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ISSN 1805-9600 (Online)

Radioengineering

Radioeng

Proceedings of Czech and Slovak Technical Universities

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April 2015, Volume 24, Number 1 [DOI: 10.13164/re.2015-1]

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S. Zvanovec, P. Chvojka, P. A. Haigh, Z. Ghassemlooy [references] [full-text] [DOI: 10.13164/re.2015.0001] [Download Citations]
Visible Light Communications towards 5G

5G networks have to offer extremely high capacity for novel streaming applications. One of the most promising approaches is to embed large numbers of co-operating small cells into the macro-cell coverage area. Alternatively, optical wireless based technologies can be adopted as an alternative physical layer offering higher data rates. Visible light communications (VLC) is an emerging technology for future high capacity communication links (it has been accepted to 5GPP) in the visible range of the electromagnetic spectrum (~370–780 nm) utilizing light-emitting diodes (LEDs) simultaneously provide data transmission and room illumination. A major challenge in VLC is the LED modulation bandwidths, which are limited to a few MHz. However, myriad gigabit speed transmission links have already been demonstrated. Non line-of-sight (NLOS) optical wireless is resistant to blocking by people and obstacles and is capable of adapting its’ throughput according to the current channel state information. Concurrently, organic polymer LEDs (PLEDs) have become the focus of enormous attention for solid-state lighting applications due to their advantages over conventional white LEDs such as ultra-low costs, low heating temperature, mechanical flexibility and large photoactive areas when produced with wet processing methods. This paper discusses development of such VLC links with a view to implementing ubiquitous broadcasting networks featuring advanced modulation formats such as orthogonal frequency division multiplexing (OFDM) or carrier-less amplitude and phase modulation (CAP) in conjunction with equalization techniques. Finally, this paper will also summarize the results of the European project ICT COST IC1101 OPTICWISE (Optical Wireless Communications - An Emerging Technology) dealing VLC and OLEDs towards 5G networks.

Keywords: 5G networks, light emitting diodes, visible light communications

B. Dimitrijevic, B. Nikolic, S. Aleksic, N. Raicevic [references] [full-text] [DOI: 10.13164/re.2015.0010] [Download Citations]
Optimization of Excitation in FDTD Method and Corresponding Source Modeling

Source and excitation modeling in FDTD formulation has a significant impact on the method performance and the required simulation time. Since the abrupt source introduction yields intensive numerical variations in whole computational domain, a generally accepted solution is to slowly introduce the source, using appropriate shaping functions in time. The main goal of the optimization presented in this paper is to find balance between two opposite demands: minimal required computation time and acceptable degradation of simulation performance. Reducing the time necessary for source activation and deactivation is an important issue, especially in design of microwave structures, when the simulation is intensively repeated in the process of device parameter optimization. Here proposed optimized source models are realized and tested within an own developed FDTD simulation environment.

Keywords: Finite difference time domain, source modeling, excitation, optimization.

S. Fatima, S. S. Muhammad, A. D. Raza [references] [full-text] [DOI: 10.13164/re.2015.0017] [Download Citations]
Bandwidth Efficient Root Nyquist Pulses for Optical Intensity Channels

Indoor diffuse optical intensity channels are bandwidth constrained due to the multiple reflected paths between the transmitter and the receiver which cause considerable inter-symbol interference (ISI). The transmitted signal amplitude is inherently non-negative, being a light intensity signal. All optical intensity root Nyquist pulses are time-limited to a single symbol interval which eliminates the possibility of finding bandlimited root Nyquist pulses. However, potential exists to design bandwidth efficient pulses. This paper investigates the modified hermite polynomial functions and prolate spheroidal wave functions as candidate waveforms for designing spectrally efficient optical pulses. These functions yield orthogonal pulses which have constant pulse duration irrespective of the order of the function, making them ideal for designing an ISI free pulse. Simulation results comparing the two pulses and challenges pertaining to their design and implementation are discussed.

Keywords: Nyquist Pulse, optical intensity signaling, PSWF (Prolate Spheroidal Wave Functions), MHPF (Modified Hermite Polynomial Function), ISI (Inter Symbol Interference)

M. Z. Ur Rehman, Z. Baharudin, M. A. Zakariya, M. H. M. Khir, M. T. Jilani [references] [full-text] [DOI: 10.13164/re.2015.0025] [Download Citations]
RF MEMS Based Tunable Bowtie Shaped Substrate Integrated Waveguide Filter

A tunable bandpass filter based on a technique that utilizes substrate integrated waveguide (SIW) and double coupling is presented. The SIW based bandpass filter is implemented using a bowtie shaped resonator structure. The bowtie shaped filter exhibits similar performance as found in rectangular and circular shaped SIW based bandpass filters. This concept reduces the circuit foot print of SIW; along with miniaturization high quality factor is maintained by the structure. The design methodology for single-pole triangular resonator structure is presented. Two different inter-resonator couplings of the resonators are incorporated in the design of the two-pole bowtie shaped SIW bandpass filter, and switching between the two couplings using a packaged RF MEMS switch delivers the tunable filter. A tunning of 1 GHz is achieved for two frequency states of 6.3 and 7.3 GHz. The total size of the circuit is 70mm x 36mm x 0.787 mm (LxWxH).

Keywords: Substrate integrated waveguide (SIW), tunable filter, bowtie filter, RF MEMS, double coupling.

