Interference Mitigation by Adaptive Analog Spatial Filtering for MIMO Receivers

• Published in: IEEE transactions on microwave theory and techniques 2021-09, Vol.69 (9), p.4169-4179
• Main Authors: Alaei, Masoud Abbasi, Golabighezelahmad, Sajad, de Boer, Pieter-Tjerk, van Vliet, Frank E., Klumperink, Eric A. M., Kokkeler, Andre B. J.
• Format: Article
• Language: English
• Subjects: Adaptive algorithms; Adaptive spatial filtering; Analog to digital conversion; Analog to digital converters; Antenna arrays; Antenna measurements; Array signal processing; Beamforming; CMOS; Computer architecture; Constellations; Dipole antennas; hybrid beamforming; Interference; interference rejection; MIMO communication; multiple-input–multiple-output (MIMO); Mutual coupling; Optimization; Radio frequency; receiver; Receivers; Receivers & amplifiers; software-defined radio; Spatial filtering; vector modulator (VM)
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2021.3081110

Exposed to strong cochannel/adjacent-channel interference, digital multiple-input-multiple-output (MIMO) receivers require high-dynamic-range analog-to-digital converters (ADCs). Hybrid beamforming featuring spatial filtering before the ADCs can adaptively mitigate interference in both the analog and digital domains; hence relaxing the required dynamic ranges of the ADCs. This article demonstrates the effectiveness of hybrid beamforming in this mitigation utilizing adaptive minimum mean square error (MMSE) and error vector magnitude (EVM) as an optimization criterion. Extensive EVM measurements are carried out with a conductive setup using a four-element 22-nm FD-SOI CMOS prototype MIMO receiver chip to verify the performance of the adaptive MMSE algorithm. Over-the-air (OTA) measurements with a linear four-element dipole antenna array with half-wavelength spacing in the 2.4-GHz industrial scientific and medical (ISM) band quantify the improvement for real-world scenarios, e.g., having a multipath propagation channel and mutual coupling between the antenna array elements. OTA results show that a rejection of 22.5 and 24.5 dB can be achieved on average in an in-door laboratory environment utilizing vector modulator (VM) constellations with 16 and 64 points, respectively.