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A new estimator for evolutionary spectrum (ES) based on short time Fourier transform (STFT) and modified group delay function (MGDF) by signal decomposition (SD) is proposed. The STFT due to its built-in averaging, suppresses the cross terms and the MGDF preserves the frequency resolution of the rectangular window with the reduction in the Gibbs ripple. The present work overcomes the magnitude distortion observed in multi-component non-stationary signals with STFT and MGDF estimation of ES using SD. The SD is achieved either through discrete cosine transform based harmonic wavelet transform (DCTHWT) or perfect reconstruction filter banks (PRFB). The MGDF also improves the signal to noise ratio by removing associated noise. The performance of the present method is illustrated for cross chirp and frequency shift keying (FSK) signals, which indicates that its performance is better than STFT-MGDF (STFT-GD) alone. Further its noise immunity is better than STFT. The SD based methods, however cannot bring out the frequency transition path from band to band clearly, as there will be gap in the contour plot at the transition. The PRFB based STFT-SD shows good performance than DCTHWT decomposition method for STFT-GD. Keywords--Evolutionary Spectrum, Modified Group Delay, Discrete Cosine Transform, Harmonic Wavelet Transform, Perfect Reconstruction Filter Banks, Short Time Fourier Transform., I INTRODUCTION IN general, signals like speech, seismic, biomedical signals (EEG, ECG), communication signals (frequency shift keying, radar returns involving Doppler shift, etc.) and communications over time varying channels (interference [...]

A novel signal-analysis technique that is capable of extracting periodic signals from noisy discrete-time observations without an additional external reference is presented. It is based on a derived formulation estimating the maximally allowable synchronous error for a given attenuation threshold after the timedomain averaging. First, a continuous signal is reconstructed from the discrete samples by using cubic-spline interpolation. Second, the region that the signal fundamental frequency may lie in is finely discretized, resulting in a number of candidates of the fundamental-frequency estimate. Third, for each candidate, the continuous signal is synchronously sampled, and the resultant discrete sequence is processed with the time-domain average. Such an operation of repeated sampling and averaging is referred to as scanning. Finally, the obtained series of average waveforms and their amplitude spectra are depicted as two gray images to visualize the computational results, and the waveforms and spectra of interest are picked out for further analysis. Examples are given to confirm the validity of the approach to diagnose machine faults under complicated conditions. Index Terms--Condition monitoring, machine-fault diagnosis, periodic signal, scanning, signal analysis, time-domain average.

This paper discusses bistatic synthetic aperture radar processing (complex image formation) using the Range Doppler Algorithm. The key step is to use an analytical form of the signal spectrum derived by the method of series reversion. The spectrum is used for secondary range compression (SRC), range cell migration correction, and azimuth compression. The algorithm is able to focus the azimuth-invariant bistatic configuration where the transmitter and receiver platforms are moving in parallel tracks with identical velocities. Moreover, the algorithm is able to handle reasonably high squints and wide apertures because SRC can be performed in the 2-D frequency domain. Index Term--Bistatic synthetic aperture radar (SAR) processing, range cell migration correction (RCMC), Range Doppler Algorithm (RDA), secondary range compression (SRC), series reversion.

We study the effect of imperfect channel estimation (ICE) on the error probability performance of M-level quadrature amplitude modulation (M-QAM) with maximal-ratio combining and equal-gain combining diversity formats in Nakagami fading channels. We provide a novel formulation of the biterror rate (BER) of M-QAM with ICE in terms of the signal constellation-dependent effective signal-to-noise ratios (SNRs) or amplitudes, which allows us to derive the general, accurate, and easy-to-evaluate BER formulas for square and rectangular diversity M-QAM with channel estimation errors. Our result shows that the performance loss caused by ICE may be manifested by the signal decision space distortion and a scaling of the effective SNR. Using our analytical result, we evaluate the performance of M-QAM with pilot-symbol assisted modulation and present some insightful findings. Index Terms--Error rate analysis, imperfect channel estimation (ICE), Nakagami fading channels, pilot symbol assisted modulation (PSAM), quadrature amplitude modulation (QAM).