N. Khajavi, S. V. Makki, S. Majidifar [references] [full-text] [DOI: 10.13164/re.2015.0032] [Download Citations]
Design of High Performance Microstrip Dual-Band Bandpass Filter

This paper presents a new design of dual-band bandpass filters using coupled stepped-impedance resonators for wireless systems. This architecture uses multiple couple stubs to tune the passband frequencies and the filter characteristics are improved using defected ground structure (DGS) technique. Measurement results show insertion losses of 0.93 dB and 1.13 dB for the central frequencies of 2.35 GHz and 3.61 GHz, respectively. This filter is designed, fabricated and measured and the results of the simulation and measurement are in good agreement.

Keywords: Dual-band bandpass filters, stepped-impedance resonators, defected ground structure (DGS), insertion loss

M. S. R. Bashri, M. Ibn Ibrahimy, S. M. A Motakabber [references] [full-text] [DOI: 10.13164/re.2015.0038] [Download Citations]
Design of a Wideband Inductively Coupled Loop Feed Patch Antenna for UHF RFID Tag

A planar wideband patch antenna for ultra-high frequency (UHF) radio frequency identification (RFID) tag for metallic applications is presented in this research work. Three different shape patches are inductively coupled to a triangle loop to form wide impedance bandwidth for universal application UHF (860-960 MHz) RFID. The structure of proposed antenna exhibits planar profile to provide ease of fabrication for cost reduction well suited for mass production. The simulation of the antenna was carried out using Finite Element Method (FEM) based software, Ansoft HFSS v13. The simulated and measured impedance bandwidth of 113 MHz and 117 MHz (Return Loss≥6 dB) were achieved to cover the entire UHF RFID operating frequency band worldwide. The simulated and measured radiation patterns at the operating frequency of 915 MHz are in good agreement. Moreover the simulated minimum antenna gain at the bore sight direction in free space and when mounted on 200 x 200 mm2 metal plate are -15 dBi and -14dBi respectively which is enough to provide reasonable read range over the entire UHF RFID system operating band.

Keywords: Complex impedance matching, patch antenna, radio frequency identification (RFID), metallic object, ultra high frequency (UHF)

M. N.Osman, M. K. A. Rahim, P. Gardner, M. R. Hamid, M. F. M. Yusoff, H. A. Majid [references] [full-text] [DOI: 10.13164/re.2015.0045] [Download Citations]
An Electronically Reconfigurable Patch Antenna Design for Polarization Diversity with Fixed Resonant Frequency

In this paper, an electronically polarization reconfigurable circular patch antenna with fixed resonant frequency operating at Wireless Local Area Network (WLAN) frequency band (2.4-2.48 GHz) is presented. The structure of the proposed design consists of a circular patch as a radiating element fed by coaxial probe, cooperated with four equal-length slits etched on the edge along x-axis and y-axis. A total of four switches was used and embedded across the slits at specific locations, thus controlled the length of the slits. By activating and deactivating the switches (ON and OFF) across the slits, the current on the patch is changed, thus modifying the electric field and polarization of the antenna. Consequently, the polarization excited by the proposed antenna can be switched into three types, either linear polarization, left-hand circular polarization or right-hand circular polarization. This paper proposes a simple approach that able to switch the polarizations and excited at the same operating frequency. Simulated and measured results of ideal case (using copper strip switches) and real case (using PIN diode switches) are compared and presented to demonstrate the performance of the antenna.

Keywords: Polarization reconfigurable antenna, circular patch, slit perturbations

A. Savascihabes, O. Ertug, E. Yazgan [references] [full-text] [DOI: 10.13164/re.2015.0054] [Download Citations]
On the Design and Performance Analysis of Low-Correlation Compact Space-Multimode Diversity Stacked Microstrip Antenna Arrays for MIMO-OFDM WLANs over Statistically-Clustered Indoor Radio Channels

The support of high spectral efficiency MIMO spatial-multiplexing communication in OFDM-based WLAN systems conforming to IEEE 802.11n standard requires the design and use of compact antennas and arrays with low correlation ports. For this purpose, compact space-multimode diversity provisioning stacked circular multimode microstrip patch antenna arrays (SCP-ULA) are proposed in this paper and their performance in terms of spatial and modal correlations, ergodic spectral efficiencies as well as compactness with respect to antenna arrays formed of vertically-oriented center-fed dipole elements (DP-ULA) and dominant-mode operating circular microstrip patch antennas (CP-ULA) are presented. The lower spatial and modal correlations and the consequent higher spectral efficiency of SCP-ULA with ML detection over statistically-clustered Kronecker-based spatially-correlated NLOS Ricean fading channels with respect to DP-ULA and CP-ULA at significantly lower antenna and array sizes represents SCP-ULA as a promising solution for deployment in terminals, modems and access points of next-generation high-speed 802.11n MIMO-OFDM WLAN systems.

Keywords: IEEE 802.11n MIMO-OFDM WLAN, spectral efficiency, spatial correlation, multimode antenna, spatial-multiplexing, Kronecker channel model, NLOS Ricean fading.

Xue Li, Jinwen Tian [references] [full-text] [DOI: 10.13164/re.2015.0064] [Download Citations]
Low-Profile Fully-Printed Multifrequency Monopoles Loaded with Complementary Metamaterial Transmission Line

The design of a new class of multifrequency monopoles by loading a set of resonant-type complementary metamaterial transmission lines (CMTL) is firstly presented. Two types of CMTL elements are comprehensively explored: the former is the epsilon negative (ENG) one by loading complementary split ring resonators (CSRRs) with different configurations on the signal strip, whereas the latter is the double negative (DNG) one by incorporating the CSRRs and capacitive gaps. In both cases, the CMTLs are considered with different number of unit cells. By cautiously controlling the geometrical parameters of element structure, five antenna prototypes coving different communication standards (GSM, UMTS, DMB and WiMAX) are designed, fabricated and measured. Numerical and experimental results illustrate that the zeroth-order resonance frequencies of the ENG and DNG monopoles are in desirable consistency. Moreover, of all operating frequencies the antennas exhibit fairly good impedance matching performances better than -10dB and quasi-omnidirectional radiation patterns.

