International Journal of Antennas and Propagation http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. On the Bivariate Nakagami-Lognormal Distribution and Its Correlation Properties Mon, 18 Aug 2014 06:59:00 +0000 http://www.hindawi.com/journals/ijap/2014/328732/ The bivariate Nakagami-lognormal distribution used to model the composite fast fading and shadowing has been examined exhaustively. In particular, we have derived the joint probability density function, the cross-moments, and the correlation coefficient in power terms. Also, two procedures to generate two correlated Nakagami-lognormal random variables are described. These procedures can be used to evaluate the robustness of the sample correlation coefficient distribution in both macro- and microdiversity scenarios. It is shown that the bias and the standard deviation of this sample correlation coefficient are substantially high for large shadowing standard deviations found in wireless communication measurements, even if the number of observations is considerable. Juan Reig, Lorenzo Rubio, and Vicent M. Rodrigo-Peñarrocha Copyright © 2014 Juan Reig et al. All rights reserved. Measurement-Based LoS/NLoS Channel Modeling for Hot-Spot Urban Scenarios in UMTS Networks Sun, 17 Aug 2014 12:21:59 +0000 http://www.hindawi.com/journals/ijap/2014/454976/ A measurement campaign is introduced for modeling radio channels with either line-of-sight (LoS) or non-line-of-sight (NLoS) connection between user equipment (UE) and NodeB (NB) in an operating universal mobile telecommunications system. A space-alternating generalized expectation-maximization (SAGE) algorithm is applied to estimate the delays and the complex attenuations of multipath components from the obtained channel impulse responses. Based on a novel LoS detection method of multipath parameter estimates, channels are classified into LoS and NLoS categories. Deterministic models which are named “channel maps” and fading statistical models have been constructed for LoS and NLoS, respectively. In addition, statistics of new parameters, such as the distance between the NB and the UE in LoS/NLoS scenarios, the life-distance of LoS channel, the LoS existence probability per location and per NB, the power variation at LoS to NLoS transition and vice versa, and the transition duration, are extracted. These models are applicable for designing and performance evaluation of transmission techniques or systems used by distinguishing the LoS and NLoS channels. Jiajing Chen, Xuefeng Yin, Li Tian, Nan Zhang, Yongyu He, Xiang Cheng, Weiming Duan, and Silvia Ruiz Boqué Copyright © 2014 Jiajing Chen et al. All rights reserved. Application of Hybrid Finite Element-Boundary Integral Algorithm for Solving Electromagnetic Scattering from Multiple Objects over Rough Sea Surface Wed, 13 Aug 2014 11:39:25 +0000 http://www.hindawi.com/journals/ijap/2014/301934/ A hybrid algorithm of the finite element method (FEM) is presented to solve two-dimensional (2D) scattering from multiple dielectric objects above the rough sea surface. Compared with traditional FEM based on approximate absorbing boundaries, FEM based on the boundary integral method (BIM) can reduce the calculational region and solution time of the scattering problem. In the hybrid method, the whole computational region is divided into the sea surface and multiple isolate interior regions for the dielectric objects. FEM is only used to simulate the scattering from multiple interior regions enclosing the objects, whereas the large sea is considered exactly by BIM. The coupled interaction among the isolate interior regions and the sea can be taken into account by BIM. The hybrid technique presented here is efficient and versatile for addressing scattering from multiple arbitrary targets above rough sea surfaces. Scattering properties of multiple dielectric objects above the sea surface under different conditions are discussed in detail. Run-Wen Xu and Li-Xin Guo Copyright © 2014 Run-Wen Xu and Li-Xin Guo. All rights reserved. Advanced MIMO Techniques in the Heterogeneous Networks Tue, 12 Aug 2014 13:08:35 +0000 http://www.hindawi.com/journals/ijap/2014/193954/ Xiang Zhang, Lin Zhang, Guangyue Lu, Xiaoli Chu, and Yulong Zou Copyright © 2014 Xiang Zhang et al. All rights reserved. Knowledge-Aided STAP Using Low Rank and Geometry Properties