Zhengqing Yun

University of Hawaiʻi at Mānoa, Honolulu, HI, United States

Are you Zhengqing Yun?

Claim your profile

Publications (61)31.93 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Cognitive radio systems adaptively adjust their radio parameters based on the feedback from the electromagnetic environment. Therefore, it is expected that cognitive radio systems will have better performance if they are integrated with accurate site-specific propagation modeling. Our group has long standing expertise in propagation modeling utilizing geo-spatial tools and indoor building models, and has focus on integrating these models as part of the environment awareness engine in cognitive radios. In this paper, we present the preliminary results for a multi-antenna based spectrum sensing algorithm with adaptive thresholds. The results show that, an almost fixed detection rate of 85% can be achieved for a mobile cognitive radio in an urban environment when the thresholds are set based on the path loss information provided by site-specific propagation modeling. On the other hand, the spectrum sensing algorithm with a fixed threshold shows a great variability in the detection performance, going as low as 65% in regions with heavy fading, which leads to harmful interference.
    2013 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting; 07/2013
  • Soo Yong Lim, Zhengqing Yun, M.F. Iskander
    [Show abstract] [Hide abstract]
    ABSTRACT: The propagation characteristics in indoor stairwell differ from those of the conventional indoor signal propagation across different floors and hence, deserve independent scrutiny. In this work, the propagation characteristics in four indoor stairwells have been examined by means of extensive field measurements at two frequency bands - 2.4 and 5.8 GHz respectively. It has been found the values of the path loss exponent n for stairwell are higher than those for other indoor environments. More importantly, the standard deviation of the n-values are high, leading to less accurate propagation models. This paper proposes the use of K-means clustering for the path loss data and values of path loss exponent n of stairwells are subsequently computed. The newly-computed path loss exponents n are lowered and their standard deviation values are significantly reduced. The path loss characteristics are useful for understanding radio propagation in pico- or femto-cells that have great potential in increasing the capacity and reducing the operational cost for wireless communications systems.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
  • N. Omaki, Zhengqing Yun, M.F. Iskander
    [Show abstract] [Hide abstract]
    ABSTRACT: The SSPE algorithm is derived from two-dimensional wave equation through different approximation methods. Different expressions of SSPE are used in different references. It is important to understand the differences for better implementation of SSPE. Our numerical results show mat all these different formulations provide similar path loss results for a flat ocean surface. Detailed explanations and derivations will be presented in the conference.
    Wireless Information Technology and Systems (ICWITS), 2012 IEEE International Conference on; 01/2012
  • Zhengqing Yun, N. Omaki, M.F. Iskander
    [Show abstract] [Hide abstract]
    ABSTRACT: When diffraction of ridges is required for predicting radio signal in mountainous regions, the realistic shape of ridges is often simplified (e.g., as a knife edge or a wedge). Also, the ridge orientation is usually ignored and the EM waves are assumed to be normally incident on the ridge. As more accurate radio propagation prediction is needed for advanced wireless communications, it is necessary to take into account more realistic features of ridges. For example, the slopes and orientation of ridges should be considered as two key features since they directly affect the values of diffraction coefficients. In this paper we present methods to extract these features of ridges based on digital terrain elevation data. The effect of the ridge orientation on the diffracted field is then investigated.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
  • N. Omaki, Zhengqing Yun, M.F. Iskander
    [Show abstract] [Hide abstract]
    ABSTRACT: Modeling radio propagation over ocean surface is important for homeland security applications. Due to its fast simulation speed, the parabolic equation (PE) method is a good candidate for and has been used in such simulations for decades. Since PE method is based on paraxial approximation of wave equation, its accuracy is not guaranteed for short ranges and larger propagation angles. On the other hand, Finite Difference Time Domain (FDTD) method is well known as an accurate method in short range but not suitable for large regions (in terms of wavelengths). For homeland security applications, it is necessary to deal with both short and long range propagation problems and it is natural to integrate PE and FDTD for simulating such scenarios. To exploit the advantages of PE and FDTD, quantifying the ranges suitable for these two methods is important and practically useful. In this paper, we examine the accuracy of PE method as a function of range (in short range regime) for smooth/flat ocean surfaces.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
  • Zhengqing Yun, M.F. Iskander, N. Omaki, A. Barrios
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper describes an overview of recent advances in propagation modeling with some focus on contributions in characterizing challenging communications environments in urban and costal communications scenarios. MIMO capacity is estimated for typical communication scenarios, and impact of mutual coupling and wall type effects on the estimated MIMO capacities are quantified for various numbers of antenna array elements.
