# December 2010, Volume 19, Number 4

**G. Baudoin, M. Villegas, M. Suarez, A. Diet, F. Robert**
[references] [full-text]

Performance Analysis of Multiradio Transmitter with Polar or Cartesian Architectures Associated with High Efficiency Switched-Mode Power Amplifiers (invited paper)

This paper deals with wireless multi-radio transmitter architectures operating in the frequency band of 800 MHz – 6 GHz. As a consequence of the constant evolution in the communication systems, mobile transmitters must be able to operate at different frequency bands and modes according to existing standards specifications. The concept of a unique multiradio architecture is an evolution of the multistandard transceiver characterized by a parallelization of circuits for each standard. Multi-radio concept optimizes surface and power consumption.

Transmitter architectures using sampling techniques and baseband ΣΔ or PWM coding of signals before their amplification appear as good candidates for multiradio transmitters for several reasons. They allow using high efficiency power amplifiers such as switched-mode PAs. They are highly flexible and easy to integrate because of their digital nature. But when the transmitter efficiency is considered, many elements have to be taken into account: signal coding efficiency, PA efficiency, RF filter. This paper investigates the interest of these architectures for a multiradio transmitter able to support existing wireless communications standards between 800 MHz and 6 GHz. It evaluates and compares the different possible architectures for WiMAX and LTE standards in terms of signal quality and transmitter power efficiency.

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Keywords: Multiradio transmitter, high-efficiency RF transmitter, polar transmitter architectures, Cartesian transmitter architectures, class E power amplifier, Sigma-Delta coding, PWM coding, WiMaX, LTE

**Y. Cui, Z. Zhao, H. Zhang**
[references] [full-text]

An Efficient Filter Banks Based Multicarrier System in Cognitive Radio Networks (invited paper)

In cognitive radio techniques, OFDM is usually regarded as the physical layer candidate. However, the weaknesses of the OFDM technique, i.e., using plain FFT for spectral analysis , decreased bandwidth efficiency due to CP (cyclic prefix), high out-of-band emission, have been pointed out and the introduction of filter banks based multicarrier (FBMC) system has been advocated by a number of authors. In this paper, we propose an efficient FBMC system for cognitive radio network. At the transmitter, we propose a decimation transform decomposition method to eliminate the unnecessary zero operations. At the receiver, we utilize the analysis filter banks to sense the spectrum bands. In order to conquer the shortages of the traditional filter banks, we propose a multistage analysis filter banks, which can reduce the computational complexity while improve the detection precision when used to sense the spectrum bands. And with an adaptive threshold scheme in the power estimator, the threshold can be kept very close to the noise power, which can increase the detection probability especially in the condition of low SNR.

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Keywords: Cognitive radio, FBMC, transform decomposition, multistage filter banks, adaptive threshold

**K. Ruttik, K. Koufos, R. Jantti**
[references] [full-text]

Modeling of the Secondary System's Generated Interference and Studying of its Impact on the Secondary System Design

In this paper we study how much capacity a cellular secondary system can achieve if the interference to the TV system is kept under control. The interference is modeled and controlled in a slow fading environment. The secondary system's capacity is computed for the adjacent and for the co-channel (with respect to the TV channel). We study the behavior of the system capacity while changing the size of the no transmission area surrounding the TV coverage area. It turns out that for most of the secondary cell sizes the network with adjacent channel is in interference limited mode and the network with co-channel is in noise limited mode. Since in the co-channel we can not use very high power it is recommended to use in bigger cells only adjacent channel.

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- ALJUAID, M., YANIKOMEROGLU, H. A cumulant based charac- terization of the aggregated interference power in wireless networks. In IEEE 71st Vehicular Technology Conference: VTC2010-spring. Taipei (Taiwan), 2010, p. 1 – 5.
- WU, M., DEVROYE, N., TAROKH, V. On the primary exclusive region of cognitive networks. IEEE Transactions on Wireless Com- munications, 2009, vol. 8, no. 7, p. 3380 – 3385.
- HARRISSON, K., MISHRA, S. A., SAHAI, A. How much white space capacity is there. In IEEE Symposium on New Frontiers in Dy- namic Spectrum: DySPAN. Singapore, 2010, p. 1 – 10.
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Keywords: Secondary spectrum usage, interference, capacity.

