International Journal of Antennas and Propagation http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . 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. Joint DOD and DOA Estimation for High Speed Target Using Bistatic MIMO Radar Wed, 16 Jul 2014 11:51:14 +0000 http://www.hindawi.com/journals/ijap/2014/914327/ In bistatic multiple-input multiple-output (MIMO) radar, range migration and invalidly synthesized virtual array resulting from the serious mismatch of matched filter make it difficult to estimate direction of departure (DOD) and direction of arrival (DOA) of high speed target using the traditional superresolution algorithms. In this study, a method for joint DOD and DOA estimation of high speed target using bistatic MIMO radar is proposed. After multiplying the received signals with the conjugate of the delayed versions of the transmitted signals, Fourier transform (FT) of the multiplied signals over both fast time and slow time is employed. Then, the target components of radar return corresponding to the different transmitted waveforms can be perfectly separated at the receivers by extracting the target frequency-domain data along slow-time frequency dimension when the delay between the transmitted signals and their subsequent returns is timed. By splicing the separated target components distributed along several range cells, the virtual array can be formed, and then DOD and DOA of high speed target can be estimated using the superresolution algorithm with the range migration and the mismatch of matched filter properly removed. Simulation results have proved the validity of the proposed algorithm. Jinli Chen, Jiaqiang Li, Peng Li, Yanping Zhu, and Weijun Long Copyright © 2014 Jinli Chen et al. All rights reserved. Research on Wideband Differential-Mode Current Injection Testing Technique Based on Directional Coupling Device Tue, 15 Jul 2014 11:59:25 +0000 http://www.hindawi.com/journals/ijap/2014/143068/ This paper presents a new kind of differential-mode current injection test method. The equal response voltage on the cable or the antenna port of the equipment under test (EUT) is regarded as equivalent principle for radiation and injection test. The injection and radiation response analysis model and the injection voltage source extrapolation model in high intensity radiated field are established. The conditions of using differential-mode current injection as a substitute for radiation are confirmed. On the basis of the theoretical analysis, the function and structure design scheme of the directional coupling device is proposed. The implementation techniques for the single differential-mode current injection method (SDMCI) and the double differential-mode current injection method (DDMCI) are discussed in detail. The typical nonlinear response interconnected systems are selected as the EUT. The test results verify the validity of the SDMCI and DDMCI test methods. Xiaodong Pan, Guanghui Wei, Xinfu Lu, Lisi Fan, and Xing Zhou Copyright © 2014 Xiaodong Pan et al. All rights reserved. MIMO-Based Forward-Looking SAR Imaging Algorithm and Simulation Tue, 15 Jul 2014 07:54:49 +0000 http://www.hindawi.com/journals/ijap/2014/783949/ Multiple-input multiple-output (MIMO) radar imaging can provide higher resolution and better sensitivity and thus can be applied to targets detection, recognition, and tracking. Missile-borne forward-looking SAR (MFL-SAR) is a new and special MIMO radar mode. It has advantage of two-dimensional (2D) imaging capability in forward direction over monostatic missile-borne SAR and airborne SAR. However, it is difficult to obtain accurate 2D frequency spectrum of the target echo signal due to the high velocity and descending height of this platform, which brings a lot of obstacles to imaging algorithm design. Therefore, a new imaging algorithm for MFL-SAR configuration based on the method of series reversion is proposed in this paper. This imaging method can implement range compression, secondary range compression (SRC), and range cell migration correction (RCMC) effectively. Finally, some simulations of point targets and comparison results confirm the efficiency of our proposed algorithm. Ziqiang Meng, Yachao Li, Shengqi Zhu, Yinghui Quan, Mengdao Xing, and Zheng Bao Copyright © 2014 Ziqiang Meng et al. All rights reserved. A Multiband Printed Log-Periodic Dipole Array for Wireless Communications Tue, 15 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/ijap/2014/646394/ A multiband printed Log-periodic dipole array (LPDA) antenna for wireless communications is presented. The antenna has been designed starting from Carrel’s theory, optimized using CST Microwave Studio 2012, and then realized. The comparison between simulated and measured results shows that the proposed antenna can be used for wireless communications both in the S (2.4–3 GHz) and in the C (5.2–5.8 