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Recently, an observer-based algorithm was reviewed that is able to perform recursive sliding discrete Fourier transform (SDFT) [1]. DFT is the basic algorithm used for Fourier analysis [2], but it provides unbiased estimates only if the sampling is coherent, i.e., the ratio of the sampling frequency fs and the input signal frequency fin is a rational number. Coherent sampling of real-life periodic signals (e.g., mains voltage) can only be achieved if fin and fs are synchronized.

Despite the enormous technical progress seen in the past few years, the maturity of indoor localization technologies has not yet reached the level of GNSS solutions. The 23 selected papers in this special issue present recent advances and new developments in indoor localization systems and technologies, proposing novel or improved methods with increased performance, providing insight into various aspects of quality control, and also introducing some unorthodox positioning methods.

2020 presented unprecedented challenges in the higher education system. The first wave and the still-lasting COVID-19 pandemic brought the need for a new mindset, both from educators-teachers and students around the world. In this paper, we focus on our country Hungary and present the general feedback on distance education at Budapest University of Technology, Faculty of Electrical Engineering, and Informatics from the viewpoint of teachers. After a survey within the course coordinators at the faculty, we present the general results and the lessons learned from the obtained data. The feedback form questions focused on the aspect of knowledge transfer and the examination methodologies at the faculty. The results and the responses give an overall outlook on the success of the transitional semester and might offer directions for future problem-solving in remote education.

Nowadays, the usage radio channel or Internet connection grows for real-time transmission of measurement data or signals. For these applications, not reliable communication needs to be analyzed from a signal processing point of view. Our paper contributes to this topic with the analysis of data loss as a signal distorting phenomenon. The paper contains a possible mathematical description of the data loss via the indicator function. Moreover, the Gilbert-Elliott data loss model class is presented, which gives a framework to analyse numerous data loss phenomena in general. In order to analyse the data loss in the frequency domain, the spectrum of the indicator function is required. This paper presents the derivation of the power spectral density of the Gilbert-Elliott model. The paper reviews a possible identification method for the simpler models derived from the Gilbert-Elliott model. Theoretical analysis and simulations are supported by measurements. The measurement results are used to show how the data loss models function in practice.

The efficiency of active noise control (ANC) is largely dependent on the arrangement of the microphones and loudspeakers, and the acoustic environment as well. The paper presents a simulation tool, which allows the performance evaluation of ANC systems without the difficulty of physical experiments. The proposed simulation integrates sound field calculation and noise control. Field calculation is based on robust FDTD techniques, while the discrete time controller is realized in a usual way. The simulation is performed in three stages. First the program determines the discrete transfer function models of the acoustic paths between specific points of interest. In the next stage the controller’s operation is evaluated without field simulation. Having the steady state parameters of the adaptive controller, the field simulation is re-run for the reverberation time providing the sound pressure map. Sound field calculation is implemented on modern GPGPU devices. A series of ANC experiments were compared to the results of the simulations, and they prove the applicability of our simulation method in a convincing manner.

The GOCE satellite observes gravity gradients with unprecedented accuracy and resolution. The GOCE observations are reliable within a well-defined measurement bandwidth. In this study, different finite and infinite impulse response filters have been designed to obtain the demanded pass. Exhaustive time and frequency domain investigations prove that the proposed infinite impulse response filter can be a real competitor of the existing solution of the filtering problem.

This paper investigates the behavior of the spectral resonator-based spectral observer (RBO) for lossy measurements. The RBO is an efficient real-time method designed for measuring the harmonic components of periodic signals. Recently, some experiments have shown that RBO can tolerate some data loss, but no exact criteria of the convergence have been available. The main contribution of this paper is a set of conditions which enable to predict whether the observer is able to find the harmonic components or not. The necessary condition of convergence helps to recognize the situations when the error-free estimation of the harmonic components is not possible. The sufficient conditions of convergence give safe regions of data loss parameters (e.g., data loss ratio) where the unbiased harmonic estimation can always be ensured. Simulations are also presented to demonstrate the effect of data loss in different situations.

This paper introduces a new, adaptive-filter-based controller that shows advantageous properties from the viewpoint of its communication requirement. The algorithm is called signed-error filtered-x LMS (SE-FxLMS). Its novelty is characterized by the fact that it makes possible data compression in the feedback path of adaptive-filter-based control loops in a very simple way. This feature is especially useful in such closed-loop systems where the feedback signals are transmitted over a low-bandwidth communication channel. This is a typical case in so-called networked control systems (NCS), where the communication is carried out over a shared communication channel, e.g., using a wireless sensor network. The paper introduces an analysis of the algorithm as well.

