What is (PIM) Passive Intermodulation?

Hello dear experts.

What is PIM in telecommunications?

PIM Definition

When transmitting 2 (or more) signals with different frequency into a passive component, due to bad connection or non-linear material in the component, it will generate a new frequency signal.

We call it Passive Intermodulation (PIM).

If the PIM is strong and falls into the receiving band, it will affect the performance of receiving channel.

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Different Duplex Modes

In TDD the uplink and downlink occupy the same spectrum bandwidth. The receiving channel and transmitting channel are divided by time. The BS (Base Station) and UE (User Equipment) can cooperate with each other successfully when adopting the same configuration .

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In FDD the receiving channel and transmitting channel are divided by spectrum bandwidth. The uplink and downlink are symmetrical, and will work at the same time.

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Different RF Module Architectures

For all TDD systems, the receiving and transmitting channels work in different time at the same band. Therefore, a T/R RF switch is required to connect the receiving/transmitting channel of the system in different time slot.
When the downlink works, the RF switch is switched to the load . When the uplink works, the RF switch is switched to the receiver. Therefore, even if the PIM is generated in the downlink, it does not affect the uplink channel because the receiving channel is inactive.

So PIM is unnecessary for TDD antenna.

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For FDD systems, the receiving and transmitting channels operate at different bands and a duplexer (equivalent to two filters) is required to separate the receiving and transmitting channels.

Since the uplink and downlink are working at the same time, if the PIM generated by the TX signal is strong and falls into the receiving band, the receiver’s noise will raise, the sensitivity will be deteriorated, and the uplink throughput will be lower.

So PIM is necessary for FDD antenna.

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