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With an incredible increase in the number of wireless devices and an ever-growing demand for high data rates, 5G needs to provide a solution to satisfy the demand for the next decade. Multiple-input multiple-output (MIMO) systems are seen as one of the primary solutions—allowing for spatial multiplexing and the use of millimeter-wave (mmWave) frequencies, which can provide much larger bandwidths and, thus, data rates. MIMO is very closely related to phased arrays, which have been used for radar for the past few decades and requires many antennas and transceivers—on the order of hundreds or thousands for massive MIMO. To make such systems affordable, low-cost, low-power, and low-complexity is required—inherently compromising other system characteristics, such as linearity. The main focus of this paper will be in summarizing the challenges, recent advances, and potential future breakthroughs concerning MIMO/digital array sensitivity to interferers and nonlinear distortion. Specifically, this paper gives an overview of MIMO/digital array architectures and different techniques currently researched for the characterization and mitigation of spatial and spectral interferers and nonlinearities, which can be used to extend the effective dynamic range of low-cost MIMO/digital array systems. [ABSTRACT FROM AUTHOR]

As active electronically steerable arrays become more prominent, a new paradigm of assigning bits to a set of digital phase shifters, necessary for analog and digital beamforming, is proposed. It is well known that a modern day digital phase shifter which is associated with each transmit/receive module typically relies on three to seven bits. Each of these phase shifters provide a desired resolution of 45^\circ to 2.8125^\circ, respectively. When an array is steered with a fixed precision set of phase shifters, there are some angles where results are significantly better than others. For example, six bit phase shifters can provide exact 11.25^\circdifferential phases in a linear array, but not 15^\circ, and subsequent quantization errors lead to reduced pointing accuracy and increased sidelobe levels. However, these errors can be minimized if the set of shifters operate collectively instead of independently with “blind” quantization. In particular this study seeks the solution for the following problem: for a set of N phase shifters, each defined by B bits, determine the optimal way to distribute the N\times B bits so that the array performance is maximized. [ABSTRACT FROM PUBLISHER]

A near-field cancellation duplexing system is demonstrated using multiple coordinated transceivers with symmetrically arranged antenna elements and a digital backend for baseband waveform phase and amplitude weighting controls. By adapting weights of multiple transmit elements, coupled interference at receiver elements deconstructively interferes, providing up to 50 dB of additional isolation over the coupling of a single transmitter to a receiving element. Bandwidth considerations of the array are presented. It is shown that uncorrelated transmit noise from multiple transmitters can be removed through tunable filtering or through adaptive beamforming of multiple receiving elements, both providing an additional 30–40 dB of interference reduction that is tunable over the frequency range of the system. [ABSTRACT FROM PUBLISHER]