Tue, 12 Aug 2014 12:40:55 +0000 http://www.hindawi.com/journals/ijap/2014/196507/ This paper presents knowledge-aided space-time adaptive processing (KA-STAP) algorithms that exploit the low-rank dominant clutter and the array geometry properties (LRGP) for airborne radar applications. The core idea is to exploit the clutter subspace that is only determined by the space-time steering vectors, by employing the Gram-Schmidt orthogonalization approach to compute the clutter subspace. Simulation results illustrate the effectiveness of our proposed algorithms. Zhaocheng Yang, Rodrigo C. de Lamare, Xiang Li, and Hongqiang Wang Copyright © 2014 Zhaocheng Yang et al. All rights reserved. Graph-Based Resource Allocation for D2D Communications Underlying Cellular Networks in Multiuser Scenario Tue, 12 Aug 2014 11:41:20 +0000 http://www.hindawi.com/journals/ijap/2014/783631/ With the characteristics of considerable user equipment, massive traffic and numerous local services, but limited frequency resources, the mobile communications in the future require efficient use of frequency resources. Device-to-device (D2D) communications underlying cellular networks have been considered as a promising solution to improve the resources utilization in local scenario. In this paper, we investigated the resources allocation problem in multiuser scenario and proposed a graph-based resources allocation scheme which can achieve suboptimal performance but with low computational complexity and less feedback information. Bin Guo, Shaohui Sun, and Qiubin Gao Copyright © 2014 Bin Guo et al. All rights reserved. Joint Two-Dimensional Ambiguity Resolving Based on Space-Time Filtering for MIMO-SAR Tue, 12 Aug 2014 10:54:54 +0000 http://www.hindawi.com/journals/ijap/2014/452141/ In order to resolve the range and azimuth ambiguity in MIMO-SAR imaging, this paper proposed a joint two-dimensional ambiguity resolving method based on space-time filtering, which according to the ambiguity in different subscene is relative to different nearest echo range, and different azimuth time is relative to different instantaneous incidence angle, to make two-dimensional space-time steering vector for resolving ambiguity of the echo, which also can finish the imaging processing at the same time. Simulation results validate the proposed processing approach for the MIMO-SAR system. Ping-ping Huang, Hua-sheng Li, Sheng Zhang, and Guang-Cai Sun Copyright © 2014 Ping-ping Huang et al. All rights reserved. The Radiation Problem from a Vertical Hertzian Dipole Antenna above Flat and Lossy Ground: Novel Formulation in the Spectral Domain with Closed-Form Analytical Solution in the High Frequency Regime Tue, 12 Aug 2014 09:45:22 +0000 http://www.hindawi.com/journals/ijap/2014/989348/ We consider the problem of radiation from a vertical short (Hertzian) dipole above flat lossy ground, which represents the well-known “Sommerfeld radiation problem” in the literature. The problem is formulated in a novel spectral domain approach, and by inverse three-dimensional Fourier transformation the expressions for the received electric and magnetic (EM) field in the physical space are derived as one-dimensional integrals over the radial component of wavevector, in cylindrical coordinates. This formulation appears to have inherent advantages over the classical formulation by Sommerfeld, performed in the spatial domain, since it avoids the use of the so-called Hertz potential and its subsequent differentiation for the calculation of the received EM field. Subsequent use of the stationary phase method in the high frequency regime yields closed-form analytical solutions for the received EM field vectors, which coincide with the corresponding reflected EM field originating from the image point. In this way, we conclude that the so-called “space wave” in the literature represents the total solution of the Sommerfeld problem in the high frequency regime, in which case the surface wave can be ignored. Finally, numerical results are presented, in comparison with corresponding numerical results based on Norton’s solution of the problem. K. Ioannidi, Ch. Christakis, S. Sautbekov, P. Frangos, and S. K. Atanov Copyright © 2014 K. Ioannidi et al. All rights reserved. Network-Coded Relaying in Multiuser Multicast D2D Network Tue, 12 Aug 2014 08:58:27 +0000 