• Journal of the Korea Society of Computer and Information
• /
• v.24 no.5
• /
• pp.19-26
• /
• 2019

In this paper, we consider the D2D Transmitter(Tx) and Receiver(Rx) pair assignment problem in the cellular system. Sharing the resource of the cellular system, D2D users may cause interference to the cellular system, though it is beneficial to improve the D2D user Capacity. Therefore, to protect the cellular users, D2D transmit power should be carefully controlled. Previously, optimal Tx-Rx assignment to minimize the total transmit power of users was investigated. Accordingly, the iterative algorithm to find the optimum Tx-Rx asignment was obtained. In this work, we consider the case where Tx group users becomes Rx group users, and Rx group users become Tx group users. We prove that the Tx-Rx assignment problem has the duality property. We present the numerical examples that show the duality between U-link and D-link.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.12 no.1
• /
• pp.258-269
• /
• 2020

This paper proposes Snapping Shrimp Noise (SSN) detection and corrupted Orthogonal Frequency Division Multiplexing (OFDM) reconstruction methods to increase Bit Error Rate (BER) performance when OFDM transmitted signal is corrupted by impulsive SSNs in underwater acoustic communications. The proposed detection method utilizes multilayer wavelet packet decomposition for detecting impulsive and irregularly concentrated and SSN energy in specific frequency bands of SSN, and the proposed reconstruction scheme uses iterative decision directed-subcarrier reconstruction to recover corrupted OFDM signals using multiple carrier characteristics. Computer simulations were executed to show receiver operating characteristics curve for the detection performance and BER for the reconstruction. The practical ocean experiment of SAVEX 15 demonstrated that the proposed method exhibits a better detection performance compared with conventional detection method and improves BER by 250% and 1230% for uncoded and coded data, respectively, compared with the conventional reconstruction scheme.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.18 no.8
• /
• pp.1226-1237
• /
• 1993

For data transmission over strictly band-limited non-ideal channels, different types of filters with arbitrary responses are needed. In this paper. we proposed two efficient techniques for the design of such FIR filters whose response is specified in either the time or the frequency domain. In particular when a fractionally-spaced structure is used for the transceiver, these filters can be efficiently designed by making use of characteristics of oversampling. By using a minimum mean-squared error criterion, we design a fractionally-spaced FIR filter whose frequency response can be controlled without affecting the output error. With proper specification of the shape of the additive noise signals, for example, the design results in a receiver filter that can perform compromise equalization as well as phase splitting filtering for QAM demodulation. The second method ad-dresses the design of an FIR filter whose desired response can be arbitrarily specified in the frequency domain. For optimum design, we use an iterative optimization technique based on a weighted least mean square algorithm. A new adaptation algorithm for updating the weighting function is proposed for fast and stable convergence. It is shown that these two independent methods can be efficiently combined together for more complex applications.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.11A
• /
• pp.1182-1189
• /
• 2007

Frequency reuse in a cellular wireless communication environment gives rise to a phenomenon of cochannel interference. This paper introduces a power control strategy for OFDM based communication systems operating in such an environment. Among the existing power control schemes, IWF(iterative waterfilling) is known to exhibit relatively good performance. However, it requires feedback of power level and bit allocation information for each subcarrier from a receiver to its associated transmitter, which can lead to a considerable overhead, especially for the case of employing large number of subcarriers. Motivated by this, we present a simplified power control scheme with reduced overhead feedback, which allocates some nonzero identical power to the subcarriers of which channel conditions are above a certain threshold and zero power to the other ones. Computer simulations show that the proposed strategy produces a good approximation to the performance of the IWF in terms of the transmission power level while it requires less overhead feedback.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.2C
• /
• pp.139-147
• /
• 2010

A novel turbo coded modulation scheme, called turbo-APPM, for deep space optical communications is constructed. The constructed turbo-APPM is a serial concatenations of turbo codes, an accumulator and a pulse position modulation (PPM), where turbo codes act as an outer code while the accumulator and the PPM act together as an inner code. The generator polynomial and the puncturing rule for generating turbo codes are chosen to show the low bit error rate. At the receiver, the joint decoding is performed by exchanging soft information iteratively between the inner decoder and the outer decoder. In the outer decoder, a local iterative decoding for turbo codes is conducted before transferring soft information to the inner decoder. Poisson distribution is used to model the deep space optical channel. It is shown by simulations that the constructed turbo-APPM provides coding gains over all previously proposed schemes such as LDPC-APPM, RS-PPM and SCPPM.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.3C
• /
• pp.304-310
• /
• 2009

