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Purpose: In this study, the authors investigated the hypothesis that the perceived tight temporal synchrony of speech and gesture is evidence of an integrated spoken language and manual gesture communication system. It was hypothesized that experimental manipulations of the spoken response would affect the timing of deictic gestures. Method: The authors manipulated syllable position and contrastive stress in compound words in multiword utterances by using a repeated-measures design to investigate the degree of synchronization of speech and pointing gestures produced by 15 American English speakers. Acoustic measures were compared with the gesture movement recorded via capacitance. Results: Although most participants began a gesture before the target word, the temporal parameters of the gesture changed as a function of syllable position and prosody. Syllables with contrastive stress in the 2nd position of compound words were the longest in duration and also most consistently affected the timing of gestures, as measured by several dependent measures. Conclusion: Increasing the stress of a syllable significantly affected the timing of a corresponding gesture, notably for syllables in the 2nd position of words that would not typically be stressed. The findings highlight the need to consider the interaction of gestures and spoken language production from a motor-based perspective of coordination. Key Words: gesture, prosody, synchronization, stress, speech-hand coordination, capacitance, gesture, prosody, Although spoken language and manual gestures temporally overlap, it is less clear what variables affect the apparent shared timing of speech and gesture, or whether a predictable relationship of these [...]

Multicarrier code-division multiple access (CDMA) with time and frequency spreading has been recently considered as a candidate for fourth-generation (4G) wireless systems. This signaling scheme simultaneously utilizes code spreading in the time and frequency domains to simultaneously improve frequency diversity and minimize multiuser access interference. As a result, it is capable of outperforming multicarrier CDMA systems that employ 1-D spreading. In this paper, a novel adaptive subcarrier allocation algorithm is developed for multicarrier CDMA with time and frequency spreading to improve the overall bit error rate (BER) performance for all spreading configurations. This algorithm assigns users to subcarrier groups that provide favorable fading characteristics while simultaneously reducing the amount of interference caused to other users. The proposed algorithm is shown to provide a performance improvement, ranging from 1.5 dB with 2 x 16 (time x frequency) and spreading to 7 dB with 16 x 2 (time x frequency) spreading. The algorithm is also shown to maintain or improve the BER floor for each spreading configuration. It is concluded that at higher and lower levels of [E.sub.b]/[N.sub.o], a higher frequency- and time-domain spreading should be, respectively, employed to improve BER performance. Furthermore, the [E.sub.b]/[N.sub.o] threshold level to switch between time and frequency spreading for the analyzed system is found to be 2.5 dB. Index Terms--Adaptive subcarrier allocation, multicarrier code-division multiple access (CDMA), synchronous reverse links, time- and frequency-domain spreading.

This paper develops a synchronization-based scheme for calculating ambiguity function (AF) of a wideband chaotic signal. In the direct implementation, the formulation of the time-scaling chaotic signal takes much computational load and its accuracy determines the quality of the calculated AF diagrams. By exploring the generation of the chaotic signal, the impulsive synchronization theory can be used to produce its time-delay and time-scaling versions. With this observation, the AF diagrams can be accurately obtained by following correlation operation. A distinct characteristic of the proposed scheme is that the generation of the time-delay and time-scaling versions is implemented in an analog way, while the correlation operation can be implemented in a digital way. This mixed analog-digital structure provides the proposed scheme with implementation advantages and practical applicability.

Inverters for medium voltage drives operate at re. duced switching frequency so as to restrain the dynamic losses of the power semiconductor devices. The resulting current harmonics can be reduced by synchronous optimal pulsewidth modulation (PWM), provided that steady-state conditions prevail. Transient conditions, however, interfere adversely with the optimal modulation patterns. Such conditions necessarily occur when the modulator forms part of a conventional closed-loop control scheme. Trajectory tracking control is employed to achieve high dynamic control in conjunction with synchronous optimal PWM. An optimal trajectory of the stator flux linkage vector is derived from the pulse pattern in actual use. The stator flux linkage vector is forced to follow this target trajectory. Modifying the target trajectory in transient conditions enables closed-loop torque control in a deadbeat fashion while conserving optimal modulation. Experimental results obtained from a 30-kW prototype drive operated at only 200 Hz switching frequency demonstrate the effectiveness of the approach. Index Terms--High-performance control, medium-voltage drive, rotor field orientation, synchronous optimal puisewidth modulation (PWM), trajectory tracking control.