http://www.hindawi.com/journals/ijap/2014/589794/ D2D communication trades short-range communication for achieving high communication rate and short communication latency. Relay aided D2D communication can further tackle the problem of intermediate obstacles blocking the communication. In this work, multidevice multicast communication via a layer of parallel relay nodes is considered. Two relaying strategies, respectively, called the conventional relaying (CR) and network-coded relaying (NCR), are proposed. The throughput of these two schemes is analytically derived and evaluated through numerical study. Theoretically, NCR shows advantage over CR in twofold: one is higher throughput and the other is requiring less relay nodes and, hence, consuming less aggregate power. Numerical studies verify the analysis and show that the throughput performance gap between the two schemes increases significantly, actually exponentially with the number of devices. Mingjun Dai, Shengli Zhang, Hui Wang, Bin Chen, Xiaohui Lin, Hongwei Liu, and Li Zhang Copyright © 2014 Mingjun Dai et al. All rights reserved. Near-Field to Far-Field Transformation Techniques with Spiral Scannings: A Comprehensive Review Sun, 10 Aug 2014 00:00:00 +0000 http://www.hindawi.com/journals/ijap/2014/143084/ An overview of the near-field-far-field (NF-FF) transformation techniques with innovative spiral scannings, useful to derive the radiation patterns of the antennas commonly employed in the modern wireless communication systems, is provided in this paper. The theoretical background and the development of a unified theory of the spiral scannings for quasi-spherical and nonspherical antennas are described, and an optimal sampling interpolation expansion to evaluate the probe response on a quite arbitrary rotational surface from a nonredundant number of its samples, collected along a proper spiral wrapping it, is presented. This unified theory can be applied to spirals wrapping the conventional scanning surfaces and makes it possible to accurately reconstruct the NF data required by the NF-FF transformation employing the corresponding classical scanning. A remarkable reduction of the measurement time is so achieved, due to the use of continuous and synchronized movements of the positioning systems and to the reduced number of needed NF measurements. Some numerical and experimental results relevant to the spherical spiral scanning case when dealing with quasi-planar and electrically long antennas are shown. Renato Cicchetti, Francesco D’Agostino, Flaminio Ferrara, Claudio Gennarelli, Rocco Guerriero, and Massimo Migliozzi Copyright © 2014 Renato Cicchetti et al. All rights reserved. Fading Evaluation in the 60 GHz Band in Line-of-Sight Conditions Thu, 07 Aug 2014 10:55:03 +0000 http://www.hindawi.com/journals/ijap/2014/984102/ An exhaustive analysis of the small-scale fading amplitude in the 60 GHz band is addressed for line-of-sight conditions (LOS). From a measurement campaign carried out in a laboratory, we have estimated the distribution of the small-scale fading amplitude over a bandwidth of 9 GHz. From the measured data, we have estimated the parameters of the Rayleigh, Rice, Nakagami-m, Weibull, and - distributions for the small-scale amplitudes. The test of Kolmogorov-Smirnov (K-S) for each frequency bin is used to evaluate the performance of such statistical distributions. Moreover, the distributions of the main estimated parameters for such distributions are calculated and approximated for lognormal statistics in some cases. The matching of the above distributions to the experimental distribution has also been analyzed for the lower tail of the cumulative distribution function (CDF). These parameters offer information about the narrowband channel behavior that is useful for a better knowledge of the propagation characteristics at 60 GHz. J. Reig, M.-T. Martínez-Inglés, L. Rubio, V.-M. Rodrigo-Peñarrocha, and J.