Keukjoon Bang

A new PAPR reduction technique for OFDM systems using advanced peak windowing method

In this paper, we investigate an advanced peak windowing method as a peak-to-average power ratio (PAPR) reduction technique in orthogonal frequency division multiplexing (OFDM) systems. The advanced peak windowing method is performed by introducing new weighting coefficients in case that successive peaks are generated within a half of the window length. Applying the new weighting coefficients, we can tightly limit the successive peaks to the given threshold level. Through a computer simulation, we verify that the BER performance improvement can be achieved by the proposed peak windowing method while maintaining almost the same complementary cumulative distribution function (CCDF) and spectral characteristics.

PC-based receiver for Eureka-147 digital audio broadcasting

We present the design and implementation for a Eureka-147 digital audio broadcasting (DAB) receiver. We establish the specifications for the receiver and design the blocks required for DAB reception. Due to the fact that orthogonal frequency division multiplexing (OFDM) is the transmission technique used in the DAB system, the synchronization block plays a key role in the overall system performance among the receiving blocks in the DAB receiver, and for this reason we describe it in detail here. We also include descriptions of several implementation techniques that enable the receiver to run in real-time on a PC. Our findings show that the receiver implemented as described here satisfactorily meets our predetermined specifications.

A coarse frequency offset estimation in an OFDM system using the concept of the coherence phase bandwidth

A new coarse frequency offset estimation algorithm is proposed which performs robust operation in the presence of a symbol timing offset in an allowed range. The effect of a symbol timing offset on estimating a coarse frequency offset is analyzed and the coherence phase bandwidth according to the allowed symbol timing offset is introduced. In addition, a new technique for performing the coarse frequency estimation using the coherence phase bandwidth is described. Simulation results show that the proposed algorithm estimates a coarse frequency offset well under both AWGN and multipath channels even in the presence of the symbol timing offset within an allowed range.

A fast burst synchronization for OFDM based wireless asynchronous transfer mode systems

This paper proposes a burst synchronization method with a preamble for high data rate wireless asynchronous transfer mode (WATM) systems that use orthogonal frequency division multiplexing (OFDM). The preamble for synchronization is composed of four identical periods. Using this signal repetition, the correlation for symbol timing detection and frequency offset estimation are calculated. The proposed method improves the performance of synchronization by increasing the size of data used in the correlation operation. The analytic results show that by using the proposed method a gain of 1 dB in SIR (signal to interference ratio) is possible.

A New Timing Offset Estimation Algorithm Using Phase Difference Between Adjacent Subcarriers in Interleaved OFDMA Uplink Systems

A new timing estimator using phase difference between adjacent subcarriers is proposed for interleaved orthogonal frequency-division multiple access (OFDMA) uplink systems. The phase difference of adjacent subcarriers is represented as the summation of the information of timing offset which we want to estimate and the phase difference of channel frequency responses which can cause performance degradation. Thus, a method to reduce the phase difference of channel frequency responses is applied in time domain, and then timing offset information is estimated from phase difference in frequency domain. Simulation results confirm that the proposed estimator can decrease the mean square error (MSE) compared with channel impulse response (CIR) based method when the information of channel length is unknown.

A Robust Timing Recovery Algorithm for OFDM Systems

We propose a new robust timing recovery algorithm with small symbol timing jitter for orthogonal frequency-division multiplexing (OFDM) systems. The concept of coarse FFT window selection and adaptive reference pilot generation are employed in this paper. This proposed scheme avoids inter-symbol interference (ISI) as well as delayed locked loop (DLL) tracking failure over frequency selective time-varying channels. In addition, the proposed algorithm has much smaller and smoother steady state DLL tracking error than the conventional algorithm.

An Error-controlled Detection Method For PR-IV Magnetic Recording Systems

The major advantage of PR-IV channel modeling on high-density magnetic recording systems is that the maximum-likelihood sequence detector (MLSD) with optimal performance can be used. However, the MLSD has a complex structure and a high cost. Another detection method is the three-level detector (TLD). Its structure is simpler than the MLSDs, but its performance is extremely poor. Sometimes it is necessary to use a detection method that has a simpler structure than the MLSD, yet performs competitively. In this paper, a new detection scheme called an error-controlled detection (ECD), is proposed for PR-IV systems. Its hardware complexity is greatly reduced and the performance is competitive with the MLSD.

Improving The Spectral Efficiency For The Ofdm System Using The Time And Frequency Domain Equalization

In an OFDM system, data symbols are transmitted in parallel over multiple subchannels with a long symbol dzrration. A simple equalizer is expected to yield satisfactoly results provided that it uses a sufficiently long guard interval. But a long guard interval results in an excessive prolongation of the symbol duration and thus in bandwidth eflciency loss. In this article, we propose the dual equalization in both time and frequency domain. Thus it is possible to shorten the guard interval while maintaining the bit error rate performance or impvove the bit error rate performance while maintaining the guard interval DFEfDecision Feedback Equalization) is introduced for timedomain equalization while conventional I-tap linear equalizers are used for frequency-domain equalization. Simulation results show the effectiveness of the proposed algorithm on the multipath channel specified in ETSI Draft prETS 300 744.

Separation of character strings and high quality vectorization for digitized Korean cadastral map images

When making an automatic map interpreter for a geographic information system (GIS) using printed maps, some difficulties lie in the interconnections between character strings and lines, and the distortions of vectorization at the line crossings and junctions. In this paper, the authors focus on the fact that the problems are only found at the line crossings and junctions, which can be extracted using the conventional thinning algorithm. They propose a new method to overcome the two difficulties at the same time. The proposed method is applied to Korean cadastral maps, and the experimental results show that the method is effective in separating the character strings from the lines and getting high quality vectorization for the digitized map images. At the same time the processing time can be reduced.