This paper proposes a successive MAP (maximum a posteriori probability) detection scheme with SoIC(soft interference cancellation) to reduce the receiver complexity of hierarchical M-ary QAM system. For the successive MAP detection, modulation symbols generated from the other data streams are treated as Gaussian noise or eliminated as the soft interference according to their priorities. The log-likelihood ratio of the a posteriori probability (LAPRP) of each bit is calculated by the MAP detector with an adjusted noise variance in order to take the elimination and Gaussian assumption effect into account. By separating the detection process into the successive steps, the detection complexity is reduced to increase linearly with the number of bits per hierarchical M-ary QAM symbol. Simulation results show that the proposed detection provides a small performance degradation as compared to the optimal MAP detection.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.10A
• /
• pp.1042-1049
• /
• 2007

Frequency reuse in a cellular wireless communication environment gives rise to a phenomenon of cochannel interference. This paper introduces a power control strategy for OFDM based communication systems operating in such an environment. Among the existing power control schemes, IWF(iterative waterfilling) is known to exhibit relatively good performance. However, it requires feedback of power level and bit allocation information for each subcarrier from a receiver to its associated transmitter, which can lead to a considerable overhead, especially for the case of employing large number of subcarriers. Motivated by this, we present a simplified power control scheme with reduced overhead feedback, which allocates some nonzero identical power to the subcarriers of which channel conditions are above a certain threshold and zero power to the other ones. Computer simulations show that the proposed strategy produces a good approximation to the performance of the IWF in terms of the transmission power level while it requires less overhead feedback.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.47 no.3
• /
• pp.16-21
• /
• 2010

In this paper, the linear source and relay precoders are designed for AF MIMO relay systems. In order to minimize mean squared error (MSE) of received symbol vector, the source and relay precoders are proposed, and MMSE receiver which is suitable to those precoders is utilized at the destination node. As the optimal precoders for source and relay nodes are not represented in closed form and induced by iterative method, we suggest a simple precoder design scheme. Simulation results show that the performance of the proposed precoding scheme is comparable with that of optimal scheme and outperforms other relay precoding schemes. Moreover, in high SNR region, it is revealed that SNR between source and relay node is more influential than SNR between relay and destination node in terms of bit error rate.

• Economic and Environmental Geology
• /
• v.43 no.4
• /
• pp.349-358
• /
• 2010

For imaging complex subsurface structures such as salt dome, faults, thrust belt, and folds, seismic prestack reverse-time migration in depth domain is widely used, which is performed by the cross-correlation of shot-domain wavefield extrapolation with receiver-domain wavefield extrapolation. We apply the prestack reverse-time migration, which had been developed at KIGAM, to the seismic field data set of Block 5 in Jeju basin of Korea continental shelf in order to improve subsurface syncline stratigraphy image of the deep structures under the shot point 8km at the surface. We performed basic data processing for improving S/N ratio in the shot gathers, and constructed a velocity model from stack velocity which was calculated by the iterative velocity spectrum. The syncline structure of the stack image appears as disconnected interfaces due to the diffractions, but the result of the prestack migration shows that the syncline image is improved as seismic energy is concentrated on the geological interfaces.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.2C
• /
• pp.306-314
• /
• 2004

Some receiver(and most transmit) beamforming algorithms with an array antenna at a cellular CDMA base stations require accurate internal and external calibrations. The external calibration, which usually needs to be done only once, determines the array manifolds, i.e. the complex response of each antenna as a function of DOA(Directions of Arrival). The internal calibrations are necessary because characteristics of RF/IF circuity of each receiver chain vary differently in response to temperature or humidity changes. We propose an iterative subspace-based calibration algorithm for an asynchronous CDMA-based antenna away in the presence of unknown gain and phase error is presented. We verify the subspace-based calibration algorithms by performing the experiment using measured data. Also, we propose an efficient algorithm using the simulated annealing technique. This algorithm overcomes the problem of the initial guessing in the subspace-based approach.