    Wireless Information Technology and Systems (ICWITS), 2012 IEEE International Conference on; 01/2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: Emerging homeland security applications require low-cost and rapid installation of HF radar systems in challenging terrain environments. One example concerns hills with natural slopeandsurfaceirregularityandroughness.Inthisletter,through the investigation of radio-wave propagation in such an environ- ment, we examine the effect of the slope and surface roughness of the terrain on the performance of HF radars. It is shown that the slope and surface irregularity affect the effective electrical spacing between array elements and cause beamforming and scanning errors, which lead to misdetection of targets. It is also shown by an investigation of an actual HF radar site in the area of Koko Head in Hawaii that scattering from surface roughness of the terrain adds extra error to the phase difference between antenna array elements , hence degrades the radar performance further. canoperatewithnegligible site preparation and provide multiple operating frequencies in the HF band. Here, and denote the free-space wavenumber and the radius of the sphere enclosing the antenna, respectively. Another difficulty is associated with operating HF radars in challenging propagation environments.Thisincludesdeploying HF radars on sloping sites, in areas within dense vegetation, and in proximity to buildings near coastal areas. These issues result in the deterioration of radar performance and the need for time-consuming and possibly expensive calibrations. In this letter, we specifically address the propagation issues and errorsinthe performanceofan HF radarplaced on asloping site and quantify phase errors between the array elements. The effect of the slope and the surface roughness is then incorpo- rated in evaluating the beamforming performance of radar on a sloping site with rough surface.
    IEEE Antennas and Wireless Propagation Letters 12/2011; 10:1143-1146. · 1.67 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Emerging homeland security applications require low-cost and quickly deployable HF radar systems. In order to overcome the significant costs/unavailability of land lease in coastal areas for fixed applications, deployment of HF radar systems in challenging terrain environments is necessary. One such environment is the hilltops which naturally have slope and roughness. In this paper, through the investigation of radio wave propagation in such environments, we examined the effect of the slope and roughness of the terrain on the performance of HF radars. It is shown that the slope of the terrain will affect the effective inter-element spacing of the array and causes beamforming and scanning errors. It is also shown that surface roughness of the terrain also changes the effective inter-element phase differences and hence array performance. While the effect of the slope could be very significant diffraction effects from surface roughness resulted in a much smaller error of about 18°.
    Antennas and Propagation (APSURSI), 2011 IEEE International Symposium on; 08/2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: The detection and classification of buried targets such as unexploded ordnance (UXO) using ground penetrating radar (GPR) technology involves complex qualitative features and 2-D scattering images. These processes are often performed by human operators and are thus subject to error and bias. Artificial intelligence (AI) technologies, such as neural networks (NN) and fuzzy systems, have been applied to develop autonomous classification algorithms and have shown promising results. Genetic programming (GP), a relatively new AI method, has also been examined for these classification purposes. In this letter, the results of a comparison between the classification performances of NN versus the GP techniques for GPR UXO data are presented. Simulated 2-D scattering patterns from one UXO target and four non-UXO objects are used in this comparison. Different levels of noise and cases of untrained data are also examined. Obtained results show that GP provides better performance than NN methods with increasing problem difficulty. Genetic programming also showed robustness to untrained data as well as an inherent capability of providing global optimal searching, which could minimize efforts on training processes.
    IEEE Antennas and Wireless Propagation Letters 02/2011; · 1.67 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, a low complexity hybrid smart antenna system with directional elements and reduced-size digital beamformer is proposed to combat the inter-symbol interference (ISI) problem over frequency-selective fading channels. The conventional smart antenna systems with omni-directional elements utilize the full-size digital beamformer to suppress interference and obtain the optimum performance. However, the proposed hybrid smart antenna system with directional elements can split the linear receive array into two subarrays. One subarray contains the elements with no ISI, which can be processed with a simple maximum ratio combiner (MRC). The second subarray includes the elements with the ISI interference, which require the use of a reduced-size optimum beamformer for interference suppression. Finally, the outputs of the two subarrays are combined for optimal detection of the transmitted signals. Simulation results confirm that the proposed low complexity hybrid smart antenna system can provide robust performance under the multipath fading channel with ISI, and outperform the conventional smart antenna systems due to the use of directional antennas and utilization of multipath diversity gain.
    IEICE Transactions. 01/2011; 94-B:3610-3613.
  • Zhengqing Yun, Soo Yong Lim, M.F. Iskander
    [Show abstract] [Hide abstract]
    ABSTRACT: Realistic 3D modeling of propagation environments is a key step for accurate path loss/gain predictions using ray-tracing methods. As the cell sizes of wireless communications systems are getting smaller, the detailed geometries of the terrain and building structures should be considered. This paper deals with the extraction of terrain elevation data available in Google Earth. A region in Rosslyn City, VA, is investigated and the 3D terrain is reconstructed. The terrain data is combined with the building structures and the path gains along 5 routes are simulated and compared with the results. Good match between our simulation results and the measurement results is observed except in some regions. With the continued demand on improving the accuracy of the developed propagation prediction models, we have identified some issues that need further study. These are related to the accuracy of the GE elevation data, the accuracy of the terrain representation, and the impact of the ground representation on the obtained simulation results. We will investigate these general issues and the results will be presented in the conference.
    Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
  • Soo Yong Lim, Zhengqing Yun, M.F. Iskander
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we focus on the identification and characterization of various propagation mechanisms in close vicinity of a periodically structured building facade. The purpose is to quantitatively characterize the accuracy of ray tracing when the facade is approximated by some simpler geometry, such as a flat smooth surface. This quantitative characterization is very much needed because it is common in practical ray tracing software and is used to replace a building facade with a smooth surface. Our investigation would thus provide an indication of how much accuracy would be compromised in a ray tracing simulation when the complex building facade is approximated by a simpler structure.
    Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we examined the natural resonance frequency and polarization features of UXO-Like IED target in forward-looking GPR configuration. Based on the simulation results, we confirm that these feature not only exist but also measurable in the case of FLGPR. It is therefore, strongly suggested that these features be included in the target classification algorithms as they are expected to improve detection, increase stand off distance and minimize false alarm rate.
    Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we present the results of our next step effort in comparison of classification performances between the NN and the GP techniques based on the simulated scattering patterns of UXO-like object and non-UXO objects. For this comparative study, 2 dimensional scattering images from one UXO target and four non-UXO objects were generated by numerical simulation tool (FEKO). For non-UXO objects, the most challenging targets to discriminate from UXO, since all these objects produce resonance signal as UXO-like targets do [6], were selected. Classification performances of both techniques (NN vs. GP) in different level of noise and in the case of presence of untrained data were examined and the results and observations are discussed.
    Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, the authors present studies a higher frequency of 5.8 GHz. We also analyze the antenna polarizations effect on stairwell propagation at 2.4 GHz and 5.8 GHz. The research findings can be used for characterizing radio propagation in picoor femto-cells which have great potential in increasing the capacity and reducing the operational cost for wireless communications systems.
    01/2010;
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper the authors consider the radio propagation in the shadow region of a circular cylinder which is assumed a perfect electric conductor (PEC). A line source parallel to the cylinder is considered. Thus the problem is equivalently two-dimensional (2D) and the cylinder can be represented by a circle in the following discussions. The propagation mechanism involved is mainly creeping waves going around the cylinder surface and scattering in all directions.
    01/2010;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Phased array antennas have and will continue to be a critically important component in the development of future wireless systems with applications in communications, radar, and satellite technologies. In spite of the significant advances in the design of modern phased array antennas, there continue to be significant and growing need for developing high performance systems that are also low cost and with beam steering capabilities. In this paper we describe some of the antenna array designs that focus on achieving this goal. We will start with one approach that is based on an analog phase-shifting approach and involves an integrated use of ferroelectric materials and the Continuous Transverse Stub (CTS) antenna array technologies. A complementary design which is based on digital beamforming and the utilization of the Hybrid Smart Antenna technique recently developed by our group will then be described. This will be followed with comments regarding the trade-off between the analog and digital phase shifting techniques. We will conclude the chapter with a description of a novel ultra-wideband and low profile ground plane which is based on a hybrid ferrite and Electromagnetic Band Gap (EBG) materials design. In all cases simulation results and experimental validation, whenever available, will be presented and aspects of the required future work to fully enable these technologies will be discussed.
    Microwaves, Communications, Antennas and Electronics Systems, 2009. COMCAS 2009. IEEE International Conference on; 12/2009
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper summarizes the results of an ongoing design effort to miniaturize HF antennas for HFSWR and OTHR systems. The proposed design is based on a meander antenna described in [1]. Design modifications include a multi-element folding to increase the radiation efficiency and improve the impedance matching and also the incorporation of a back conducting plane reflector to improve the gain. Based on simulation results using the FEKO and IE3D software and experimental measurements, we were able to successfully demonstrate the anticipated advantages of the proposed prototype design.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
  • [Show abstract] [Hide abstract]
    ABSTRACT: Propagation characteristics in a stairwell are investigated through simulation and experimental measurements. Field measurement has been carried out at 2.4 GHz on every step of the stairwell up to second and half of the 3<sup>rd</sup> floor. In our measurements, the transmitter was placed outside the building. These results are then used for comparison with simulation results that take into consideration four different types of rays, namely the direct rays, reflected rays, transmitted rays, and hybrid rays. There is a good agreement between the measurement and the simulation results.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
  • [Show abstract] [Hide abstract]
    ABSTRACT: A comparative study of neural networks and genetic programming was conducted on six character classification problems. Based on the obtained results of the six problems, genetic programming showed better performance than neural networks in the various levels of problem difficulty. Genetic programming also showed robustness to untrained data, which caused difficulties for the neural networks. The optimization of the neural network structure was observed to be integral in obtaining both convergence and acceptable performance. A clear trend for structure optimization is not evident in the case of neural networks, and a global optimal solution may not be practical. On the other hand, because of the global searching nature of genetic programming, these problems with neural networks could be solved by using genetic programming.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009

Publication Stats

492 Citations
31.93 Total Impact Points

Institutions

  • 2004–2011
    • University of Hawaiʻi at Mānoa
      • College of Engineering
      Honolulu, HI, United States
  • 2008
    • Honolulu University
      Honolulu, Hawaii, United States
  • 2004–2006
    • Hawaii Pacific University
      Honolulu, Hawaii, United States
  • 2001
    • University of Utah
      • Department of Electrical and Computer Engineering
      Salt Lake City, UT, United States