So Ryoung Park

An efficient frequency offset estimator for OFDM systems and its performance characteristics

In this paper, we propose a new frequency synchronization algorithm for orthogonal frequency division multiplexing (OFDM) systems requiring only one training symbol, based on a conventional method which requires two training symbols. While the timing synchronization is obtained by using the conventional method, the carrier frequency offset is efficiently estimated by the proposed method. It is shown that the proposed method not only reduces the number of the training symbols but also possesses better performance than the conventional method without increase in complexity.

A multicarrier CDMA system with adaptive subchannel allocation for forward links

Multicarrier transmission schemes have been introduced into code-division multiple access (CDMA) systems to gain advantages for high data rate transmission. One of the methods is to transmit identical narrowband direct-sequence (DS) waveforms in parallel over a number of subchannels using frequency diversity. In this paper, we propose a multicarrier CDMA system with an adaptive subchannel allocation method for forward links. In the proposed system, instead of identical DS waveforms being transmitted over a number of subchannels in parallel, each users DS waveform is transmitted over the users favourite subchannel which has the largest fading amplitude among all the subchannels. We analyze the performance characteristics of the system when orthogonal and random signature sequences are used. The proposed system is shown to have performance gain over the conventional multicarrier CDMA system. We also investigate how the performance is influenced when the signal is not perfectly allocated into the best subchannel.

Multiple-access interference reduction for QS-CDMA systems with a novel class of polyphase sequences

In this paper, a new class of polyphase sequences for CDMA systems and its generation method are suggested, and the correlation properties of the sequence are investigated. The performance of the sequence in quasi-synchronous CDMA (QS-CDMA) systems is investigated under a frequency-selective, time-nonselective, slow Nakagami fading channel with additive white Gaussian noise (AWGN). It is shown that the performance of the QS-CDMA systems using the suggested sequence is independent of the number of users and is much better than that using the PN sequence.

Evaluation of directivity for planar antenna arrays

In this paper, the directivity, including phase shift factors, for several types of uniformly excited planar arrays is obtained. Four types of dipole arrays are considered: arrays of collinear short dipoles, and of parallel short dipoles; and broadside and end-fire arrays of crosses of short dipoles. Curves of directivity versus inter-element spacing and scan angle for planar arrays with these element power patterns are presented.

A DS-CDMA code acquisition scheme robust to residual code phase offset variation

We first investigate the effect of residual code phase offset on the direct-sequence code-division multiple-access code acquisition scheme using a noncoherent matched filter receiver. We then propose a new code acquisition scheme that is robust to the variation of the residual code phase offset and outperforms the conventional scheme. When the code phase offset normalized to the chip duration between two sequences is within the advancing step size, the sum of two successive matched filter outputs has a constant value regardless of the residual code phase offset when the noise is absent. Based on this observation, we propose a new code acquisition scheme and investigate the performance of the scheme. The proposed code acquisition scheme is analyzed in an additive white Gaussian noise and multiple-access interference environment. Finally, numerical results are given to show that the proposed scheme is more robust to the variation of the residual code phase offset and has better performance than the conventional scheme on average.

A novel detection criterion for weak m-ary signals and its application to ultrawideband multiple access systems

In this paper, we propose a novel criterion for the detection of weak m-ary signals. In the sense of minimizing the error probability, the proposed criterion is optimal when the signal strength approaches zero. Based on the proposed criterion, a detection scheme for ultrawideband multiple access systems is proposed and analyzed in the presence of impulsive interference. Numerical results show that the proposed detector requires less complexity than, and possesses almost the same performance as, the maximum likelihood detector. In impulsive interference, the proposed detector also offers significant performance improvement over the detector optimized for a Gaussian environment.

A new polyphase sequence with perfect even and good odd cross-correlation functions for DS/CDMA systems

A class of polyphase signature sequences for direct-sequence code-division multiple-access (DS/CDMA) systems is proposed. The proposed class has zero periodic (=even) cross-correlation (CC) function and approximate maximum magnitude N//spl pi/ of odd cross-correlation (OCC), where N is the length of sequences. Although the maximum magnitude is relatively large, it is observed that the maximum magnitude has little effect on the performance of the DS/CDMA system, since its frequency is very low. The performance of the proposed sequence in DS/CDMA systems is investigated and shown to be better than that of other sequences for an asynchronous additive white Gaussian noise channel environment with and without Rayleigh multipath fading.

Detection Schemes for Weak Signals in First-Order Moving Average of Impulsive Noise

In this paper, the detection of weak signals in additive noise described by the first-order moving average (FOMA) of an impulsive process is considered. Specifically, decision regions of the maximum likelihood (ML) and suboptimum ML (S-ML) detectors are derived in the FOMA noise model, and specific examples of the ML and S-ML decision regions are obtained. The ML and S-ML detectors are employed in the antipodal signaling system and compared in terms of bit error rate in an impulsive noise environment. Numerical results show that the S-ML detector, despite its reduced complexity and simpler structure, exhibits practically the same performance as the optimum ML detector. It is also observed that the performance gap between detectors for FOMA and independent and identically distributed noise becomes larger as the degree of noise impulsiveness increases

Nonparametric PN code acquisition using the signed-rank statistic for DS/CDMA systems in frequency-selective Rician fading channels

In this paper, signed-rank based nonparametric detectors are used for pseudonoise (PN) code acquisition in frequency-selective Rician fading channels. We first derive the locally optimum rank detector and then propose the locally suboptimum rank (LSR) and kth order modified signed-rank (MSR/sub k/) detectors using approximate score functions. We compare the hybrid parallel double-dwell scheme using the LSR and MSR/sub k/ detectors with that using the conventional squared-sum (SS) and modified sign (MS) detectors. From the simulation results, it is shown that the LSR and MSR/sub k/ detectors perform better than the SS detector using the cell averaging constant false-alarm rate processor and the MS detector by about 2-3 dB.

Locally optimum detector for correlated random signals in a weakly dependent noise model

In this paper, we consider a discrete-time random signal detection problem under the presence of additive noise exhibiting weak dependence. We derive the test statistic of the locally optimum detector under a weakly dependent noise model. The performance characteristic of the locally optimum detector is analyzed and compared with that of the square-law detector in term of asymptotic relative eƒciency. ( 1999 Elsevier Science B.V. All rights reserved. Zusmmenfassung In dieser Arbeit wird ein Problem der Detektion eines zeitdiskreten Zufallssignals in additivem Rauschen mit schwacher Abha‹ ngigkeit betrachtet. Die Teststatistik des lokal optimalen Detektors wird fu‹ r ein Rauschmodell mit schwacher Abha‹ ngigkeit abgeleitet. Die Leistungsfa‹ higkeit des lokal optimalen Detektors wird analysiert und mit jener des quadratischen Detektors in Hinblick auf asymptotische relative Eƒzienz verglichen. ( 1999 Elsevier Science B.V. All rights reserved. Re« sume«