• Journal of the Korean Institute of Intelligent Systems
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• v.24 no.1
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• pp.28-32
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• 2014

For a signal such as speech showing piece-wise linear shape in a very short time period, a nonuniform sampling method based on the inflection point detection (IPD) is proposed to reduce data rate. The method exploits the geometrical characteristics of signal further than the existing local maxima/minima detection (MMD) based sampling method. As results, the reconstructed signal by the interpolation of the IPD based sampled data resembles the original speech more. Computer simulation shows that the proposed IPD based method produces about 9~23 dB improvement over the existing MMD method. To show the usefulness of the IPD technique, it is applied to speech coding, and compared to the continuously variable slope delta modulation (CVSD). The nonuniformly sampled data is binary coded with one bit flag set "1". Noninflection samples are not sent, but only flag bits set 0 are sent. The method shows 0.3 ~ 9 dB SNR and 0.5 ~ 1.3 mean opinion score (MOS) improvements over the CVSD.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6A
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• pp.420-425
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• 2012

A forward error correction (FEC) coding techniques is one of time diversity techniques with which the effect of channel impairments due to noise and fading are spreaded over independently, and thus the performance could be improved. Therefore, the performance of the FEC scheme can be maximized if we minimize the correlation of channel information across over a codeword. In this paper, we propose a block turbo code with the maximized time diversity effect which may be reduced due to utilization of high order modulation schemes and due to transmission over a comparatively fast fading environment. Especially, we propose a very simple formula to calculate the address of coded bit allocation, and thus we do not need any additional outer interleavers, i.e., inter-codeword interleavers. The simulation resuts investigated in this paper reveal that the proposed scheme can provide the performance gain of more than a few decibels compared to the conventional schemes.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.3
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• pp.193-201
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• 2022

SOQPSK-TG is a modulated signal for aircraft telemetry with excellent frequency efficiency and power efficiency. In this paper, the phase waveform of the partial response SOQPSK-TG modulation is linearly approximated and modeled as a full response double duobinary SOQPSK (SOQPSK-DD) signal. And using the XTCQM method and the Laurent decomposition method, the SOQPSK-DD signal was approximated as OQPSK having linear pulse waveforms, and the results of the two methods were proved to be the same. In addition, it was confirmed that the Laurent decomposition waveform of the SOQPSK-DD signal approximates the Laurent decomposition waveform of the original SOQPSK-TG signal. And it was shown that the decision feedback IQ-detector, which applied the Laurent decomposition waveform of SOQPSK-DD to the detection filter, exhibits almost the same performance even with a simpler waveform than before.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.3A
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• pp.151-156
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• 2012

In this paper, design of quasi-cyclic(QC) low-density parity-check codes is proposed to have full diversity for space-time bit-interleaved coded modulation(ST-BICM) systems. Necessary and sufficient conditions that the proposed scheme has full diversity are proved as the condition that submatrices corresponding to the system part of codewords are invertible. And new construction method of binary invertible matrices for QC LDPC codes in ST-BICM systems are also proposed and modification for parity-check matrices are also explained.

• Proceedings of the IEEK Conference
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• 2004.08c
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• pp.653-657
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• 2004

The average bit error rate (HER) performance of a Gray coded arbitrary rectangular quadrature amplitude modulation (AR-QAM) signal with maximal ratio combining (MRC) diversity in an arbitrarily correlated Nakagami-m fading channel is derived and analyzed. The derived two types of general solutions are a simple closed-form and an integral form, depending on the types of the values (integer and non-integer) of the fading parameter. Using the derived equations in this paper, we analyzed the HER performances numerically based on the practical base station antenna configuration. The results show that MRC reception is a very effective scheme so far even though the combined signals are not independent each other because of the correlation values. The antenna height and separation of the MRC system relate to the correlation coefficient value between antennas, and go a long way with the diversity advantage. In particular, it is needed to be determined the antenna height that is carefully do for the diversity advantage because the correlation coefficient and the antenna height gain are contrary to each other from the aspect of the system performance. The expressions presented here can offer a convenient way to evaluate the exact HER performance of an arbitrary rectangular QAM signal with MRC diversity reception for various cases of practical interest on a correlated Nakagami fading channel.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.549-551
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• 2002

A Wireless Local Area Network (WLAN) is a flexible data communication system implemented as an extension to, or as an alternative for, a wired LAN with in a building or campus. However, communications in an indoor environment present problems not encountered in outdoor wireless communication systems. Since cellular type systems are interference limited, the indoor environment is more hostile than the outdoor environment due to the lower propagation constant. In this paper, the equation for the signal to interference ratio in a multistory building will be derived. Knowing the S/I ratio, the floor frequency reuse can be determined. Finally, the simulation in this research is designed to study the performance (BER) of WLAN system in the multistory environment by applying the 8-PSK Trellis Coded modulation technique. The procedure allows a quick evaluation of BER in Wireless LAN system due to the co-channel interference.

• Journal of Broadcast Engineering
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• v.12 no.4
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• pp.373-376
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• 2007

Recently, research on the enhancement of the conventional VSB scheme for DTV signal transmission have been done. Not to affect on the performance of the widely spread conventional receivers and at the same time be able to receive the enhanced stream. there have been efforts to enhance the coding scheme which is backward compatible with the conventional method. The conventional schemes proposed so far is based on the idea of combining a new trellis encoder with the standard 8-VSB trellis encoder. In this paper, we Propose serial concatenated turbo TCM scheme which combines two trellis encoder with the interleaver between them. We compare the performance of the proposed scheme and the existing scheme through computer simulation.

• Journal of Information Processing Systems
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• v.9 no.1
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• pp.53-68
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• 2013

We investigate the rate-compatible punctured convolutional (RCPC) codes concatenated with hierarchical QAM for designing a cross-layer unequal error protection scheme for H.264 coded sequences. We first divide the H.264 encoded video slices into three priority classes based on their relative importance. We investigate the system constraints and propose an optimization formulation to compute the optimal parameters of the proposed system for the given source significance information. An upper bound to the significance-weighted bit error rate in the proposed system is derived as a function of system parameters, including the code rate and geometry of the constellation. An example is given with design rules for H.264 video communications and 3.5-4 dB PSNR improvement over existing RCPC based techniques for AWGN wireless channels is shown through simulations.

• 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.

• 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.