Appendix C: Avoiding Passive Intermodulation During Rf Module And Rrh Operation - Nokia Flexi Multiradio BTS Technical-Operating Documentation

Flexi Multiradio BTS Radio Module and Remote Radio
Head Description
13 Appendix C: Avoiding Passive
Issue: 05
Intermodulation during RF Module and RRH
operation
In wideband frequencies when several transmitting and receiving signals are sharing
same hardware there could be noted effect called Passive Intermodulation (PIM)
Interference. Using RF Modules might cause a potential risk of generating third-order
intermodulation that results in distortions in own receiver (RX) channel. Antenna Line
Devices (ALD) have important role in preventing Passive Intermodulation generation,
even if used RF Module and RRH performance at the antenna connector complies with
3GPP requirements. Poor PIM performance of ALD might degrade significantly the
reference sensitivity. ALDs, like MHAs, provided by NSN have high PIM requirements.
The risk might be high in the following cases:
maximum bandwidth (BW) used for the carriers is more than 0.5 x duplex separation
•
of the band
carriers in configuration are wideband in nature (for example WCDMA or LTE), or
•
combination of wideband and narrow band carriers (for example RF sharing GSM-
WCDMA or GSM-LTE).
antenna line PIM performance is poor, or not on the required level for the
•
configuration.
Table 24 Typical reference sensitivity degradation with different Antenna line PIM
performance.
PIM Typical
performance degradation
-140 dBc @ 2x43 ~10 dB
dBm
-153 dBc @ 2x43 ~2 dB
dBm
-161 dBc @ 2x43 ~0.2 dB
dBm
When using wideband carrier configurations where PIM products fall into own receiver
band, it is recommended that antenna line PIM performance is at least -153 dBc
measured with 2 x 43dB test signals.
However, this kind of performance might be very difficult to achieve and maintain over
time in outdoor environment due to mechanisms behind the PIM including corrosion,
oxidation, material imperfections, and defects in workmanship. Some of these
parameters might change, and can degrade performance during operation. Taking that
into consideration, it is highly recommended not to use carrier configurations which are
generating intermodulation results in landing in own receiver channels.
Appendix C: Avoiding Passive Intermodulation during
Note
High degradation, carrier configuration unusable in many
cases
Modest degradation, tolerable in many cases
Minimal degradation, however, difficult to reach on the
typical site environment.
DN0951745
RF Module and RRH operation
61