Influence of amplitude and phase imbalance of quadratures on the noise immunity of coherent reception of signals with quadrature amplitude modulation

Quadrature amplitude modulation (QAM) is used for high-speed information transmission in many radio systems and, in particular, in DVB-S and DVB-S2/S2X digital satellite television systems. A receiver included as a part of the transmitting equipment of such systems has a block for the formation of quadrature oscillations used as a reference for signal demodulation. Due to hardware instabilities, amplitude and phase errors may occur, which leads to quadratures imbalance. These inaccuracies cause additional errors in the received signal demodulation. This can significantly degrade the noise immunity of the reception. The paper investigates the influence of amplitude and phase errors in the formation of quadrature oscillations (imbalance of quadratures) on the noise immunity of coherent reception of QAM signals. Using the methods of statistical radio engineering the parameters of the distributions of processes in the receiver are obtained, and the probability of a bit error is estimated. The dependences of the bit error probability on the amplitude unbalance factor, on the phase error of quadrature formation and on signal-to-noise ratio are obtained. It is shown that the amplitude imbalance of the quadratures leads to a significant decrease in the noise immunity of QAM signals reception at M ≥ 16. The acceptable amplitude deviation in this case can be considered to be equal to 5%. At M= 4, the amplitude imbalance in a wide range of values practically does not affect the noise immunity. The phase imbalance of quadratures markedly affects the noise immunity of coherent reception of QAM signals. The permissible phase error is no more than 0.05 rad (3 degrees). As the signals positionality increases, this influence also increases.

CORRECTION OF ERRORS IN INSTRUMENTS FOR MEASURING ELECTRIC POWER PARAMETERS

A study of methods for correcting amplitude and phase errors in devices for measuring the parameters of electric power with digital signal processing with a sampling frequency multiple of the network frequency was made. The generalized flow diagram of measuring device that consists of a few entrance channels was presented. Mathematical expositions that explain the process of correction of additive and multiplicative errors are given. Through a temporal diagram a few variants of encoding of entrance signals are shown. The possibility of correcting phase errors by shifting the moment of the ADC start-up and by turning the axes and transforming the coordinates of the voltage and current vectors is shown. The possibility of correction when measuring the reactive and reactive powers is investigated. Referencese 11, table 1, figures 5.

A High Channel Consistency Subarray of Plane-Wave Generators for 5G Base Station OTA Testing

A high channel consistency subarray of plane-wave generators (PWG) is described for fifth-generation (5G) base station (BS) over-the-air (OTA) testing. Firstly, the variation of the near field radiation characteristics of the subarray based on the feed amplitude and phase errors of the traditional power divider network is analyzed. The recommended amplitude and phase errors between channels are given. After that, a novel subarray which combines four pyramidal horn antennas and a compact 1:4 waveguide power divider is designed. The optimized perfectly symmetrical zigzag waveguide transmission lines are used to realize consistent power allocation among antenna elements. No intermediate pins are employed, which avoids the significant deterioration of channel consistency caused by assembly errors. The size of the subarray is 4.89 λ0 × 4.97 λ0 × 1.23 λ0 (λ0 is the working wavelength corresponding to the subarray center frequency at 3.5 GHz). The VSWR < 1.5 impedance bandwidth covers 3.4 GHz to 3.6 GHz. The amplitude difference between the four elements of the subarray is less than 0.5 dB, and the phase difference is less than 3°. The simulated and measured results agree well in this design.

Infiltration Losses Calculated for the Flash Flood in the Upper Catchment of Geru River, Galaţi County, Romania

MIKE software created by Danish Institute of Hydraulics can be used to perform mathematical modelling of rainfall-runoff process on the hillslopes, resulting in a runoff hydrograph in the closing section of a catchment. The software includes a unitary hydrograph method - UHM in the hydrological module Rainfall - Runoff. Excess rainfall is routed to the river and transited through unit hydrograph method. The model divides the flood generating precipitation in excess rainfall (net rainfall) and losses (infiltration). This paper analyzes data from the flash flood that occurred between the 11th and 13th of September 2013 in the upper catchment of the river Geru. The catchment chosen for study, is controlled by the hydrometric station located in the village Cudalbi. Simulations of this flash flood were performed with MIKE by DHI –UHM software, alternatively using as input data the precipitations recorded by AHSS (Automated Hydrological Sensor Station) Cudalbi and radar precipitations generated by ROFFG (Romanian Flash Flood Guidance) software system in ArcGIS module for determining the areas affected by flash floods. The Unitary Hydrograph Method - UHM from the hydrological module Rainfall – Runoff calculates excess rainfall and determines infiltration losses by four methods. For each set of input data, the four methods for calculating infiltration losses were subsequently used. The comparison between the results highlights that the amplitude and phase errors for the maximum discharge are smaller when the model uses for simulation radar precipitations as input data, and calculates infiltration losses with the Proportional Loss method. This method reproduces with a better accuracy the peaks of the discharge hydrograph. The model can be used in the future to forecast a discharge hydrograph based on estimated radar precipitations in the catchment