**N. Milosevic, Z. Nikolic, B. Dimitrijevic, B. Nikolic**
[references] [full-text]

The Effects of Interference Suppression by a Reconfigurable Structure at DSSS-DPSK Receiver

In this paper we show the performances of DSSS-DPSK receiver where the interference rejection circuit is reconfigurable and is using ξ-structure. The results will be shown for the case of packet, as well as for the continuous QPSK interference. The results show that the proposed reconfiguration circuit, in case of packet QPSK interference, significantly decreases the error probability, compared to the system using only ξ-structure. Also, in case of continuous interference, the reconfigurable structure has equally good performance, regardless of interference power and its bitrate.

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Keywords: Interference suppression, spread spectrum system, reconfiguration, error probability

**R. Pust, K. Burda**
[references] [full-text]

A New Technique of Frequency Hopping with Collision Avoidance

This article proposes a new technique of frequency hopping with collision avoidance (FH/CA). Currently there are well-known systems of frequency hopping which adapt their behavior based on previously measured data (such as PER) for individual channels. The FH/CA system adjusts its behavior based on the current occupancy of several test channels. Using a mathematical model, the performance of the newly proposed FH/CA technique is compared with the currently used techniques FH and AFH. Comparison criteria are the probability of a collision between an FH/CA communication system and a static or dynamic jammer (i.e. other FH or AFH systems).

- PUST, R., BURDA, K. Comparing performance of FH and AFH systems. International Journal of Computer Science and Network Security, 2010, vol. 10, no. 2, p. 82-85. ISSN: 1738- 7906.
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Keywords: Frequency hopping, collision avoidance, static jammer, dynamic jammer.

**J. Blumenstein, Z. Fedra, V. Sebesta**
[references] [full-text]

Performance of Pilot Aided Channel Estimation Technique in 2D Spreading Based Systems

It has recently been observed that the combination of the OFDM (Orthogonal Frequency Division Multiplex) and the CDMA (Code Division Multiple Access) can achieve notably lower BER (Bit Error Rate) performance in comparison with OFDM itself. The paper reports on the actual topic of the efficient channel estimation in 2D spreading based systems e.q. VSF-OFCDM (Variable Spreading Factor - Orthogonal Frequency Multiple Acces). The different methods for acquisition of channel state information from pilot carriers are used. The simulations are made for different ETSI channel models.

- HARADA, H., PRASAD, R. Simulation and software radio for mo- bile communications. Boston: Artech House, 2002.
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Keywords: VSF-OFCDM, Two-dimensional spreading, Channel estimation, Channel state information, Pilot subcarriers, ETSI channel model, OFDM, CDMA

**Zs. Kollar, P. Horvath**
[references] [full-text]

Modulation Schemes for Cognitive Radio in White Spaces

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 mainly based on the side effects of various non-ideal analog components (power amplifier, local oscillator) and residual synchronization errors such as frequency offset. As we will show, each technique has different sensitivity to the various impairments. The comparisons will be performed via spectral density functions and bit error rates (BER).

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Keywords: Cognitive radio, physical layer, Orthogonal Frequency Division Multiplexing, DFT-spread OFDM, Constant Envelope OFDM, Filter Bank Multicarrier, synchronization error, white space.

**Z. Jing, B. Bai, X. Ma**
[references] [full-text]

Compensation-based Game for Spectrum Sharing in the Gaussian Interference Channel

This paper considers an optimization problem of sum-rate in the Gaussian frequency-selective channel. We construct a competitive game with an asymptotically optimal compensation to approximate the optimization problem of sum-rate. Once the game achieves the Nash equilibrium, all users in the game will operate at the optimal sum-rate boundary. The contributions of this paper are twofold. On the one hand, a distributed power allocation algorithm called iterative multiple waterlevels water-filling algorithm is proposed to efficiently achieve the Nash equilibrium of the game. On the other hand, we derive some sufficient conditions on the convergence of iterative multiple waterlevels water-filling algorithm in this paper. Through simulation, the proposed algorithm has a significant improvement of the performance over iterative water filling algorithm and achieves the close-to-optimal performance.

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Keywords: Interference channel, Iterative water filling algorithm (IWFA), Power allocation, Game theory

**B. Hu, X. Yu, L. He, W. Lim, K. Yeo**
[references] [full-text]

Analysis and Design of Wideband Low Noise Amplifier with Digital Control

The design issues in designing low noise amplifier (LNA) for Software-Defined-Radio (SDR) are reviewed. An inductor-less wideband low noise amplifier aiming at low frequency band (0.2-2GHz) for Software-Defined-Radio is presented. Shunt-shunt LNA with active feedback is used as the first stage which is carefully optimized for low noise and wide band applications. A digitally controlled second stage is employed to provide an additional 12dB gain control. A novel method is proposed to bypass the first stage without degrading input matching. This LNA is fabricated in a standard 0.18 um CMOS technology. The measurement result shows the proposed LNA has a gain range of 6dB-18dB at high gain mode and -12dB-0dB at low gain mode, as well as a –3dB bandwidth of 2GHz. The noise figure (NF) is 3.5-4.5dB in the high gain setting mode. It consumes 20mW from a 1.8V supply.

