Hong Gil Kim

Performance analysis of a coded OFDM system in time-varying multipath Rayleigh fading channels

We analyze the combined influence of the interchannel and intersymbol interferences, which result from the time variation and delay spread of mobile channels, on the performance of an orthogonal frequency-division multiplexing (OFDM) system. Both analysis and simulation results are presented for uncoded 16-QAM. We also investigate the performance of a Reed-Solomon (RS) coded 16-QAM OFDM system when the number of subcarriers varies: it is observed that there is an optimum number of subcarriers that minimizes the post decoding symbol error probability of the RS code for each channel state.

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.

Design and performance analysis of a convolutionally coded overlapping multicarrier DS/CDMA system

We consider convolutionally coded multicarrier direct-sequence code-division multiple access (DS/CDMA) systems using overlapping subchannels in time-limited and band-limited channels. A tight hound on the bit error probability of the decoder output is obtained in Rayleigh fading channels when the channel state information is ideally available. It is shown that the proposed system, the convolutionally coded overlapping multicarrier DS/CDMA system with a symbol mapping method utilizing the diversity, outperforms the conventional single carrier and nonoverlapping multicarrier systems using the same convolutional code. It is also shown that the proposed system can provide a larger system capacity and more effectively combat the partial band interference than the conventional ones.

PN code acquisition using signed-rank-based nonparametric detectors in DS/SS systems

In this paper, signed-rank based nonparametric detectors are used for pseudonoise (PN) code acquisition in direct-sequence spread-spectrum (DS/SS) systems. We first derive the locally optimum rank (LOR) detector and then propose the locally suboptimum rank (LSR) and modified signed-rank (MSR) detectors using approximate score functions. We compare the single-dwell scheme without the verification mode using the proposed LSR and MSR detectors with that using the conventional squared-sum (SS) and modified sign (MS) detectors. From the simulation results, it is shown that the proposed LSR and MSR detectors perform better than the MS detector by about 2-3 dB and are nearly optimum.

Estimation of distributed elevation and azimuth angles using linear arrays

Many results on the estimation of direction of arrival (DOA) have been obtained based on the assumption that the signal sources are point sources. Recently, it has been shown that signal source localization can be accomplished more adequately with distributed source models. In this paper, we consider modeling of S-dimensional distributed signal sources, in which a distributed source is represented by the center angles and degrees of dispersion. We address estimation of the elevation and azimuth angles of distributed sources based on the proposed distributed source modeling in the 3-dimensional space. Some examples are also included to more explicitly show the estimation procedures under the model: computer simulation results obtained by MUSIC-based methods with two uniform linear arrays are discussed.

Adaptive code acquisition using a GO-CFAR processor in DS/CDMA systems

We propose to use a greatest of (GO) CFAR processor for PN code acquisition in DS/CDMA systems. We compare the single-dwell scheme without the verification mode using the GO CFAR processor with that using the cell averaging (CA) and order statistics (OS) CFAR processors. From the simulation results, we can observe that the DS/CDMA systems with the GO CFAR processor has better performance than those with the CA and OS CFAR processors at abrupt change of the variance.

A multiuser receiver for trellis-coded DS/CDMA systems in asynchronous channels

We propose and analyze a multiuser receiver using a decorrelating filter and Viterbi decoders for trellis-coded direct-sequence code-division multiple-access (DS/CDMA) systems with biorthogonal signal constellation in asynchronous channels. The biorthogonality is implemented by user signature waveforms and the decorrelating filter. The performance of the proposed system is investigated with emphasis on the asymptotic cases: it is shown that the proposed system provides us with some coding gain and near-far resistance. It is confirmed that we can enhance the performance of the proposed system by using base-station antenna arrays.

An analysis of the median-shift sign detector under various noise distributions

We propose a new detector of which the basis is on the median-shift (MS) sign: the median-shift sign (MSS) detector is a generalization of the classical (standard) sign detector. We obtain the finite sample size and asymptotic optimum MS values for various noise probability density functions (pdfs). We analyze the problem of detecting known signals in noise of known distributions. The optimum MSS detector is shown to perform better than the sign detector in Gaussian noise: it has the best performance among the detectors compared in the non-Gaussian noise cases. It is noteworthy that the performance of the MSS detectors with constant MS values are nearly equal to that of the optimum MSS detector. We also investigate signal detection when only partial information is available on the noise. The MSS detectors with constant MS values perform almost equal to the sign detector in Gaussian noise: they perform better than the sign and Wilcoxon detectors for most signal strength ranges in the non-Gaussian noise cases. ( 1998 Elsevier Science B.V. All rights

Performance enhancement of the decorrelating detector using antenna arrays

A vector channel model is proposed and some statistical properties of the asymptotic efficiency of the decorrelating detector with base-station antenna arrays are investigated. It is shown that we can get gain over the conventional decorrelator by employing antenna arrays and the gain increases as the number of antennas increases and the angle dispersion decreases. It is also shown that we can increase the asymptotic efficiency of the decorrelating detector with base-station antenna arrays up to unity if we use an infinite number of antennas when the channel is angle-nondispersive: we cannot, however, increase the asymptotic efficiency of the decorrelating detector by employing base-station antenna arrays if the dispersion is infinite.

An adaptive multicarrier DS/CDMA system for forward links

We propose a multicarrier CDMA system with an adaptive subchannel allocation method for forward links. In the proposed system, each users DS waveform is transmitted over the users favorite subchannel having the largest fading amplitude among the subchannels. We analyze the performance of the system when orthogonal and random signature sequences are used and compare the performance with that of the multicarrier DS/CDMA system using frequency diversity. The results show that the proposed system has a performance gain over the frequency diversity system. We also investigate how the performance is influenced when the users signal is not perfectly allocated into the best subchannel.