• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7C
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• pp.691-699
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• 2006

Despite of the in-depth effort to cantrol the variability in IP networks, quality of service (QoS) is still not guaranteed in the IP networks. Thus, it is necessary to deal with the audible artifacts caused by packet lasses. To overcame the packet loss problem, most speech coding standard have their own embedded packet loss concealment (PLC) algorithms which adapt extrapolation methods utilizing the dependency on adjacent frames. Since many low bit rate CELP coders use predictive schemes for increasing coding efficiency, however, error propagation occurs even if single packet is lost. In this paper, we propose an efficient PLC algorithm with consideration about the speech characteristics of lost frames. To design an efficient PLC algorithm, we perform several experiments on investigating the error propagation effect of lost frames of a predictive coder. And then, we summarize the impact of packet loss to the speech characteristics and analyze the importance of the encoded parameters depending on each speech classes. From the result of the experiments, we propose a new PLC algorithm that mainly focuses on reducing the error propagation time. Experimental results show that the performance is much higher than conventional extrapolation methods over various frame erasure rate (FER) conditions. Especially the difference is remarkable in high FER condition.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.3
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• pp.19-28
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• 1998

This paper is concerned with the implementation of the equalization technique in a DCS 1800 system employing the soft-decision output Viterbi algorithm (SOVA), which makes the hardware complexity comparable to the hard decision MLSE and gives reliable performance. Also, the channel estimation technique with enhances the perfdormance of the soft-decision output equalizer is proposed, and the Viterbi decoder which operates effectively with the soft-decision output of the qualizer is implemented using the Very High Speed ICs Hardware Description Language (VHDL). From the simulation results, it is shown that the implemented Viterbi decoder operates effectively and the SOVA outperforms the hard-decision MLSE in terms of the frame erasure rate (FER) and bit error rate (BER).

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.6
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• pp.141-148
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• 2009

Space-time block codes (STBC) have no coding gain but they provide a full diversity gain with relatively low encoder/decoder complexity. Therefore, STBC should be concatenated with an outer code which provides an additional coding gain. In this paper, we consider the concatenation of multiple trellis-coded modulation (MTCM) codes with STBC for achieving significant coding gain with full antenna diversity. Using criteria of equal transmit power, spectral efficiency and the number of trellis states, the performance of concatenated scheme is compared to that of previously known space-time trellis codes (STTC) in terms of frame error rate (FER). Simulation results show that MTCM codes concatenated with STBC offer better performance on fast Rayleigh fading channels, than previously known STTC with two transmit antennas and one receive antenna.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.1
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• pp.1-11
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• 2004

This paper presents an implementation of smart antenna system channel card that executes modulation/demodulation. Operations and performances of modules of implemented channel card is confirmed and field test of channel card shows the performance of smart antenna systems. Based on the analysis obtained from the field test in cdma2000 1x environments which contains multipath lading, it is confirmed that smart antenna system channel card provide exact beampattern to the DOA and performance of proposed channel card has better FER by 5∼8 times, compared to 2 antenna diversity system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5C
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• pp.338-343
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• 2005

MIMO(Multiple Input Multiple Output) systems are considered as one of the most promising systems for next generation mobile communication systems which require efficient frequency resource utilization as well as high data rate transmissions. BLAST-STTC is the MIMO system which transmits information from many of STTC encoder groups with two transmit antennas and cancels the interference from other groups in receiver. In this paper we propose a reverse-ordered iterative decoding scheme for BLAST-STTC systems which achieve full diversity gain for all groups and improve the performance of interference cancellation, and compare the error performance of the proposed scheme with general schemes.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.05b
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• pp.1085-1088
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• 2003

본 논문은 3 세대 이동통신(IMT-2000) 방식으로 고려되고 있는 CDMA2000 1X 환경에서의 성능 향상을 위해 스마트 안테나기술을 기지국에 적용하였다. 본 논문에서는 스마트 안테나 시스템의 핵심 모듈인 채널카드를 하드웨어로 실제 구현하여 각 구성 모듈의 결과들을 확인하였고, 또한 실제 구현된 스마트안테나의 채널카드를 이용해 성능 분석을 수행하였다. 필드 테스트 결과 스마트 안테나 시스템이 기존의 2 안테나 다이버시티보다 1/10정도 FER(Frame Error Rate)이 낮은 것을 확인했다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.10
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• pp.52-56
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• 2009