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Keywords: Low Noise Amplifier, Inductor-less, Software-Defined-Radio, Digital Gain Control

**O. Jakubov, P. Kovar, P. Kacmarik, F. Vejrazka**
[references] [full-text]

The Witch Navigator - A Low Cost GNSS Software Receiver for Advanced Processing Techniques

The developement of advanced GNSS signal processing algorithms such as multi-constellation, multi-frequency and multi-antenna navigation requires an easily reprogrammable software defined radio solution. Various receiver architectures for this purpose have been introduced. RF front-end with FPGA universal correlators on ExpressCard connected directly to PC was selected and manufactured. Such a~unique hardware combination provides the GNSS researchers and engineers with a~great convenience of writing the signal processing algorithms including tracking, acquisition and positioning in the Linux application programming interface and enables them to reconfigure the RF front-end easily by the PC program. With more of these ExpressCards connected to the PC, the number of the RF channels, correlators or antennas can be increased to further boost the computational power. This paper reveals the implementation aspects of the receiver, named the Witch Navigator, and~gives the key test results.

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Keywords: GNSS, Universal Correlator, GPS, Galileo, GLONASS, Compass, SDR

**Qihui Wu, Han Han, Jinlong Wang, Zhitao Zhao, Ze Zhang**
[references] [full-text]

Sensing Task Allocation for Heterogeneous Channels in Cooperative Spectrum Sensing

In the traditional centralized cooperative spectrum sensing, all secondary users sense the same channel. But, for a given channel, there exists detection performance diversity among all the users, due to the different signal-fading process. Involving the user with poor performance in cooperative sensing will not only deteriorate the detection correctness but also waste the sensing time. In the heterogeneous channels, the problem is even severe. A novel idea is to allocate the secondary users to sense different channels. We analyze the allocation problem before formulate it to be an optimization problem, which is a NP-hard problem. Then we propose the declined complexity algorithm in equal secondary user case and the two-hierarchy approach algorithm in unequal case. With the simulation, we verify the near optimality of the proposed algorithms and the advantage of the task allocation.

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Keywords: Cognitive radio, spectrum sensing, sensing task allocation

**H. Zhang, X. Wang, G. S. Kuo, T. M. Bohnert**
[references] [full-text]

Optimum Detection Location-Based Cooperative Spectrum Sensing in Cognitive Radio

Cognitive radio arises as a hot research issue in wireless communications recently, attributed to its capability of enhancing spectral efficiency and catering for the growing demand for bandwidth. As a good embodiment of cognitive radio’s unique feature, i.e. making use of every bit spectral resource, spectrum sensing plays a vital role in the implementation of cognitive radio. To alleviate negative effect on cooperative spectrum sensing brought by bit errors, we introduce a novel concept, i.e. Optimum Detection Location (ODL) and present two algorithms of different computational complexity for locating ODL, together with an ODL-Based cooperative spectrum sensing scheme, with the motivation to exploit the gain derived from geographic advantages and multiuser diversity. Numerical and simulation results both demonstrate that our proposed spectrum sensing scheme can significantly improve the sensing performance in the case of reporting channel with bit errors.

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Keywords: Cognitive radio, spectrum sensing, Wireless Region Area Network (WRAN), Optimum Detection Location (ODL).

**S. Tascioglu, O. Ureten, Z. Telatar**
[references] [full-text]

Impact of Noise Power Uncertainty on the Performance of Wideband Spectrum Segmentation

The objective of this work is to investigate the impact of noise uncertainty on the performance of a wideband spectrum segmentation technique. We define metrics to quantify the degradation due to noise uncertainty and evaluate the performance using simulations. Our simulation results show that the noise uncertainty has detrimental effects especially for low SNR users.

