• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.44 no.7 s.361
• /
• pp.59-69
• /
• 2007

In this paper, we propose a MIMO-OFDMA (Multi Input Multi Output-Orthogonal Frequency Division Multiple Access) system based on Grassmannian beamforming for performance improvement of downlink real-time traffic transmission in harsh channel conditions with low CIR (Carrier-to-Interference Ratio). In the proposed system to reduce feedback information for the beamforming, we also apply Grassmannian Beamforming. Furthermore, we propose antenna selection scheme which performs the beamforming with more useful transmit antennas. In the proposed system, the optimal combination of transmit antennas with maximum MRT (Maximum Ratio Transmission) beamforming gain, is selected. Simulation results reveal that the proposed MIMO-OFDMA system achieves significant improvement of spectral efficiency in low CIR region as compared to a typical open-loop MIMO-OFDMA system using pseudo-orthogonal space time block code.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.14 no.5
• /
• pp.825-832
• /
• 2011

In this paper, we described the design and measurement results of a Front-End Receiver for S-band active phased array radar. The Front-End Receiver has input P1dB of -4dBm and IIP3 of 7dBm. The measurement results show that gain is $24{\pm}0.7dB$, noise figure are less than 2.3dB over the frequency range of $fc{\pm}0.2GHz$. The Front-End Receiver can protect the receiver path from large input signals with a maximum peak power of multi-kW and recovery time is less than 0.8us. The measurement results satisfy all specifications.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.27 no.3C
• /
• pp.241-247
• /
• 2002

In this paper, we proposed a continuously variable true time-delay for transmit linear phased-array antenna sing chirped fiber gratings(CFGs) and a tunable laser source. Average group delay-slope of the CFG was treasured to be 177 ps/nm at L-, S-, and X-band. Simulation results show that the maximum gain of the transmit linear phased-array antenna with the beam steering angle of 180$^{\circ}$ is 11.6 dB at 10 GHz.

• Proceedings of the KAIS Fall Conference
• /
• 2006.05a
• /
• pp.348-351
• /
• 2006

This paper proposes a modified IMC-PID controller that introduces controlling factor of the system identification to the standard IMC-PID controller in order to meet the design specifications such as gain, phase margin and maximum magnitude of sensitivity function in the frequency domain as well as the design specifications in time domain, settling, rising time and overshoot, and so on.

• Computers and Concrete
• /
• v.23 no.2
• /
• pp.133-143
• /
• 2019

The paper presents the experimental investigations into the effect of ground granulated blast furnace slag (GGBFS) on the time-dependent tensile strength of concrete. The splitting and flexural tensile strength of concrete was determined at the ages of 3, 7, 28, 56, 90, 150 and 180 days using the cylindrical and prism specimens respectively for plain and GGBFS concrete. The amount of cement replacement by GGBFS was 0%, 40% and 60% on the weight basis. The maximum curing age was kept as 28 days. The results showed that the splitting and flexural tensile strength of concrete containing GGBFS has been found lower than the plain concrete at all ages and for all mixes. The tensile strength of 40 percent replacement has been found higher than the 60 percent at all ages and for all mixes. The rate of gain of splitting and flexural tensile strength of 40 percent GGBFS concrete is found higher than the plain concrete and 60 percent GGBFS concrete at the ages varying from 28 to 180 days. The experimental results of time-dependent tensile strength of concrete are compared with the available models. New models for the prediction of time-dependent splitting and flexural tensile strength of concrete containing GGBFS are proposed. The present experimental and analytical study will be helpful for the designers to know the time-dependent tensile properties of GGBFS concrete to meet the design requirements of liquid retaining reinforced and pre-stressed concrete structures.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2008.05a
• /
• pp.213-217
• /
• 2008

In this paper, a new design method for IMC-PID that adds a phase scaling factor of system identifications to the standard IMC-PID controller as a control parameter is proposed. Based on analytically derived frequency properties such as gain, phase margin and maximum magnitude of sensitivity function, this tuning rule is an optimal control method determining the optimum values of controlling factors to minimize the cost function, integral error criterion of the step response in time domain, in the constraints of design parameters to guarantee qualified frequency design specifications. The proposed controller improves existing single-parameter design methods of IMC-PID in the inflexibility problem to be able to consider various design specifications. Its effectiveness is examined by a simulation example, where a comparison of the performances obtained with the proposed tuning rule and with other common tuning rules is shown.