The recent pairwise model, which generalizes the hidden Markov chain, one to the unsupervised restoration of hidden data is aimed at. They show the advantages of the pairwise Markov chain model with respect to the classical hidden Markov chain one for supervised and unsupervised restorations.

A demonstration is presented to show that a novel form of a stochastic resonance effect, under the form of a noise-improved performance is possible for an optimal Bayesian estimator is possible. The results provide a new step in the exploration of stochastic resonance and its potentialities for signal processing.

Byline: Tad Matsumoto (1), Tetsushi Abe (2), Kimmo Kansanen (1) Keywords: multi-dimensional channel sounding; turbo equalization; single carrier signaling; MIMO system; link- and system-level simulations Abstract: Current advances in multi-dimensional channel sounding techniques make it possible to evaluate performances of signal processing algorithms in realistic conditions. By using channel impulse response measurement data collected in the real fields, link-level performances of signal transmission techniques in the fields such as bit error rate (BER) and frame error rate (FER) performances can be evaluated. This technique is called link-level simulation. Through statistical analysis of link-level simulation results, system-level performances of the techniques such as geographical distribution of BER and FER in the area of interest can also be evaluated. This technique is called system-level simulation. This paper focuses on link- and system-level performances of a multiple-input multiple-output (MIMO) Turbo Equalizer in real fields. Methodologies for the link- and system-level simulations using field measurement data are first presented. Results of link- and system-level simulations using two-dimensional channel sounding field measurement data collected in Tokyo are then presented. Author Affiliation: (1) University of Oulu, Tutkjantie 2E, FIN-90014, University of Oulu, Finland (2) NTT DoCoMo, 3--5 Hikari-no-Oka, Yokosuka-Shi, Kanagawa-Ken, 239-8536, Japan Article History: Registration Date: 11/10/2004

Byline: YAWPO Yang (1), Joy Iong-Zong Chen (2), Ji-Chyun Liu (2) Keywords: order diversity; Nakagami fading; ordered statistics Abstract: Order diversity combining technique is one of efficient methods to lower the complexity but not to significantly degrade performance. Recently, Eng and Milstein [1] proposed a novel order-combining technique, called the second order diversity combining (SC2) and third order diversity combining (SC3) and applied to Rayleigh fading channel. SC2 and SC3 schemes mean that the two (three) signals with the first two (three) largest amplitudes among the branches are chosen and coherently combined. However, when compared to Rayleigh distribution, the Nakagami-m distribution [10] provides a more general and versatile way to model wireless channel. For the reason, the bit error rate (BER) performance of proposed schemes were then analyzed with order statistic method and compared to the traditional diversity technique over Nakagami fading environment in this paper. The results are compared to maximal ratio combining (MRC), and conventional selection combining (SC) in coherent reception and to equal gain combining (EGC) in noncoherent reception. The results show that SC is in performance the worst for either in coherent or in noncoherent schemes, as expected. The performance differences between SC2 (SC3) and MRC (EGC) are not significant when the diversity order L a$? 3, but the difference will increase when L aY= 5. It is worth noting that the result of [1] is a special case with fading figure, m = 1. It is also observed the performance is much affected by the number of diversity branches L, the fading figure m, and the signal-to-noise ratio (SNR). Author Affiliation: (1) Department of Electronics Engineering, China Institute of Technology, No. 245, Sec. 2, Yen-Chiu-Yuan Rd, Taipei, Taiwan R.O.C. (2) Department of Electrical Engineering, Chung Cheng Institute of Technology, National Defense University, Ta-Hsi, Tao-Yuan, Taiwan R.O.C. Article History: Registration Date: 11/10/2004

