Zsolt Kollar

Budapest University of Technology and Economics · Department of Measurement and Information Systems

Multisine signals are commonly used in the measurement of dynamic systems and wireless channels. For optimal measurements with a high dynamic range, a low Crest Factor (CF) excitation signal is required. In this paper, a modified approach to optimize the crest factor for complex-valued multisine signals is presented. The approach uses a nonlinear o...

Artificial neural networks (ANN) have been shown to be flexible and effective function estimators for identification of nonlinear state-space models. However, if the resulting models are used directly for nonlinear model predictive control (NMPC), the resulting nonlinear optimization problem is often overly complex due the size of the network, requ...

In frequency-domain system identification, multisine waveforms are frequently used as an excitation signal. Supplying a low Crest Factor (CF) input signal to the actuator of the system is essential for measuring transfer functions with a high signal-to-noise ratio. In this paper, we present a method for achieving a lower CF compared to state-of-the...

The 5G wireless access technology will supersede its predecessor, 4G, in the current decade, at first coexisting with it and later as a standalone technology. This work examines and compares the performance of the following orthogonal multicarrier schemes: Cyclic Prefix Orthogonal Frequency Division Multiplexing (CP-OFDM), Windowed Orthogonal Frequ...

This paper investigates Filter Bank MultiCarrier (FBMC) modulation implemented with frequency spreading and polyphase network-based in terms of the introduced quantization noise. As FBMC is considered one of the future candidates for 5G/6G communication systems due to its advantageous spectral properties, the introduced quantization noise in the im...

Chromatic confocal surface profilometry has been a widespread technique in industrial applications for many years. Beside excellent resolution and speed, the contactless measuring capability make it ideal in applications where no physical contact is possible, (e.g. measurement of fluid levels), or where physical contact could damage the part to be...

Bandwidth and latency in future 5G and beyond multiple access systems are two extremely important metrics for which the requirements are very strict. Filter Bank Multi-Carrier (FBMC) is a promising scheme that can satisfy many future requirements due to its advantageous spectral characteristics. However, the required computational complexity is one...

Discrete Fourier transform (DFT) is a widely used method of signal analysis in digital signal processing. The DFT converts a signal from time domain to frequency domain for further processing. For fixed-size sliding window applications of the DFT, the observer-based sliding DFT (oSDFT) algorithm has been shown to be stable, accurate, and theoretica...

Filter Bank Multi-Carrier (FBMC) modulation is a promising modulation technique that is expected to play an important role in future 5G systems alongside Orthogonal Frequency Division Multiplexing (OFDM). In spite of its attractive properties, mainly the signal is well localized in frequency and time, a major drawback to FBMC is the high signal pro...

Massive multiple-input multiple-output (MIMO) systems operating in the centimeter-wave (cmWave) and millimeter-wave (mmWave) region offer huge spectral efficiencies, which enable to satisfy the urgent need for higher data rates in mobile communication networks. However, the proper design of those massive MIMO systems first requires a deep understan...

p>Massive multiple-input multiple-output (MIMO) systems operating in the centimeter-wave (cmWave) and millimeter-wave (mmWave) region offer huge spectral efficiencies, which enable to satisfy the urgent need for higher data rates in mobile communication networks. However, the proper design of those massive MIMO systems first requires a deep underst...

p>Massive multiple-input multiple-output (MIMO) systems operating in the centimeter-wave (cmWave) and millimeter-wave (mmWave) region offer huge spectral efficiencies, which enable to satisfy the urgent need for higher data rates in mobile communication networks. However, the proper design of those massive MIMO systems first requires a deep underst...

div>Hybrid beamforming systems represent an efficient architectural solution to realize massive multiple-input multiple-output (MIMO) communication systems in the centimeter wave (cmW) and millimeter wave (mmW) region. These hybrid beamforming systems separate the beamforming process into a digital and analog beamforming network. The analog beamfo...

div>Hybrid beamforming systems represent an efficient architectural solution to realize massive multiple-input multiple-output (MIMO) communication systems in the centimeter wave (cmW) and millimeter wave (mmW) region. These hybrid beamforming systems separate the beamforming process into a digital and analog beamforming network. The analog beamfo...