-M. Molina-García-Pardo Copyright © 2014 J. Reig et al. All rights reserved. Rigorous 2D Model for Study of Pulsed and Monochromatic Waves Propagation Near the Earth’s Surface Thu, 07 Aug 2014 00:00:00 +0000 http://www.hindawi.com/journals/ijap/2014/158297/ A model problem considered in the paper allows solving rather complex 2D problems of the electromagnetic wave propagation with a required accuracy using conventional personal computers. The problems are of great importance for the theory and practical applications. The association of FDTD schemes with exact absorbing conditions makes up the basis for constructing models of the kind. This approach reduces the original open initial boundary value problems to the equivalent closed problems which can be solved numerically using the standard grid methods. Seil S. Sautbekov, Yuriy K. Sirenko, Nataliya P. Yashina, and Aleksey A. Vertiy Copyright © 2014 Seil S. Sautbekov et al. All rights reserved. Low-Complexity Transmit Antenna Selection and Beamforming for Large-Scale MIMO Communications Wed, 06 Aug 2014 07:45:20 +0000 http://www.hindawi.com/journals/ijap/2014/159375/ Transmit antenna selection plays an important role in large-scale multiple-input multiple-output (MIMO) communications, but optimal large-scale MIMO antenna selection is a technical challenge. Exhaustive search is often employed in antenna selection, but it cannot be efficiently implemented in large-scale MIMO communication systems due to its prohibitive high computation complexity. This paper proposes a low-complexity interactive multiple-parameter optimization method for joint transmit antenna selection and beamforming in large-scale MIMO communication systems. The objective is to jointly maximize the channel outrage capacity and signal-to-noise (SNR) performance and minimize the mean square error in transmit antenna selection and minimum variance distortionless response (MVDR) beamforming without exhaustive search. The effectiveness of all the proposed methods is verified by extensive simulation results. It is shown that the required antenna selection processing time of the proposed method does not increase along with the increase of selected antennas, but the computation complexity of conventional exhaustive search method will significantly increase when large-scale antennas are employed in the system. This is particularly useful in antenna selection for large-scale MIMO communication systems. Kun Qian, Wen-Qin Wang, and Huaizong Shao Copyright © 2014 Kun Qian et al. All rights reserved. Indoor Massive MIMO Channel Modelling Using Ray-Launching Simulation Wed, 06 Aug 2014 07:42:58 +0000 http://www.hindawi.com/journals/ijap/2014/279380/ Massive multi-input multioutput (MIMO) is a promising technique for the next generation of wireless communication networks. In this paper, we focus on using the ray-launching based channel simulation to model massive MIMO channels. We propose one deterministic model and one statistical model for indoor massive MIMO channels, both based on ray-launching simulation. We further propose a simplified version for each model to improve computational efficiency. We simulate the models in indoor wireless network deployment environments and compare the simulation results with measurements. Analysis and comparison show that these ray-launching based simulation models are efficient and accurate for massive MIMO channel modelling, especially with application to indoor network planning and optimisation. Jialai Weng, Xiaoming Tu, Zhihua Lai, Sana Salous, and Jie Zhang Copyright © 2014 Jialai Weng et al. All rights reserved. A Fully Reconfigurable Polarimetric Phased Array Antenna Testbed Wed, 06 Aug 2014 05:50:08 +0000 http://www.hindawi.com/journals/ijap/2014/439606/ The configurable phased array demonstrator (CPAD) is a low-cost, reconfigurable, small-scale testbed for the dual-polarized array antenna and radar prototype. It is based on the concept that individual transmit and receive (TR) modules and radiating elements can be configured in different ways to study the impact of various array manifolds on radiation pattern performance. For example, CPAD is configured as (a) a 4 × 4 planar array, (b) a planar array with mirror configuration, and (c) a circular array to support the multifunctional phased array radar (MPAR) system risk reduction studies. System descriptions are given in detail, and measurements are made and results are analyzed. Sudantha Perera, Yu Pan, Yan Zhang, Xining Yu, Dusan Zrnic, and Richard Doviak Copyright © 2014 Sudantha Perera et al. All rights reserved. Rateless Space Time Block Code for Massive MIMO Systems Sun, 03 Aug 2014 06:33:36 +0000 http://www.hindawi.com/journals/ijap/2014/154261/ This paper presents a rateless space time