range multicarrier BTSs, the frequency offset shall not exceed:
0,05 ppm
For pico BTSs and Local Area multicarrier BTSs, the frequency offset shall not exceed:
0,1 ppm
The peak EVM values, excluding the effect of passive combining equipment, shall not exceed:
22 %
The 95:th percentile EVM value, excluding the effect of passive combining equipment, shall not exceed:
11 %
6.2.5 Requirement reference
3GPP TS 45.004, clause 2; 3GPP TS 45.005, subclause 4.6; 3GPP TS 45.010, subclause 5.1.