• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.9A
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• pp.1265-1275
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• 1999

An adaptive MMSE detector can be used to cancel the MAI in CDMA system. But standard adaptive MMSE detector cannot be used in real mobile environment due to fast fading channel. Furthermore multipath reception make it more difficult to converge to optimum weight values. In this paper we discuss and model the multipath fading environment in Forward-link Synchronous CDMA channels and propose adaptive MMSE RAKE detector structure which can be applied in the mobile station. A proposed adaptive MMSE detector requires estimation of received signal delay and complex channel coefficients such as amplitude and phase variation. These burden can be solved by utilizing the common pilot channel. The pilot channel may have higher power than the traffic channel, which give more exact channel estimation. Moreover RAKE structure gives more accurate and stable result which can be used as reliable reference signal in multipath fading channel environment. With this structure, conventional adaptive algorithm such as LMS or NLMS can be applied in adaptive MMSE detector.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.6
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• pp.881-888
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• 1993

A new stabilizing algorithm for the fast transversal filter (FTF) which is known to exhibit a very unstable behavior, due basically to the accumulation in two different ways, we define a emasure counting these at each step of the algorithm in order to reduce the roundoff error. It has been shown that required amount of computation for the proposed algorithm is linearly increased as the order of equalizer and that stability is improved in comparison with the other existing algorithm. It has been shown that the proposed algorithm exhibits a good performance using computer simulation of adaptive equalization for multipath fading channel in urban mobile radio environment.

• Journal of the Korea Society of Computer and Information
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• v.3 no.2
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• pp.155-160
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• 1998

We applied a pilot symbol assisted modulation technique to QPSK system for improving BER performance over mobile communication channel. We demonstrate through computer simulation, that the proposed scheme achieves a prominent improvement comparison to that of conventional QPSK in a fast flat Rayleigh fading environment.

• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.55-58
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• 2004

This this paper, we propose vertical Bell laboratories layered space time (V-BLAST) system based on variable rate Low-Density Parity Check (LDPC) codes to improve performance of receiver when QR decomposition interference suppression combined with interference cancellation is used over independent Rayleigh fading channel. The different rate LDPC codes can be made by puncturing some rows of a given parity check matrix. This allows to implement a single encoder and decoder for different rate LDPC codes. The performance can be improved by assigning stronger LDPC codes in lower layer than upper layer because the poor SNR of first detected data streams makes error propagation. Keeping the same overall code rates, the V-BLAST system with different rate LDPC codes has the better performance (in terms of Bit Error Rate) than with constant rate LDPC code in fast fading channel.

• Journal of the Korean Institute of Telematics and Electronics
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• v.24 no.3
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• pp.370-375
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• 1987

In this study, the Rayleigh fast fading simualtors encountered in channel modelling of mobile radio have been implemented and evaluated. Two models used for the fading environment were frequency composition of phase modulated signals and shaping spectrum of noise sources with filters. The spectrum chosen for our purpose is appropriate to an omnidirectional antenna. From results of the experiment with various parameters, we have obtained satisfying results which are closely agreed to theoretical values.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.05a
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• pp.54-56
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• 2015

In this paper, we investigate a physical-layer network coding (PNC) in a two-way relay channel (TWRC) where two sources send and receive data with each other by help of a relay node with multiple antennas. We focus on the multiple-access phase of the TWRC in this paper. It is assumed that the source nodes do not know the wireless channel and the wireless channel independently varies in time, that is, fast fading environments. At the relay node, the channel is assumed to be perfectly known. The relay node utilizes the channel sate information and applies maximum likelihood ratio for detecting received signals. Through extensive simulations, it is shown that a bit error rate (BER) performance becomes improved as the number of antennas at the relay node increases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.6B
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• pp.1082-1091
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• 2000

