• Proceedings of the KSR Conference
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• 2005.05a
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• pp.776-781
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• 2005

In this paper, using received channel information, we analyze performance in MIMO multiuser system in low-to-medium mobile speed by selecting each user's constellations, powers, and transmit antennas. Given a target of symbol error, we determine each user's constellations, powers, selected tranprobability smit antennas such that the required signal-to-noise(SNR) is minimized for MMSE, V-BLAST receiver according to each user's information and channel estimation information. When we do power control with antenna selection technique through uplink channels of MIMO system in low-to-medium mobile speed, we analyze system performance with wireless channel information from Base-Station(BS) to Users. By simulation, it has been shown that the proposed antenna selection scheme for transmitting data offer better performance improvement than all transmit antennas for transmitting data.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.6
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• pp.1161-1166
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• 2005

In this paper, for spatial multiplexing with limited feedback, we propose subspace based precoding in which the active bases are selected at the receiver from a finite number of basis sets known at both receiving and transmitting ends, conveyed to the transmitter using limited feedback, and assembled into a preceding matrix at the transmitter. The selected bases are conveyed to the transmitter using feedback information on both the index of a basis set, which indicates the most appropriate set of coordinates for describing a MIMO channel, and the active bases having the significant amounts of energy in the selected basis set. We show that the proposed subspace based precoding provides capacity similar to that of the closed-loop MIMO even with limited feedback.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.464-466
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• 2018

In this paper, a dense cellular network is considered in which each base station equipped with multiple antennas simultaneously communicates with multiple single-antenna users. Based on limited feedback, each user feeds back its quantized channel state information (CSI) to its associated transmitter, and the transmitter broadcasts multiple data streams prepared for the scheduled users using a space-division multiple access scheme. As the amount of CSI is limited at the transmitter, the downlink throughput increases with the number feedback bits. However, the increased number of feedback bits requires the correspondingly increased amount of uplink resources. Thus, an appropriate balance between the downlink throughput and the uplink resource usage should be considered in realistic systems. A net spectral efficiency defined in this context is used in this paper, and the optimal number of feedback bits that maximizes the net spectral efficiency is analyzed. This paper particularly focuses on the case when the received signal power is much smaller than the noise power.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6C
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• pp.560-569
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• 2005

This paper proposes an algorithm for transmit antenna selection in a multi-input multi-output(MIMO) spatial multiplexing system with per antenna rate control(PARC) and an ordered successive interference cancellation (OSIC) receiver. The active antenna subset is determined at the receiver and conveyed to the transmitter using feedback information on transmission rate per antenna. We propose a serial decision procedure consisting of a successive process that tests whether antenna selection gain exists when the antenna with the lowest pre-processing signal to interference and noise ratio(SINR) is discarded at each stage. Furthermore, we show that 'reverse detection ordering', whereby the signal with the lowest SINR is decoded at each stage of successive decoding, widens the disparities among fractions of the whole capacity allocated to each individual antenna and thus maximizes a gain of antenna selection. Numerical results show that the proposed reverse detection ordering based serial antenna selection approaches the closed-loop MIMO capacity and that it induces a negligible capacity loss compared with the heuristic selection strategy even with considerably reduced complexity.

• The Journal of the Acoustical Society of Korea
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• v.32 no.3
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• pp.191-198
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• 2013

In this paper, we designed a wideband Tonpilz transducer, and verified the validity of the design through experiments. The wide frequency bandwidth was achieved by coupling the fundamental longitudinal mode of the transducer with a flapping mode of the head mass. Structure of the Tonpilz transducer was optimized by means of the finite element method and genetic algorithm to achieve the widest fractional bandwidth under design constraints. The optimized structure showed a far wider -6 dB fractional bandwidth of transmitting responses than that of single mode transducers. For verification of the design result, we manufactured a transducer prototype of the designed structure and characterized its performance, which showed good agreement with the design results.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.4
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• pp.761-766
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• 2004

Rayleigh fading due to multi-path degrades the mobile service quality, especially high data rate mobile services such as 1xEVDO and W-CDMA. The field test showed that down load date rate of 1xEVDO is seriously affected by Rayleigh fading. To reduce the effect of Rayleigh fading, transmit diversity was implemented in RF repeater. In field test, transmit diversity function increased the data rate about twice comparing with no transmit diversity repeater. Recently high data rate service is getting more important, so transmit diverstiy function will be an important function in repeater.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.2
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• pp.301-307
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• 2015

In this paper, we consider wiretap channels in the presence of an eavesdropper assuming spatially correlated MIMO(multiple-input multiple-output) channels, where we analyze a physical layer security performance of orthogonal space-time block code(OSTBC) using one-bit feedback assuming cross polarized antennas at each node. In this paper, we present a method to select a transmit-antenna group for OSTBC using one-bit feedback(O-OSTBC) and compare secrecy outage probabilities of various transmit-antenna grouping methods. Especially, we propose an efficient transmit-antenna grouping method by comparing secrecy outage probabilities of O-OSTBC and conventional OSTBC in highly correlated MIMO channels.

• The Journal of the Acoustical Society of Korea
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• v.21 no.2
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• pp.120-127
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• 2002

As a new type of a linear decorrelating receiver, the Pseudo-Decorrelator was presented for asynchronous code division multiple access systems by the author. In this paper, the concept of the Pseudo-Decorrelator is extended to derive a multiuser receiver for WCDMA uplink systems over a Rayleigh fading multipath channel. Starting with the analysis of the multiple access components of the decision statistics, a non-square cross-correlation matrix for each bit is obtained. This cross-correlation matrix is then inverted, and the inverted matrix is applied to the decision statistics obtained from a conventional receiver. This receiver is near-far resistant and outperforms conventional receivers even for the cases in which synchronization errors, such as time delay errors and phase errors exist.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7A
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• pp.587-596
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• 2005

In this paper, we propose an OFDMA/CDM-based cellular system, which accommodates multiple users in frequency-domain and multiplexes user data with frequency-domain spreading. The proposed system utilizes random codes to discriminate cells and adopts the pre-equalization to enhance the performance. For cellular applications, a number of pre-equalization techniques are compared and an efficient power allocation scheme is suggested with a transmit power constraint. Especially, the validity of OFDMA/CDM based cellular system is investigated, by comparing the performance for varying the number of multiplexed data symbols at different locations. Finally the pre/post-equalization is proposed to reduce the performance degradation caused by time delay.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.7
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• pp.1-5
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• 2009

Random beanforming exploits multiuser diversity gain in static channels. Since the gain is restricted by the user population, some extended works have been proposed. Among them, a codebook-based opportunistic beamforming technique forms multiple random beams with small pilots. The technique however has difficulty in designing beams flexibly by the channel statistics. In this paper, we propose a technique forming the multiple random beams by rotating codebooks. The proposed technique enables the flexible design of beams so that multiuser diversity and beam selection diversity are exploited simultaneously with small pilots robust to the channel statistics.