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Every new generation of mobile systems should provide higher capacity, serve more users, be more energy efficient, and have lower cost. Radio-access hardware constitutes a major bottleneck for reaching these goals, which is a particularly noticeable issue now that 5G communication systems are being developed. A combination of breakthroughs in communication theory-as in massive multiple input/multiple output (MIMO) [1], highly integrated semiconductor and packaging technologies, and extended spectrum allocations- has enabled a paradigm shift in the way radio hardware will be realized. Today's high-power, fewantenna, sectorized systems will soon be replaced with highly integrated active antenna systems having up to hundreds of individually driven low-power radios operating with very wideband signals. [ABSTRACT FROM AUTHOR]

In this paper, a digital predistortion (DPD) technique for wideband multi-antenna transmitters is proposed. The proposed DPD compensates for the combined effects of power amplifier (PA) nonlinearity, antenna crosstalk, and impedance mismatch. The proposed technique consists of a linear crosstalk and mismatch model block shared by all transmit paths and a dual-input DPD block in every transmit path. By avoiding the use of multi-input DPD blocks in every transmit path, the complexity of the proposed technique is kept low and scales more favorably with the number of antennas than competing techniques. It is shown that all blocks can be identified from measurements of the PA output signals using least-squares estimation. Measurement results of a four-path transmitter are presented and used to evaluate the proposed DPD technique against existing techniques. The results show that the performance of the proposed DPD technique is similar to those of existing techniques, while the complexity is lower. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a technique for comprehensive analysis of nonlinear and dynamic characteristics of multi-antenna transmitters (TXs). The analysis technique is enabled by the development of a Volterra series-based dual-input model for power amplifiers (PAs), which is capable of considering the joint effects of PA nonlinearity, antenna crosstalk, and mismatch for wideband modulated signals. By combining multiple instances of the PA model with linear dynamic antenna simulations, we develop the analysis technique. The proposed method allows the prediction of the output signal of every antenna in an arbitrarily sized TX array, as well as the total far-field radiated wave of the TX for any input signal with low computational effort. A 2.12-GHz four-element TX demonstrator based on GaAs PAs is implemented to verify simulation results with measurements. The proposed technique is a powerful tool to study hardware characteristics as, for example, the effects of antenna design and element spacing. It can be used in cases where experiments are not feasible, and thus aid the development of next generation wireless systems. [ABSTRACT FROM AUTHOR]

Digital pulsewidth modulators are used to transform nonconstant amplitude signals into pulsed signals, such that the information lying in the signal amplitude is encoded in the widths of pulses. Because of the inherent aliasing distortion in digital pulsewidth-modulated signals, additional signal processing steps are required to make pulsewidth modulation (PWM) suitable for applications like digital audio amplification or burst-mode radio-frequency transmitters. These processing steps, however, entail an undesirable increase in computational effort. This brief presents a multiplierless implementation of a digital aliasing-free pulsewidth modulator using lookup tables, adders, and arithmetic shifts only. Mathematical equations of asymmetric double-edge PWM are given, as well as a modified aliasing-free version of this PWM technique that directly integrates the distortion-avoiding signal processing steps into the pulsewidth modulator. Based on these equations, a multiplierless implementation of the aliasing-free PWM (AF-PWM) is developed. Simulation results obtained with a Simulink fixed-point model show that the proposed modulator implementation provides a feasible solution for realizing AF-PWM with low computational effort. [ABSTRACT FROM PUBLISHER]