Outage probability computation is investigated for the Nakagami/Rician and Rician/Nakagami fading combinations under the assumption of independent identical distributed interferers. We show that with the consideration of both a minimum carrier-to-interference ratio and a minimum carrier-to-noise ratio, closed-form expressions can still be obtained in these two particular scenarios if the Nakagami parameter is restricted to integer values. These expressions are given in terms of the Marcum Q-function and modified Bessel functions, and therefore readily allow numerical evaluation for various cases of practical interest. When applicable, the results obtained as special cases of the offered closed-form expressions have been compared to those previously reported in the literature. Some numerical examples have been provided and discussed. Index Terms--Cellular mobile radio systems, cochannel interference, Nakagami fading, outage, Rayleigh fading, Rician fading.

Two uses of noninvertible maps (NIMs), one concerned with the problem of communication via chaos synchronization in signal processing, and the other with information storage in cycles of piecewise constant NIM, are introduced. A method is suggested, to obtain the assembled information from a disordered NIM cycle through control of chaos by a feedback loop.

Byline: Vicente Zarzoso (1), Asoke K. Nandi (1) Keywords: bicomplex numbers; blind source separation; closed-form estimators; complex mixtures; higher-order statistics; independent component analysis; multiuser detection Abstract: The problem of multiuser detection in wireless communications systems adopts, in flat-fading channels, a blind source separation (BSS) formulation of instantaneous linear mixtures. This contribution addresses the closed-form solutions to BSS in the complex-mixture scenario. The algebraic devices which span a unifying framework for the complex BSS closed-form estimators are developed. With the aid of these tools, results originally encountered in the real-mixture case are extended to the complex case, thus highlighting the remarkable parallelism existing between the real and complex problems in the context of their analytic solutions. Computer simulations illustrate the theoretical results and compare the proposed methods to other BSS procedures. Author Affiliation: (1) Signal Processing and Communications Group, Department of Electrical Engineering and Electronics, The University of Liverpool, Brownlow Hill, Liverpool, L69 3GJ, U.K. Article History: Registration Date: 13/10/2004

Byline: Vicente Zarzoso (1), Asoke K. Nandi (1) Keywords: blind source separation; closed-form estimators; contrast functions; higher-order statistics; independent component analysis; multiuser detection; performance analysis Abstract: The problem of multiuser interference cancellation in wireless cellular communication systems accepts a blind source separation (BSS) model. The present contribution studies the closed-form solutions to BSS in the real-mixture case. Connections among a number of seemingly disparate methods are unveiled, new procedures are put forward, and their asymptotic (large-sample) performance is analyzed. Simulation experiments illustrate and validate the theoretical results. Altogether, a unifying generic framework for closed-form BSS methods is developed. Author Affiliation: (1) Signal Processing and Communications Group, Department of Electrical Engineering and Electronics, The University of Liverpool, Brownlow Hill, Liverpool, L69 3GJ, U.K. Article History: Registration Date: 13/10/2004

We consider initial timing acquisition in discrete-sequence code-division multiple- access (DS-CDMA) when propagation is affected by multipath and fading, and where the base-station broadcasts a synchronization pilot signal in the form of bursts of modulated chips transmitted periodically and separated by long silent intervals. Subject to certain simplifying assumptions, we derive the maximum-likelihood (ML) estimator by solving a constrained maximization problem. Our ML timing estimator has constant complexity per observation sample. The relation to other estimation methods is addressed, and performance comparisons are provided by simulation. The proposed estimator yields good performance independently of the multipath-intensity profile of the channel, provided that the delay spread is not larger than a given maximum spread. Moreover, our estimator is fairly robust to the mismatch in the fading Doppler spectrum and provides good performance for both fast and slow fading. Index Terms--DS-CDMA systems, synchronization, timing estimation, wireless communications.