Disinfection of raw water is essential to the production of drinking water. However, by-products of disinfection may exert toxic effects. The potential toxic effects of two of these compounds, 4-ethylbenzaldehyde (EBA) and 2,4-difluoroaniline (DFA) were investigated using the zebrafish (Danio rerio) model. The two compounds, dissolved, were introduced in duplicate aquariums containing zebrafish in two different concentrations based on LC50 values. The aquarium water containing EBA or DFA was changed every 96 h throughout the 3 months of treatment. Behavior of the fish in each replicate was inspected twice daily. In course of treatment with both concentrations, fish exposed to DFA displayed behavior associated with visible anxiety, while EBA treated were lethargic and did not evade capture. Application of both concentrations of each component into the aquarium water resulted in dystrophic lesions in the liver, kidney and skin of the fish while preneoplastic lesions and tumors were not observed.

Office employees are exposed to acoustic noise, especially in an open office environment. Passive or active headsets sufficiently reduce the level of noise, but their long-time wear is uncomfortable. The paper presents an active headrest system built into a chair. Feedforward control is utilized with multiple reference microphones, and flexible gooseneck microphones serve as error sensors. The reference sensors surround the chair, allowing the suppression of sound waves arriving from any direction. The concept of multiple reference control has been tested by extensive experiments showing that multiple reference signals help to increase the suppression in normal rooms where reverberation occurs, even if only one noise source is present. The preliminary experiments are completed by a series of simulations aiming to explore the zones of quiet at the user&rsquo, s ears. The paper introduces the construction details of the noise-canceling chair: The two loudspeakers are controlled by the signals of two error microphones and four reference signals. The controller is based on the normalized filtered error least mean squared algorithm, implemented on an Analog Devices ADSP-21262 signal processor-based hardware. Experimental results are reported that show the efficient suppression of tonal, as well as broadband disturbances.

Recently measurement data loss has been of greater interest, due to the spread of sensor networks and the idea of Internet of things. A procedure is proposed that is able to identify the most frequently employed data loss models. It is assumed that the communication protocol provides information about data loss, i.e. the so-called data availability indicator function is known. The power spectral density (PSD) of the indicator function is representative for the model, and can be used for identification. Spectral estimation is carried out by Fast Fourier Transform (FFT) based techniques. The paper introduces the identification procedure for random independent, random block-based and general Markov model-based data loss patterns. The efficiencyof the proposed method is demonstrated by simulation and measurement results.

This paper introduces a “proof of concept” system for Active Noise Control (ANC) where the audio data from the reference microphones are travelling through the already existing Ethernet network. The system realizes the active noise control with the help of a multi channel DSP card. The noise control algorithm is the Filtered Error Least Mean Square (ELMS) - an LMS variant -, which has already proven its efficiency previously in different environments. The audio data from the reference microphone to the DSP card are digitalised with the help of an ADSP-BF537 Ez-Lite Kit, and transmitted over Ethernet to a counterpart ADSP-BF537 Ez-Lite Kit card, which converts it back to an analogue signal to be able to be fed into the multi channel DSP card. The article highlights the usage of Ethernet network for audio transmission, and shows the problems that are caused by the properties of such medium, as well as the potential that lies in it. The working of the system and its efficiency is illustrated by measurement results.

Mutagenic potential of drinking water samples derived from ranneywells was studied. 100-100 l of untreated (rough) and ozone-treated as well as chlorinated-disinfected water were dropped on and adsorbed by macroreticular resin columns (Serdolit PAD-III and Amberlite XAD-2). The adsorbed material was desorbed by methanol and dichloromethane. After elimination of the solvents by vacuum distillation the adsorbed material was dissolved in dimethylsulfoxide. The mutagenic activity was tested in the Ames-Salmonella/rat liver microsome system. The tester strains were TA-98 and TA-100. The material adsorbed to Serdolit PAD-III from rough and also disinfected water did not induce mutagenicity in case of the TA-98 tester strain, irrespective of activation by liver microsomes. However, the material adsorbed to Amberlite XAD-2 exerted mutagenic effect on the TA-98 tester strain, with and without liver microsome activation, both in case of rough and disinfected water. The TA-100 tester strain showed mutation after, but not without activation, when treated with the material adsorbed by either Serdolit PAD-III or Amberlite XAD-2, in case of rough water. Material derived from disinfected water and adsorbed to Serdolit PAD-III, caused mutation of the TA tester strain also only after activation. The material derived from disinfected water and adsorbed to Amberlite XAD-2 proved to be mutagenic to the TA-100 tester strain both without and after activation. Mutagenic activity was exerted by the amount of concentrates derived from 0.28 to 0.83 l of rough and 0.83-2.5l of disinfected water. The mutagenic activity of drinking water raises the possibility of carcinogenic effect, too. Search for alternative methods of water disinfection may be recommended.

