Centrum senzorických, informačních a komunikačních systémů

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    On Mutual Information of Measured 60 GHz Wideband Indoor MIMO Channels: Time Domain Singular Values
    (IEEE, 2017-10-08) Blumenstein, Jiří; Maršálek, Roman; Götthans, Tomáš; Nissel, Ronald; Rupp, Markus
    This paper presents a report on mutual information based on measured indoor millimeter-wave (mmWave) channels with multiple antennas at input and output (MIMO). We show that for fixed indoor communication systems, an optimal antenna element spacing can be found such that the measured mutual information almost reaches the capacity of a perfectly orthogonal (theoretical) MIMO channel (with the same number of receiver (RX) and transmitter (TX) antennas). Secondly, we present, that even though the measured channel transfer functions (CTFs) exhibit large fluctuations (i.e., temporal dispersion), the mutual information is mainly determined by the mean singular value of the line-of-sight (LOS) components. Due to their strong variations over frequency mmWave channels are tedious when describing them with classical methods in the frequency domain. An approximation by numerous flat subbands leads to an error in mutual information (MI) by 2bit/s/Hz (for 80% probability). In comparison, our proposed method in the time domain, however, offers a notably smaller error (1bit/s/Hz for 80% probability).
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    Second-order Simple Multiphase Oscillator Using Z-Copy Controlled-Gain Voltage Differencing Current Conveyor
    (Kaunas University of Technology, 2014-11-19) Šotner, Roman; Jeřábek, Jan; Petržela, Jiří; Herencsár, Norbert; Prokop, Roman; Vrba, Kamil
    Interesting type of the second-order electronically controllable multiphase oscillator is introduced in this paper. Modified voltage differencing current conveyor, so-called z-copy controlled gain voltage differencing current conveyor (ZC-CG-VDCC), offers interesting features for synthesis of this type of multiphase oscillator. Available controllable parameters of the ZC-CG-VDCC (intrinsic resistance, transconductance and current gain) are fully utilized for independent adjusting of oscillation condition and oscillation frequency. Specific matching condition allows linear control of oscillation frequency that is not so typical in such simple types of oscillators. Available phase shifts are 45, 90, 135 and 180 degree. Simulation results based on CMOS model of active element confirms intentions of the proposal in the bandwidth of several MHz.
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    Novel Oscillator Based on Voltage and Current-Gain Adjusting Used for Control of Oscillation Frequency and Oscillation Condition
    (Kaunas University of Technology, 2013-06-13) Šotner, Roman; Jeřábek, Jan; Jaikla, Winai; Herencsár, Norbert; Vrba, Kamil; Dostál, Tomáš
    The paper deals with novel controllable oscillator where two types of electronic control are used. Proposed second-order circuit contains current follower, adjustable current amplifier, adjustable voltage amplifier, two resistors and two grounded capacitors. Oscillation frequency is tuned by voltage gain of used voltage amplifier that is represented by high-frequency voltage-mode multiplier. Oscillation condition is automatically regulated by current gain of the adjustable current amplifier which is based on current-mode multiplier. Experimental results confirmed workability of the circuit.
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    Analysis of Dynamic Performance of Half-Wave Rectifiers and its Improvements
    (Kaunas University of Technology, 2014-02-03) Koton, Jaroslav; Herencsár, Norbert; Vrba, Kamil
    This paper deals with the analysis of dynamic behaviour of half-wave rectifiers and compares circuit solutions using standard operational amplifiers and current conveyors as active elements. The voltage and current sourcing principle and their influence to dynamic limits of diodes are given. Using the voltage or current biasing scheme, improvements in the dynamic performance of the diodes and rectifier are shown and discussed. The theoretical conclusions are supported by experimental results.
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    Application of Stochastic Differential-Algebraic Equations in Hybrid MTL Systems Analysis
    (Kaunas University of Technology, 2014-05-01) Brančík, Lubomír; Kolářová, Edita
    The paper deals with the application of stochastic differential-algebraic equations (SDAE) in the field of the time-domain simulation of hybrid (lumped/distributed) systems with randomly varying parameters. A core of the method lies on the theory of stochastic differential equations (SDE) considering the system responses as stochastic processes. However, due to a hybrid nature of the system, namely its lumped parameter part, non-differential (algebraic) parts arise generally in the solution. Herein, multiconductor transmission lines (MTL) play a role of the distributed-parameter parts of the hybrid system. The MTL model is designed as a cascade connection of generalized RLCG T-networks, while the state-variable method is applied for its description. The MTL boundary conditions are incorporated through a modified nodal analysis (MNA) to cover arbitrarily complex circuits. System responses are formed by the sets of stochastic trajectories completed by corresponding sample means and respective confidence intervals. To get the results a weak stochastic backward Euler scheme is used, consistent with the Itô stochastic calculus. All the computer simulations have been performed in the Matlab language environment.