Keywords: Metamaterial transmission line, planar monopole, multi-frequency antenna, complementary, zeroth-order resonator (ZOR).

P. Yoiyod, M. Krairiksh [references] [full-text] [DOI: 10.13164/re.2015.0070] [Download Citations]
Dielectric Properties Determination of a Stratified Medium

The method of detection of variation in dielectric properties of a material covered with another material, which requires nondestructive measurement, has numerous applications and the accurate measurement system is desirable. This paper presents a dielectric properties determination technique whereby the dielectric constant and loss factor are extracted from the measured reflection coefficient. The high frequency reflection coefficient shows the effect of the upper layer, while the dielectric properties of the lower layer can be determined at the lower frequency. The proposed technique is illustrated in 1-11 GHz band using 5 mm-thick water and 5% saline solution. The fluctuation of the dielectric properties between the high frequency and the low frequency, results from the edge diffraction in the material and the multiple reflections at the boundary of the two media, are invalid results. With the proposed technique, the dielectric properties of the lower layer can be accurately determined. The system is validated by measurement and good agreement is obtained at the frequency below 3.5 GHz. It can be applied for justifying variation of the material in the lower layer which is important in industrial process.

Keywords: Dielectric properties, stratified medium, reflection coefficient, diffraction coefficient

H. M. Elkamchouchi, M. M. Hassan [references] [full-text] [DOI: 10.13164/re.2015.0080] [Download Citations]
A Wideband Direct Data Domain Genetic Algorithm Beamforming

In this paper, a wideband direct data-domain genetic algorithm beamforming is presented. Received wideband signals are decomposed to a set of narrow sub-bands using fast Fourier transform. Each sub-band is transformed to a reference frequency using the steering vector transformation. So, narrowband approaches could be used for any of these sub-bands. Hence, the direct data-domain genetic algorithm beamforming can be used to form a single ‘hybrid’ beam pattern with sufficiently deep nulls in order to separate and reconstruct frequency components of the signal of interest efficiently. The proposed approach avoids most of drawbacks of already-existing statistical and gradient-based approaches since formation of a covariance matrix is not needed, and a genetic algorithm is used to solve the beamforming problem.

Keywords: Wideband array, direct data-domain, genetic algorithm, signal of interest, matrix pencil method

C.H. Qi, Z.Q. Zhao [references] [full-text] [DOI: 10.13164/re.2015.0087] [Download Citations]
Electromagnetic Scattering and Statistic Analysis of Clutter from Oil Contaminated Sea Surface

In order to investigate the electromagnetic (EM) scattering characteristics of the three dimensional sea surface contaminated by oil, a rigorous numerical method multilevel fast multipole algorithm (MLFMA) is developed to preciously calculate the electromagnetic backscatter from the two-layered oil contaminated sea surface. Illumination window and resistive window are combined together to depress the edge current induced by artificial truncation of the sea surface. By using this combination, the numerical method can get a high efficiency at a less computation cost. The differences between backscatters from clean sea and oil contaminated sea are investigated with respect to various incident angles and sea states. Also, the distribution of the sea clutter is examined for the oil-spilled cases in this paper.

Keywords: Oil contaminated sea, sea clutter, MLFMA, resistive loading.

M. Kvicera, P. Pechac [references] [full-text] [DOI: 10.13164/re.2015.0093] [Download Citations]
First-Order Statistics Prediction for a Propagation Channel of Arbitrary Non-Geostationary Satellite Orbits

A method enabling the prediction of first-order statistics of received signal level for arbitrary non-geostationary satellite orbits based on a reference dataset for a wide range of elevation angles is introduced for azimuth-independent scenarios and high elevation angles. The method is further validated by experimental data obtained during measurements performed at a frequency of 2.0 GHz at two scenarios at Stromovka Park in Prague, the Czech Republic, in August 2013 and March 2014. An excellent match between the predicted and actual cumulative distribution functions of received signal levels was identified for both scenarios.

Keywords: Satellite-to-Earth propagation, channel measurements, modeling, vegetation

S. Cho, S. K. Park [references] [full-text] [DOI: 10.13164/re.2015.0098] [Download Citations]
Uplink Multiuser MIMO Detection Scheme with Reduced Computational Complexity

The wireless communication systems with multiple antennas have recently received significant attention due to their higher capacity and better immunity to fading channels as compared to single antenna systems. A fast antenna selection scheme has been introduced for the uplink multiuser multiple-input multiple-output (MIMO) detection to achieve diversity gains, but the computational complexity of the fast antenna selection scheme in multiuser systems is very high due to repetitive pseudo-inversion computations. In this paper, a new uplink multiuser detection scheme is proposed adopting a switch-and-examine combining (SEC) scheme and the Cholesky decomposition to solve the computational complexity problem. K users are considered that each users is equipped with two transmit antennas for Alamouti space-time block code (STBC) over wireless Rayleigh fading channels. Simulation results show that the computational complexity of the proposed scheme is much lower than the systems with exhaustive and fast antenna selection, while the proposed scheme does not experience the degradations of bit error rate (BER) performances.