block code (RSTBC) for massive MIMO systems. The paper illustrates the basis of rateless space time codes deployments in massive MIMO transmissions over wireless erasure channels. In such channels, data may be lost or is not decodable at the receiver due to a variety of factors such as channel fading, interference, or antenna element failure. We show that RSTBC guarantees the reliability of the system in such cases, even when the data loss rate is 25% or more. In such a highly lossy channel, the conventional fixed-rate codes fail to perform well, particularly when channel state information is not available at the transmitter. Simulation results are provided to demonstrate the BER performance and the spectral efficiency of the proposed scheme. Ali H. Alqahtani, Ahmed Iyanda Sulyman, and Abdulhameed Alsanie Copyright © 2014 Ali H. Alqahtani et al. All rights reserved. Capacity of κ-μ Shadowed Fading Channels Thu, 24 Jul 2014 12:07:05 +0000 http://www.hindawi.com/journals/ijap/2014/975109/ The ergodic capacity of fading channels modeled with a κ-μ shadowed distribution is investigated to derive closed-form expressions. The κ-μ shadowed distribution is of particular interest because it contains, as special cases, other classical ones like one-side Gaussian, Rayleigh, Rician, Nakagami-m, κ-μ, and Rician shadowed distributions. The paper discusses the physical meaning of the distribution parameter variations and also their impact on the channel capacity. These results can be used to study the behavior of different channels like the ones in underwater acoustic communications, land mobile satellite systems, body centric communications, and other wireless communication applications. The analytical closed-form expression results are validated with numerical simulations. Celia García-Corrales, Francisco J. Cañete, and José F. Paris Copyright © 2014 Celia García-Corrales et al. All rights reserved. Technique of Coaxial Frame in Reflection for the Characterization of Single and Multilayer Materials with Correction of Air Gap Thu, 24 Jul 2014 09:22:08 +0000 http://www.hindawi.com/journals/ijap/2014/324727/ Techniques based on fixture probes in reflection are used in microwave reflectometry as a novel diagnostic tool for detection of skin cancers, for complex permittivity measurements on liquid samples and oil shale, and for complex dielectric permittivity of animals’ organs and tissues measurements in microwave band for the needs of modern veterinary medicine. In this work, we have developed a technique to characterize multilayer materials in a broadband frequency range. A coaxial probe in reflection has been specially developed for microelectronic substrate. Using SMA connector, loss tangent of 10−4 and relative permittivity have been measured with an error of 0.145%. The extension of the coaxial probe in reflection technique to multilayer substrates such as Delrin and Teflon permitted to measure bilayer material provided the good knowledge of electrical parameters and dimensions of one layer. In the coaxial transmission line method, a factor that greatly influences the accuracy of the results is the air gaps between the material under test and the coaxial test fixture. In this paper, we have discussed the influence of the air gaps (using samples of 0.5 mm air gaps) and the measures that can be taken to minimize that influence when material is measured. The intrinsic values thus determined have been experimentally verified. We have described the structure of the test fixture, its calibration issues, and the experimental results. Finally, electromagnetism simulations showed that the best results can be obtained. Zarral Lamia, Djahli Farid, and Ndagijimana Fabien Copyright © 2014 Zarral Lamia et al. All rights reserved. A Passive Harmonic Tag for Humidity Sensing Wed, 23 Jul 2014 11:01:02 +0000 http://www.hindawi.com/journals/ijap/2014/670345/ This paper describes a passive harmonic tag for radio frequency identification (RFID) and wireless sensor applications. The tag uses a dual polarized UHF patch antenna as an input antenna. One of the outputs is connected to a frequency doubler, which consists of a Schottky diode with its output connected to a patch tuned at twice the input frequency. The other output of the input antenna feeds a DC power harvested converter that drives an oscillator