Pavol Galajda

A Robust Chaos-Based True Random Number Generator Embedded in Reconfigurable Switched-Capacitor Hardware

This paper presents a new chaos-based True Random Number Generator (TRNG) with decreased voltage supply sensitivity. Contrary to the traditionally used sources of randomness it uses well-defined deterministic switched-capacitor circuit that exhibits chaos. The whole design is embedded into commercially available mixed-signal PSoC reconfigurable device without any external components. Proposed design is optimized for reduction of influence of supply voltage to the quality of generated random bit stream. The influence of circuit non-idealities is significantly reduced by the proposed XOR corrector and optimized circuit topology. The ultimate output bit rate of proposed TRNG is 60 kbit/s and quality of generated bit-streams is confirmed by passing standard FIPS and correlation statistical tests performed in the full range of PSoC device supply voltages.

CHUA'S SINGULARITIES: GREAT MIRACLE IN CIRCUIT THEORY

In the work [Chua, 1992], a deep intuition of its author gave rise to the choice of singularities corresponding to Chuas circuit. Therefore, it is the only one probably exhibiting three saddle points named Chuas singularities in this paper. One of the singularities is a saddle in forward time (dt > 0) of integration, whereas the other two are saddles in backward time (dt < 0) of integration. In the following, the term Chuas Chaos denotes chaos related to Chuas singularities. These singularities are the source of all special surfaces that are the subject of this contribution. We named the surface to which all other surfaces are bound as the Double-Arm Stable Manifold (DASM). The beauty and multifunctionality of this surface represents the unfathomable Intelligence in the sense of [Tolle, 2003]. The presence of the DASM in the state space is a sufficient condition for the generation of Chuas chaos or corresponding periodic windows. Since Chuas singularities are not limited by circuit morphology or the order of state equations, the research on Chuas chaos seems to be still very promising.

Receiver technique for iterative estimation and cancellation of nonlinear distortion in MIMO SFBC-OFDM systems

Multiple-input multiple-output (MIMO) techniques and orthogonal frequency-division multiplexing (OFDM) can be combined to obtain a promising candidate for next generation wireless communications. However, like a single- input single output (SISO) systems one main disadvantage of MIMO-OFDM is high sensitivity to nonlinear distortion that results in significant loss in power efficiency and performance. In order to improve overall system performance this paper introduces a new iterative method for the detection of nonlinearly distorted symbols received by the receiver of the space-frequency block coded (SFBC) MIMO-OFDM transmission system. The proposed approach is based on the Bussgang theorem application and consists in iterative estimation and accurate cancellation of the nonlinear distortion due to the high power amplifier of the transmitter. The numerical performance evaluation shows that the proposed scheme can achieve significant performance improvement compared to conventional receivers.

Receiver based compensation of nonlinear distortion in MIMO-OFDM

Multiple antenna orthogonal frequency division multiplex (MIMO-OFDM) is transmission technique being employed in the future software defined/cognitive radio solutions. The main disadvantage of using MIMO-OFDM is its high sensitivity to the nonlinear amplification due to the specific characteristic of the high power amplifier (HPA) in the transmitter front-end. This phenomena results in the large overall performance degradation in terms of the bit error rate (BER). In this contribution, we present an iterative receiver scheme to reduce the BER of MIMO-OFDM systems undergoing nonlinear distortion. The technique consist in the iterative estimation and compensation of the nonlinear distortion introduced by transmitters HPA. As it will be shown by means of the numerical performance evaluation, the proposed technique reduces significantly BER of MIMO-OFDM systems.

Multi-user Detection of Nonlinearly Distorted MC-CDMA Symbols by Microstatistic Filtering

Multi-carrier code division multiple access is a powerful modulation technique that is being considered in many emerging broadband communication systems. In a downlink scenario orthogonal spreading sequences are used since they reduce multiple access interference compared to non-orthogonal. However, the nonlinear amplification of the transmitted signal destroys the orthogonality and, thus, reduces the system performance. In order to avoid performance degradation without requiring large back-offs in the transmitter amplifier, it becomes necessary to use multi-user detection techniques at the receiver side. Conventional multi-user detectors (MUD) are designed for linear environments and, as a result, might not exhibit enough performance improvement. In this paper a new MUD based on microstatistic filtering is proposed. The presented MUD uses piece-wise linear filtering in conjunction with threshold decomposition of the input signal, which introduces a nonlinear effect, to improve performance when a nonlinearity is present. Maximum performance improvement compared to conventional MUD is achieved for low spreading factors and user loads no greater than 50%.