Keywords: Cholesky decomposition, fast antenna selection, multiuser MIMO, SEC, STBC

K. Rajeswari, S. J. Thiruvengadam [references] [full-text] [DOI: 10.13164/re.2015.0105] [Download Citations]
Optimal Power Allocation for Channel Estimation in MIMO-OFDM System with Per-Subcarrier Transmit Antenna Selection

A novel hybrid channel estimator is proposed for multiple-input multiple-output orthogonal frequency- division multiplexing (MIMO-OFDM) system with per-subcarrier transmit antenna selection having optimal power allocation among subcarriers. In practice, antenna selection information is transmitted through a binary symmetric control channel with a crossover probability. Linear minimum mean-square error (LMMSE) technique is optimal technique for channel estimation in MIMO-OFDM system. Though LMMSE estimator performs well at low signal to noise ratio (SNR), in the presence of antenna-to-subcarrier-assignment error (ATSA), it introduces irreducible error at high SNR. We have proved that relaxed MMSE (RMMSE) estimator overcomes the performance degradation at high SNR. The proposed hybrid estimator combines the benefits of LMMSE at low SNR and RMMSE estimator at high SNR. The vector mean square error (MSE) expression is modified as scalar expression so that an optimal power allocation can be performed. The convex optimization problem is formulated and solved to allocate optimal power to subcarriers minimizing the MSE, subject to transmit sum power constraint. Further, an analytical expression for SNR threshold at which the hybrid estimator is to be switched from LMMSE to RMMSE is derived. The simulation results show that the proposed hybrid estimator gives robust performance, irrespective of ATSA error.

Keywords: MIMO-OFDM, per-subcarrier antenna selection, antenna-to–subcarrier assignment, LMMSE, relaxed MMSE, hybrid estimator.

T. Zhang, W. Yang, Y. Cai [references] [full-text] [DOI: 10.13164/re.2015.0115] [Download Citations]
Exact Outage Performance Analysis of Multiuser Multi-relay Spectrum Sharing Cognitive Networks

In this paper, we investigate the outage performance of dual-hop multiuser multi-relay cognitive radio networks under spectrum sharing constraints. Using an efficient relay-destination selection scheme, the exact and asymptotic closed-form expressions for the outage probability are derived. From these expressions it is indicated that the achieved diversity order is only determined by the number of secondary user (SU) relays and destinations, and equals to M+N (where M and N are the number of destination nodes and relay nodes, respectively). Further, we find that the coding gain of the SU network will be affected by the interference threshold $bar I$ at the primary user (PU) receiver. Specifically, as the increases of the interference threshold, the coding gain of the considered network approaches to that of the multiuser multi-relay system in the non-cognitive network. Finally, our study is corroborated by representative numerical examples.

Keywords: Spectrum sharing, cognitive relay, outage probability, diversity order, coding gain.

S. Peng, Z. Yuan, J. You, Y. Shen, W. Jian [references] [full-text] [DOI: 10.13164/re.2015.0122] [Download Citations]
A Simplified Scheme of Estimation and Cancellation of Companding Noise for Companded Multicarrier Transmission Systems

Nonlinear companding transform is an efficient method to reduce the high peak-to-average power ratio (PAPR) of multicarrier transmission systems. However, the introduced companding noise greatly degrades the bit-error-rate (BER) performance of the companded multicarrier systems. In this paper, a simplified but effective scheme of estimation and cancellation of companding noise for the companded multicarrier transmission system is proposed. By expressing the companded signals as the summation of original signals added with a companding noise component, and subtracting this estimated companding noise from the received signals, the BER performance of the overall system can be significantly improved. Simulation results well confirm the great advantages of the proposed scheme over other conventional decompanding or no decompanding schemes under various situations.

Keywords: Multicarrier transmission systems, peak-to-average power ratio (PAPR), nonlinear companding transform (NCT), companding noise cancellation

V. Panko, S. Banas, R. Burton, K. Ptacek, J. Divin, J. Dobes [references] [full-text] [DOI: 10.13164/re.2015.0130] [Download Citations]
Enhanced Model of Nonlinear Spiral High Voltage Divider

This paper deals with the enhanced accurate DC and RF model of nonlinear spiral polysilicon voltage divider. The high resistance polysilicon divider is a sensing part of the high voltage start-up MOSFET transistor that can operate up to 700 V. This paper presents the structure of a proposed model, implemented voltage, frequency and temperature dependency, and scalability. A special attention is paid to the ability of the created model to cover the mismatch and influence of a variation of process parameters on the device characteristics. Finally, the comparison of measured data vs. simulation is presented in order to confirm the model validity and a typical application is demonstrated.

Keywords: High voltage start-up MOSFET, pinch-off, high voltage spiral divider, statistical modeling

M. Hayati, A. Abdipour , A. Abdipour [references] [full-text] [DOI: 10.13164/re.2015.0137] [Download Citations]
A Wilkinson Power Divider with Harmonic Suppression and Size Reduction using High-low Impedance Resonator Cells

A miniaturized Wilkinson power divider using high-low impedance resonator cells are designed and fabricated. The proposed power divider occupies 23.7% of the conventional structure circuit area at the operating frequency of 0.9 GHz and it is also able to suppress harmonics. According to the measured results at 0.9 GHz, the insertion-losses of output ports are 3.087 dB, the return-losses at all ports are more than 30 dB, and the isolation between output ports is better than 35 dB. Also, 2nd to 10th spurious frequencies are suppressed. According to the measured S11, when it is less than -15 dB (from 0.65 GHz to 1.1 GHz) the fractional bandwidth of the proposed structure is 50%. Good agreement between simulation and measured results is achieved.

Keywords: Harmonic suppression, high-low impedance resonator, miniaturized Wilkinson power divider.

