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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of electromagnetic engineering and science
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Journal DOI :
The Korean Institute of Electromagnetic Engineering and Science
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Volume & Issues
Volume 11, Issue 4 - Dec 2011
Volume 11, Issue 3 - Sep 2011
Volume 11, Issue 2 - Jun 2011
Volume 11, Issue 1 - Mar 2011
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Low Complexity Multiuser Scheduling in Time-Varying MIMO Broadcast Channels
Lee, Seung-Hwan ; Lee, Jun-Ho ;
Journal of electromagnetic engineering and science, volume 11, issue 2, 2011, Pages 71~75
DOI : 10.5515/JKIEES.2011.11.2.071
The sum-rate maximization rule can find an optimal user set that maximizes the sum capacity in multiple input multiple output (MIMO) broadcast channels (BCs), but the search space for finding the optimal user set becomes prohibitively large as the number of users increases. The proposed algorithm selects a user set of the largest effective channel norms based on statistical channel state information (CSI) for reducing the computational complexity, and uses Tomlinson-Harashima precoding (THP) for minimizing the interference between selected users in time-varying MIMO BCs.
Dual-Band Negative Group Delay Circuit Using λ/4 Composite Right/Left-Handed Short Stubs
Choi, Heung-Jae ; Mun, Tae-Su ; Jeong, Yong-Chae ; Lim, Jong-Sik ; Eom, Soon-Young ; Jung, Young-Bae ;
Journal of electromagnetic engineering and science, volume 11, issue 2, 2011, Pages 76~82
DOI : 10.5515/JKIEES.2011.11.2.076
In this paper, a novel design for a dual-band negative group delay circuit (NGDC) is proposed. Composite right/left-handed (CRLH)
short stubs are employed as a dual-band resonator. A CRLH
short stub is composed of a typical transmission line element as the right-handed component and a high-pass lumped element section as the left-handed component. It is possible to simultaneously obtain open impedances at two separate frequencies by the combination of distinctive phase responses of the right/left-handed components. Negative group delay (NGD) can be obtained at two frequencies by using dual-band characteristics of the CRLH stub. In order to achieve a bandwidth extension, the proposed structure consists of a two-stage dual-band NGDC with different center frequencies connected in a cascade. According to the experiment performed, with wide-band code division multiple access (WCDMA) and worldwide interoperability for microwave access (WiMAX), NGDs of
ns are obtained at 2.12~2.16 GHz and 3.46~3.54 GHz, respectively.
Design of Low-Pass Type Inverter: UWB Band-Pass Filter with Low Spurious Characteristics
Cho, Young-Ho ; Choi, Moon-Gyu ; Yun, Sang-Won ;
Journal of electromagnetic engineering and science, volume 11, issue 2, 2011, Pages 83~90
DOI : 10.5515/JKIEES.2011.11.2.083
In this paper, we present the design method for a low-pass type inverter, which can effectively suppress the spurious response associated with band-pass filters. The inverter has a length of
and employs not only a stepped-impedance configuration but also asymmetrical and bending structures in order to improve frequency selectivity and compactness. The inverter is applied as an impedance/admittance inverter to the ultra-wideband (UWB) band-pass filter. The UWB band-pass filter configuration is based on a stub band-pass filter consisting of quarter-wavelength impedance inverters and shunt short-circuited stubs
in length. The asymmetrical stepped-impedance low-pass type inverter improves not only the spurious responses, but also the return loss characteristics associated with a UWB band-pass filter, while a compact size is maintained. The UWB band-pass filter using the proposed inverters is fabricated and tested. The measured results show excellent attenuation characteristics at out-band frequencies, which exceed 18 dB up to 39 GHz. The insertion loss within the pass-band (from 3.1 to 10.6 GHz) is below 1.7 dB, the return loss is below 10 dB, and the group delay is below 1 ns.