which modulates its output signal by controlling the bias point of the Schottky diode. The antenna’s output is also used as a humidity sensor. To achieve this, the antenna is loaded with an interdigital capacitor with humidity-dependent capacitance. The antenna is consequently detuned when humidity varies, and therefore the second harmonic power is received. The tag is manufactured using standard fiberglass substrate. The basic theory of harmonic tag operation is described and compared with the standard backscattering approach. Experimental results with a proof of concept using commercial components are presented. Antonio Lazaro, Ramon Villarino, and David Girbau Copyright © 2014 Antonio Lazaro et al. All rights reserved. Capacity Estimation of the Very Short-Range Electromagnetic Underwater Channel Based on Measurements Tue, 22 Jul 2014 14:08:28 +0000 http://www.hindawi.com/journals/ijap/2014/318421/ The significant attenuation experienced by electromagnetic waves in sea water is the main reason why acoustic waves are generally preferred in underwater communication. Nevertheless, acoustic waves have various drawbacks. For example, they are negatively affected by factors such as mechanical noise, slow propagation speed, and, particularly, low bandwidth, which leads to digital links at a lower bit rate. However, in short-range links, these problems can be overcome by reconsidering the use of electric current communications. For instance, data collected by remote-control vehicles in offshore oil and gas and renewable energy plants can be transmitted at distances of even 1 m or less. This study uses previous frequency response measurements taken in deep water to explore the capacity of a short-range electromagnetic underwater channel. Because of water movement, the nonstatic position of the vehicle when the transmission occurs means that the channel is regarded as randomly time-variant. A statistical model is proposed and the ergodic capacity is calculated for a 7 MHz bandwidth channel at distances ranging from 0.5 m to 5 m as well as for different values of transmitter power. The results of this study reflect capacity values of tens of kbps at distances of approximately 5 m to several Mbps at distances of less than 1.5 m. Jesús López-Fernández, Unai Fernández-Plazaola, and Jose F. Paris Copyright © 2014 Jesús López-Fernández et al. All rights reserved. Path Loss Model with Antenna Height Dependency under Indoor Stair Environment Tue, 22 Jul 2014 11:22:55 +0000 http://www.hindawi.com/journals/ijap/2014/482615/ A novel, receiving antenna-height-dependent path loss model under indoor stair environment is presented. The effect of a cross-beam in the stairs is also considered. The proposed model can be applied to describe both of the line-of-sight (LOS) and the non-LOS (NLOS) cases. By using least square criterion, the parameters of proposed model are extracted. Finally, using the maximum likelihood estimation, the precision of the proposed model is evaluated by the standard deviation of shadowing. Yu Yu, Yang Liu, Wen-Jun Lu, and Hong-Bo Zhu Copyright © 2014 Yu Yu et al. All rights reserved. Yagi Array of Microstrip Quarter-Wave Patch Antennas with Microstrip Lines Coupling Tue, 22 Jul 2014 11:18:05 +0000 http://www.hindawi.com/journals/ijap/2014/102362/ A new kind of Yagi array of quarter-wave patch antennas is presented. The Yagi array has a low profile, a wide bandwidth, and a high gain. A main beam close to endfire is produced, with a vertical polarization in the horizontal plane. A set of microstrip lines are introduced between the driven element and the first director element to enhance the coupling between them, and therefore the bandwidth could be increased and the back lobes could be suppressed. Measured results show that the Yagi array with 4 elements generates a peak gain of about 9.7 dBi, a front-to-back ratio higher than 10 dB, and a 10 dB return loss band from 4.68 GHz to 5.24 GHz, with a profile of 1.5 mm and an overall size of 80 × 100 mm2. An increase of the number of director elements would enhance the gain and have the main beam pointing closer to endfire. Juhua Liu, Yue Kang, Jie Chen, and Yunliang Long Copyright © 2014 Juhua Liu et al. All rights reserved. Beamforming Techniques for Wireless MIMO Relay Networks Tue, 22 Jul 2014 09:07:58 +0000 