Multi-User Hybrid MIMO at 60 GHz Using 16-Antenna Transmitters

© 2004-2012 IEEE. Given the high throughput requirement for the next generation wireless communication systems, merging millimeter wave technologies and multi-user MIMO seems a very promising strategy to achieve the required 20 Gbps. Although a full digital architecture provides the best performance and flexibility, its implementation at millimeter-wave frequencies today seems unrealistic due to the prohibitive costs and high power consumption. Hybrid analog-digital architectures, efficiently sharing beamforming operations between analog and digital domains, appear as a feasible way to implement multi-user MIMO systems at millimeter wave frequencies. While hybrid architectures have been studied intensively, an effective and flexible demonstration proving the feasibility is still missing. In this paper, we introduce the design of a millimeter wave multi-user MIMO system with hybrid analog and digital processing using 60 GHz radios equipped with phased arrays. A base station, employing two 16-antennas transmitters, serves simultaneously two user equipment devices, each with 4 antenna elements, effectively realizing spatial multiplexing. We propose a complete system design comprising the description of millimeter radio transceivers, the multi-user hybrid MIMO algorithms including a strategy for channel estimation and frequency selective precoding along with the transmission protocol. We show that the spatial multiplexing is achieved in several scenarios, most importantly in a strong interference-limited scenario.status: publishe

A low-power reflection-coefficient sensor for 28-GHz beamforming transmitters in 22-nm FD-SOI CMOS

Active load impedance variations in a phased array transmitter cause significant power amplifier (PA) performance degradation, in terms of output power, linearity, and power-added efficiency, which are key parameters to enable high-speed data throughputs using spectrally efficient modulation schemes. The system performance can be restored by using PAs having active or passive reconfigurability with the help of antenna impedance sensors. This article presents a low-power reflection-coefficient sensor for 5G millimeter-wave phased-array applications. The complex load impedance of the PA is determined based on the complex voltage over a sensing element, which can be integrated and co-designed with the PA output matching network, with minimal loss (<0.2 dB) and a negligible area penalty. A full-range phase detector with improved detection resolution is proposed, enabling an amplitude-insensitive phase detection. Fabricated in a 22 nm FD-SOI process, the sensor prototype occupies a silicon area of 0.024 mm(2) and consumes 13.2 mW power. The sensor demonstrates a wide detection range with vertical bar Gamma vertical bar up to 0.7 (VSWR 5.67) in a load-pull test at 28 GHz. From Gamma circle of 0.2 up to 0.7, the maximum detection errors in the magnitude and phase of the Gamma are 0.14 degrees and 40 degrees, respectively