EVM-based Performance Evaluation of Co-channel Interference Mitigation using Spatial Filtering for Digital MIMO Receivers

Abstract

Digital Multiple-Input Multiple-Output (MIMO) receivers, exposed to strong co-channel interference, require high dynamic range Analog-to-Digital Converters (ADCs) and a highly linear RF front-end. Hybrid analog-digital beamforming can mitigate this co-channel interference by spatial filtering before the ADC and improve interference robustness. This paper demonstrates and characterizes this mitigation effect in detail utilizing Error Vector Magnitude (EVM) as a criterion. A 4-element 22 nm FD-SOI CMOS prototype MIMO Receiver chip is characterized with a linear 4-element dipole antenna array with half-wavelength spacing in the 2.4 GHz ISM-band. EVM measurements demonstrate the effectiveness of spatial filtering for co-channel interference mitigation and dynamic range extension. The receiver is exposed to interference while using different QAM formats (16-QAM to 256-QAM). It is demonstrated how interference reduces the acceptable-EVM input power range, while hybrid beamforming extends this range. This is done by extensive conductive measurements for reliable results, while also demonstrating an Over-the-Air (OTA) result.