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Keywords: Cognitive radio, spectrum sensing, wideband RF spectrum monitoring, noise uncertainty, Markov chain Monte Carlo

**S. M. Kamruzzaman, Md. Abdul Hamid, M. Abdullah-Al-Wadud**
[references] [full-text]

An Energy Efficient MAC Protocol for QoS Provisioning in Cognitive Radio Ad Hoc Networks

The explosive growth in the use of real-time applications on mobile devices has resulted in new challenges to the design of medium access control (MAC) protocols for ad hoc networks. In this paper, we propose an energy efficient cognitive radio (CR) MAC protocol for QoS provisioning called ECRQ-MAC, which integrate the spectrum sensing at physical (PHY) layer and the channel-timeslots allocation at MAC layer. We consider the problem of providing QoS guarantee to CR users as well as to maintain the most efficient use of scarce bandwidth resources. The ECRQ-MAC protocol exploits the advantage of both multiple channels and TDMA, and achieves aggressive power savings by allowing CR users that are not involved in communication to go into sleep mode. The proposed ECRQ-MAC protocol allows CR users to identify and use the unused frequency spectrum of licensed band in a way that constrains the level of interference to the primary users (PUs). Our scheme improves network throughput significantly, especially when the network is highly congested. The simulation results show that our proposed protocol successfully exploits multiple channels and significantly improves network performance by using the licensed spectrum opportunistically and protects QoS provisioning over cognitive radio ad hoc networks.

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Keywords: Cognitive radio, multichannel MAC, energy efficiency, QoS, ad hoc networks, frequency spectrum, TDMA, channel sensing.

**J. Trdlicka, Z. Hanzalek**
[references] [full-text]

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This work proposes a distributed algorithm for energy optimal routing in a wireless sensor network. The routing problem is described as a mathematical problem by the minimum-cost multi-commodity network flow problem. Due to the separability of the problem, we use the duality theorem to derive the distributed algorithm. The algorithm computes the energy optimal routing in the network without any central node or knowledge of the whole network structure. Each node only needs to know the flow which is supposed to send or receive and the costs and capacities of the neighboring links. An evaluation of the presented algorithm on benchmarks for the energy optimal data flow routing in sensor networks with up to 100 nodes is presented.

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Keywords: Routing, In-network distributed algorithms, Multi-commodity network flow, Dual decomposition

**R. Marsalek, M. Nekovee**
[full-text]

Guest Editorial: Cognitive Radio Communications and Software Defined Radio

**H. Henniger, A. Ludwig, J. Horwath**
[references] [full-text]

Performance Bounds of DPSK and OOK for Low Elevation Optical LEO Downlinks

Optical wireless LEO downlinks are seen as an emerging solution to increase available bandwidth to multigigabits per second. One of the biggest challenges is the impact of the atmosphere on the optical signal. The atmosphere causes time-varying link degradation due to index of refraction turbulence, especially at low elevation angles. Since the influence of the turbulence for low elevation downlinks is hardly investigated we perform numerical propagation simulations in order to achieve reliable received signal statistics. These results are further utilized to evaluate performance bounds of optical wireless systems from an information theory perspective. We focus on the two most common optical wireless systems, i.e. NRZ-DPSK and NRZ-OOK. This work shows that under low elevation angles acceptable quality of service can only be reached with high code rates.

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Keywords: Free-space optical communications, channel capacity, index of refraction turbulence, fading, LEO downlink, system performance

**F. Nadeem, T. Javornik, E. Leitgeb, V. Kvicera, G. Kandus**
[references] [full-text]

Continental Fog Attenuation Empirical Relationship from Measured Visibility Data

Free Space Optics (FSO) has the great potential for future communication applications. However, weather influenced reduced availability had been the main cause for its restricted growth. Among different weather influences fog plays the major role. A new model generalized for all FSO wavelengths, has been proposed for the prediction of continental fog attenuation using visibility data. The performance of the proposed model has been compared with well known models for measured attenuation data of Continental fog. The comparison has been performed in terms of Root Mean Square Error (RMSE).

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Keywords: FSO, attenuation, simulation, fog, model comparison.

**X. Zhao, S. Huang**
[references] [full-text]

Influence of Sea Surface Roughness on the Electromagnetic Wave Propagation in the Duct Environment

This paper deals with a study of the influence of sea surface roughness on the electromagnetic wave propagation in the duct environment. The problem of electromagnetic wave propagation is modeled by using the parabolic equation method. The roughness of the sea surface is computed by modifying the smooth surface Fresnel reflection coefficient to account for the reduction in the specular reflection due to the roughness resulting from sea wind speed. The propagation model is solved by the mixed Fourier split-step algorithm. Numerical experiments indicate that wind-driven roughened sea surface has an impact on the electromagnetic wave propagation in the duct environment, and the strength is intensified along with the increment of sea wind speeds and/or the operating frequencies. In a fixed duct environment, however, proper disposition of the transmitter could reduce these impacts.