This paper proposes a novel fault-tolerant optimal neurocontrol scheme (FTONC) for a static synchronous series compensator (SSSC) connected to a multimachine benchmark power system. The dual heuristic programming technique and radial basis function neural networks are used to design a nonlinear optimal neurocontroller (NONC) for the external control of the SSSC. Compared to the conventional external linear controller, the NONC improves the damping performance of the SSSC. The internal control of the SSSC is achieved by a conventional linear controller. A sensor evaluation and (missing sensor) restoration scheme (SERS) is designed by using the autoassociative neural networks and particle swarm optimization. This SERS provides a set of fault-tolerant measurements to the SSSC controllers, and therefore, guarantees a fault-tolerant control for the SSSC. The proposed FTONC is verified by simulation studies in the PSCAD/EMTDC environment. Index Terms--Dual heuristic programming (DHP), faulttolerant optimal neurocontrol, missing sensor restoration (MSR), particle swarm optimization (PSO), radial basis funtion network, static synchronous series compensator (SSSC).

This paper presents a cost-effective electronic lamp driver design for high-intensity discharge (HID) burners based on a stacked buck converter topology. The circuit is operated in zero-voltage switching mode to improve the efficiency, and thereby, enable miniaturization. Among the several possible low-frequency-square-wave topologies, the proposed synchronous stacked buck converter, combined with a boost converter stage operating as power factor corrector, provides a two-stage HID lamp driver with excellent performance. Index Terms--High-intensity discharge (HID) electronic, synchronous buck converter, synchronous commutation, two-stage ballast.

This paper analyzes a number of basic coordination algorithms running on synchronous robotic networks. We provide upper and lower bounds on the time complexity of the move-to-ward-average and circumcenter laws, both achieving rendezvous, and of the centroid law, achieving deployment over a region of interest. The results are derived via novel analysis methods, including a set of results on the convergence rates of linear dynamical systems defined by tridiagonal Toeplitz and circulant matrices. Index Terms--Circumcenter and centroid laws, coordination algorithms, deployment, rendezvous, robotic networks, time complexity.

This paper proposes a formal model for a network of robotic agents that move and communicate. Building on concepts from distributed computation, robotics, and control theory, we define notions of robotic network, control and communication law, coordination task, and time and communication complexity. We illustrate our model and compute the proposed complexity measures in the example of a network of locally connected agents on a circle that agree upon a direction of motion and pursue their immediate neighbors. Index Terms--Complexity measures, cooperative control, coordination tasks, distributed algorithms, formal models, robotic networks.

In constant bit-rate timing transfer, the reference clocks which encode and reconstruct the service clock at origin and destination may be jittered. We present new, straightforward approaches to finding and visualizing jitter spectra in timing transfer for jittered destination and reference clocks, and confirm our results by simulation. Index Terms--Jitter, nonuniform sampling, sigma-delta modulator, synchronization, synchronous residual time stamp (SRTS).

Variable length codes (VLCs) exhibit loss of synchronization problems when transmitted over noisy channels. Trellis decoding techniques based on Maximum A Posteriori (MAP) estimators are often used to minimize the error rate on the estimated sequence. If the number of symbols and/or bits transmitted is known by the decoder, termination constraints can be incorporated in the decoding process. All the paths in the trellis which do not lead to a valid sequence length arc suppressed. This correspondence presents an analytic method to assess the expected error resilience of a VLC when trellis decoding with a sequence length constraint is used. The approach is based on the computation, for a given code, of the amount of information brought by the constraint. It is then shown that this quantity is not significantly altered by appropriate trellis states aggregation. This proves that the performance obtained by running a length-constrained Viterbi decoder on aggregated state models approaches the one obtained with the bit/symbol trellis, with a significantly reduced complexity. It is then shown that the complexity can be further decreased by projecting the state model on two state models of reduced size. Index Terms--Data compression, entropy, soft decoding, source coding, synchronization, variable length codes (VLCs).