Comparative evaluation of OFDMA and SC-FDMA based transmission systems

New evolving standards of the cellular systems, like e.g. Long Term Evolution (LTE), WiMax and Advanced LTE, consider Orthogonal Frequency Division Multiplex Access (OFDMA) as a mature and suitable solution to cope with the Inter Symbol Interference (ISI) due to the multi-path propagation. However, a major drawback of OFDMA which largely limited its application in the real environment is large envelope fluctuation which results in strong nonlinear distortion due to the nonlinear characteristic of power amplifier (PA). One possible solution to tackle this problem has been introduced by the the 3rd Generation Partnership Project (3GPP) consortium. This solution is based on spreading the base-band modulated signal before the application of OFDMA by using Discrete Fourier Transformation (DFT) that leads eventually to lower envelope fluctuation in comparison with that of OFDMA. The presented method is widely recognized as Single Frequency Division Multiplex (SC-FDMA). This paper aims to provide general comparison of both conventional OFDMA and SC-FDMA and draws important conclusions from this comparison.

Short-range UWB radar: Surveillance robot equipment of the future

Autonomous robots are intelligent machines capable of performing tasks by themselves, without explicit human control. They can find quit a number of unique applications. Here, their utilisation for surveillance, monitoring and reconnaissance in hostile and dangerous to life environment intent on human being detection and/or static object imaging is up-to-date, promising and challenging as well. The fruitfulness of this application of robot systems is determined by many factors. The effective and reliable sensor system for human being detection and localization and static object imaging under wide variety of scenarios can be rated among them. In the last decade, it has been shown that ultra-wideband (UWB) radars (sensors) can be used with advantage as day and night, and under all-weather conditions sensors for person localization and static object imaging. Taking into account this fact, this paper will be intent on the analyses of UWB sensor applicability as the part of the smart sensor systems of robots to be used at emergency situation solutions. Summarizing the results of theoretical analyses and experiments with UWB sensors presented in the paper, it will be concluded that the short-range UWB radars have the great potential to be used as a standard equipment of surveillance and reconnaissance robot systems of future.

Design of microstrip band pass filter based on LTCC for UWB sensor system

This paper deals with design, simulation, manufacturing and experimental testing of microstrip bend pass (BP) filter for I - Q (In-phase Quadrature) demodulator that is a part of Ultra Wide-Band (UWB) sensor system. Paper refers to the needs that should be focused on the design and manufacturing of microstrip filters based on LTCC (Low Temperature Co-fired Ceramic) with emphasis on issues of quality of transmitted signals in the high frequency (HF) area in the terms of actual production. There are presented simulated and measured results of insertion loss (S21) and return loss (S11) of microstrip BP filter for I - Q demodulator made from material system Green Tape 951 XP. This paper demonstrates the design and full-wave electromagnetic simulation of microstrip BP filter using the HyperLynx 3D EM Designer (from Mentor Graphics). It assesses the suitability of LTCC material system Green Tape 951 XP as well as conductor paste DuPont 6145 for the production of microstrip BP filters for HF area. The presented filters should be used as a BP filter mean for I - Q demodulator presented in [1] which is a part of laboratory UWB sensor system.

The control of a memory cell with the multiple stable states

The subject of this paper is control of a memory cell with the multiple stable states consisting of two resonant tunnel diodes (RTDs). One of the RTDs is an element and the other represents a load. The circuit can be described with a third-order system so that its state space is R3 and exhibits three stable states. Although we are dealing with a specific circuit and three stable states, the results presented can be generalized to the space Rn (for both n = 2 and n > 2) and multiple stable states, as well. The RTDs, however, are mentioned here only to demonstrate the all-new phenomena in R3 space.

MC-CDMA performance analysis for different spreading codes at HPA Saleh model

Multi-carrier code division multiple access (MC- CDMA) is a powerfull modulation technique that is being considered in many emerging broadband communication systems. However the high peak to average power ratio (PAPR) of the MC-CDMA signal, a special drawback of multicarrier transmission, has limited its wider aplication due to inefficient use of power amplifiers. PAPR strongly depends on particular spreading sequences considered for transmission. Therefore, the performance analysis of uplink MC-CDMA for different spreading sequences and for different receivers in the presence of Saleh model of high power amplifier (HPA) is presented. The results of our analysies show that the aplication of Golay codes in conduction with micro statistic multi-user receiver (MSF-MUD) provide significant better result as the other investigated spreading sequences and receivers.