This paper presents a novel design and evaluation procedure for capacity enhancing multiple-input multiple-output (MIMO) antenna systems for mobile communication. Based on channel simulations, optimized patterns are defined prior to antenna design. A multiple antenna system is proposed, which switches between patterns covering desired directions. T...

Filter Bank MultiCarrier (FBMC) modulation with one of its variants, the Offset Quadrature Amplitude Modulation (OQAM) is considered as one of the most favored candidates for future 5G air interface. The transceiver architectures of FBMC-OQAM is categorized into two main design approaches: using PolyPhase Network (PPN) and using Frequency Spreading...

Computational complexity is one of the key factors considered for evaluating transmitter performance of future 5G applications. In this contribution we have chosen Filter Bank MultiCarrier (FBMC) as it is the most possible candidate to replace/coexist with the Orthogonal Frequency Division Multi-plexing (OFDM) modulation. In the literature two main...

In the field of digital signal analysis and processing, the ubiquitous domain transformation is the discrete Fourier transform (DFT), which converts the signal of interest within a limited time window from discrete time to the discrete frequency domain. The active use in real-time or quasi-real-time applications has been made possible by a family o...

Filter Bank MultiCarrier (FBMC) modulation is currently considered as one of the key enablers for future 5G technologies. In the literature, two approaches are applied for the modulation of FBMC signals: Frequency Spreading (FS) and PolyPhase (PP) implementation. The complexity requirements of FBMC transmitters is considered to be one of the key re...

In this paper we present parameter estimation methods for IEEE 802.11ad transmission to estimate the frequency offset value and channel impulse response. Furthermore a less known low complexity signal processing architecture-the Recursive Discrete Fourier Transform (R-DFT)-is applied which may improve the estimation results. The paper also discusse...

This paper presents channel estimation methods based on cyclic complementary Golay sequences. First, the conventional Golay correlator is investigated, then a frequency domain approach using Discrete Fourier Transform (DFT) is provided. A complex valued fast Golay correlator is introduced which can be used for the estimation of complex valued chann...

We present a peak-to-average power ratio (PAPR) reduction method for orthogonal frequency-division multiplexing (OFDM) or similar modulation schemes based on dynamic range compression and decompression. Initially, the decompressor was developed for compressed audio signals. With regard to OFDM, the greatest benefit of the method is that it can be e...

Orthogonal frequency division multiplexing (OFDM) is a commonly used modulation scheme for high speed digital communication. The high peak-to-average power ratio (PAPR) of the modulated signal is a major drawback, which may negatively affect the overall system performance if amplifiers with limited linear range are applied. One of the many PAPR red...

Orthogonal frequency division multiplexing (OFDM) is a widely adopted modulation scheme in digital telecommunications systems. However, its high peak-to-average power ratio (PAPR) is one of the major challenges to overcome in practical systems. Active constellation extension (ACE) is an effective way to reduce the PAPR of the OFDM signal. In this p...

This paper investigate the channel equalization problem in opportunistic white space communication systems, with an emphasis on transmission over channels with high delay spread. We consider the equalization problems of Orthogonal Frequency Division Multiplexing (OFDM) and three alternative multicarrier modulation schemes, namely DFT-spread OFDM (D...

Staggered MultiTone (SMT) is a modulation technique showing significantly reduced Adjacent Channel Leakage Ratio (ACLR) resulting in a more compact Power Spectrum Density (PSD) for the transmitted signal, than the well-known and already widely adopted Orthogonal Frequency Division Multiple Access (OFDMA) scheme. However, the unique spectral propert...

This paper investigates filter bankmulticarrier (FBMC), a multicarrier modulation technique exhibiting an extremely low adjacent channel leakage ratio (ACLR) compared to conventional orthogonal frequency division multiplexing (OFDM) technique. The low ACLR of the transmitted FBMC signal makes it especially favorable in cognitive radio applications,...

Filter Bank Multicarrier (FBMC) systems are a class of multicarrier modulation schemes for high speed wireless communication. These systems are known for their low adjacent channel leakage. In this paper we focus on the problem of channel equalization for FBMC systems. Most solutions in the literature use a per subcarrier equalization suffering fro...