In this paper, a new approach for synchronization of complex dynamical networks is proposed based on state observer design. Unlike the common diagonally coupling networks, where full state coupling is typically needed between two nodes, here it is suggested that only a scalar coupling signal is required to achieve network synchronization. Some conditions for synchronization, in the form of an inequality, are established based on the Lyapunov stability theory, which can be transformed to a linear matrix inequality and easily solved by a numerical toolbox. Two typical dynamical network configurations, i.e., global coupling and nearest-neighbor coupling, with each node being a modified Chua's circuit, are simulated. It is demonstrated that the proposed scheme is effective in achieving the expected chaos synchronization in the complex network. Index Terms--Complex dynamical network, linear matrix inequality (LMI), Lyapunov stability, state observer, synchronization.

A systematic approach to the problem of nondata aided symbol-timing estimation for linear modulations is provided under the unconditional maximum likelihood framework. The square-law nonlinearity is found to provide not only the symbol-timing but also the carrier-phase error.

The Cramer-Rao lower bound (CRB) is used for the joint estimation of the carrier phase and the frequency offset by observing 'hybrid' burst that contains random data symbols (DSs) as well as the pilot symbols (PSs). The results show that a 'hybrid algorithm' using both DSs as well as PSs are much superior than the ones that uses only the PSs or the received signals ignoring the priori knowledge about the PSs.

The carrier frequency offset (CFO) effect of a new multiaccess orthogonal frequency division multiplexing transceiver is analyzed and shows that multiaccess interference due to CFO can be mitigated by choosing a proper set of orthogonal codes. Results show that it does not demand sophisticated multiuser detection or signal processing in achieving multiuser communications, and CFO compensation can be done at the receiver side.

Anticipated or retarded synchronization of a mutually coupled nonlinear system is experimentally studied through a mutually coupled semiconductor laser system subject to optoelectronic feedback. The two types of synchronization are found to arise from a predictable relation between feedback/coupling delay times under particular feedback/coupling strength combinations

A simple synchronization mechanism called Feedback based Synchronization (FBS), which uses built- in flow control signals was proposed. Results reveal that the maximum bounded skew of FBS is 5.79 (mu)sec or less over all the experiments and hence it is concluded that FBS is a feasible synchronization in system area networks.

The effect of fixed timing offsets and clock frequency offsets on the performance of multicarrier direct-sequence CDMA (MC-DS-CDMA) for both uplink and downlink communication, assuming orthogonal spreading sequences and a slowly varying multipath channel is studied. Results reveal that a constant timing effect offset does no give rise to performance degradation for neither uplink nor downlink MC-DS-CDMA.

A novel Kalman filtering algorithm for end-to-end time synchronization between a client computer and a server of 'true' time using messages transmitted over packet-switched networks was described. Performance was evaluated according to the estimation error of frequency offset and time offset between client and server clock, the standard deviation of the estimates and the number of packets used for a specific estimation.

The tracking performance of a simplified (no transition detector in the in-phase arm and no delay in the quadrature arm) data transition tracking loop (SDTTL) suggested in the conference literature (Chiu and Lee, 1987) a number of years ago for symbol synchronization of an NRZ data stream is presented. It is shown that, contrary to what was previously stated in Chiu and Lee, 1987, the SDTTL and the traditional DTTL have performances that are quite different, the latter always being the more superior. In fact, asymptotically for large symbol SNR, the mean-squared timing error of the SDTTL is 3 dB worse than that of the DTTL which considerably negates its implementation simplification. Even at low SNR, where neither scheme would be motivated by maximum a posteriori (MAP) estimation of symbol sync considerations, the DTTL still outperforms the SDTTL. Index Terms--Bit synchronization, tracking loops.