Longitudinal vibration of piano strings greatly contributes to the distinctive character of low piano notes. In this paper a simplified modal model is developed, which describes the generation of phantom partials and longitudinal free modes jointly. The model is based on the simplification that the coupling from the transverse vibration to the longitudinal polarization is unidirectional. The modal formulation makes it possible to predict the prominent components of longitudinal vibration as a function of transverse modal frequencies. This provides a qualitative insight into the generation of longitudinal vibration, while the model is still capable of explaining the empirical results of earlier works. The semi-quantitative agreement with measurement results implies that the main source of phantom partials is the transverse to longitudinal coupling, while the string termination and the longitudinal to transverse coupling have only small influence. The results suggest that the longitudinal component of the tone can be treated as a quasi-harmonic spectrum with formantlike peaks at the longitudinal modal frequencies. The model is further simplified and applied for the real-time synthesis of piano sound with convincing sonic results.

Adaptive Fourier analyzers have been developed for measuring periodic signals with unknown or changing fundamental frequency. Typical applications are vibration measurements and active noise control related to rotating machinery and calibration equipment that can avoid the changes of the line frequency by adaptation. Higher frequency applications have limitations since the computational complexity of these analyzers are relatively high as the number of the harmonic components to be measured (or suppressed) is usually above 50. In this paper, based on the concept of transformed domain signal processing, a fast filter-bank structure is proposed to reduce the above computational complexity. The first step of the suggested solution is the application of the filter-bank version of the fast Fourier transform or any other fast transformations that convert input data into the transformed domain. These fast transform structures operate as single-input multiple-output filter-banks, however, they can not be adapted since their efficiency is due to their special symmetry. As a second step, the adaptation of the filter-bank is performed at the transform structure's output by adapting a simple linear combiner to the fundamental frequency of the periodic signal to be processed.

Spectral observer is appropriate for investigating the frequency domain properties of signals. Since the spectral analysis is a very common method, this observer can be used widely in many applications. The paper introduces a novel resonator based spectral observer and control algorithm that require reduced amount of data for the operation, so they are appropriate for the utilization in signal processing systems with limited resources (e.g. wireless sensor networks). The data reduction is achieved by the deployment of the sign error principle. For the improvement of the transient properties of the sign error structures a new method is proposed that tunes the speed of the adaptation according to the norm of the error. This algorithm makes possible to find a trade-off between the settling time and the amount of data required for the operation. The algorithm can be used for recursive Fourier analysis of signals and control of linear systems. As a practical application a wireless active noise control system is presented.

The effect of irradiance during low temperature hardening was studied in a winter wheat variety. Ten-day-old winter wheat plants were cold-hardened at 5 °C for 11 days under light (250 μmol m-2 s-1) or dark (20 μmol m-2 s-1) conditions. The effectiveness of hardening was significantly lower in the dark, in spite of a slight decrease in the Fv/Fm chlorophyll fluorescence induction parameter, indicating the occurrence of photoinhibition during the hardening period in the light. Hardening in the light caused a downshift in the far-red induced AG (afterglow) thermoluminescence band. The faster dark re-reduction of P700+, monitored by 820-nm absorbance, could also be observed in these plants. These results suggest that the induction of cyclic photosynthetic electron flow may also contribute to the advantage of frost hardening under light conditions in wheat plants.

Our paper introduces a closed-loop wireless control application based on Berkeley MICAz motes and an Analog Devices AD21061 EZ-KIT LITE board. The system realizes active noise control (ANC) for the suppression of periodic acoustic disturbances. The paper highlights the role of synchronous sampling in wireless ANC applications and introduces the solutions in detail. A PLL-like mechanism takes care of the synchronization, while linear interpolation fits the wireless measurement data for processing in the signal processor. The noise controller is a resonator-based one which has proven its efficiency previously in different physical environments. The working of the system is illustrated by measurement results.

Reconfigurable digital filters are promising solutions to filtering problems in hybrid systems, where digital filters with time-invariant configuration are found to be inappropriate. However, reconfiguration of digital filters causes intermediate disturbances, reconfiguration transients that have to be minimized by proper transient management. In this paper, the one-step reconfiguration method is analyzed for reconfigurable digital filters in case of sinusoidal excitation. First, the energy function of the reconfiguration transient is formulated, and later analyzed. The implementation structure is identified as key factor influencing the energy of the reconfiguration transients. Orthogonal implementation structures are proposed as the most suitable alternatives.

The apoptosis-inducing activity of concentrated sediments of disinfected and non-disinfected water samples from the waterworks in Budapest, Hungary, was investigated using cultures of human peripherial blood lymphocytes. Chlorine-treated water and untreated (raw) water sediments were concentrated with the use of Amberlite XAD-2 resin columns. The concentrates were dissolved in dimethyl sulfoxide and added to cultures of human peripherial blood lymphocytes. Apoptotic index was determined in lymphocytes after treatment with the raw or disinfected concentrates by flow cytometry. Disinfected water concentrates of 100 microl/ml increased the apoptotic ratio of lymphocyte culture. The same amount of raw water concentrate also enhanced apoptosis. Both raw water and disinfected water contain substances that induced a significant rate of apoptosis in lymphocyte cultures.