In this paper, we investigate the performance of the ARQ-aided downlink Time Switched Transmit Diversity (TSTD) in the WCDMA LCR-TDD system, when power ramping is applied. The proposed power ramping scheme ramps up the transmission power and then retransmits the data, when the receiver sends the response signal (ACK or NACK signal) to the transmitter and the response signal is NACK signal. Simulation results demonstrate that the proposed scheme yields about 0.7dB performance gain in terms of average Eb/N0, compared with the conventional ARQ-aided TSTD when a mobile speed is 3km/h and an frame error rate (FER) is 1%, respectively. In addition, 2.5% of throughput gain is shown when average Eb/N0 is equal to 0dB.

• Journal of Communications and Networks
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• v.5 no.2
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• pp.141-149
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• 2003

In this paper, we investigate design criteria and the performance of the space-frequency bit-interleaved coded modulation (SF-BICM) systems in frequency-selective Rayleigh fading channels. To determine the key parameters that affect the performance of SF-BICM, we derive the pairwise error probability (PEP) in terms of the determinant of the matrix corresponding to any two codewords. We prove that the bit-interleavers do the function of distributing the nonzero bits uniformly such that two or more nonzero bits are seldom distributed into the symbols that are transmitted in the same frequency bin. This implies that the bit-interleavers transform an SF-BICM system into an equivalent 1-antenna system. Based on this, we present design criteria of SFBICM systems that maximizes the diversity order and the coding gain. Then, we analyze the performance of SF-BICM for the case of 2-transmit antennas and 2-multipaths by deriving a frame error rate (FER) bound. The derived bound is accurate and requires only the distance spectrum of the constituent codes of SF-BICM. Numerical results reveal that the bound is tight enough to estimate the performance of SF-BICM very accurately.

• Journal of Communications and Networks
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• v.6 no.3
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• pp.258-268
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• 2004

We demonstrate rotationally invariant space-time (ST) trellis codes with a 4-D rectangular signal constellation for data transmission over fading channels using two transmit antennas. The rotational invariance is a good property to have that may alleviate the task of the carrier phase tracking circuit in the receiver. The transmitted data stream is segmented into eight bit blocks and quadrature amplitude modulated using a 256 point 4-D signal constellation whose 2-D constituent constellation is a 16 point square constellation doubly partitioned. The 4-D signal constellation is simply the Cartesian product of the 2-D signal constellation with it-self and has 32 subsets. The partition is performed on one side into four subsets A, B, C, and D with increased minimum-squared Euclidian distance, and on the other side into four rings, where each ring includes four points of equal energy. We propose both linear and nonlinear ST trellis codes and perform simulations using an appropriate multiple-input multiple-output (MIMO) channel model. The 4-D ST codes constructed here demonstrate about the same frame error rate (FER) performance as their 2-D counterparts, having however the added value of rotational invariance.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.6
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• pp.101-108
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• 2013

In this paper, we propose a method in which the negative acknowledge (NACK) message is used as command for cooperation and spectrum sharing. This allows for an automatic request for cooperation and sharing when the direct link of the primary user is in outage, and also allows for saving the number of control messages in cooperation-spectrum sharing based paradigm. In the sharing phase, the selected relay shares a power fraction of $1-{\alpha}$ for secondary transmitted signal while the remaining of ${\alpha}$ is for primary retransmitted signal. In the case of no relay collected, primary transmitter uses NACK as a command to retransmit the signal with fully power fraction (${\alpha}=1$). Both systems are assumed to employ BPSK signals. In this scheme, we propose the joint optimal decoding in the secondary user. The frame error rate (FER) performance at both systems is then analyzed. The theoretical and simulation results validate the analysis and confirm the efficiency of the protocol.