In this paper, we introduce a new and advanced algorithm, namely, multiple-shift algorithm for code acquisition in optical code-division multiple access (CDMA) systems using unipolar optical orthogonal codes (OOCs) as signature sequences. We analyze the performance of the newly proposed algorithm and obtain a bound on its performance and show its advantage in reducing the mean time of synchronization when compared with other synchronization methods. The algorithm can be used with many different receiver structures, like active or passive correlator with or without hardlimiter(s). However, in this paper, we only consider the simple active correlator structure for further discussions and analysis. Index Terms--Code acquisition and synchronization, code-division multiple access (CDMA), optical CDMA, optical orthogonal codes (OOCs).

In this paper, we introduce the concept of switching from one supervisory control to another one when changes in the state of an embedded sensory network occur. The sensory devices are assumed to be single functional, that is, they are programmed to observe and report only one event. The switching model is built based on the two criteria of language observability and state synchronization. Switching model is the basis for a megacontroller, which monitors the state of the sensory network embedded in the plant as well as the state of the supervisor in charge. Every time the state of this network changes, the megacontroller reconfigures the control system by finding an appropriate supervisor. Index Terms--Control switching, observability, reconfigurability, sensor failure, synchronization.

We present a new algorithm for blind symbol synchronization in orthogonal frequency division multiplexing (OFDM) systems. The new algorithm declares symbol synchronization when a certain autocorrelation matrix, constructed from the received signal, achieves minimum rank. Unlike previously proposed blind algorithms, the new rank method guarantees correct symbol synchronization, even in the presence of intersymbol interference. Also, it does not assume that the OFDM time samples are i.i.d. In particular, the rank method works even with OFDM systems that employ pulse shaping. The increased complexity of the algorithm would be acceptable for systems, such as fixed-receiver broadcast systems, that require guaranteed synchronization under all conditions. Index Terms--Blind algorithm, intersymbol interference, orthogonal frequency division multiplexing, symbol synchronization.

An adaptive serial search pseudonoise (PN) code acquisition scheme is proposed, in which the detection threshold is scaled by the instantaneous received power measured prior to PN code correlation. We observe that the proposed scheme achieves significantly improved mean acquisition times compared to the conventional nonadaptive schemes under Rayleigh fading and pulsed Gaussian noise jamming. Furthermore, the proposed scheme is shown to be optimum under pulsed Gaussian noise jamming in the sense that it forces the worst case jamming fraction to unity. Index Terms--Adaptive system, fading channels, jamming, pseudonoise coded communication, synchronization.

This paper investigates maximum a posteriori probability (MAP) frame alignment strategies based on raw (analog) and quantized samples from a noise-contaminated channel. Particular attention is paid to systems with significant channel noise (for example, wireless systems), where accurate frame alignment is still possible, provided that the noise is compensated for by high transmitter frame integrity. A functional central limit theorem is derived that characterizes the performance of the MAP strategies in such high-noise cases. This prescribes optimal thresholds for the quantization process, and shows in particular that, for binary systems, worthwhile gains can be made by the use of raw or multibit quantized samples, rather than the usual 1-bit samples used by alignment strategies operating post bit decisions. It also shows that, for systems with significant channel noise, the performance of frame alignment strategies depends on the alignment pattern only through its autocorrelation function. Simulations confirm the validity of the characterization. Index Terms--Bayesian estimation, frame synchronization, high-noise asymptotics, quantization.

Synchronous CDMA systems whose transmission bandwidth is quantified through the fractional out-of-band energy (FOBE) constraint are considered. Either a conventional matched filter (MF) receiver or a minimum mean-square error (MMSE) receiver is employed for users' data detection. The total squared correlation (TSC) and the total mean-square error (TMSE) are proposed as the performance parameters for the MF and MMSE receivers respectively. These parameters need to be minimized in order to maximize the signal-to-interference ratios (SIR's) at the receivers' outputs. For a given FOBE bandwidth constraint, the sets of signature waveforms that minimize either TSC or TMSE are obtained from the prolate spheroidal wave functions (PSWFs). Furthermore, if the number of users is the size of a Hadamard matrix, then optimal signature waveforms can be obtained to maximize the individual SIR for every user. Due to the complicated nature of the PSWFs, simplified MF and MMSE receivers based on the Walsh signal space are developed. Index Terms--Signature waveforms, code-division multiple access, receiver design, Walsh signal space.

