• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.4 s.95
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• pp.397-401
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• 2005

In this paper, a slot-coupled microstrip antenna with switchable polarization is proposed for the polarization diversity applications in the complicated communication environment. The proposed antenna is fed by a microstrip line through one of two slots located with the interval of $\lambda{g}/4$ in the ground plane. By switching the PIN diode between opened and shorted termination which is located at the tip of the microstrip line, the switching function between horizontal and vertical polarization was confirmed experimentally. The measured resonant frequencies of the fabricated antenna are $2.41\;\cal{GHz}\;2.40\;\cal{GHz}$ and the cross polarization levels are $19\;\cal{dB},\;23\;\cal{dB},\;the\;-10\;\cal{dB}$ return loss bandwidths are $95\;\cal{MHz}\;100\;\cal{MHz}$ in horizontal and vertical polarization, respectively, and the antenna gain is almost $6\;\cal{dBi}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12B
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• pp.1752-1757
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• 2011

In a traditional phased array radar, closely spaced antenna elements transmit a scaled version of single waveform to maximize the signal energy. On the contrary, a multiple-input multiple-output (MIMO) radar consists of widely separated antennas and transmits an arbitrary waveform from each antenna element. These waveforms and spatial diversity enable superior capabilities compared with phased array radar. At high signal-to-noise ratio (SNR), the detection performance of the MIMO radar is better than the phased array radar due to the diversity gains. However, the phased array radar outperforms the MIMO radar at low SNR, due to the energy maximization. In this paper, we investigate the compromised scheme between the MIMO radar and the phased array radar. Employing the MIMO radar equipped with phased array elements, the compromised scheme achieves both array gain and diversity gain. Also, we compare the performance degradation when the steering direction is incorrect.

• Journal of Satellite, Information and Communications
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• v.6 no.2
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• pp.20-25
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• 2011

The authors have proposed novel TDD-CDMA systems with Pre-Rake transmit diversity schemes (system 1 and system 2) using multiple transmit antennas in [2] and have also evaluated the system performance through the theoretical analysis and computer simulation. However, the performance of system 2 which transmit a signal using all antennas has not been evaluated for multi-user environment. Therefore in this paper, we analyze the performance of system 2 for multi-user environment and compare the performance with that of the already proposed system 1 which chooses only one antenna. From the numerical results, it is found that system 2 outperforms system 1 as the number of users increases while system 1 outperforms system 2 at a small number of users. Therefore in order to achieve the best system performance, the Pre-Rake transmit diversity type should be selected at the base station according to the number of users.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.6
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• pp.757-763
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• 2018

It is very difficult to achieve sufficient data rate and required quality of service due to the time-varying nature of the radio channel and various jammers such as path loss, delay, Doppler, shadowing and interference. Especially, the propagation path between the transmitting antenna and the tracking antenna mounted on the fuselage during the test and evaluation of the projectile system considered in this paper is based on the rapid movement of the projectile, the interference due to multipath fading due to the terrain, The propagation path may be blocked. In order to effectively improve the multipath fading occurring in the wireless communication system, a diversity combiner technique is required. In this paper, to derive the design and improvement schemes for the space diversity combiner technique among the diversity combiner schemes, the BER performance of maximum ratio combining (MRC) and selection combining (SC) In an adaptive SC / MRC diversity combiner that operates with MRC when it is lower than the specified threshold criterion when comparing the SNR between two signals received from the channel and operates with SC at high and combines the two received signals The BER performance of the system was compared and analyzed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7A
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• pp.720-726
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• 2008

In this paper, we propose a multi-cell cooperation method for broadcast packet data services in the orthogonal frequency division multiplexing (OFDM)-based cellular system with multiple transmit antennas. In the proposed method, to transmit two streams of spatially demultiplexed or transmit diversity coded symbols over a number of transmit antennas, we divide a coded packet into multiple subparts to which different cell groups and antenna pairs are assigned. The proposed method enhances the diversity order by transforming the channel frequency responses of two symbol streams in each subpart of the broadcast packet. The increase in diversity of the proposed method is shown with the outage probability under various configurations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7C
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• pp.644-651
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• 2007

In multiple antenna systems, vertical Bell Labs Layered Space-Time (V-BLAST) systems enable very high throughput by nulling and cancelling at each layer detection. In this paper, we propose a V-BLAST system which combines with signal space diversity technique. The benefit of the signal space diversity is that we can obtain an additional gain without extra bandwidth and power expansion by applying inphase/quadrature interleaving and the constellation rotation. Through simulation results, it is shown that the performance of the proposed system is less than 0.5dB away from the ideal upper bound.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.12
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• pp.1-7
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• 2010

In this paper, the technique for obtaining diversity gain without increasing the antenna is proposed using symbol share in the OFDM systems. Proposed technique groups symbols which are mapped into different sub-carriers and these symbols are modulated by proposed constellation. Proposed constellation has the identical minimum distance with QPSK modulation constellation and obtain more frequency diversity gain. Also, proposed modulation scheme make it possible to increase data rate using subcarriers allocated symbols.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.2
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• pp.293-300
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• 2015

Recently, multiuser diversity(MUD) technique is used to improve the performance of OFDM transmission systems. With STBC antenna diversity technique, the performance of OFDM systems can be also improved. Pilot symbol is used for the channel estimation in OFDM systems. However, imperfect channel estimates in this systems degrade the performance. The performance of MUD STBC OFDM systems using pilot symbol, gauged by the bit error rate, is analyzed considering the channel estimation error. Result shows that MUD can improve the required power by a factor of approximately 5 dB for users number 32.

• Journal of Satellite, Information and Communications
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• v.11 no.3
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• pp.58-64
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• 2016

This paper proposes the efficient transmit antenna selection (TAS) scheme considering trade-off between the performance and the complexity in massive MIMO system. The massive MIMO system is a core technology to achieve performance objectives for 5 generation wireless communication. It achieve high spectral efficiency, a reliability, and a diversity gain. However many RF chains required by massive transmit antennas equipped in a base station create the problem such as high hardware cost and complexity. Therefor we investigates the transmit antenna selection scheme, in which the number of RF chains of BS is reduced, and the trade-off between the performance and the complexity is considered for proposed scheme. And, the spectral efficiency and complexity are analysed by transmit antenna selection schemes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2A
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• pp.202-213
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• 2004

In this paper, we propose a preamble structure and synchronization/channel estimation methods for OFDM-based multiple antenna WLAN systems that have 200Mbps transmit rate. With the proposed preamble structure, multiple antenna WLAN systems are backward-compatible with IEEE 802.11a systems which use the same 5㎓ band and synchronization performance is better than that of single antenna OFDM systems. For channel estimation, the preamble overhead is small and performance degradation by timing synchronization error that causes the critical problem of conventional comb-type multiple antenna channel estimation method also can be minimized by frequency domain phase recovery. Synchronizer and channel estimator for proposed preamble structure are implemented and verified using Verilog HDL. For the system with 4 transmit antennas and 4 receive antennas, about 150K gates are needed for synchronizer and 12K gates for channel estimator.