A 25–34-GHz Eight-Element MIMO Transmitter for Keyless High Throughput Directionally Secure Communication

A primary advantage of antenna arrays is their spatial selectivity, which has been widely utilized to support various applications, such as beam-steering, blocker rejection, massive multi-in--multi-out (MIMO), targeting communication, radar, and imaging. In this article, we exploit and engineer this spatial selectivity in an MIMO array for directionally secured wireless communication. We propose constellation decomposition array (CDA) and spatial carrier aggregation (SCA) schemes to achieve high throughput keyless physical layer security using antenna arrays. In CDA, lower order quadratic-amplitude modulation (QAM) signals are fed into an MIMO array and are spatially combined in the target direction to realize desired higher order QAM signals but distort the modulation in unintended directions. In SCA, we feed different carriers to different elements in an MIMO array to perform spectral carrier aggregation spatially. In addition, we adopt temporal swapping to further enhance security by creating one-to-many symbol mapping in unintended directions. The concept is demonstrated on an eight-channel MIMO transmitter (TX) fabricated in 45-nm CMOS silicon on insulator (SOI) and on-board antenna array for over-the-air (OTA) measurements. Using four channels of the TX array in the CDA mode, an information beamwidth of 5°/10° is realized by spatially constructing a single carrier 64QAM signal using three QPSK signals or one QPSK signal plus one 16QAM signal with a total 64QAM data rate up to 3 Gb/s. Using SCA with two carriers of 64QAM signals and temporal swapping, an rms error vector magnitude (EVM) of 6.3% at broadside with an aggregated data rate of 1.2 Gb/s is achieved, in contrast to greatly distorted rms EVM of 10% at only 4° angle.