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Keywords: Electromagnetic wave propagation, parabolic equation, sea wind speed, evaporation duct.

**V. Prajzler, O. Lyutakov, I. Huttel, J. Spirkova, V. Jerabek**
[references] [full-text]

Design of Polymer Wavelength Splitter 1310 nm/1550 nm Based on Multimode Interferences

We report about design of 1x2 1310/1550 nm optical wavelength division multiplexer based on polymer waveguides. The polymer splitter was designed by using RSoft software based on beam propagation method. Epoxy novolak resin polymer was used as core waveguides layer, silicon substrate with silica layer was used as buffer layer and polymethylmethacrylate was used as protection cover layer. The simulation shows that the output energy for the fundamental mode is 67.1 % for 1310 nm and 67.8 % for 1550 nm wavelength.

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Keywords: Multimode Interference couplers, polymer optical waveguides, Epoxy Novolak Resin, beam propagation method

**L. Subrt, D. Grace, P. Pechac**
[references] [full-text]

Controlling the Short-Range Propagation Environment Using Active Frequency Selective Surfaces

This paper deals with a new approach to the control of the propagation environment in indoor scenarios using intelligent walls. The intelligent wall is a conventional wall situated inside a building, but equipped with an active frequency selective surface and sensors. The intelligent wall can be designed as a self-configuring and self-optimizing autonomous part of a collaborative infrastructure working within a high-capacity mobile radio system. The paper shows how such surfaces can be used to adjust the electromagnetic characteristics of the wall in response to changes in traffic demand, monitored using a network of sensors, thereby controlling the propagation environment inside the building. Some of the potential problems (mainly controlling coverage and interference) relating to an increased usage of wireless systems both inside and outside buildings are discussed and possible solutions using intelligent walls with the active FSS are suggested. The positive influence of intelligent walls on system performance is shown and results obtained from the simulations are shown and discussed.

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Keywords: Frequency Selective Surfaces, cognitive networks, intelligent infrastructure, indoor propagation modeling

**O. Baran, M. Kasal**
[references] [full-text]

Modeling of the Simultaneous Influence of the Thermal Noise and the Phase Noise in Space Communication Systems

Our work deals with studies of a noise behavior in space communication systems. Two most important noise types the additive thermal noise and the multiplicative phase noise, respectively, are included. A simple model of the narrowband communication system is created and simulated in the Ansoft Designer system simulator. The additive thermal noise is modeled as AWGN in a communication channel. The phase noise is produced in transmitter and receiver oscillators. The main intention is to investigate the receiver filter bandwidth decrease effect on powers of both noise types. Results proposed in this paper show that for defined system conditions and for a certain filter bandwidth value, the power of the multiplicative phase noise equals to the additive thermal noise power. Another decrease of the filter bandwidth causes the phase noise power exceeding. To demonstrate the noise behavior transparently, input system parameters are properly selected. All simulation results are documented by theoretical calculations. Simulation outcomes express a good coincidence with presumptions and calculations.

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Keywords: Ansoft Designer, thermal noise, AWGN, phase noise, FIR filter, noise bandwidth.

**P. Tosovsky, D. Valuch**
[references] [full-text]

Improvement of RF Vector Modulator Performance by Feed-forward Based Calibration

RF Vector Modulator enables independent control of a narrowband RF signal amplitude and phase. Unfortunately practical realization of an analog vector modulator suffers from misbalances and imperfections in the I and Q signal paths. Use of a feed-forward based calibration can compensate for them and significantly improve RF performance and control accuracy of a real vector modulator. Achieved improvements and results on a small series of vector modulator based phase shifters using feed-forward calibration are presented.

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Keywords: Phase shifter, vector modulator, calibration, feed-forward, phase error, set point

**P. Vsetula, Z. Raida**
[references] [full-text]

Sierpinski-Based Conical Monopole Antenna

Planar Sierpinski monopole exhibits a multi-band behavior, but its parameters in operation frequency bands are not optimal. By mapping the Sierpinski monopole on a conical surface, a symmetrical three-dimensional (3-D) structure is obtained. In this way, a larger bandwidth and a better radiation pattern is achieved. The symmetrical 3D Sierpinski-based monopole is an original contribution of this paper. In the paper, different versions of the conical Sierpinski-based monopole are designed, and results of simulations performed in CST Microwave Studio are mutually compared. Then, the simulated versions of the conical monopole are optimized according to specified criteria. The optimized conical Sierpinski-based monopole is manufactured and its properties are experimentally verified. Results of measuring the Sierpinski-based conical monopole antenna are published here for the first time.