Microstrip Bandpass Filter Using Stepped-Impedance Coupled-Line Hairpin Resonators with Enhanced Stopband Performance
Lee, Hye-Min ; Ha, Jung-Hyun ; Wang, Xu-Guang ; Cho, Young-Ho ; Yun, Sang-Won ;
Journal of electromagnetic engineering and science, volume 11, issue 2, 2011, Pages 91~96
DOI : 10.5515/JKIEES.2011.11.2.090
In this paper, we propose a microstrip bandpass filter using stepped-impedance coupled-line hairpin resonators. The stepped-impedance coupled-line hairpin resonator has extended harmonic suppression in comparison with a conventional hairpin resonator due to transmission zero and the movement of harmonic frequencies resulting from the stepped-impedance characteristic. A high-pass type impedance/admittance inverter is employed in order to improve the lower frequency skirt characteristics of the passband. A 4-pole bandpass filter is designed and fabricated at 1.8 GHz. The measured results show the excellent attenuation performance at the stopband which is greater than 30 dB up to 10 GHz.
Design of a Planar Slotted Waveguide Array Antenna for X-band Radar Applications
Bhatti, Rashid Ahmad ; Park, Byeong-Yong ; Im, Yun-Taek ; Park, Seong-Ook ;
Journal of electromagnetic engineering and science, volume 11, issue 2, 2011, Pages 97~104
DOI : 10.5515/JKIEES.2011.11.2.097
A planar slotted waveguide array antenna has been designed at 9.37 GHz for X-band radar applications. The antenna consists of multiple branchline waveguides with broadwall radiating shunt slots and a main waveguide to feed the branch waveguides through a series of inclined coupling slots. The antenna feed point is located at the center of the main waveguide. Element weights in the array have been calculated bysampling a continuous circular Taylor aperture distribution at the 25 dB sidelobe level in both the E and Hplanes. A commercially available electromagnetic (EM) simulation tool has been used to characterize the individual isolated slot and that data hassubsequently been used to design the planar array. The array is finally analyzed in a CST Microwave studio and the measured and simulated results have been found to be in good agreement.
A Lock-Time Improvement for an X-Band Frequency Synthesizer Using an Active Fast-Lock Loop Filter
Heo, Yun-Seong ; Oh, Hyun-Seok ; Jeong, Hae-Chang ; Yeom, Kyung-Whan ;
Journal of electromagnetic engineering and science, volume 11, issue 2, 2011, Pages 105~112
DOI : 10.5515/JKIEES.2011.11.2.105
In phase-locked frequency synthesizers, a fast-lock technique is frequently employed to overcome the trade-off between a lock-time and a spurious response. The function of fast-lock in a conventional PLL (Phased Lock Loop) IC (Integrated Circuit) is limited by a factor of 16, which is usually implemented by a scaling of charge pumper, and consequently a lock time improvement of a factor of 4 is possible using the conventional PLL IC. In this paper, we propose a novel external active fast-lock loop filter. The proposed loop filter provides, conceptually, an unlimited scaling of charge pumper current, and can overcome conventional trade-off between lock-time and spur suppression. To demonstrate the validity of our proposed loop-filter, we fabricated an X-band frequency synthesizer using the proposed loop filter. The loop filter in the synthesizer is designed to have a loop bandwidth of 100 kHz in the fast-lock mode and a loop bandwidth of 5 kHz in the normal mode, which corresponds to a charge pumper current change ratio of 400. The X-band synthesizer shows successful performance of a lock-time of below 10
and reference spur suppression below -64 dBc.
Boosting the Uplink Throughput of OFDM Systems by Creating Resolvable Interference
Mohaisen, Manar ; Hui, Bing ; Chang, Kyung-Hi ;
Journal of electromagnetic engineering and science, volume 11, issue 2, 2011, Pages 113~121
DOI : 10.5515/JKIEES.2011.11.2.113
Multiple-input multiple-output with orthogonal frequency division multiplexing technology (MIMO-OFDM) is considered to be the ultimate solution for increasing system throughput and for enhancing communication reliability. In this paper, we propose to increase the uplink (UL) throughput by assigning the same UL resources to multiple single-antenna mobile stations. This leads to the loss of orthogonality among sub-carriers. Thus, at the base station (BS), MIMO-OFDM detection techniques are used to separate the streams of different users assigned the same UL resources. To obtain a realistic performance evaluation, different channel scenarios are applied with different correlation values among the antennas of the users. Simulation results show that the proposed MIMO-OFDM system linearly increases the uplink capacity of the OFDM system while maintaining a mobile station transmitter as simple as that used in a conventional OFDM system. For instance, when 4 users are assigned the same UL resources, the throughput of the proposed system is 3.07 times that achieved by a conventional single input single output OFDM system.
