Secure Massive MIMO Communication with Low-resolution DACs

In this paper, we investigate secure transmission in a massive multiple-input multiple-output (MIMO) system adopting low-resolution digital-to-analog converters (DACs). Artificial noise (AN) is deliberately transmitted simultaneously with the confidential signals to degrade the eavesdropper's channel quality. By applying the Bussgang theorem, a DAC quantization model is developed which facilitates the analysis of the asymptotic achievable secrecy rate. Interestingly, for a fixed power allocation factor $\phi$, low-resolution DACs typically result in a secrecy rate loss, but in certain cases they provide superior performance, e.g., at low signal-to-noise ratio (SNR). Specifically, we derive a closed-form SNR threshold which determines whether low-resolution or high-resolution DACs are preferable for improving the secrecy rate. Furthermore, a closed-form expression for the optimal $\phi$ is derived. With AN generated in the null-space of the user channel and the optimal $\phi$, low-resolution DACs inevitably cause secrecy rate loss. On the other hand, for random AN with the optimal $\phi$, the secrecy rate is hardly affected by the DAC resolution because the negative impact of the quantization noise can be compensated for by reducing the AN power. All the derived analytical results are verified by numerical simulations.Comment: 14 pages, 10 figure

The Effect of Chinese Imports on European Innovation Activities in the Medium-Long Term Period

Studies have been conducted about the role of foreign trade-driven technology transfer in the achievement of the Chinese miracle; however, when focusing on the opposite direction, the literature is not uniform: how are Western businesses affected by trade dealings which China? To what extent does this impact apply to the innovation cycle? In this research we focused on the linear correlation between innovation in European countries (proxied by patent applications) and imports from China, over the 15-year time period following China's accession to the World Trade Organization in 2001. Patent applications are used as a measure of innovation, integrated in an economic model inspired by the "Trapped Factors" model, that makes it possible to account for escape-competition effects. The model analyzes the 2002-2016 period across 22 European countries. Apart from evaluating the impact of Chinese imports on European innovation, our study provides a review of the major contributions that have characterized this research area in the most recent years, trying to categorize and to present them from a proactive and comprehensive point of view. Keywords: innovation, import, China, Europe, patent applications DOI: 10.7176/EJBM/12-12-03 Publication date: April 30th 202

Transient analysis of interline dynamic voltage restorer using dynamic phasor representation

Computer planning and simulation of power systems require system components to be represented mathematically. A method for building a dynamic phasor model of an Interline Dynamic Voltage Restorer (IDVR) is presented, and the resulting model is tested in a simple radial distribution system. Mathematical analysis is carried out for each individual component of the IDVR as modular models, which are then aggregated to generate the final model. The proposed technique has the advantage of simplifying the modelling of any flexible AC transmission system (FACTS) device in dynamic phasor mode when compared to other modelling techniques reported in the literature. The IDVR, including the series injection transformer, is analysed in both ABC and DQ dynamic phasor modes, and IDVR power management is also presented. The ensure compatibility with transient stability programs, the analysis is performed for the fundamental frequency only, with other frequency components being truncated and without considering harmonics. Results produced by the IDVR dynamic phasor model are validated by comparison with results gained from a detailed MATLAB/Simulink IDVR model

Stability norms control using the virtual impedance concept for power frequency applications

In small-signal stability studies, various stability criteria have been proposed based on impedance or admittance norms to assess the stability of power systems. Controlling these norms can drag a system from a stable to an unstable operating condition. Therefore, finding a control variable that has a direct linear relation with these norms will facilitate the utilisation of data-driven control principles to build a control system based on small-signal impedance. For a STATCOM connected to a power network, the control system parameters of the STATCOM are tested to identify their relationships with the stability norms. Different types of virtual impedance are tested, and the suitability of each virtual impedance type and connection is examined and presented