Cheolsung Kim

Low-power auto focus algorithm using modified DCT for the mobile phones

A new focus value calculation method based on the middle frequency component of DCT and applicable in auto focus function of a mobile phone is presented. Experimental results confirm the exactness in focus value calculation, power efficiency and immunity to impulsive noises of the proposed method.

Performance Evaluation for A closed loop power control using An Efficient Channel Estimation in SAT-CDMA

This paper presents an efficient closed-loop power control algorithms for the next generation mobile satellite systems. Although we could not see any active role of a satellite system in the 3G networks, satellite system will provide strong advantages in future systems for certain applications. Because a satellite link has longer round trip delay than a terrestrial link, we need time delay compensation- and efficient channel estimation algorithms that would make the satellite component especially efficient. After presenting the satellite radio interface of the 3G system, we suggest powerful power control which need to be considered in the beyond 3G systems

Cell Range Expansion and Time Partitioning for Enhanced Inter-cell Interference Coordination in Heterogeneous Network

In this paper, we propose a cell selection scheme and interference management scheme in Heterogeneous Network (HetNet). The cell selection scheme is based on the SINR, and the cell expansion range can vary through the offset value. We can manage the interference between the macro cell and Picocell, using ABS in the time domain. Also, a flexible ABS density is applied, to increase the spectrum efficiency. We show the simulation results of the selection scheme based on SINR with different offset values (6dB, 12dB) and the interference management scheme. Simulation results show that the proposed scheme can improve the user spectrum efficiency of the macro cell and Pico cell user. Eventually, the proposed scheme can improve overall user performance.

On the performance of an OFDM/CDMA system under realistic channel conditions

There has been increasing interest in applying multicarrier (MC)/code division multiple access (CDMA) system for wireless personal and multimedia communication applications. We evaluate the performance of an OFDM/CDMA communication system in the frequency domain using autoregressive (AR) modeling. Owing to AR modeling, the transmission channel can be modeled more closely to the realistic mobile radio environment based on measured data and also we can save enormously on the simulation time. We compare the performance of the OFDM/CDMA system corresponding to the variation of the SNR and the number of users.

Statistical modeling of W-CDMA signals for use over frequency-selective multipath channels

This letter presents a mathematical model for the statistics of wideband code-division multiple-access signals which experience multipath fading. The statistics are obtained from numerically generated signals, and are then modeled with an offset noncentral chi distribution with three degrees of freedom. The mathematical model is tested against the numerically generated data by the use of a chi-square goodness-of-fit test.

New 4-dimensional constellation-rotation modulation method for DVB-NGH

This paper proposes a new 4-dimensional constellation-rotation (CR) method that uses two consecutive CR operations for the constellation of QAM signals. The computer simulation results show that the proposed method performs better than a conventional 2-dimensional CR method as both a channel code rate and an erasure ratio increase.

Statistical model of W-CDMA signals over realistic multipath channel

This paper proposes a statistical model of the wideband code division multiple access (W-CDMA) signals. The performance of a W-CDMA system is evaluated by calculating the average bit error rate (BER) which is derived from the probability distribution of the W-CDMA receiver output. If a statistical model of the receiver output is available, the performance evaluation becomes much simpler and it enables diverse analyses of the system for channel coding and other purposes. In this paper the statistical model of W-CDMA signals, more specifically those of the receiver outputs, is represented as a Nakagami-m distribution, considering two cases of bandwidths and channel environments. The adequacy of a statistical model is verified by chi-square test of 1% significance level and the comparison of BER obtained from simulation data and the statistical model.

Simulation results according to bit truncation in 4k-FFT algorithm

In this paper, we present an efficient design and implementation of FFT algorithm which is an important part of OFDM system. 4k-FFT algorithm is proposed and implemented in field programmable gate arrays (FPGAs). We measure the quantization error of FFT algorithm. Measured results show the maximum quantization error of 6.793259/5.662575 (real/imaginary value in 12 stage MSB truncation), 3.112945/2.627586 (real/imaginary value in 12 stage LSB truncation), 0.000756/0.000458 (real/imaginary value in 6 stage LSB/6 stage MSB truncation).

Improvement of the Combined AMC-MIMO Systems with Independent MCS Level Selection

In this paper, we propose and observe a system that adopts Independent MCS (Modulation and Coding Scheme) level for each layer in the combined AMC-V-BLAST (Adaptive Modulation and Coding-Vertical-Bell-lab Layered Space-Time) system. Also, comparing with the combined system using Common MCS level, we observe how much throughput performance is improved. As a result of simulation, Independent MCS level case adapts modulation and coding scheme for maximum throughput to each channel condition in separate layer, resulting in improved throughput compared to Common MCS level case. Especially, the results show that the combined AMC-V-BLAST system with Independent MCS level achieves a gain of 700kbps in 7~9dB SNR (Signal-to-Noise Ratio) range.

Performance of DS-CDMA system with smart antenna for different bandwidths in the wideband multipath channel

In this paper, the performance of DS-CDMA system with smart antenna is analyzed for different bandwidths (1.25 MHz, 5 MHz) and different channel environments (rural, urban). For the analysis of DS-CDMA system with smart antenna, the vector channel having spatio-temporal correlation is modeled as a time-variant linear filter in time, and each multipath is assumed as a reflective wave from only one direction (only one cluster) in space. Several multipaths within one chip are distinguished into each one and the strongest signal is elected. DS-CDMA system with smart antenna using wider bandwidth presents better performance than that using narrow bandwidth. It is shown that smart antenna is more effective in urban area when using 2D-RAKE receiver.