In distributed signal processing systems, every node samples analog signals by its own AD converter. Sampling is controlled by autonomous clocks, that are generally not synchronizable. In order to ensure synchronized operation among the different nodes of the distributed system, both the drift of these clocks, and the jitter of the sampling is handled. This problem is investigated in this paper, and signal processing methods are proposed to guarantee the synchronized operation and to reduce the effect of the jitter. The proposed solution is based on low-level interpolation and resampling of the sampled signals. A realization of this method is demonstrated on a test-system.

This paper deals with the synchronization in wireless adaptive signal processing systems. Wireless communication offers high flexibility, however, the distributed structure of wireless systems requires the synchronization of the subsystems. The synchronization becomes particularly important if the signal bandwidth is in the kHz range, and it is inevitable in distributed control systems. The demand on the synchronization is presented through the introduction of a wireless active noise control system. In this system wireless sensors (microphones) receive the signal, and the main signal processing algorithm is implemented on a central unit which produces the signal for the actuators (loudspeakers). In spite of the special application, the system has a general structure, so the results are valid for other adaptive systems. First a PLL like algorithm is described for the synchronization of the sampling in a wireless real-time signal processing system, then a higher-level synchronization is introduced for a distrib uted Fourier-analyzer based noise control system. The effectiveness of the algorithms is demonstrated by measurement results.

The paper presents an on-line digital signal processing method for active cancelation of distortion of sinusoidal sources. Generation of a sinusoidal signal of several volts is a simple task, but many measurements need high voltage, current, or nonelectrical excitation. This signal conversion often leads to distortion. The proposed active distortion controller is a resonator-based observer which determines the harmonic content of the signal, and the distorting components are subtracted from the output signal. The paper introduces the controller design in details, and a practical example illustrates the effectiveness of the proposed method.

The paper presented a DSP-based electromagnetic flowmeter. There are 4 pairs of electrodes and a pressure sensor for effective flowrate measurement in partially filled pipes. Although this setup is able to measure different flow profiles, our development focused on the improvement of measurement accuracy by signal processing methods. A sinusoidal excitation is used allowing fast sampling of the flowrate. The coils are driven by class-D amplifiers minimizing the power consumption of the module. The demodulation of the electrode voltage is carried out by a linear phase Hilbert transformer. Linear phase filters guarantee that the flowrate waveform is preserved. Resonator-based controller ensures the automatic and effective suppression of disturbing electrode voltages. Measurement results clearly confirmed the expectations: tests in filled mode have shown high accuracy and reliability. Our ongoing task is testing the flowmeter in partially filled mode, while new developments can aim the exploitation of the electrode pairs for flow profile measurement

This paper presents a new nonlinear least-squares algorithm for fitting band-limited periodic signals with unknown frequency and harmonic content. The new solution features a model-based recursive calculation method that requires less memory space and has smaller computational demand than the known matrix-based algorithms.

A nonparametric identification method for linear systems is proposed. The identification is done via synchronized multisine measurements where the synchronization is ensured by a resonator based generator-observer pair. The advantage of the proposed structure is that it works as a filter bank and provides the measurement results on-line. Exponential averaging is an option of the method and it requires no extra calculations. A further advantage is that the identification can be done over any frequency set without any loss of performance. Explicit formulas are given for noise suppression and settling time. The method is illustrated by a practical example.

Active cancellation of acoustic noise seems to be a real alternative to passive isolation in the low frequency region. There are already many methods to solve this control problem, typically based on adaptive filter techniques. If the noise is periodic, a simple signal model can be integrated into the adaptive controller, the parameters of which are set using the error signal. This control loop behaves like an observer of the signal to be suppressed. The authors have developed this method which is already proved to work efficiently in practice, as well. The paper describes the design of this observer and gives the relations to the conventional structures and adaptation mechanisms.

Due to the several attractive features of wireless devices they are more and more expansively used, but the deployment of wireless sensors in control applications is not spread yet because of the unreliable data transfer. This paper introduces a testbed which serves as a platform for investigations of wireless closed loop adaptive signal processing and control systems. The novelty of this testbed is that it makes possible the practical tests of algorithms in wireless environment. Since the traditional signal processing algorithms are not prepared for peculiar problems that emerge because of wireless data transfer (e.g. data loss), the exhaustive study of their behavior is necessary. This test system plays an important role in these investigations. Since the testbed offers also an application (the active noise control), algorithms can be studied in the same circumstances so ensuring the comparability of different structures.