A. Oncu [references] [full-text] [DOI: 10.13164/re.2015.0142] [Download Citations]
A 1.2 V and 69 mW 60 GHz Multi-channel Tunable CMOS Receiver Design

A multi-channel receiver operating between 56 GHz and 70 GHz for coverage of different 60 GHz bands worldwide is implemented with a 90 nm Complementary Metal-Oxide Semiconductor (CMOS) process. The receiver containing an LNA, a frequency down-conversion mixer and a variable gain amplifier incorporating a band-pass filter is designed and implemented. This integrated receiver is tested at four channels of centre frequencies 58.3 GHz, 60.5 GHz, 62.6 GHz and 64.8 GHz, employing a frequency plan of an 8 GHz-intermediate frequency (IF). The achieved conversion gain by coarse gain control is between 4.8 dB–54.9 dB. The millimeter-wave receiver circuit is biased with a 1.2V supply voltage. The measured power consumption is 69 mW.

Keywords: 60GHz, CMOS, integrated circuit, receiver design, low-power

M. Czyzak, J. Horiszny, R. Smyk [references] [full-text] [DOI: 10.13164/re.2015.0148] [Download Citations]
Pipelined Two-Operand Modular Adders

Pipelined two-operand modular adder (TOMA) is one of basic components used in digital signal processing (DSP) systems that use the residue number system (RNS). Such modular adders are used in binary/residue and residue/binary converters, residue multipliers and scalers as well as within residue processing channels. The design of pipelined TOMAs is usually obtained by inserting an appriopriate number of latch layers inside a nonpipelined TOMA structure. Hence their area is also determined by the number of latches and the delay by the number of latch layers. In this paper we propose a new pipelined TOMA that is based on a new TOMA, that has the smaller area and smaller delay than other known structures. Comparisons are made using data from the very large scale of integration (VLSI) standard cell library.

Keywords: Carry-lookahead adder, FPGA, modular adder, parallel-prefix adder, residue number system (RNS), ripple-carry adder, VLSI design

J. Slezak, T. Gotthans [references] [full-text] [DOI: 10.13164/re.2015.0161] [Download Citations]
Design of Passive Analog Electronic Circuits Using Hybrid Modified UMDA algorithm

Hybrid evolutionary passive analog circuits synthesis method based on modified Univariate Marginal Distribution Algorithm (UMDA) and a local search algorithm is proposed in the paper. The modification of the UMDA algorithm which allows to specify the maximum number of the nodes and the maximum number of the components of the synthesized circuit is proposed. The proposed hybrid approach efficiently reduces the number of the objective function evaluations. The modified UMDA algorithm is used for synthesis of the topology and the local search algorithm is used for determination of the parameters of the components of the designed circuit. As an example the proposed method is applied to a problem of synthesis of the fractional capacitor circuit.

Keywords: Evolutionary algorithm, optimization, estimation of distribution algorithm, EDA, analog circuit design, fractional capacitor.

G. V. K. Sharma, K. Raja Rajeswari [references] [full-text] [DOI: 10.13164/re.2015.0171] [Download Citations]
Fast Implementation of Transmit Beamforming for Colocated MIMO Radar

Multiple-input Multiple-output (MIMO) radars benefit from spatial and waveform diversities to improve the performance potential. Phased array radars transmit scaled versions of a single waveform thereby limiting the transmit degrees of freedom to one. However MIMO radars transmit diverse waveforms from different transmit array elements thereby increasing the degrees of freedom to form flexible transmit beampatterns. The transmit beampattern of a colocated MIMO radar depends on the zero-lag correlation matrix of different transmit waveforms. Many solutions have been developed for designing the signal correlation matrix to achieve a desired transmit beampattern based on optimization algorithms in the literature. In this paper, a fast algorithm for designing the correlation matrix of the transmit waveforms is developed that allows the next generation radars to form flexible beampatterns in real-time. An efficient method for sidelobe control with negligible increase in mainlobe width is also presented.

Keywords: Multiple-input multiple-output radar, transmit beamforming, fast implementation, waveform diversity, zero-lag correlation matrix

F. Zaplata, M. Kasal [references] [full-text] [DOI: 10.13164/re.2015.0178] [Download Citations]
Efficient Spectral Power Estimation on an Arbitrary Frequency Scale

The Fast Fourier Transform is a very efficient algorithm for the Fourier spectrum estimation, but has the limitation of a linear frequency scale spectrum, which may not be suitable for every system. For example, audio and speech analysis needs a logarithmic frequency scale due to the characteristic of a human’s ear. The Fast Fourier Transform algorithms are not able to efficiently give the desired results and modified techniques have to be used in this case. In the following text a simple technique using the Goertzel algorithm allowing the evaluation of the power spectra on an arbitrary frequency scale will be introduced. Due to its simplicity the algorithm suffers from imperfections which will be discussed and partially solved in this paper. The implementation into real systems and the impact of quantization errors appeared to be critical and have to be dealt with in special cases. The simple method dealing with the quantization error will also be introduced. Finally, the proposed method will be compared to other methods based on its computational demands and its potential speed.

Keywords: Goertzel algorithm, Mel frequency cepstral coefficients, MFCCs, Q-constant transform, Spectral power estimation

B. Jaksic, D. Stefanovic, M. Stefanovic, P. Spalevic, V. Milenkovic [references] [full-text] [DOI: 10.13164/re.2015.0185] [Download Citations]
Level Crossing Rate of Macrodiversity System in the Presence of Multipath Fading and Shadowing

Macrodiversity system including macrodiversity SC receiver and two microdiversity SC receivers is considered in this paper. Received signal experiences, simultaneously, both, long term fading and short term fading. Microdiversity SC receivers reduces Rayleigh fading effects on system performance and macrodiversity SC receiver mitigate Gamma shadowing effects on system performance. Closed form expressions for level crossing rate of microdiversity SC receivers output signals envelopes are calculated. This expression is used for evaluation of level crossing rate of macrodiversity SC receiver output signal envelope. Numerical expressions are illustrated to show the influence of Gamma shadowing severity on level crossing rate.