A new frame synchronization technique, which is robust to carrier frequency and phase errors, is proposed for M-ary PSK systems. This technique is derived through modification of the procedure used for obtaining the maximum-likelihood (ML) rule in the paper by Gansman et al. The proposed rule is based on an operation called a double correlation which evaluates a correlation after properly multiplying the received signal with a sync pattern. It was shown through computer simulation that the proposed rule generally outperformed the existing rules when a frequency offset existed. Index Terms--Correlation, frame synchronization, frequency offset.

Byline: Nour Mohammad Murad (1), Jean Claude Belfiore (2), George Rodriguez Guisantes (2) Keywords: synchronization; decision criteria; DS-WCDMA; UMTS Abstract: In DS-WCDMA mobile systems such the UMTS, asynchronous cell site operation,assigning different long spreading code to each cell, yields the advantageof flexible system deployment. We can design an indoor system basedon an outdoor one. However, in general, much longer search time isrequired in asynchronous operation than in synchronous. This paperproposes three techniques to take decisions about synchronizationbased on observation of correlated signals. Classical decision criterialike maximum and threshold criterion are presented. A new decisioncriteria that we call Threshold&amp Max combined decision criteriais analyzed. The results of this new introduced technique is comparedwith the classical ones. Author Affiliation: (1) COM-ELEC Dept., ENST -- Alcatel CIT Velizy, 46, Rue Barrault, 75013, Paris, France (2) COM-ELEC Dept., Telecom Paris, 46, Rue Barrault, 75013, Paris, France Article History: Registration Date: 13/10/2004

The operating Es/No of the European Digital Video Broadcasting over Satellite (DVB-S) system can be reduced by utilizing turbo codes, although this reduces the performance of both carrier and symbol synchronizers. While maximum likelihood decision directed (ML-DD) feedback algorithms for both carrier and symbol synchronization can be shown to approach the Cramer-Rao Bound (CRB), at reasonable Es/No, at low Es/No incorrect decisions reduce their performance. If improved decisions are made available to the algorithms then even at low Es/No the CRB can be approached. By utilizing a turbo code to provide improved symbol estimates tracking performance can be improved. In a practical system, however, there is an unavoidable delay caused by the decoder, which reduces tracking performance. This paper is concerned with examining the tradeoff between improved decisions and unavoidable delay. Limits are shown for performance and interleaver size to make this approach to the synchronization problem practical. Index Terms--Digital video broadcasting (DVB), digital video broadcasting over satellite (DVB-S), maximum likelihood decision directed (ML-DD), synchronization.

Starting out with a strong justification for phase synchronization, we derive the symbol error probability for 8-vestigial sideband (VSB) in the presence of phase errors and compare it with the symbol error rates for 8-PAM and 64-QAM. Monte Carlo simulations support the theoretical expressions. Phase misadjustments lead to error floors, which are computed, and which further reveal the susceptibility of VSB signals to phase errors. Phase synchronizers can either work in a data-aided manner or blindly. We focus on the latter and show the relationship between phase synchronization and blind source separation (BSS). Finally, a method suitable for the phase synchronization of VSB signals as used by the ATSC DTV transmission system is presented and evaluated. Its performance is measured against that of the decision-directed approaches that have been suggested in the literature. Depending on the SNR of the VSB signal, either blind or decision-directed approaches exhibit superior performance. A semiblind method, which combines the advantages of the decision-directed and the blind mode in their respective SNR regions, is introduced and set in perspective with the other algorithms. Index Terms--Blind carrier recovery, blind phase synchronization, blind signal processing, semiblind algorithms, vestigial sideband (VSB) modulation.

