6.7 Intermodulation attenuation (GSM 400, GSM 900, ER-GSM 900 and DCS 1800)
3GPP51.021Base Station System (BSS) equipment specificationRadio aspectsRelease 17TS
6.7.1 Test purpose
To verify that the RF transmit equipment is able to restrict the generation of signals in its non‑linear elements caused by the presence of the RF output from the transmitter and an interfering signal reaching the transmitter via its antenna to below specified levels.
6.7.2 Test case
If SFH is supported by the BSS, it shall be disabled during this measurement.
The Manufacturer shall declare how many TRXs the BSS supports. The BSS shall be configured with the maximum number of TRXs supported. The test shall be performed for the number of TRXs and the frequencies defined in the minimum requirement.
Only the TRX under test shall be active. All remaining TRXs shall be idle on an ARFCN within the transmit operating band for the BSS.
NOTE 1: It is particularly important, for a BSS which uses a tuned transmitter combiner, that all sections of the combiner are set to frequencies within the transmit operating band of the BSS during this test.
The antenna output of the RF transmit equipment under test, including the combiner, shall be connected to a coupling device, presenting to the RF equipment a load with an impedance of 50 ohms. The frequency of the test signal shall be within the transmit operating band (see subclause 4.2). The test signal shall be unmodulated and the frequency shall be X MHz offset from the frequency of the RF transmit equipment under test. The TRX under test shall be set to highest static power control level and the test signal power level shall be adjusted 30 dB below this value. The test signals are illustrated in figure 6.7-1. The power level of the test signal shall be measured at the antenna output end of the coaxial cable, when disconnected from the RF transmit equipment and then correctly matched into 50 ohms. The antenna output power of the RF transmit equipment shall be measured directly at the antenna output terminal connected to an artificial antenna. Intermodulation product frequencies in the relevant TX band and relevant RX band shall be identified and measured according to the following process.
Figure 6.7-1: Example of TX intermodulation attenuation
For the measurements in the operating RX band:
Use a measurement and filter bandwidth of 100 kHz, frequency scan mode, averaged over 200 sweeps, with a sweep time of at least 75 ms. The frequency offset X shall be chosen to cause the lowest order intermodulation product to fall in the operating RX band.
For measurements in the relevant TX band:
i) For BTSs not belonging to a multicarrier BTS class
The measurement shall be made for frequency offsets X of: 0.8 MHz, 2.0 MHz, 3.2 MHz, 6.2 MHz. The power of all third and fifth order intermodulation products shall be measured. The method of measurement specified below depends on the frequency offset of the intermodulation product from the carrier frequency:
For measurements at frequency offsets from the active TRX of more than 6 MHz the peak power of any intermodulation components shall be measured with a bandwidth of 300 kHz, zero frequency span, over a time slot period. This shall be measured over sufficient time slots to ensure conformance according to methodology of annex A. The reference power for relative measurements is the power measured in a bandwidth of at least 300 kHz for the TRX under test.
For measurements at frequency offsets from the active TRX 1.8 MHz or less the intermodulation product power shall be measured selectively using video averaging over 50 to 90 % of the useful part of the time slot excluding the mid‑amble. The averaging shall be over at least 200 time slots and only active bursts shall be included in the averaging process. The RF and video filter bandwidth of the measuring instrument shall be 30 kHz.
For measurements at frequency offsets in the range 1.8 to 6 MHz the intermodulation product power shall be measured in a frequency scan mode, with a minimum sweep time of 75 ms and averaged over 200 sweeps. The RF and video filter bandwidth of the measuring instrument shall be 100 kHz.
ii) For BTSs belonging to a multicarrier BTS class
The measurements shall be made for frequency offsets X of: 0.8 MHz, 2.0 MHz, 3.2 MHz and 6.2 MHz. The power of all third and fifth order intermodulation products shall be measured in a 600 kHz band centered at their centre frequencies. The method of measurement specified below depends on the frequency offset of the intermodulation product from the carrier frequency:
For measurements at frequency offsets from the active TRX of more than 6 MHz the average power of any intermodulation components shall be measured with a bandwidth of 300 kHz, zero frequency span, over a time slot period. This shall be measured over sufficient time slots to ensure conformance according to methodology of annex A. The reference power for relative measurements is the power measured in a bandwidth of at least 300 kHz for the TRX under test. The measurement shall be performed with center frequencies of the measurement bandwidth in the frequency band ± 150 kHz around the center frequencies of the intermodulation components.
For measurements at frequency offsets in the range from 1.8 MHz up to and including 6 MHz the average power of any intermodulation components shall be measured with a bandwidth of 100 kHz, zero frequency span, over a time slot period. This shall be measured over sufficient time slots to ensure conformance according to methodology of annex A. The reference power for relative measurements is the power measured in a bandwidth of at least 100 kHz for the TRX under test. The measurement shall be performed with center frequencies of the measurement bandwidth in the frequency band ± 250 kHz around the center frequencies of the intermodulation components.
