• Journal of Communications and Networks
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• v.14 no.3
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• pp.273-279
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• 2012

In this paper, we propose an iterative interstream interference cancellation technique for system with frequency selective multiple-input multiple-output (MIMO) channel. Our method is inspired by the fact that the cancellation of the interstream interference can be regarded as a reduction in the magnitude of the interfering channel. We show that, as iteration goes on, the channel experienced by the equalizer gets close to the single input multiple output (SIMO) channel and, therefore, the proposed SIMO-like equalizer achieves improved equalization performance in terms of normalized mean square error. From simulations on downlink communications of $2{\times}2$ MIMO systems in high speed packet access universal mobile telecommunications system standard, we show that the proposed method provides substantial performance gain over the conventional receiver algorithms.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.5
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• pp.1588-1603
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• 2014

In space diversity combining, conventional methods such as maximal ratio combining (MRC), equal gain combining (EGC) and selection combining (SC) are commonly used to improve the output signal-to-noise ratio (SNR) provided that the channel is perfectly estimated at the receiver. However, in practice, channel estimation is often imperfect and this indeed deteriorates the system performance. In this paper, diversity combining techniques based on two evolutionary algorithms, namely genetic algorithm (GA) and particle swarm optimization (PSO) are proposed and compared. Numerical results indicate that the proposed methods outperform the conventional MRC, EGC and SC methods when the channel estimation is imperfect while it shows similar performance as that of MRC when the channel is perfectly estimated.

• 전기의세계
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• v.19 no.3
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• pp.18-25
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• 1970

Chesin-1 telephone currently used in Korea is quite similar in design to early Japanese model of Type-4 telephone which is now being replaced by Type-600 having much improved characteristics. Chesin-1 telephone has a relatively high side-tone level, since the line impedance was taken as a purely resistive component for simplicity in the design of its transmission networks. To meet a current trend of using a smaller diameter of wire for telephone line, it is necessary to improve the present type which has a limited receiving efficiency. A new telephone set has been designed to have an amplifier and a R-C coupled side-tone balancing network. The set offers 8dB gain in the overall performance of transmitting and receiving without any unbearable side-tone disturbances. The paper describes both theoretical and experimental characteristics of the new set.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11C
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• pp.1059-1066
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• 2009

In this paper, we propose the precoder with superimposed pilots for orthogonal frequency-division multiple access (OFDMA) systems in order to enhance the transmission efficiency of the system and reduce peak-to-average power ratio (PAPR) which is the problem in OFDMA uplink. In wireless communication systems, the way to improve transmission efficiency is 1) to reduce bit error rate (BER) or 2) to increase data rate. In the proposed scheme, we design the precoder and superimposed pilots in the transmitter and use them in the receiver for increasing data rate, caused by the saved transmission bandwidth thanks to the superimposed pilots. In addition, we improve BER performance with the help of the frequency diversity gain caused by precoding. Also using superimposed pilots, we enhance the PAPR performance by increasing the average output power of the signal.

• Proceedings of the KIEE Conference
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• 2003.11b
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• pp.339-342
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• 2003

This paper describes an RF/IF module for 2.4GHz wireless video and audio receivers The designed circuits are implemented using a Teflon board of which the size is $53mm\times42mm$. The measured LNA gain is 15dB, and the VCO output levels are around 2dBm. The sensitivity of the receiver is about -80dBm. The manufactured module consumes 140nA from a 8V supply.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.617-618
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• 2006

A CMOS quadrature Up-converter for a direct-conversion receiver of 5.15-5.825GHz wireless LAN is described. The Up-converter consists of two sub-harmonic mixers, for I and Q channels, and an LO generation network. In order to decrease the number of inductor, I and Q path are merged. The simulation results including all the parasitics show -17.3dB conversion gain at center and -8 dBv oIP3 while consuming 22.968mW under 1.8V supply. The quadrature Up-converter is under fabrication with the other transmitter blocks in a $0.18{\mu}m$ CMOS technology.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5C
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• pp.506-513
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• 2003

Most existing space-time coding (STC) schemes have been developed for flat fading channels. To obtain antenna diversity gain, they rely on channel state information (CSI) required at the receiver through channel estimation techniques. This paper proposes a new decision feedback decoding scheme for Alamouti-based space-time block coding (STBC) transmission over time-selective fading channels. In wireless channels, time-selective fading effects arise mainly due to Doppler shift and carrier frequency offset, Modelling the time-selective fading channels as the first-order Gauss-Markov processes, we use recursive algorithms such as Kalman filtering, LMS and RLS algorithms for channel tracking. The proposed scheme consists of the symbol decoding stage and channel tracking algorithms. Computer simulations confirm that the proposed scheme shows the better performance and robustness to time-selectivity.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.2
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• pp.100-105
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• 2006

In this paper, a low noise amplifier(LNA) in a receiver of a low noise block down converter (LNB) for direct broadcasting service(DBS) is implemented using GaAs HEMT. The LNA is designed for the bandwidth of 11.7 GHz-12.2 GHz. The two-stage LNA consists of a input matching circuit, a output matching circuit, DC-blocks and RF-chokes. Experimental results of the LNA show the noise figure less than 1.4 dB, the gain greater than 23 dB and the flatness of 1 dB in the bandwidth of 11.7 to 12.2 GHz.

• Journal of Communications and Networks
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• v.9 no.2
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• pp.150-158
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• 2007

We consider channel-coded multi-input multi-output (MIMO) orthogonal frequency-division multiplexing (OFDM) transmission and obtain a condition on its signal for it to attain the maximum diversity and coding gain. As this condition may not be realizable, we propose a suboptimal design that employs an orthogonal transform and a space-frequency interleaver between the channel coder and the multi-antenna OFDM transmitter. We propose a corresponding receiving method based on block turbo equalization. Attention is paid to some detailed design of the transmitter and the receiver to curtail the computational complexity and yet deliver good performance. Simulation results demonstrate that the proposed transmission technique can outperform the conventional coded MIMO OFDM and the MIMO block single-carrier transmission with cyclic prefixing.

• 한국정보통신설비학회:학술대회논문집
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• 2005.08a
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• pp.443-447
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• 2005

In this paper, a low noise amplifier(LNA) in a receiver of a Low Noise Block Down Converter (LNB) for direct broadcasting service(DBS) is implemented using GaAs HEMT. The 2-stage LNA is designed for the bandwidth of 11.7GHz - 12.2GHz. The result of a simulation of the LNA using Advanced Design System(ADS) shows that the noise figure is less than 1.4dB, the gain is greater than 23dB and the flatness is 1dB in the bandwidth of 11.7 to 12.2GHz.