We propose an efficiently structured nonlinear finite-memory filter for denoising (filtering) a Gaussian signal contaminated by additive impulsive colored noise. The noise is modeled as a zero-mean Gaussian mixture (ZMGM) process. We first derive the optimal estimator for the static case, in which a Gaussian random variable (RV) is contaminated by an impulsive ZMGM RV. We provide an analytical derivation of the resulting mean-squared error (MSE), and compare the performance to that of the optimal linear estimator, identifying cases of significant improvement. Building upon these results, we develop a suboptimal finite-memory filter for the dynamic case, which is nearly optimal in the minimum MSE sense. The resulting filter is a nonlinearly weighted combination of a fixed number of linear filters, for which a computationally efficient architecture is proposed. Substantial improvement in performance over the optimal linear filter is demonstrated using simulation results.

A discrete-time multirate formulation has been introduced for asynchronous code division multiple access (CDMA) systems. The formulation can incorporate asynchronous user delays and multipath effects, and reveals links between CDMA receivers and array processing problems such as source separation and beamformer design. Linear receivers that can suppress multiuser interference, also called decorrelating receivers, can be obtained by using this framework.

This paper analyzes the effect of quantization in a digital signal component separator (SCS) for linear amplification with nonlinear components (LINC) transmitters. The analysis relies on the fact that the two signal components can be obtained as the source signal plus/minus a signal in quadrature to the source signal. The equations derived are vital because they allow the designer to optimize digital signal processor (DSP) power consumption and bandwidth. The word lengths that are required for the source signal and the quadrature signal can be calculated from the amplifier gain characteristic, the probability density function for the modulation scheme, and the specified adjacent channel interference (ACI). The validity of the analysis has been verified by means of simulations.

A comparison between the least mean square (LMS) and the ideal LMS/Newton algorithms was carried out via steady-state transient-time measurements with the model error as a performance gauge. The study demonstrated that the disparity between the performance of the two algorithms may not be as wide as initially thought if misalignments of the filter's tap-gains are considered. Computer simulations confirm the analytical results.

We evaluated the performance of fixed-delay tree-search detector with decision feedback (FDTS/DF) when used for nonlinear magnetoresistive (MR) read head channels. The feedback section of the FDTS/DF was replaced by RAM lookup table for nonlinear equalization. The evaluation was based on a computer simulation in which the read-back signal from the MR head was modeled from a measured MR transfer characteristic function and actual real reproduced isolated pulses. This performance was compared to that of PRML channels. We also compared the sensitivity of the FDTS/DF and PRML channels to variations in the recording channel frequency response due to head-medium spacing fluctuation. The results show that the FDTS/DF channel has good resistance to MR nonlinear distortion and channel response variations, and is superior to the PRML channels in terms of realistic recording channel response.

In this paper, we analyze the performance (power and bandwidth efficiency) of a recently proposed scheme with multidimensional signals, and both optimal detector and nonoptimal but simple detector, and show that they are inferior to known schemes with narrowband Nyquist signals and optimal detectors.

The experimental data on the spin wave pulse propagation in a magnetic thin film under static, spatially nonuniform magnetic fields is presented. The findings for the field dependent wave number and phase velocity properties provide potential microwave signal processing applications such as novel delay lines, wave number selective devices, dispersion control devices, millimeter wave compression and expansion devices, and chirp control devices.

We propose a theoretical evaluation of the matched filter bound (MFB) of L-branch antenna diversity with maximal-ratio-combining (MRC) in a frequency-selective Rayleigh fading channel. The theoretical derivation is based on a Karhunen-Loeve expansion. Although many previous approaches of this kind have been presented in the past, we give a more general and straightforward one as our model accounts for the correlations between the branches and between the channel taps within each branch, as well as the mismatch between the average received power per branch. The usefulness of our approach is shown through two different applications. First the benefits of a two branch receiver (L = 2) using spatial or polarization diversity for global system for mobile communication (GSM) and Interim Standard 95 (IS-95) downlink systems both using binary signaling, are compared. Second, with the use of our theoretical model, it is proved that diversity gain is in variant by any unitary transformation. As a result, and contrary to widespread belief polarization diversity gain is shown to be in-variant by spatial rotation of the receiver antennas. Index Terms--Code division multiple access (CDMA), Karhunen-Loeve expansion, matched filter bound, mobile communication systems, polarization diversity, space diversity, time division multiple access (TDMA).