For measurements at frequency offsets in the range from 1.2 MHz up to 1.8 MHz the average power of any intermodulation components shall be measured with a bandwidth of 30 kHz, zero frequency span, over a time slot period. This shall be measured over sufficient time slots to ensure conformance according to methodology of annex A. The reference power for relative measurements is the power measured in a bandwidth of at least 30 kHz for the TRX under test.
NOTE 2: When the above measurements are performed precautions should be taken, so that non‑linearity in the selective measuring device does not influence the results appreciably. Furthermore it should be ensured that intermodulation components which may be generated by non‑linear elements in the test equipment (e.g. signal generator, coupling device, selective measuring device) are sufficiently reduced. The RF transmit equipment under test and the test signal source should be physically separated in such a way that the measurement is not influenced by direct radiation. A possible measurement set‑up is shown in annex B.2.
6.7.3 Void
6.7.4 Conformance requirement
Test Environment
Normal:
Minimum requirement
The test shall be performed until three TRXs, or the maximum number supported by the BSS (whichever is the less) have each been tested at B, M, and T. For BTS belonging to a multicarrier BTS class, the test shall be performed on B, M and T for each transmitting antenna connector.
For the measurements in the operating RX band:
In the operating receive band the measured intermodulation components shall never exceed the values given in table 6.7-1 under normal test conditions.
Table 6.7-0 Intermodulation lower limit
|
Maximum output power |
Intermodulation |
|
> 33 dBm |
-36 dBm |
|
> 24 dBm and ≤ 33 dBm |
-41 dBm |
|
≤ 24 dBm |
-46 dBm |
Table 6.7-1: Maximum Receive Band transmitter intermodulation limits
|
GSM 400, GSM 900, ER-GSM 900 (dBm) |
DCS 1800 (dBm) |
|
|
Normal BTS |
‑98 |
‑98 |
|
Micro‑BTS M1 |
‑91 |
‑96 |
|
Micro‑BTS M2 |
‑86 |
‑91 |
|
Micro‑BTS M3 |
‑81 |
‑86 |
|
Pico‑BTS P1 |
‑70 |
‑80 |
|
R‑GSM 900 BTS |
‑89 |
n/a |
|
ER-GSM 900 BTS |
-89 |
n/a |
|
Wide Area multicarrier BTS |
-98 |
-98 |
|
Medium Range multicarrier BTS |
-91 |
-91 |
|
Local Area multicarrier BTS |
-84 |
-84 |
|
NOTE: Micro and pico-BTS is not defined for GSM400. |
||
For the measurements in the relevant TX band:
i) For BTSs not belonging to a multicarrier BTS class
At frequencies offset from the wanted signal carrier frequency by more than 6 MHz and up to the edge of the relevant transmit band, the intermodulation components measured shall not exceed ‑70 dBc or ‑36 dBm, whichever is the higher. 1 in 100 time slot periods may fail the requirement by up to 10 dB.
At frequencies offset from the wanted signal carrier frequency of less than 6 MHz, the requirements are those specified in subclause 6.5.1.4, Continuous Modulation Spectrum. The exceptions given in subclause 6.5.1.4 also apply.
ii) For BTSs belonging to a multicarrier BTS class:
In the relevant transmit band, at offsets from the wanted signal carrier frequency by more than 6 MHz and up to 10 MHz outside the edge of the relevant transmit band, the measured intermodulation products shall not exceed the limit in table 6.7-0 or -70 dBc or the requirements specified in subclause 6.5.1.4, Continuous Modulation Spectrum, whichever less stringent. In addition, the measured third order intermodulation products may increase up to -60 dBc or -36 dBm, whichever is less stringent.
In the relevant transmit band, at offsets of less than or equal to 6 MHz, the requirements are those specified in subclause 6.5.1.4, except that the measured intermodulation products shall not exceed the limit in table 6.7-0 or -70 dBc or the requirements specified in subclause 6.5.1.4, Continuous Modulation Spectrum, whichever less stringent. In addition, the measured third order intermodulation products may increase up to -60 dBc or -36 dBm whichever is less stringent.
For offsets of the measurement frequency point from the wanted signal carrier frequency higher or equal to 1.8 MHz the dBc value specified in table 6.5-1 must be reduced by 5 dB to account for the bandwidth conversion from 100 kHz to 30 kHz.
In case of multicarrier BTS operating with one carrier, the level and number of allowable exceptions up to 10MHz outside the relevant transmit band as defined in subclause 6.12.4 using N= 1 apply.
The intermodulation products shall never exceed -16 dBm, measured in 100 kHz bandwidth.
6.7.5 Requirement reference
3GPP TS 45.005 subclause 4.7.1.