• Journal of Advanced Navigation Technology
• /
• v.11 no.3
• /
• pp.288-295
• /
• 2007

In this paper, we proposed two systems, STTC scheme and STBC-TCM scheme, to enhance the reliability of HDR-WPAN system and analyzed BER(bit error rate) performance of the proposed systems over the slow fading channel. The proposed systems had a diversity gain and coding gain without increasing an additional channel bandwidth. However, in terms of reliability, about 4dB improvement at BER=$10^{-4}$ was obtained by the STBC-TCM scheme. In addition, HDR-WPAN system with STBC-TCM scheme had a linear rise in system complexity of ML(maximum likelihood). From the results, STBC-TCM scheme was more appropriate to improve the reliability and channel efficiency and to reduce complexity of HDR-WPAN system.

• ETRI Journal
• /
• v.20 no.2
• /
• pp.133-148
• /
• 1998

The objective of this paper is to present an adaptive algorithm for computing the weight vector which provides a beam pattern having its maximum gain along the direction of the mobile target signal source in the presence of interfering signals within a cell. The conjugate gradient method (CGM) is modified in such a way that the suboptimal weight vector is produced with the computational load of O(16N), which has been found to be small enough for the real-time processing of signals in most land mobile communications with the digital signal processor (DSP) off the shelf, where N denotes the number of antenna elements of the array. The adaptive procedure proposed in this paper is applied to code division multiple access (CDMA) mobile communication system to show its excellent performance in terms of signal to interference plus noise ratio (SINR), bit error rate (BER), and capacity, which are enhanced by about 7 dB, ${\frac{1}{100}}$ times, and 7 times, respectively, when the number of antenna elements is 6 and the processing gain is 20 dB.

• Korean Journal of Optics and Photonics
• /
• v.13 no.4
• /
• pp.289-294
• /
• 2002

We propose optical true time-delays (TTDs) for phased-array antennas (PAAs) composed of 2${\times}$2 MEMS switches and fiber delay lines, and implement a TTD which shows a maximum scan angle of $120^{o}$ with $30^{o}$ resolution. Since this structure uses only one fixed wavelength laser diode, it provides several advantages such as easy control, high speed operation, and low cost compared with those of the optical TTDs using tunable laser sources. We design a four element linear PAA using the proposed TTDs at 10 ㎓. Simulation results show that the maximum gain is 11.6 dB at the radiation angle $0^{o}$, 11.2 dB at $\pm$$30^{o}$, and 10.6 dB at $\pm$$60^{o}$.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.8 no.2
• /
• pp.265-275
• /
• 2004

In this paper, an OFDM-CDMA broadband system is considered for a possible candidate of fixed wireless broadband access network applications. With an emphasis on a preamble design for multi-channel separation, we address a channel estimation based on the time-domain windowing and its imperfectness in OFDM-based multiple-antenna transmission systems. By properly designing each preamble for multiple antennas to be orthogonal in the time domain, the channel estimation can be applied to the ETSI HlPERLAN/2 and IEEE-802.11a standards in the case of more than two transmit antennas. Also, an effect of diversity techniques on the performance of OFDM-CDMA based broadband wireless access networks is investigated and the maximum achievable diversity gain for a two-path Rayleigh fading environment is evaluated Simulation results show that the OFDM-CDMA system applying a space-time-frequency diversity with a full-rate full diversity code can give the diversity of D = 4 and D = 8 for both multi-user cases of maximum user and half user capacities, respectively.