Air-Induced PIM Cancellation in FDD MIMO Transceivers

Abstract

In this letter, air-induced passive intermodulation (PIM) modeling and cancellation schemes are presented in a multiple-input multiple-output (MIMO) frequency-division duplexing (FDD) transceiver context. PIM is distortion generated by nonlinear passive devices either within the transmitter chain or outside the transceiver system, as is the case in air-induced PIM. In FDD systems, the PIM products may lie on the receiver band, thus possibly desensitizing the receiver chain. Unlike previous PIM cancellation works, we consider a challenging rank-2 dual-carrier MIMO transceiver scenario, with two spatially multiplexed signals per component carrier (CC). Stemming from the PIM modeling, we first present a cancellation method based on a complete set of identified basis functions (BFs). Additionally, to relax the processing complexity, we propose an alternative canceller solution with a reduced number of BFs, inspired by the problem modeling. RF measurements conducted with real-life equipment indicate favorable PIM suppression levels of up to 20 dB using both introduced techniques.

Air-Induced Passive Intermodulation in FDD MIMO Systems: Algorithms and Measurements

“…In [16], basic modeling and digital cancellation of air-induced PIM were pursued in a simple two-CC scenario. Finally, our preliminary work in [17] addresses the air-induced PIM cancellation in a multiple-input-multiple-output (MIMO) scenario with four simultaneous carriers.…”

“…In this article, building on our initial work in [17], we focus on the modeling and digital cancellation of air-induced PIM stemming from the interaction of the radiated electromagnetic wave with external materials outside the transceiver system. Specifically, we consider a challenging rank-2 dual-carrier MIMO FDD system where four CCs are transmitted simultaneously.…”

“…Specifically, we consider a challenging rank-2 dual-carrier MIMO FDD system where four CCs are transmitted simultaneously. Besides our initial work in [17], the authors are not aware of any works explicitly aiming to model and cancel air-induced PIM in MIMO scenarios although the issue of PIM has been mentioned in MIMO literature, e.g., in [36], [37], and [38]. To this end, the so-called full basis function (BF) canceller solution is first described.…”

“…This work was supported in part by the Academy of Finland under Grant 319994, Grant 323461, and Grant 338224; and in part by Nokia Mobile Networks. This article is an extended version from the 2022 IEEE MTT-S International Microwave Symposium (IMS-2022) [17] [DOI: 10.1109/LMWC.2022.3164718]. (Corresponding author: Vesa Lampu.)…”

“…If the source of the nonlinearity is a passive device, the distortion is called passive intermodulation (PIM) [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]. Typically, loose connections of cables, filters, switches, antennas [12], [13], [14], [15], [18], [19], [20], [21], or even external metallic objects in the radiation field of the antennas [16], [17] can be the cause of PIM. The PIM caused by external sources is in focus in this work, and such distortion is referred to as airinduced PIM.…”