Digital Cancellation of Passive Intermodulation in FDD Transceivers

Abstract

Modern radio systems and transceivers utilize carrier aggregation (CA) to meet the demands for higher and higher data rates. However, the adoption of CA in the existing Long Term Evolution (LTE)-Advanced and emerging 5G New Radio (NR) mobile networks, in case of frequency division duplexing (FDD), may incur self-interference challenges with certain band combinations. More specifically, the nonlinear distortion products of the transmit signals or component carriers (CCs), stemming from the passive radio frequency (RF) front-end components of the transceiver, can appear in one or more of the configured receiver bands, potentially leading to the receiver desensitization. In this paper, we present advanced baseband equivalent signal models for such passive intermodulation (PIM) distortion viewed from the RX point of view, considering also potential memory effects in the PIM generation. Then, building on these signal models, a digital self-interference cancellation technique operating in the transceiver digital front-end is presented. The performance of the proposed solution is evaluated with real-life RF measurements for LTE-Advanced type user equipment (UE) with dual CC interband CA, demonstrating excellent suppression properties. The findings in this work indicate that digital cancellation is a feasible approach for improving the receiver sensitivity of mobile devices that may be prone to RF front-end induced PIM challenges.

A Survey of Self-Interference in LTE-Advanced and 5G New Radio Wireless Transceivers

“…Fig. 14(c) shows a cancellation approach for the interference effect of Type G, as presented in [76]. In this so-called parallel Hammerstein model [77], a static nonlinearity is placed at the input of an adaptive linear combiner.…”

Passive Intermodulation Effects in Modern Radio Communication Systems

“…PIM has a significant impact on FDD radios [9,75,77] and radios that have high-power TX collocated with sensitive RXs [32,57,59,78,79]. FDD is a widely adopted duplexing scheme for FR1 bands, in which a paired spectrum for simultaneous transmission and reception at different RF frequencies is used [16,80,81].…”

“…OFDM-based transmissions enable wider transmission bandwidth [3]. CA allows increased bandwidth by aggregating up to five component carriers (CCs) of 20 MHz from the same operating frequency band (contiguous) or different operating frequency bands (non-contiguous) of the spectrum, 100 MHz in total, and thus increases data rates [4][5][6][7][8][9][10][11][12]. Moreover, in advanced multi-antenna technology, MIMO uses multiple antennas to transmit higher data rates to the same user equipment, both in the uplink (UL) and downlink (DL) transmission directions [11,13].…”

“…Allocating UL and DL resources strategically can mitigate PIM, but this approach limits spectrum utilization and peak data rates. Lastly, improving the quality and isolation of RF equipment incurs significant costs [8,9,[30][31][32][33][34][35][36][37][38][39].…”