PIM lowers the reliability, capacity, and data rate of cellular systems. It does this by limiting the receive sensitivity. You could in the past select channel frequencies that would produce PIM in the desired receive bands. The challenge now is that cellular usage has grown and the licensed spectrum has become real crowded. As a result engineers often select less desired carrier frequencies and just accept PIM issues. PIM products that fall within the receive band of the cell site radio make the receiver less sensitive to weak signals that limits receive coverage. The result is the increase in BER (bit-error rate) and creates more dropped calls. Today, we have a major shift from the use of our smart phones from voice to data. As cell usage and throughput exponentially grows the peak power produced by the new digital modulations increase dramatically contributing dramatically to PIM problems. Interference from PIM creates more error protection bits and resends which causes a lower overall data rate. There is potential for receiver blocking and a shut-down of the sector. PIM issues can manifest themselves into receive-noise-floor diversity imbalance, high noise floors, shorter average call duration, higher dropped call rates, lower data rates, and lower call volume. Left uncorrected, PIM problems can cause the BTS (base transceiver station) to assume a certain Rx noise level exist during calibration periods causing gross Tx power and Rx gain figures to be utilized. PIM is a serious issue for cellular operators wanting to maximize their network’s reliability, data rate, capacity, and return on their investment.
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