Keywords: Macrodiversity selection combining (SC) receiver, Rayleigh multipath fading, Gamma shadowing, level crossing rate, correlation

M. T. Mushtaq, I. Khan, M. S. Khan, O. Koudelka [references] [full-text] [DOI: 10.13164/re.2015.0192] [Download Citations]
Signal Detection for QPSK Based Cognitive Radio Systems using Support Vector Machines

Cognitive radio based network enables opportunistic dynamic spectrum access by sensing, adopting and utilizing the unused portion of licensed spectrum bands. Cognitive radio is intelligent enough to adapt the communication parameters of the unused licensed spectrum. Spectrum sensing is one of the most important tasks of the cognitive radio cycle. In this paper, the auto-correlation function kernel based Support Vector Machine (SVM) classifier along with Welch's Periodogram detector is successfully implemented for the detection of four QPSK (Quadrature Phase Shift Keying) based signals propagating through an AWGN (Additive White Gaussian Noise) channel. It is shown that the combination of statistical signal processing and machine learning concepts improve the spectrum sensing process and spectrum sensing is possible even at low Signal to Noise Ratio (SNR) values up to -50 dB.

Keywords: Cognitive radio, autocorrelation function, machine learning, Support Vector Machine, spectrum sensing, statistical signal processing, opportunistic dynamic spectrum access

C. G. Shi, F. Wang, J.J. Zhou, J. Chen [references] [full-text] [DOI: 10.13164/re.2015.0199] [Download Citations]
Fuzzy Chance-constrained Programming Based Security Information Optimization for Low Probability of Identification Enhancement in Radar Network Systems

In this paper, the problem of low probability of identification (LPID) improvement for radar network systems is investigated. Firstly, the security information is derived to evaluate the LPID performance for radar network. Then, without any prior knowledge of hostile intercept receiver, a novel fuzzy chance-constrained programming (FCCP) based security information optimization scheme is presented to achieve enhanced LPID performance in radar network systems, which focuses on minimizing the achievable mutual information (MI) at interceptor, while the attainable MI outage probability at radar network is enforced to be greater than a specified confidence level. Regarding to the complexity and uncertainty of electromagnetic environment in the modern battlefield, the trapezoidal fuzzy number is used to describe the threshold of achievable MI at radar network based on the credibility theory. Finally, the FCCP model is transformed to a crisp equivalent form with the property of trapezoidal fuzzy number. Numerical simulation results demonstrating the performance of the proposed strategy are provided.

Keywords: Security information, low probability of identification (LPID), power allocation, fuzzy chance-constrained programming (FCCP), radar network systems

H. Chen, Q. Wan, R. Fan, F. Wen [references] [full-text] [DOI: 10.13164/re.2015.0208] [Download Citations]
Direction-of-Arrival Estimation Based on Sparse Recovery with Second-Order Statistics

Traditional direction-of-arrival (DOA) estimation techniques perform Nyquist-rate sampling of the received signals and as a result they require high storage. To reduce sampling ratio, we introduce level-crossing (LC) sampling which captures samples whenever the signal crosses predetermined reference levels, and the LC-based analog-to-digital converter (LC ADC) has been shown to efficiently sample certain classes of signals. In this paper, we focus on the DOA estimation problem by using second-order statistics based on the LC samplings recording on one sensor, along with the synchronous samplings of the another sensors, a sparse angle space scenario can be found by solving an $ell_1$ minimization problem, giving the number of sources and their DOA's. The experimental results show that our proposed method, when compared with some existing norm-based constrained optimization compressive sensing (CS) algorithms, as well as subspace method, improves the DOA estimation performance, while using less samples when compared with Nyquist-rate sampling and reducing sensor activity especially for long time silence signal.

Keywords: Direction-of-arrival estimation, level crossing, compressive sensing, dantzing selector, convex optimization

R. Guo, X. Mao, S. Li, Y. Wang, X. Wang [references] [full-text] [DOI: 10.13164/re.2015.0214] [Download Citations]
A Fast DOA Estimation Algorithm Based on Polarization MUSIC

A fast DOA estimation algorithm developed from MUSIC, which also benefits from the processing of the signals' polarization information, is presented. Besides performance enhancement in precision and resolution, the proposed algorithm can be exerted on various forms of polarization sensitive arrays, without specific requirement on the array's pattern. Depending on the continuity property of the space spectrum, a huge amount of computation incurred in the calculation of 4-D space spectrum is averted. Performance and computation complexity analysis of the proposed algorithm is discussed and the simulation results are presented. Compared with conventional MUSIC, it is indicated that the proposed algorithm has considerable advantage in aspects of precision and resolution, with a low computation complexity proportional to a conventional 2-D MUSIC.

Keywords: Polarization sensitive array, DOA, MUSIC, fast algorithm.

A. Kizilkaya, A. Ukte, M. D. Elbi [references] [full-text] [DOI: 10.13164/re.2015.0226] [Download Citations]
Statistical Multirate High-Resolution Signal Reconstruction Using the EMD-IT Based Denoising Approach

The reconstruction problem of a high-resolution (HR) signal from a set of its noise-corrupted low-resolution (LR) versions is considered. As a part of this problem, a hybrid method that consists of four operation units is proposed. The first unit applies noise reduction based on the empirical mode decomposition interval-thresholding to the noisy LR observations. In the second unit, estimates of zero-interpolated HR signals are obtained by performing up-sampling and then time shifting on each noise reduced LR signal. The third unit combines the zero-interpolated HR signals for attaining one HR signal. To eliminate the ripple effect, finally, median filtering is applied to the resulting reconstructed signal. As compared to the work that employs linear periodically time-varying Wiener filters, the proposed method does not require any correlation information about desired signal and LR observations. The validity of the proposed method is demonstrated by several simulation examples.