In this paper a systematic approach, based on the linear-state-observer design for constructing two chaotically synchronized systems, is developed. The proposed method is then applied to suggest a means to secure communications. The method combines chaotic masking and chaotic modulation, where the information signal is injected into the transmitter and simultaneously transmitted to the receiver. Furthermore, two well-known chaotic systems, Rossler and Lorenz, and a hyperchaotic ROssler system are considered as illustrative examples to demonstrate the effectiveness of the proposed approach. Index Terms - Chaos, chaotic synchronization, secure communication, state observer.

We investigate a novel nondata-aided method for jointly estimating timing and carrier frequency offset in MSK-type modulation. The algorithm has a feedforward structure and lends itself to a simple digital implementation. Its estimation accuracy depends on a design parameter that may be varied to trade performance for computational complexity. Setting the parameter to unity yields a synchronization scheme already known in the literature. Computer simulations are used to assess the synchronizer performance on AWGN Rayleigh fading channels with MSK and Gaussian MSK modulation. Index Terms - Frequency offset. MSK-type modulation, timing offset.

We analyze the acquisition time performance of the distributed sample acquisition (DSA) scheme recently proposed for a fast DS/CDMA signal acquisition. To analyze the composite acquisition mechanism, we first define several acquisition-related probability parameters which can describe all the essential events in the DSA synchronization, along with the basic states that constitute the eventual DSA state transition diagram. Then, we construct the state transition diagram employing these basic states and the moment generating functions which are entirely based on the above defined probability parameters. Applying this state transition diagram and determining the acquisition-related parameters, we finally analyze the mean acquisition time performance of the DSA. Index Terms - Distributed sample acquisition, distributed sample scrambling, igniter sequence.

In this contribution we consider the Cramer-Rao bound (CRB) for the estimation of a scalar parameter in the presence of nuisance parameters. Whereas this true CRB is hard to evaluate in general, we present a simple analytical expression for its high SNR asymptote, i.e., the asymptotic CRB (ACRB). We show that this ACRB is related to the CRB for the joint estimation of the scalar parameter and the nuisance parameters. Recently, a modified CRB (MCRB) for the estimation of a scalar parameter in the presence of nuisance parameters has been derived. This MCRB is also simple to evaluate and is related to the CRB for the estimation of the scalar parameter assuming that the value of the nuisance parameters is a priori known. We show that the MCRB can be quite loose at high SNR, when the scalar parameter is coupled with the nuisance parameters. In the case of synchronization parameter estimation, we find that the ACRB equals the MCRB, whether or not (some of) the nuisance parameters are a priori known. Index Terms - Communication system performance, parameter estimation, synchronization.

Torque per unit velocity is a practical method to study the subsynchronous resonance instability of electric power systems. The torque per unit velocity method is justified as an eigenvalue perturbation technique and extended to power systems with thyristor switching devices and multiple torsional modes. A new method to estimate the damping of the swing mode is proposed.

In a chaotic switching scheme, a binary message signal is scrambled by two chaotic attractors. In this paper we present examples to show how generalized chaotic synchronization (GS) can be used to break chaotic switching schemes. Since GS is a very robust phenomenon, we find that an intruder can recover the binary information signal from chaotic switching schemes without knowing both the structure and parameters of the chaotic transmitter. The breaking method presented in this paper is not sensitive to the order of the transmitter, which means that even in a chaotic switching scheme which uses two hyperchaotic systems, the degree of security may still be low. The simulation results for both low order and high order transmitters are presented.

Three techniques are introduced to enhance simulation speed of communication systems including a charge-pump phase-locked loop. First, a technique using exact explicit solutions of differential equations is extended to nonuniformly sampled circuits. This allows arbitrarily large time and voltage steps in an event-driven simulator without introducing numerical errors. Then, event prediction using mathematical limits enables large time steps and unlimited accuracy. Finally, an interpolator is combined with delay-partitioning to reduce the required oversampling rate. High accuracy is demonstrated with as low as four events per cycle of the system clock and an oversampling ratio of 3. Index Terms - Circuit simulation, discrete event simulation, interpolation, phase-locked loops, simulation, switching circuits, synchronization, time-varying circuits.

