Cancellation of Air-Induced Passive Intermodulation in FDD MIMO Systems: Low-Complexity Cascade Model and Measurements

This paper presents a low-complexity cascade scheme for identifying and cancelling air-induced passive intermodulation (PIM) in multiple-input multiple-output (MIMO) frequency division duplex (FDD) transceivers. PIM is in general generated by nonlinear passive devices, while in the special case of air-induced PIM, the interference stems from objects outside the transceiver system. In FDD systems, the induced intermodulation products may cause severe self-interference to the receiver (RX) band. This work presents a general solution to air-induced PIM mitigation, allowing for any number of parallel transceiver chains, unlike previous works. Moreover, the utilization of spline-interpolated lookup table (LUT) and least mean squares (LMS)-based parameter adaptation allows for a great reduction in the overall complexity of the cancellation engine, compared to previous works. This is achieved without compromising the cancellation performance, as is evidenced in real-life RF measurements at 5G NR band n3.