A monolithic implementation of a cryptosystem based on the Corron and Hahs scheme [1] is hereby presented. The baseband chaotic encryption/decryption system has been designed at the transistor level and fabricated using AMI 1.2 [micro]m CMOS technology available through the MOSIS foundry. While the mathematical model of the Lorenz system is straightforward, its silicon implementation is not. Typical circuit design considerations need to be considered such as the system's dynamic range, internal signal processing mode and basic building blocks all with the intent to provide an optimal design. This brief addresses in detail: 1) practical design considerations of the cryptosystem and 2) actual measurement results that verify theoretical findings.

Pipelined analog-to-digital converters (ADCs) tend to be sensitive to component mismatches in their internal digital-to-analog converters (DACs). The component mismatches give rise to error, referred to as DAC noise, which is not attenuated or cancelled along the pipeline as are other types of noise. This paper describes an all-digital technique that significantly mitigates this problem. The technique continuously measures and cancels the portion of the ADC error arising from DAC noise during normal operation of the ADC, so no special calibration signal or auto-calibration phase is required. The details of the technique are described in the context of a nominal 14-bit pipelined ADC example at both the signal processing and register transfer levels. Through this example, the paper demonstrates that in the presence of realistic component matching limitations the technique can improve the overall ADC accuracy by several bits with only moderate digital hardware complexity.

A millimeter-wave optical frequency shifter (OFS) using coupled inverted slot lines (ISL's) described here is integrated on an X-cut LiNb[O.sub.3] substrate. Theoretical analysis shows that the use of the coupled ISL's makes it possible to decrease the distance between the arms of a Mach-Zehnder interferometer for optical frequency shifting. The ISL coupling characteristics measured at 60 GHz coincide well with the calculated ones. A 60-GHz frequency shifting of a 1.3-[micro]m optical carrier is experimentally demonstrated using two- and four-branch OFS's. The theoretical analysis and experimental results of the two-branch OFS show that the ratio of the frequency-shifted signal intensity to the optical image intensity is in proportion to the difference between the applied dc-bias voltage and the half-wave voltage. The four-branch OFS consists of two two-branch OFS's excited 180 [degrees] out of phase, and can suppress the optical image and original carrier simultaneously. The measurements of the four-branch OFS reveal the optical image suppression of over 12 dB and the original carrier suppression of 5 dB below the desired 60-GHz frequency-shifted signal. Index Terms-- Inverted slot lines, LiNb[O.sub.3] modulators, millimeter-wve phase shifters, millimeter-wave photonics, optical frequency shifter, traveling-wave optical modulation.

Index Terms-- Interactive learning, MATLAB, signal processing. I. SUMMARY Signal processing is now being used in many disciplines of engineering because of the omnipresence of desktop computers and sophisticated application environments. Many concepts involved in signal processing are difficult to learn because: they are embedded in discrete mathematics and not easy to visualize; and the background in which to embed the learning is lacking. This usually leads to erroneous implementation of a technique and difficulty in finding relevance of the material. In order to address these issues and teach techniques such as frequency analysis and signal modeling, a series of interactive notebooks have been developed. These notebooks are written in the integrated environment of Microsoft Word and MATLAB. Each notebook presents a principle and demonstrates its implementation via script in MATLAB. The student is then asked to exercise other aspects of the principle interactively by making simple changes in the MATLAB script. The student then receives immediate feedback concerning what is happening and can relate theoretical concepts to real effects upon a signal. He is finally required to implement the learned procedure on a signal from a database of actual measurements. Signals measured from real-world applications are used as much as possible. Students enjoy learning in this environment because it helps them visualize immediately the results of the mathematical manipulations and enables them to explore interactively.