The contradiction between the shortness upstream bandwidth of hybrid fiber-coax (HFC) networks and a large number of services to be transmitted, is very sharp. Specially, a part of bandwidth assigned to real-time variable bit rate (rt-VBR) services, is redundancy. Thus, the algorithm of assigning upstream bandwidth must have high bandwidth multiplexing. The algorithm described here bases on ATM's traffic descriptor parameters and the quality of service (QoS) parameters, and is designed for rt-VBR services. The algorithm utilizes the bursts and cell loss rate of rt-VBR services to multiplex bandwidth. The algorithm has also the function of call admission control.

This paper is concerned with the effect of multipath fading on the performance of frequency hop (FH) time synchronization and the resultant bit-error rate (BER) performance. The expressions of the mean value and the variance of the estimated FH timing error and BER are derived for the case of multipath Rayleigh fading, which is characterized by a path-delay vector and a path-strength distribution vector. Somewhat surprisingly, our results show that in comparison with single-path fading, multipath fading does not degrade the mean and variance of the estimated timing error and BER performance, but rather improves them owing to multipath diversity. The significance of our results is to demonstrate quantitatively the robustness of FH in the presence of multipath fading as far as the establishment of hop timing is concerned. Furthermore, we identify the spectral estimator as a robust method for establishing FH timing. Index Terms - Bit-error rate, frequency hop, multipath fading, spread spectrum, time synchronization.

The focus of this paper is on the initial acquisition of a direct sequence (DS) spread-spectrum signal utilizing a purely parallel search strategy. A parallel search strategy is utilized because it reduces the acquisition time compared to either serial or partially parallel strategies. In particular, the purpose of this paper is to derive the optimal decision rule, based on the maximum-likelihood criterion, for frequency-selective fading channels. The performance of the conventional decision rule, optimized for additive white Gaussian noise and flat-fading channels, the optimal decision rule, derived in this paper, and a suboptimal decision rule, also presented in this paper, are compared. It is shown that the optimal and suboptimal decision rules for Rayleigh-fading channels outperform the conventional decision rule. For Rician-fading channels, it is shown both that the optimal decision rule outperforms the conventional decision rule, and that the optimum decision rule for Rayleigh-fading channels, when implemented on a Rician-fading channel, yields approximately optimum performance. Index Terms - Acquisition, Rayleigh fading, Rician fading, spread spectrum.

This work is targeted toward understanding the performance in terms of residual timing error of the over-the-air autonomous decentralized interbase-station synchronization system. An exact solution for the uniform weights case and an approximate solution for the power weights case are obtained in closed form. The residual timing error, system stability, and system convergence performance are studied based on the closed-form solutions. It is shown that timing can converge very fast for the uniform weights case; the power weights case has lower residual timing error measured in terms of standard deviation than that of the uniform weights case when all transmitted power levels are the same. Index Terms - Mobile communications, synchronization, timing, timing error.

This paper describes a carrier-frequency offset estimator derived using maximum-likelihood techniques. The estimator is designed for a digital space-diversity receiver, operating in a wide-band frequency-selective multipath fading channel. The estimator is suited to a burst-mode time-division-multiple-access system, because the estimate is formed in an open-loop manner, and relies on a training sequence normally used in burst-mode systems. The main advantage is that it does not require channel state information; rather, it only requires knowledge of the autocorrelation of the channel. Simulation results show the estimator to be unbiased over a wide frequency range. The normalized error standard deviation is shown to be 0.0015 across the frequency offset range for a receiver with four diversity branches, when the normalized channel delay spread is 0.1, the signal-to-noise ratio (SNR) is 10 dB, and the training sequence length is 23 symbols. It is found that, for most parameter configurations, there is approximately a factor of two improvement in the estimate error standard deviation when the antenna diversity is doubled.