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Keywords: Sierpinski monopole, multi-band antenna, conformal antenna, fractals, conical monopole.

**V. Schejbal, J. Pidanic**
[references] [full-text]

Broadband Approximations for Doubly Curved Reflector Antenna

The broadband approximations for shaped-beam doubly curved reflector antennas with primary feed (rectangular horn) producing uniform amplitude and phase aperture distribution are derived and analyzed. They are very valuable for electromagnetic compatibility analyses both from electromagnetic interference and susceptibility point of view, because specialized more accurate methods such as physical optics are only used by antenna designers. To allow quick EMC analyses, typical values, beamwidth changes, sidelobe levels and aperture efficiencies are given for frequency changes approximately up to four times operating frequency. A comparison of approximated and measured patterns of doubly curved reflector antennas shows that the given approximation could be reliably used for analyses of pattern changes due to very broad frequency changes.

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Keywords: Broadband approximation, radiation patterns, shaped-beam reflector antennas, doubly curved reflector, electromagnetic compatibility

**E. Demircioglu, M. H. Sazli**
[references] [full-text]

Behavioral Modeling of a C-Band Ring Hybrid Coupler Using Artificial Neural Networks

Artificial Neural Networks (ANNs) gained importance on the RF microwave (MW) design area and behavioral modeling of MW components in the past few decades. This paper presents a cost effective neural network (NN) approach to overcome design, modeling and optimization problems of an 180deg ring hybrid coupler operating in C-Band. The proposed NN model is trained by data sets obtained from electromagnetic (EM) simulators and neural test results are compared with simulator findings to determine the network accuracy. Moreover, necessary trade-offs are applied to improve the networks’ performance. Finally correlation factors, which are defined as comparison criteria between EM-simulator and proposed neural models, are calculated for each trade-off case.

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Keywords: Artificial Neural Networks (ANN), Ring Hybrid Coupler (RHC), C-band, optimization, behavioral modeling

**J. W. Horng**
[references] [full-text]

DVCCs Based High Input Impedance Voltage-Mode First-Order Filters Employing Grounded Capacitor and Resistor

A voltage-mode high input impedance first-order highpass, lowpass and allpass filters using two differential voltage current conveyors (DVCCs), one grounded capacitor and one grounded resistor is presented. The highpass, lowpass and allpass signals can be obtained simultaneously from the circuit configuration. The suggested filter uses a canonical number of passive components without requiring any component matching condition. The simulation results confirm the theoretical analysis.

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Keywords: Current conveyors, first-order, allpass filter, analog circuit design

**S. Minaei, E. Yuce**
[references] [full-text]

New Squarer Circuits and a Current-Mode Full-Wave Rectifier Topology Suitable for Integration

In this paper, three squarer configurations and a current-mode (CM) full-wave rectifier circuit are suggested. The first and second squarer configurations respectively use two PMOS and two NMOS transistors while the third one employs three PMOS and one NMOS transistors. A CM full-wave rectifier with high output impedance current is developed. All of the proposed circuits provide several advantages such as low number of components and less power consumption. The proposed circuits are simulated using SPICE program to demonstrate their performance and workability.

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Keywords: CMOS, squarer circuit, rectifier, current-mode

**G. Koukiou , C. Psychalinos**
[references] [full-text]

Modular Filter Structures Using Current Feedback Operational Amplifiers

The concept of the wave filtering is followed in the derivation of high-order filter topologies by employing Current Feedback Operational Amplifiers as active blocks. For this purpose, the wave equivalent of an appropriate passive element chosen to be the elementary building block is introduced. As the wave equivalents of the other passive elements are derived by performing appropriate manipulations in the configuration of the wave equivalent of the elementary building block, an attractive characteristic offered by the derived filter topologies is the modularity of their structures. The validity of the proposed method is verified through experimental results in the case of a 3rd-order lowpass filter.

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Keywords: Current feedback operational amplifiers, continuous-time filters, wave active filters, analog signal processing.