Keywords: Empirical mode decomposition (EMD), statistical multirate signal reconstruction, noise reduction, high-resolution, median filtering

M. R. Dincic, Z. H. Peric [references] [full-text] [DOI: 10.13164/re.2015.0233] [Download Citations]
Multiproduct Uniform Polar Quantizer

The aim of this paper is to reduce the complexity of the unrestricted uniform polar quantizer (UUPQ), keeping its high performances. To achieve this, in this paper we propose the multiproduct uniform polar quantizer (MUPQ), where several consecutive magnitude levels are joined in segments and within each segment the uniform product quantization is performed (i.e. all levels within one segments have the same number of phase levels). MUPQ is much simpler for realization than UUPQ, but it achieves similar performances as UUPQ. Since MUPQ has low complexity and achieves much better performances than the scalar uniform quantizer, it can be widely used instead of scalar uniform quantizers to improve performances, for any signal with the Gaussian distribution.

Keywords: Unrestricted uniform polar quantization, multiproduct uniform polar quantization, polar coordinates, Gaussian distribution

M. Cedillo-Hernandez, A. Cedillo-Hernandez, F. Garcia-Ugalde, M. Nakano-Miyatake, H. Perez-Meana [references] [full-text] [DOI: 10.13164/re.2015.0240] [Download Citations]
Copyright Protection of Color Imaging Using Robust-Encoded Watermarking

In this paper we present a robust-encoded watermarking method applied to color images for copyright protection, which presents robustness against several geometric and signal processing distortions. Trade-off between payload, robustness and imperceptibility is a very important aspect which has to be considered when a watermark algorithm is designed. In our proposed scheme, previously to be embedded into the image, the watermark signal is encoded using a convolutional encoder, which can perform forward error correction achieving better robustness performance. Then, the embedding process is carried out through the discrete cosine transform domain (DCT) of an image using the image normalization technique to accomplish robustness against geometric and signal processing distortions. The embedded watermark coded bits are extracted and decoded using the Viterbi algorithm. In order to determine the presence or absence of the watermark into the image we compute the bit error rate (BER) between the recovered and the original watermark data sequence. The quality of the watermarked image is measured using the well-known indices: Peak Signal to Noise Ratio (PSNR), Visual Information Fidelity (VIF) and Structural Similarity Index (SSIM). The color difference between the watermarked and original images is obtained by using the Normalized Color Difference (NCD) measure. The experimental results show that the proposed method provides good performance in terms of imperceptibility and robustness. The comparison among the proposed and previously reported methods based on different techniques is also provided.

Keywords: Digital watermarking, image normalization, geometric and signal processing distortions, convolutional encoder, Viterbi decoder, discrete cosine transform.

A. Kar, M. Chandra [references] [full-text] [DOI: 10.13164/re.2015.0252] [Download Citations]
An Improved Variable Structure Adaptive Filter Design and Analysis for Acoustic Echo Cancellation

In this research an advance variable structure adaptive Multiple Sub-Filters (MSF) based algorithm for single channel Acoustic Echo Cancellation (AEC) is proposed and analyzed. This work suggests a new and improved direction to find the optimum tap-length of adaptive filter employed for AEC. The structure adaptation, supported by a tap-length based weight update approach helps the designed echo canceller to maintain a trade-off between the Mean Square Error (MSE) and time taken to attain the steady state MSE. The work done in this paper focuses on replacing the fixed length sub-filters in existing MSF based AEC algorithms which brings refinements in terms of convergence, steady state error and tracking over the single long filter, different error and common error algorithms. A dynamic structure selective coefficient update approach to reduce the structural and computational cost of adaptive design is discussed in context with the proposed algorithm. Simulated results reveal a comparative performance analysis over proposed variable structure multiple sub-filters designs and existing fixed tap-length sub-filters based acoustic echo cancellers.

Keywords: Adaptive filter, acoustic echo cancellation, variable structure design, multiple sub-filters, least mean square, mean square error, convergence.

P. C. Xu, Y. H. Shen, H. Li [references] [full-text] [DOI: 10.13164/re.2015.0262] [Download Citations]
New Negentropy Optimization Schemes for Blind Signal Extraction of Complex Valued Sources

Blind signal extraction, a hot issue in the field of communication signal processing, aims to retrieve the sources through the optimization of contrast functions. Many contrasts based on higher-order statistics such as kurtosis, usually behave sensitive to outliers. Thus, to achieve robust results, nonlinear functions are utilized as contrasts to approximate the negentropy criterion, which is also a classical metric for non-Gaussianity. However, existing methods generally have a high computational cost, hence leading us to address the problem of efficient optimization of contrast function. More precisely, we design a novel “reference-based” contrast function based on negentropy approximations, and then propose a new family of algorithms (Alg.1 and Alg.2) to maximize it. Simulations confirm the convergence of our method to a separating solution, which is also analyzed in theory. We also validate the theoretic complexity analysis that Alg.2 has a much lower computational cost than Alg.1 and existing optimization methods based on negentropy criterion. Finally, experiments for the separation of single sideband signals illustrate that our method has good prospects in real-world applications.

Keywords: Negentropy criterion, blind signal extraction, quadratic optimization, global convergence, reference system.