GHz) frequency bands, with very good input matching and a satisfactory end-fire radiation pattern. Moreover, it has a compact size, is very easy to realize, and presents an excellent out-of-band rejection, without the use of stop-band filters, thus avoiding interference out of its operating frequency band. Giovanni Andrea Casula and Paolo Maxia Copyright © 2014 Giovanni Andrea Casula and Paolo Maxia. All rights reserved. Property Analysis of MIMO-Based Missile-Borne Forward-Looking SAR Mon, 14 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/ijap/2014/578792/ As a special multiple-input multiple-output (MIMO) radar networking mode, missile-borne forward-looking synthetic aperture radar (MFL-SAR) has many potential applications. This paper describes and analyzes properties of this new configuration. Range history and Doppler history are analyzed and derived using the designed geometric configuration. Then the expressions of range and Doppler resolution are determined based on the validity of two-dimensional (2D) resolution imaging capability. To help to design the proper system and motion parameters of this configuration, key parameters affecting the imaging ability are found out. Due to high velocities and accelerations of both transmitter and receiver, high-order terms in the slant range equation should be kept to reduce the approximation error. The range resolution and Doppler resolution of MFL-SAR are both space-variant and time-variant owing to the complexity of this configuration. The tiny changes of 2D resolution during the synthetic aperture time should be considered when designing the imaging algorithm of MFL-SAR. Yachao Li, Ziqiang Meng, Shengqi Zhu, Yinghui Quan, Mengdao Xing, and Zheng Bao Copyright © 2014 Yachao Li et al. All rights reserved. Planar MIMO Antenna with Slits for WBAN Applications Sun, 13 Jul 2014 14:57:56 +0000 http://www.hindawi.com/journals/ijap/2014/151425/ A planar MIMO antenna with slits for WBAN applications is proposed. The antenna consists of two PIFAs, ground pads, and two slits. By adding ground pads, the antenna size is reduced with improved impedance matching. Through two slits in a ground plane, the isolation characteristic is improved and the resonant frequency can be controlled. To analyze the antenna performance on a human body, the proposed antenna on a human equivalent flat phantom is investigated through simulations. Regardless of the existence of the phantom, the antenna operates in 2.4 GHz ISM band with the isolation higher than 18 dB. Do-Gu Kang, Jinpil Tak, and Jaehoon Choi Copyright © 2014 Do-Gu Kang et al. All rights reserved. Joint Direction-of-Departure and Direction-of-Arrival Estimation in a UWB MIMO Radar Detecting Targets with Fluctuating Radar Cross Sections Sun, 13 Jul 2014 07:33:04 +0000 http://www.hindawi.com/journals/ijap/2014/847815/ This paper presents a joint direction-of-departure (DOD) and direction-of-arrival (DOA) estimation in a multiple-input multiple-output (MIMO) radar utilizing ultra wideband (UWB) signals in detecting targets with fluctuating radar cross sections (RCS). The UWB MIMO radar utilized a combination of two-way MUSIC and majority decision based on angle histograms of estimated DODs and DOAs at each frequency of the UWB signal. The proposed angle estimation scheme was demonstrated to be effective in detecting targets with fluctuating RCS, compared to conventional spectra averaging method used in subband angle estimations. It was found that a wider bandwidth resulted in improved estimation performance. Numerical simulations along with experimental evaluations in a radio anechoic chamber are presented. Idnin Pasya, Naohiko Iwakiri, and Takehiko Kobayashi Copyright © 2014 Idnin Pasya et al. All rights reserved. Advances in the Statistical Characterization of Fading: From 2005 to Present Thu, 10 Jul 2014 11:55:16 +0000 http://www.hindawi.com/journals/ijap/2014/258308/ This review paper presents some of the most significant advances in statistical characterization of wireless communication fading. We will focus on the fundamental statistical characterizations of the fading distributions in terms of the probability density function (PDF), the cumulative density function (CDF), and the moment generating function (MGF). The period from 2005 to present will be considered in order to complement the information which can be found in the specialized literature like Simon and Alouini’s book on digital communications over fading channels. We present both the advances on classical fading models and a brief summary of some selected new fading models. Some open problems in the field will be also stated. José F. Paris Copyright © 2014 José F. Paris. All rights reserved. Performance Analysis of 3D Massive MIMO Cellular Systems with Collaborative Base Station Thu, 10 Jul 2014 11:46:56 +0000 http://www.hindawi.com/journals/ijap/2014/614061/ Massive MIMO have drawn considerable attention as they enable significant capacity and coverage improvement in wireless cellular network. However, pilot contamination is a great challenge in massive MIMO systems. Under this circumstance, cooperation and three-dimensional (3D) MIMO are emerging technologies to eliminate the pilot contamination and to enhance the performance relative to the traditional interference-limited implementations. Motivated by this, we investigate the achievable sum rate performance of MIMO systems in the uplink employing cooperative base station (BS) and 3D MIMO systems. In our model, we consider the effects of both large-scale and small-scale fading, as well as the spatial correlation and indoor-to-outdoor high-rise propagation environment. In particular, we investigate the cooperative communication model based on 3D MIMO and propose a closed-form lower bound on the sum rate. Utilizing this bound, we pursue a “large-system” analysis and provide the asymptotic expression when the number of antennas at the BS grows large, and when the numbers of antennas at transceiver grow large with a fixed ratio. We demonstrate that the lower bound is very tight and becomes exact in the massive MIMO system limits. Finally, under the sum rate maximization condition, we derive the optimal number of UTs to be served. Xingwang Li, Lihua Li, Ling Xie, Xin Su, and Ping Zhang Copyright © 2014 Xingwang Li et al. All rights reserved. Relay Selection and Subcarrier-Pair Based Energy-Efficient Resource Allocation for Multirelay Cooperative OFDMA Networks Thu, 10 Jul 2014 11:46:54 +0000 http://www.hindawi.com/journals/ijap/2014/461713/ Energy-efficient resource allocation is investigated for a relay-based multiuser cooperation orthogonal frequency division multiple access (OFDMA) uplink system with amplify-and-forward (AF) protocol for all relays. The objective is to maximize the total energy efficiency (EE) of the uplink system with consideration of some practical limitations, such as the individual power constraint for the users and relays and the quality of service (QoS) for every user. We formulate an energy-efficient resource allocation problem that seeks joint optimization of subcarrier pairing, relay selection, subcarrier assignment, and power allocation. Unlike previous optimization throughput models, we transform the considered EE problem in fractional form into an equivalent optimal problem in subtractive form, which is solved by using dual decomposition and subgradient methods. To reduce computation costs, we propose two low-complexity suboptimal schemes. Numerical studies are conducted to evaluate the EE of the proposed algorithms. Wanming Hao, Shouyi Yang, and Wanliang Hao Copyright © 2014 Wanming Hao et al. All rights reserved. Proposal of a Planar Directional UWB Antenna for Any Desired Operational Bandwidth Tue, 08 Jul 2014 06:53:50 +0000 http://www.hindawi.com/journals/ijap/2014/608538/ A novel planar directional UWB antenna is proposed. The antenna design evolves from an oblique elliptic cone antenna by applying the planar-solid correspondence to two axes. Through a simple equation, this antenna can be designed, to operate at a specific lower cutoff frequency with a bandwidth larger than 10 GHz for a reflection coefficient magnitude lower than −10 dB. This characteristic provides the antenna with a good versatility. The directional radiation pattern has an average gain of 6 dBi. Marco A. Peyrot-Solís, Giselle M. Galvan-Tejada, and Hildeberto Jardon-Aguilar Copyright © 2014 Marco A. Peyrot-Solís et al. All rights reserved. Design of Compact 4 × 4 UWB-MIMO Antenna with WLAN Band Rejection Tue, 08 Jul 2014 06:36:43 +0000 http://www.hindawi.com/journals/ijap/2014/539094/ A compact 4 × 4 UWB-MIMO antenna with rejected WLAN band employing an electromagnetic bandgap (EBG) structure is presented in this paper. The MIMO antenna is electrically small (60 mm × 60 mm), printed on a FR4_epoxy substrate with the dielectric constant of 4.4 and a thickness of 1.6 mm. A mushroom-like EBG structure is used to reject the WLAN frequency at 5.5 GHz. In order to reduce the mutual coupling of the antenna elements, a stub structure acting as a bandstop filter is inserted to suppress the effect of the surface current between elements of the proposed antenna. The final design of the MIMO antenna satisfies the return loss requirement of less than −10 dB in a bandwidth ranging from 2.73 GHz to 10.68 GHz, which entirely covers UWB frequency band, which is allocated from 3.1 to 10.6 GHz. The antenna also exhibits a WLAN band-notched performance at the frequency band of 5.36–6.34 GHz while the values of all isolation coefficients are below −15 dB and the correlation coefficient of MIMO antenna is less than −28 dB over the UWB range. A good agreement between simulation and measurement is shown in this