Air-Induced Passive Intermodulation in FDD Networks: Modeling, Cancellation and Measurements

In this paper, we consider the effects of air-induced passive intermodulation (PIM) in frequency division duplexing (FDD) transceiver systems. Specifically, we are focusing on the issue in multiantenna frequency range 1 (FR-1) base station (BS) systems. The air-induced PIM is a special case of intermodulation distortion, which stems from metallic objects within the radiation pattern of the transceiver system, due to so-called "rusty bolt" effect, where the induced nonlinear distortion is reflected back to the receiver. In order to cancel the received PIM, we develop a model for the perceived interference at the receiver of the BS and utilize the model to produce an estimate of the PIM signal, and to suppress it from the received data. To verify the proposed air-PIM modeling and cancellation scheme, extensive experimentation is carried out with an FDD capable transceiver system at NR band n3. The experiments show great promise in the achievable PIM cancellation levels, as the received air-induced PIM can be suppressed by more than 20 dB with the developed digital cancellation solution.