http://www.hindawi.com/journals/ijap/2014/354714/ Athanasios G. Kanatas, Demosthenes Vouyioukas, Gan Zheng, and Laurent Clavier Copyright © 2014 Athanasios G. Kanatas et al. All rights reserved. A Single RF MIMO Loading Network for High-Order Modulation Schemes Tue, 22 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/ijap/2014/879127/ Recently, a novel MIMO transmitter architecture has been introduced that requires only a single radio-frequency (RF) chain and is built on parasitic antenna arrays. MIMO transmission in this case is achieved by shaping directly the radiation pattern with the aid of analog tunable loads attached to the parasitics. As it has been shown, such a single RF MIMO system can support all PSK modulation formats with purely imaginary loading values. This paper extends its capabilities and proposes a novel architecture for parasitic antennas that is able to provide complex loading values, even with a negative real part. Definitely, this will extend the flexibility of parasitic antennas to multiplex successfully over the air more complex signaling formats, for example, QAM signals. The bit error rate evaluation shows that the proposed architecture could be very promising in emerging devices and also illustrates its robustness under possible loading perturbations that might have been raised due to nonidealities in the design. Bo Han, Vlasis I. Barousis, Antonis Kalis, Constantinos B. Papadias, Athanasios G. Kanatas, and Ramjee Prasad Copyright © 2014 Bo Han et al. All rights reserved. Spatial Spectrum-Based Imaging for UWB Through-the-Wall MIMO Arrays Mon, 21 Jul 2014 14:23:19 +0000 http://www.hindawi.com/journals/ijap/2014/825403/ To keep the system complexity at a reasonable level and conform to the propagation demands, MIMO arrays are usually sparse in through-the-wall applications, which results in corrupted and gapped data. The corresponding imaging results are seriously affected by the high-level sidelobes. To solve this problem, a new imaging model for ultra-wideband (UWB) MIMO arrays is constructed via spatial spectrum theory in this paper. Based on the model, the characteristics of the spatial spectrum for the MIMO array and its effects on imaging are discussed. To improve the imaging quality, a through-the-wall imaging enhancement method is proposed via spatial spectrum estimation. Synthetic and experimental results show that, unlike the conventional amplitude weighting methods and nonlinear techniques, the proposed method can efficiently suppress sidelobes in the imagery, especially for the sparse MIMO array, and consequently improve the target image quality without degrading the mainlobe resolution. The proposed method has been successfully used in our real through-the-wall radar system. Biying Lu, Xin Sun, Yang Zhao, and Zhimin Zhou Copyright © 2014 Biying Lu et al. All rights reserved. SER Performance of Large Scale OFDM-SDMA Based Cognitive Radio Networks Mon, 21 Jul 2014 11:59:18 +0000 http://www.hindawi.com/journals/ijap/2014/594282/ This paper proposes an adaptive large scale multiple input multiple output-beamforming scheme (LSMIMO-BF) for uplink (UL) access in broadband wireless cognitive networks with multiple primary users (PUs) and secondary users (SUs) sharing the same spectrum and employing orthogonal frequency-division multiplexing (OFDM). The proposed algorithm seeks the optimal transmit/receive weight vectors that maximize the UL MIMO channel capacity for each cognitive user while controlling the interference levels to PUs. Under the assumption of very large number of antennas at the base station, a closed-form expression for the symbol error rate (SER) performance of the cognitive LSMIMO-OFDM system is derived and compared with the one based on conventional beamforming schemes such as MIMO-maximum ratio combining (MIMO-MRC). The analysis and simulation show that when SUs are transmitting with the proposed constrained capacity-aware (CCA) scheme, the total interference level at the primary base station is reduced and the SER of PUs is improved compared to the case when the secondary network is using conventional MIMO-MRC. It was also shown that, as the number of base station antennas becomes larger, the constraints imposed by the primary network could be relaxed and the symbol error rate (SER) of SUs is improved without harming the PUs performance. Mostafa