**Y. Li**
[references] [full-text]

Electronically Tunable Current-Mode Quadrature Oscillator Using Single MCDTA

This paper presents a modified current differencing transconductance amlpifier (MCDTA) and the MCDTA based quadrature oscillator. The oscillator is current-mode and provides current output from high output impedance terminals. The circuit uses only one MCDTA and two grounded capacitors, and is easy to be integrated. Its oscillation frequency can be tuned electronically by tuning bias currents of MCDTA. Finally, frequency error is analyzed. The results of circuit simulations are in agreement with theory.

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Keywords: quadrature sinusoidal oscillator; current-mode circuit; Low-component-count ; MCDTA

**P. Kejik, S. Hanus, J. Blumenstein**
[references] [full-text]

Advanced Fuzzy Logic Based Admission Control for UMTS System

The capacity of CDMA (Code Division Multiple Access) systems is interference limited. Therefore radio resources management (RRM) functions are used. They are responsible for supplying optimum coverage, ensuring efficient use of physical resources, and providing the maximum planned capacity. This paper deals with admission control techniques for UMTS (Universal Mobile Telecommunication System). A UMTS system model and four fuzzy logic based admission control algorithms are presented in this paper. Two new versions of fuzzy logic based admission control algorithms are presented there. All algorithms are mutually compared via simulations. Simulations show that the novel advanced fuzzy algorithm outperforms the other simulated algorithms (in terms of blocking probability, dropping probability and the number of active UEs in cell).

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Keywords: UMTS, CDMA, admission control, fuzzy logic

**Md. Masud Rana, J. Kim, W.-K. Cho**
[references] [full-text]

LMS Based Adaptive Channel Estimation for LTE Uplink

In this paper, a variable step size based least mean squares (LMS) channel estimation (CE) algorithm is presented for a single carrier frequency division multiple access(SC-FDMA) system under the umbrella of the long term evolution (LTE). This unbiased CE method can automatically adapts the weighting coefficients on the channel condition. Therefore, it does not require knowledge of channel,and noise statistics. Furthermore, it uses a phase weighting scheme to eliminate the signal fluctuations due to noise and decision errors. Such approaches can guarantee the convergence towards the true channel coefficient. The mean and mean square behaviors of the proposed CE algorithm are also analyzed. With the help of theoretical analysis and simulation results, we prove that the proposed algorithm outperforms the existing algorithms in terms of mean square error (MSE) and bit error rate (BER) by more than around 2.5dB.

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Keywords: SF-FDMA, PAPR, LMS, NLMS,VSS-LMS, RLS, LTE

**K. B. Baltzis**
[references] [full-text]

On the Effect of Channel Impairments on VANETs Performance

The primary means of studying the performance of vehicular ad hoc networks (VANETs) are computer simulations. Nowadays, the development of analytical models and the use of hybrid simulations that combine analytical modeling with discrete-event simulation are of great interest due to the significant reduction in computational cost. In this paper, we extend previous work in the area by suggesting an analytical model that includes distance-dependent losses, shadowing and small-scale fading. Closed-form expressions for the packet reception probability and the packet forwarding distance in the absence of simultaneous transmissions are presented. Numerical simulations validate the proposed formulation. The impact of path loss and fading on network throughput is explored. Interesting results that shows the efficacy of the approach are provided. The derived formulation is a useful tool for the modeling and analysis of vehicular communication systems.

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Keywords: VANET, packet reception, hop count, packet forwarding distance, composite fading channel, path loss.

**S. Mota, M. Outeiral Garcia, A. Rocha, F. Perez-Fontan**
[references] [full-text]

Estimation of the Radio Channel Parameters using the SAGE Algorithm

This paper presents the problem of estimating the parameters of a given number of superimposed signals, as is the case of the received signal in wireless communications. Based on the description of the received signal in the frequency domain, one version of the SAGE (Space-Alternating Generalized Expectation-Maximization) algorithm is presented, allowing the estimation, for each impinging ray, the delay, azimuth, elevation and complex amplitude. Ray retrieval results are presented in synthetic channels, using data generated with the extended Saleh Valenzuela (ESV) model, and also in real channels.

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Keywords: Parameter estimation, SAGE algorithm, radio channel measurements, multipath components

**L. Polak, T. Kratochvil**
[references] [full-text]

Simulation and Measurement of the Transmission Distortions of the Digital Television DVB-T/H Part 3: Transmission in Fading Channels

The paper deals with the third (and last) part of results of the Czech Science Foundation research project that was aimed into the simulation and measurement of the transmission distortions of the digital terrestrial television according to DVB-T/H standards. In this part the transmission of the digital television according to DVB-T/H standard over the fading channels and their models and profiles for fixed, portable and mobile reception is analyzed. Impact of the fading channels and their models on Modulation Error Rate from I/Q constellations and Bit Error Rates before and after Viterbi decoding in DVB-T/H signal decoding is presented.