Network Modeling and Circuit Characteristics of Aperture-Coupled Vertically Mounted Strip Antenna
Kim, Jeong-Phill ;
Journal of electromagnetic engineering and science, volume 11, issue 2, 2011, Pages 122~127
DOI : 10.5515/JKIEES.2011.11.2.122
A general analysis of an aperture-coupled vertically mounted strip antenna is presented to examine its circuit characteristics. Based on the present analysis, an equivalent circuit model is developed, and an analytic or semi-analytic evaluation of the related circuit element values is described. The effects of structure parameters on the antenna characteristics were studied with the developed equivalent circuit, and the design curves were obtained. To check the validity of the proposed analysis and design theory, two C-band antennas (5.0 GHz and 4.5 GHz) were designed and fabricated. Their computed characteristics, derived from the proposed network analysis, were compared with the measurement and simulation results. The error of the current model in predicting the operating center frequency was less than 0.50 %. In addition, the observed bandwidth was found to be comparable to the conventional microstrip antennas. All the results fully validated the efficiency and accuracy of the proposed analysis and network model.
Interference Tolerant Based CR System with Imperfect Channel State Information at the CR-Transmitter
Asaduzzaman, Asaduzzaman ; Kong, Hyung-Yun ;
Journal of electromagnetic engineering and science, volume 11, issue 2, 2011, Pages 128~132
DOI : 10.5515/JKIEES.2011.11.2.128
In interference tolerance based spectrum sharing systems, primary receivers (PRs) are protected by a predefined peak or average interference power constraint. To implement such systems, cognitive radio (CR) transmitters are required to adjust their transmit power so that the interference power received at the PR receivers is kept below the threshold value. Hence, a CR-transmitter requires knowledge of its channel and the primary receiver in order to allocate the transmit power. In practice, it is impossible or very difficult for a CR transmitter to have perfect knowledge of this channel state information (CSI). In this paper, we investigate the impact of imperfect knowledge of this CSI on the performances of both a primary and cognitive radio network. For fixed transmit power, average interference power (AIP) constraint can be maintained through knowledge of the channel distribution information. To maintain the peak interference power (PIP) constraint, on the other hand, the CR-transmitter requires the instantaneous CSI of its channel with the primary receiver. First, we show that, compared to the PIP constraint with perfect CSI, the AIP constraint is advantageous for primary users but not for CR users. Then, we consider a PIP constraint with imperfect CSI at the CR-transmitter. We show that inaccuracy in CSI reduces the interference at the PR-receivers that is caused by the CR-transmitter. Consequently the proposed schemes improve the capacity of the primary links. Contrarily, the capacities of the CR links significantly degrade due to the inaccuracy in CSI.
Performance Analysis of Coded Cooperation Protocol with Reactive and Proactive Relay Selection
Asaduzzaman, Asaduzzaman ; Kong, Hyung-Yun ;
Journal of electromagnetic engineering and science, volume 11, issue 2, 2011, Pages 133~142
DOI : 10.5515/JKIEES.2011.11.2.133
Coded cooperation that integrates channel coding in cooperative transmission has gained a great deal of interest in wireless relay networks. The performance analysis of coded cooperation protocol with multiple relays is investigated in this paper. We show that the diversity order achieved by the coded cooperation in a multi-relay wireless network is not only dependent on the number of cooperating relays but is also dependent on the code-rate of the system. We derive the code-rate bound, which is required to achieve the full diversity gain of the order of cooperating nodes. The code-rate required to achieve full diversity is a linearly decreasing function of the number of available relays in the network. We show that the instantaneous channel state information (CSI)-based relay selection can effectively alleviate this code-rate bound. Analysis shows that the coded cooperation with instantaneous CSI-based relay selection can achieve the full diversity, for an arbitrary number of relays, with a fixed code-rate. Finally, we develop tight upper bounds for the bit error rate (BER) and frame error rate (FER) of the relay selection based on coded cooperation under a Rayleigh fading environment. The analytical upper bounds are verified with simulation results.