Hefnawi Copyright © 2014 Mostafa Hefnawi. All rights reserved. Characterization of Path-Loss Disparity in Virtual Multiple-Input-Single-Output Links Mon, 21 Jul 2014 07:16:28 +0000 http://www.hindawi.com/journals/ijap/2014/650236/ Cooperative transmission (CT) is an effective technique to achieve spatial diversity in fading environments, where spatially separated wireless nodes collaborate to form a virtual antenna array or virtual multiple-input-multiple-output (VMISO) link. Many authors model the path loss of the VMISO link as though the elements in the virtual antenna array are colocated, even though they are spread out. In this paper, we show that the spreading causes a signal-to-noise-ratio (SNR) penalty of up to 3 dB. Moreover, in the high SNR regime, we show that the performance degradation caused by the path-loss disparity can be characterized equivalently by log-normal distribution. We use these two observations to propose a new CT link model, expressed in closed form as an outage probability based on the log-normal shadowing model. The quality of the model is evaluated by a statistical test based on Kolmogorov-Smirnov method. Haejoon Jung and Mary Ann Weitnauer Copyright © 2014 Haejoon Jung and Mary Ann Weitnauer. All rights reserved. Joint 2D Direction-of-Arrival and Range Estimation for Nonstationary Sources Thu, 17 Jul 2014 12:08:49 +0000 http://www.hindawi.com/journals/ijap/2014/849039/ Passive localization of nonstationary sources in the spherical coordinates (azimuth, elevation, and range) is considered, and a parallel factor analysis based method is addressed for the near-field parameter estimation problem. In this scheme, a parallel factor analysis model is firstly constructed by computing five time-frequency distribution matrices of the properly chosen observation data. In addition, the uniqueness of the constructed model is proved, and both the two-dimensional (2D) direction-of-arrival (DOA) and range can be jointly obtained via trilinear alternating least squares regression (TALS). The investigated algorithm is well suitable for near-field nonstationary source localization and does not require parameter-pairing or multidimensional search. Several simulation examples confirm the effectiveness of the proposed algorithm. Jian Chen, Hui Zhao, Xiaoying Sun, and Guohong Liu Copyright © 2014 Jian Chen et al. All rights reserved. Simulation of Airborne Antenna Array Layout Problems Using Parallel Higher-Order MoM Thu, 17 Jul 2014 10:31:49 +0000 http://www.hindawi.com/journals/ijap/2014/985367/ The parallel higher-order Method of Moments based on message passing interface (MPI) has been successfully used to analyze the changes in radiation patterns of a microstrip patch array antenna mounted on different positions of an airplane. The block-partitioned scheme for the large dense MoM matrix and a block-cyclic matrix distribution scheme are designed to achieve excellent load balance and high parallel efficiency. Numerical results demonstrate that the rigorous parallel Method of Moments can efficiently and accurately solve large complex electromagnetic problems with composite structures. Zhongchao Lin, Yu Zhang, Shugang Jiang, Xunwang Zhao, and Jingyan Mo Copyright © 2014 Zhongchao Lin et al. All rights reserved. Fast 3D Pattern Synthesis with Polarization and Dynamic Range Ratio Control for Conformal Antenna Arrays Thu, 17 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/ijap/2014/106741/ This paper proposes an iterative algorithm for the 3D synthesis of the electric far-field pattern of a conformal antenna array in the presence of requirements on both the polarization and the dynamic range ratio (DRR) of the excitations. Thanks to the use of selectable weights, the algorithm allows a versatile control of the DRR and of the polarization in a given angular region and requires a low CPU time to provide the array excitations. Furthermore, a modified version of the algorithm is developed to enable the optimization of the polarization state by phase-only control. Numerical results are presented to verify the usefulness of the proposed approach for the joint pattern and polarization synthesis of conformal arrays with reduced or even unitary DRR. Massimiliano Comisso and Roberto Vescovo Copyright © 2014 Massimiliano Comisso and Roberto Vescovo. All rights reserved.