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Avoiding Passive Inter-modulation 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 Nokia 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 GSMWCDMA

or GSM-LTE).

• antenna line PIM performance is poor, or not on the required level for the

configuration.

One Shot : Typical reference sensitivity degradation with different Antenna line PIM

performance.

PIM performance Typical degradation Note

-140 dBc @ 2x43 dBm ~10 dB High degradation, carrier configuration unusable in many cases

-153 dBc @ 2x43 dBm ~2 dB Modest degradation, tolerable in many cases

-161 dBc @ 2x43 dBm ~0.2 dB Minimal degradation, however, difficult to reach on the typical site environment.


When using wide band 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 inter-modulation results in landing in own receiver channels.


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