context. Nguyen Khac Kiem, Huynh Nguyen Bao Phuong, and Dao Ngoc Chien Copyright © 2014 Nguyen Khac Kiem et al. All rights reserved. Performance Analysis of Joint Base-Station Multiantenna Multibeam and Channel Assignment Scheme for Hierarchical Cellular System Mon, 07 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/ijap/2014/216890/ Different from the traditional configuration of hierarchical cellular, we introduce the joint base-station multi-antenna multi-beam and channel assignment scheme for hierarchical cellular in this paper. The proposed scheme is based on multi-beam base-station antenna splitting in the elevation-radiating plane, and a dynamic channel allocation scheme by combining the adaptive antenna technologies. Simulation results show that the proposed configuration of the hierarchical cellular can enhance the spectral efficiency remarkably. Peng Yang, Dou Liu, and Yan Zhang Copyright © 2014 Peng Yang et al. All rights reserved. LPI Optimization Framework for Target Tracking in Radar Network Architectures Using Information-Theoretic Criteria Sun, 06 Jul 2014 07:33:54 +0000 http://www.hindawi.com/journals/ijap/2014/654561/ Widely distributed radar network architectures can provide significant performance improvement for target detection and localization. For a fixed radar network, the achievable target detection performance may go beyond a predetermined threshold with full transmitted power allocation, which is extremely vulnerable in modern electronic warfare. In this paper, we study the problem of low probability of intercept (LPI) design for radar network and propose two novel LPI optimization schemes based on information-theoretic criteria. For a predefined threshold of target detection, Schleher intercept factor is minimized by optimizing transmission power allocation among netted radars in the network. Due to the lack of analytical closed-form expression for receiver operation characteristics (ROC), we employ two information-theoretic criteria, namely, Bhattacharyya distance and J-divergence as the metrics for target detection performance. The resulting nonconvex and nonlinear LPI optimization problems associated with different information-theoretic criteria are cast under a unified framework, and the nonlinear programming based genetic algorithm (NPGA) is used to tackle the optimization problems in the framework. Numerical simulations demonstrate that our proposed LPI strategies are effective in enhancing the LPI performance for radar network. Chenguang Shi, Fei Wang, Mathini Sellathurai, and Jianjiang Zhou Copyright © 2014 Chenguang Shi et al. All rights reserved. Sparse Adaptive Channel Estimation Based on -Norm-Penalized Affine Projection Algorithm Sun, 06 Jul 2014 06:49:52 +0000 http://www.hindawi.com/journals/ijap/2014/434659/ We propose an -norm-penalized affine projection algorithm (LP-APA) for broadband multipath adaptive channel estimations. The proposed LP-APA is realized by incorporating an -norm into the cost function of the conventional affine projection algorithm (APA) to exploit the sparsity property of the broadband wireless multipath channel, by which the convergence speed and steady-state performance of the APA are significantly improved. The implementation of the LP-APA is equivalent to adding a zero attractor to its iterations. The simulation results, which are obtained from a sparse channel estimation, demonstrate that the proposed LP-APA can efficiently improve channel estimation performance in terms of both the convergence speed and steady-state performance when the channel is exactly sparse. Yingsong Li, Wenxing Li, Wenhua Yu, Jian Wan, and Zhiwei Li Copyright © 2014 Yingsong Li et al. All rights reserved. A Switched Diversity Scheme for Massive MIMO Systems Thu, 03 Jul 2014 11:17:14 +0000 http://www.hindawi.com/journals/ijap/2014/627275/ With the constraint of antenna space, spatial correlation and mutual coupling must be considered to accurately predict the system performance for massive MIMO systems. Increasing the antenna quantity can degrade the system performance due to mutual coupling. Antenna selection systems have better performance and lower hardware cost than full-MIMO systems. However, the conventional selection combining (SC) scheme consumes a great amount of training overhead and has high operational complexity in the presence of mutual coupling. This paper proposes a group switch-and-examine combining (GSEC) scheme for massive MIMO systems with the spatial correlation and mutual coupling existing at both the transmitter and receiver. Simulation results demonstrate that the proposed GSEC scheme provides better effective capacity performance and lower operational complexity than the conventional selection combining (SC) and full-MIMO scheme. Qianya Wang and Hongwen Yang Copyright © 2014 Qianya Wang and Hongwen Yang. All rights reserved.