Integrated Self-Adaptive and Power-Scalable Wideband Interference Cancellation for Full-Duplex MIMO Wireless

A wideband analog/RF interference cancellation technique that is able to autonomously adapt itself to time-varying interference channels and to scale its dc power based on the number of multiple-input–multiple-output (MIMO) array elements is presented. Least-mean square (LMS) adaptive circuitry is co-designed with and partially embedded in a wideband RF/analog interference canceller and a gain-boosted mixer-first receiver (RX), significantly reducing the system complexity and dc power while achieving rapid (microsecond-scale) adaptation. In addition, the proposed canceller is able to digitally adjust its transconductance and coupling strength at the RX side, essentially trading its dc power with the element-level RX noise figure (NF). At the array level, the NF can be lowered by averaging uncorrelated noise across elements. A prototype 0.5-to-2.5-GHz full-duplex (FD) MIMO RX is designed and fabricated using a 65-nm CMOS process. With the adaptive circuitry fully integrated and consuming 14 mW, the cancellers adapt themselves to an unknown channel in 1 $\mu \text{s}$ , providing >20-dB RF/analog interference cancellation across 20-MHz bandwidth (BW) with antenna voltage-standing-wave ratio (VSWR) up to 2:1. Simultaneous self- and cross-interference cancellation in our FD MIMO RX is also demonstrated using the integrated adaptation circuitry, achieving 24-dB overall interference cancellation across 20-MHz BW. The FD MIMO RX with self- and cross-interference cancellation is power-scalable—the NF-power scalability of the FD RX enables a nearly constant canceller dc power per element, despite a quadratic increase of cancellers.