This paper evaluates the implementation aspects of Filter Bank Multicarrier (FBMC), a recently investigated multicarrier modulation scheme. FBMC signals can easily meet the Adjacent Channel Leakage Ratio (ACLR) requirements of Cognitive Radio (CR) systems. The paper presents a novel, low complexity transmitter structure, which can be efficiently im...

Orthogonal Frequency Division Multiplexing (OFDM) is the most favored modulation technique in mul- ticarrier wireless communications. Recently, the Filter Bank Multicarrier (FBMC) modulation scheme has drawn atten- tion due its low Adjacent Channel Leakage Ratio (ACLR), which makes it especially suitable for Cognitive Radio (CR) applications. In mu...

Physical layers of communication systems using Filter Bank Multicarrier (FBMC) as a modulation scheme provide low out-of-band leakage but suffer from the large Peak-to-Average Power Ratio (PAPR) of the transmitted signal. Two special FBMC schemes are investigated in this paper: the Orthogonal Frequency Division Multiplexing (OFDM) and the Staggered...

This paper presents the discussion regarding the nonlinear amplification in Staggered MultiTone (SMT) based transmission systems. It will be shown that for the sufficient large number of subcarriers, the SMT signal fol- lows Gaussian distribution and thus, Bussgang theorem for nonlinearly distorted signal could be here applied with ad- vantage. In...

This paper presents a modified Staggered MultiTone (SMT) receiver structure tailored to cognitive radio applications. SMT schemes employing Fast Fourier Transform (FFT) in the receiver for demodulation are discussed in the first part. The second part deals with Recursive Discrete Fourier Transform (R-DFT) originating from measurement systems. The r...

Cognitive Radio has been one of the key research topics in the wireless community for about 10 years. The digital switch-over in the TV bands provides opportunities for Cognitive Radio Systems (CRS) to operate in the UHF spectrum under incumbent protection restrictions. Regulation bodies, in particular the FCC and OFCOM in the UK, have specified pa...

With the opening up of white spaces, efficient use of the fragmented spectrum - TV white space in particular - has become an extremely important focus of research. Apart from efficient spectrum usage, special care needs to be taken to maintain low out-of-band radiation to avoid harmful interference to incumbent services like TV signals and wireless...

Opportunistic use of White Spaces (WS) has opened up a whole new paradigm in research on cognitive radio (CR). One of the issues addressed by the QoSMOS project is the design of a flexible and efficient physical layer (PHY) for CR systems. To this aim, different modulation techniques are being investigated and are presented in this paper. They fulf...

In this paper, we briefly describe four modulation schemes (Orthogonal Frequency Division Multiplexing (OFDM), DFT-spread OFDM, Constant Envelope OFDM (CEOFDM)and Filter Bank Multicarrier (FBMC)) for Cognitive Radios (CR) in white space. In the first part, we give a short overview of the main signal processing blocks and signal properties. Then, we...

Cognitive radio (CR) is one of the promising future possibilities for wireless broadcasting and communication. One of the key issues is the physical layer, where the modulation waveform best suitable for the CRs has to be chosen. In this paper we present the most promising modulation schemes with their advantages and disadvantages. Orthogonal frequ...

In this paper we give an overview and a comparison of the possible waveforms for white space applications. Four physical layer schemes for cognitive radio are selected for study: Orthogonal Frequency Division Multiplexing (OFDM), DFT-Spread OFDM (DFTS-OFDM), Constant Envelope OFDM (CE-OFDM) and Filter Bank Multicarrier (FBMC). The comparison is mai...

All communication systems in which Or-thogonal Frequency Division Multiplexing (OFDM) is applied suffer from a well-known problem: the high Peak-to-Average Power Ratio (PAPR) of the time domain OFDM signal. From many PAPR reduction techniques clipping is one of the simplest: although the PAPR can be easily limited, it also introduces strong nonline...

This paper presents a noise annoyance identification tool that was developed to assess the interior noise quality of passenger cars on an objective basis. The tool automatically extracts resonances, masking effects, order non-linearities, booming phenomena and amplitude modulations from a vehicle run-up sound and visualizes these features on the rp...

This paper presents a new order-based method, which has been developed to automatically identify resonances from operational data in an engine run-up. The method considers the run-up as a multi-sine sweep excitation and combines advanced Order Tracking with Operational Modal Analysis to identify the resonances. A three-steps approach is used. In a...