In this paper, the efficient equalization method for OFDM(Orthogonal Frequency Division Multiflexing) System using the QAM(Quadrature Amplitude Modulation) in multipath fading channel is proposed in order to faster and more efficiently equalize the received signals that are sent over real channel. In generally, the one-tap linear equalizers have been used in the frequency-domain as the existing equalization method for OFDM system. In this technique, if characteristics of the channel are changed fast, the one-tap linear equalizers cannot compensate for the distortion due to time variant multipath channels. Therefore, in this paper, we use one-tap non-linear equalizers instead of using one-tap linear equalizers in the frequency-domain, and also use the linear equalizer in the time-domain to compensate the rapid performance reduction at the low SNR(Signal-to-Noise Ratio) that is the disadvantage of the non-linear equalizer. In the frequency-domain, when QAM signals, consisting of in-phase components and quadrature (out-phase) components, are sent over the complex channel, the only in-phase and quadrature components of signals distorted by the multipath fading are changed the same as signals distorted by the noise. So the cross components are canceled in the frequency-domain equalizer. The time-domain equalizer and the adaptive algorithm that has lower-error probability and fast convergence speed are applied to compensate for the error that is caused by canceling the cross components in the frequency-domain equalizer. In the time-domain, To compensate for the performance of frequency-domain equalizer the time-domain equalizes the distorted signals at a frame by using the Gold-code as a training sequence in the receiver after the Gold-codes are inserted into the guard signal in the transmitter. By using the proposed equalization method, we can achieve faster and more efficient equalization method that has the reduced computational complexity and improved performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.9C
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• pp.820-825
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• 2007

Super-orthogonal space-time trellis code (SOTTC) uses the expanded set of the orthogonal space-time block code to obtain coding gain and diversity gain without loss of transmit rate. In SOSTTCs, signal set expansions are performed by rotating the first column of the code matrix. The rotating phases used previously were selected to avoid the signal constellation expansion rather than the performance improvement. In this paper, we make a design criterion to select the proper rotating phase to improve the performance of SOSTTCs for fast Rayleigh fading channels. In addition, we design improved SOSTTCs by using the proper rotating phase. Simulation results are also provided to confirm our SOSTTCs are superior to the previous SOSTTCs in the view of BER performance.

• Journal of Communications and Networks
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• v.7 no.3
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• pp.307-312
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• 2005

In this work, we study the performance of a serial concatenated scheme comprising a convolutional code (CC) and an orthogonal space-time block code (STBC) separated by an inter-leaver. Specifically, we derive performance bounds for this concatenated scheme, clearly quantify the impact of using a CC in conjunction with a STBC, and compare that to using a STBC code only. Furthermore, we examine the impact of performing antenna selection at the receiver on the diversity order and coding gain of the system. In performing antenna selection, we adopt a selection criterion that is based on maximizing the instantaneous signal-to­noise ratio (SNR) at the receiver. That is, we select a subset of the available receive antennas that maximizes the received SNR. Two channel models are considered in this study: Fast fading and quasi-static fading. For both cases, our analyses show that substantial coding gains can be achieved, which is confirmed through Monte-Carlo simulations. We demonstrate that the spatial diversity is maintained for all cases, whereas the coding gain deteriorates by no more than $10\;log_{10}$ (M / L) dB, all relative to the full complexity multiple-input multiple-output (MIMO) system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.12A
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• pp.1009-1018
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• 2003

A new fading channel estimation technique is proposed for an OFDM based modem In the ITS system. The algorithm is based on the transfer function extraction of the channel using the pilot signals and compensated the channel preceding the equalization. The newly derived algorithm is division-free arithmetic operations allows the faster circuit operation and the smaller circuit size. Proposed techniques compensate firstly the distortion which is generated at fading channels and secondly eliminate inter-symbol interference. All algorithms are suitability estimated and improved for a system implementation using digital circuits. As the results, the circuit size is reduced by 20% of the conventional design and achieved about 10% performance improvement at low SNR under 10dB in case of ITS system adapted 16-QAM mode.