S. Duangsuwan, S. Promwong [references] [full-text] [DOI: 10.13164/re.2015.0272] [Download Citations]
ISI Cancellation Using Blind Equalizer Based on DBC Model for MIMO-RFID Reader Reception

Under the dyadic backscatter channel (DBC) model, a conventional zero forcing (ZF) and minimum mean square error (MMSE) method for MIMO-RFID reader reception are not able to be rapidly cancelled inter-symbol interference (ISI) because of the error of postpreamble transmission. In order to achieve the ISI cancellation, the conventional method of ZF and MMSE are proposed to resolve a convergence rate without postpreamble by using a constant modulus algorithm (CMA). Depending on the cost function, the CMA is used which based on second order statistics to estimate the channel statement of channel transfer function. Furthermore, the multiple-tag detection is also considered under the assumption of the maximum likelihood estimation. The comparison of the conventional method and the proposed method is analyzed by using computer simulation and experimental data. We can see that the proposed method is better than the conventional method with a faster ISI cancelling and a lower bit error rate (BER) improving as up to 12 tags.

Keywords: RFID reader reception, MIMO receiver, DBC model, blind equalizer, ISI cancellation.

M. Hadavi, M. Radmard, M. M. Nayebi [references] [full-text] [DOI: 10.13164/re.2015.0280] [Download Citations]
A New MCMC Sampling Based Segment Model for Radar Target Recognition

One of the main tools in radar target recognition is high resolution range profile (HRRP)‎. ‎However‎, ‎it is very sensitive to the aspect angle‎. ‎One solution to this problem is to assume the consecutive samples of HRRP identically independently distributed (IID) in small frames of aspect angles‎, ‎an assumption which is not true in reality‎. ‎However, b‎‎ased on this assumption‎, ‎some models have been developed to characterize the sequential information contained in the multi-aspect radar echoes‎. ‎Therefore‎, ‎they only consider the short dependency between consecutive samples‎. ‎Here‎, ‎we propose an alternative model‎, ‎the segment model‎, ‎to address the shortcomings of these assumptions‎. ‎In addition‎, ‎using a Markov chain Monte-Carlo (MCMC) based Gibbs sampler as an iterative approach to estimate the parameters of the segment model‎, ‎we will show that the proposed method is able to estimate the parameters with quite satisfying accuracy and computational load‎.

Keywords: Radar target recognition‎, ‎segment model‎, ‎Markov chain Monte-Carlo‎, ‎Gibbs sampler

F. Li, L. Geng, S. Zhu [references] [full-text] [DOI: 10.13164/re.2015.0288] [Download Citations]
Joint Dynamic Radio Resource Allocation and Mobility Load Balancing in 3GPP LTE Multi-Cell Network

Load imbalance, together with inefficient utilization of system resource, constitute major factors responsible for poor overall performance in Long Term Evolution (LTE) network. In this paper, a novel scheme of joint dynamic resource allocation and load balancing is proposed to achieve a balanced performance improvement in 3rd Generation Partnership Project (3GPP) LTE Self-Organizing Networks (SON). The new method which aims at maximizing network resource efficiency subject to inter-cell interference and intra-cell resource constraints is implemented in two steps. In the first step, an efficient resource allocation, including user scheduling and power assignment, is conducted in a distributed manner to serve as many users in the whole network as possible. In the second step, based on the resource allocation scheme, the optimization objective namely network resource efficiency can be calculated and load balancing is implemented by switching the user that can maximize the objective function. Lagrange Multipliers method and heuristic algorithm are used to resolve the formulated optimization problem. Simulation results show that our algorithm achieves better performance in terms of user throughput, fairness, load balancing index and unsatisfied user number compared with the traditional approach which takes resource allocation and load balancing into account, respectively.

Keywords: Load balancing, resource allocation, LTE SON, efficiency and fairness

Zongsheng Zhang, Qihui Wu, Jinlong Wang [references] [full-text] [DOI: 10.13164/re.2015.0296] [Download Citations]
ARQ Protocols in Cognitive Decode-and-Forward Relay Networks: Opportunities Gain

In this paper, two novel automatic-repeat-request (ARQ) based protocols were proposed, which exploit coop- eration opportunity inherent in secondary retransmission to create access opportunities. If the signal was not decoded correctly in destination, another user can be acted as a relay to reduce retransmission rounds by relaying the signal. For comparison, we also propose a Direct ARQ Protocol. Specif- ically, we derive the exact closed-form outage probability of three protocols, which provides an effective means to evalu- ate the effects of several parameters. Moreover, we propose a new metric to evaluate the performance improvement for cognitive networks. Finally, Monte Carlo simulations were presented to validate the theory analysis, and a comparison is made among the three protocols.

Keywords: Cognitive relay networks, outage probability, automatic-repeat-request

Yun Liu, Jiachen Yang, Rongrong Chu [references] [full-text] [DOI: 10.13164/re.2015.0305] [Download Citations]
Objective Evaluation Criteria for Shooting Quality of Stereo Cameras over Short Distance

Stereo cameras are the basic tools used to obtain stereoscopic image pairs, which can lead to truly great image quality. However, some inappropriate shooting conditions may cause discomfort while viewing stereo images. It is therefore considerably necessary to establish the perceptual criteria that can be used to evaluate the shooting quality of stereo cameras. This article proposes objective quality evaluation criteria based on the characteristics of parallel and toed-in camera configurations. Considering the different internal structures and basic shooting principles, this paper focuses on short-distance shooting conditions and establishes assessment criteria for both parallel and toed-in camera configurations. Experimental results show that the proposed evaluation criteria can predict the visual perception of stereoscopic images and effectively evaluate stereoscopic image quality.

Keywords: stereo camera, objective evaluation, shooting princi-ples, stereoscopic image pairs, short-distance shooting, parallel and toed-in camera configurations.

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