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Keywords: Digital television, fading channel, fixed reception, portable reception, mobile reception, DVB-T/H

**M. R. Dincic, Z. H. Peric**
[references] [full-text]

Log-Polar Quantizer with the Embedded G.711 Codec

In this paper a new two-dimensional vector quantizer for memoryless Gaussian source, realized in polar coordinates, is proposed. The G.711 codec is embedded in our vector quantizer, and therefore our vector quantizer is compatible with the G.711 codec. It is simple for realization and it has much better performances, compared to the G.711 codec, such as much higher SQNR (signal-to-quantization noise ratio) for the same bit-rate, or bit-rate decrease for the same SQNR. The G.711 codec is widely used in many systems, especially in PSTN (public switched telephone network). Due to compatibility with the G.711 standard, our vector quantizer can be realized with simple software modification of the existing the G.711 codec, and therefore it can be very easily implemented in PSTN and other systems. So, small investments are needed for wide implementation of our model, but significant improvement of performances can be obtained.

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Keywords: The G.711 standard, two-dimensional quantizer, polar coordinates, compatibility

**D.Brodic, Z. Milivojevic**
[references] [full-text]

Optimization of the Gaussian Kernel Extended by Binary Morphology for Text Line Segmentation

In this paper, an approach for text line segmentation by algorithm with the implementation of the Gaussian kernel is presented. As a result of algorithm, the growing area around text is exploited for text line segmentation. To improve text line segmentation process, isotropic Gaussian kernel is extended by dilatation. Furthermore, algorithms with isotropic and extended Gaussian kernels are examined and evaluated under different text samples. Results are given and comparative analysis is made for these algorithms. From the obtained results, optimization of the parameters defining extended Gaussian kernel dimension is proposed. The presented algorithm with the extended Gaussian kernel showed robustness for different types of text samples.

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**S. A. Chatzichristofis, A. Arampatzis, Y. S. Boutalis**
[references] [full-text]

Investigating the Behavior of Compact Composite Descriptors in Early Fusion, Late Fusion and Distributed Image Retrieval

In Content-Based Image Retrieval (CBIR) systems, the visual content of the images is mapped into a new space named the feature space. The features that are chosen must be discriminative and sufficient for the description of the objects. The key to attaining a successful retrieval system is to choose the right features that represent the images as unique as possible. A feature is a set of characteristics of the image, such as color, texture, and shape. In addition, a feature can be enriched with information about the spatial distribution of the characteristic that it describes. Evaluation of the performance of low-level features is usually done on homogenous benchmarking databases with a limited number of images. In real-world image retrieval systems, databases have a much larger scale and may be heterogeneous. This paper investigates the behavior of Compact Composite Descriptors (CCDs) on heterogeneous databases of a larger scale. Early and late fusion techniques are tested and their performance in distributed image retrieval is calculated. This study demonstrates that, even if it is not possible to overcome the semantic gap in image retrieval by feature similarity, it is still possible to increase the retrieval effectiveness.

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Keywords: CBIR, Compact Composite Descriptors, Early Fusion, Late Fusion, Distributed Image Retrieval.

**F. A. Mianji, Y. Zhang, A. Babakhani**
[references] [full-text]

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Hyperspectral (HS) imaging is measuring the radiance of materials within each pixel area at a large number of contiguous spectral wavelength bands. The key spatial information such as small targets and border lines are hard to be precisely detected from HS data due to the technological constraints. Therefore, the need for image processing techniques is an important field of research in HS remote sensing. A novel semisupervised spatial-spectral data fusion method for resolution enhancement of HS images through maximizing the spatial correlation of the endmembers (signature of pure or purest materials in the scene) using a superresolution mapping (SRM) technique is proposed in this paper. The method adopts a linear mixture model and a fully constrained least squares spectral unmixing algorithm to obtain the endmember abundances (fractional images) of HS images. Then, the extracted endmember distribution maps are fused with the spatial information using a spatial-spectral correlation maximizing model and a learning-based SRM technique to exploit the subpixel level data. The obtained results validate the reliability of the technique for key information retrieval. The proposed method is very efficient and is low in terms of computational cost which makes it favorable for real-time applications.

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Keywords: Key information retrieval, hyperspectral imagery, material radiance, spectral unmixing, superresolution