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Given the need to describe, analyze and index large quantities of marine imagery data for exploration and monitoring activities, a range of specialized image annotation tools have been developed worldwide. Image annotation – the process of transposing objects or events represented in a video or still image to the semantic level, may involve human interactions and computer-assisted solutions. Marine image annotation software (MIAS) have enabled over 500 publications to date. We review the functioning, application trends and developments, by comparing general and advanced features of 23 different tools utilized in underwater image analysis. MIAS requiring human input are basically a graphical user interface, with a video player or image browser that recognizes a specific time code or image code, allowing to log events in a time-stamped (and/or geo-referenced) manner. MIAS differ from similar software by the capability of integrating data associated to video collection, the most simple being the position coordinates of the video recording platform. MIAS have three main characteristics: annotating events in real time, posteriorly to annotation and interact with a database. These range from simple annotation interfaces, to full onboard data management systems, with a variety of toolboxes. Advanced packages allow to input and display data from multiple sensors or multiple annotators via intranet or internet. Posterior human-mediated annotation often include tools for data display and image analysis, e.g. length, area, image segmentation, point count; and in a few cases the possibility of browsing and editing previous dive logs or to analyze the annotations. The interaction with a database allows the automatic integration of annotations from different surveys, repeated annotation and collaborative annotation of shared datasets, browsing and querying of data. Progress in the field of automated annotation is mostly in post processing, for stable platforms or still images. Integration into available MIAS is currently limited to semi-automated processes of pixel recognition through computer-vision modules that compile expert-based knowledge. Important topics aiding the choice of a specific software are outlined, the ideal software is discussed and future trends are presented. [ABSTRACT FROM AUTHOR]

For multiple-input multiple-output (MIMO) Rayleigh channels, it has been shown that transmitter correlations always degrade the performance of general space–time codes (STCs) in high signal-to-noise ratio (SNR) regimes. In this correspondence, however, we show that when MIMO channels experience single-keyhole conditions, the effect of spatial correlations between transmission antennas is more sophisticated for general STCs: When M>N (i.e., the number of transmission antennas is greater than the number of receiving antennas), depending on how the correlation matrix {\bf P} beamforms the codeword difference matrix {\mmb \Delta}$, the pairwise error probability performance of general STCs can be either degraded or improved in high-SNR regimes. We provide a new measure, which is based on the eigenvalues of {\mmb \Delta} and the numbers of transmission and receiving antennas, to examine if there exist certain correlation matrices that can improve the performance of general STCs in high-SNR regimes. Previous studies on the effect of spatial correlations over single-keyhole channels only concentrated on orthogonal STCs, whereas our study here is for general STCs and can also be used to explain previous findings for orthogonal STCs. Simulations also show that the results are applicable with imperfect channel knowledge. [ABSTRACT FROM PUBLISHER]

We present a novel high-precision two-way optic-fiber time transfer scheme. The Inter-Range Instrumentation Group (IRIG-B) time code is modified by increasing bit rate and defining new fields. The modified time code can be transmitted directly using commercial optical transceivers and is able to efficiently suppress the effect of the Rayleigh backscattering in the optical fiber. A dedicated codec (encoder and decoder) with low delay fluctuation is developed. The synchronization issue is addressed by adopting a mask technique and combinational logic circuit. Its delay fluctuation is less than 27 ps in terms of the standard deviation. The two-way optic-fiber time transfer using the improved codec scheme is verified experimentally over 2 m to100 km fiber links. The results show that the stability over 100 km fiber link is always less than 35 ps with the minimum value of about 2 ps at the averaging time around 1000 s. The uncertainty of time difference induced by the chromatic dispersion over 100 km is less than 22 ps. [ABSTRACT FROM AUTHOR]

Summary: Inferring which signals have a common underlying cause, and hence should be integrated, represents a primary challenge for a perceptual system dealing with multiple sensory inputs []. This challenge is often referred to as the correspondence problem or causal inference. Previous research has demonstrated that spatiotemporal cues, along with prior knowledge, are exploited by the human brain to solve this problem []. Here we explore the role of correlation between the fine temporal structure of auditory and visual signals in causal inference. Specifically, we investigated whether correlated signals are inferred to originate from the same distal event and hence are integrated optimally []. In a localization task with visual, auditory, and combined audiovisual targets, the improvement in precision for combined relative to unimodal targets was statistically optimal only when audiovisual signals were correlated. This result demonstrates that humans use the similarity in the temporal structure of multisensory signals to solve the correspondence problem, hence inferring causation from correlation. [ABSTRACT FROM AUTHOR]

In this paper, we give a new framework for constructing low ML decoding complexity space-time block codes (STBCs) using codes over the Klein group \cal K. Almost all known low ML decoding complexity STBCs can be obtained via this approach. New full-diversity STBCs with low ML decoding complexity and cubic shaping property are constructed, via codes over \cal K, for number of transmit antennas N=2^m, m\geq 1, and rates R>1 complex symbols per channel use. When R=N, the new STBCs are information-lossless as well. The new class of STBCs have the least known ML decoding complexity among all the codes available in the literature for a large set of (N,R) pairs. [ABSTRACT FROM AUTHOR]

Cooperative communications are effective in improving the performance and extend the coverage of wireless networks. One issue is to find proper methods to allocate cooperative nodes. In this paper we investigate the effects of relay position and power allocation strategy in cooperative communications employing space-time codes (STCs). We consider non-ideal links between source, relay, and destination enabling the analysis of relay allocation problem based on the performance of each link in realistic scenarios. The frame error rate for various channel conditions, available diversity, relay positions, and transmitted power levels is obtained. Both the situation of balanced and unbalanced transmit power levels for source, relay, and destination are compared. Cooperative pragmatic STCs in block fading channel (BFC) are considered for our analysis. The results provide insight on how to allocate relay nodes based on geometry, link quality, and transmitted power considerations. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, two-dimensional (2D) wavelength/time codes are designed and implemented. The 2D codes are constructed by a technique based on folding of Golomb rulers. The performance evaluation of OCDMA system based on wavelength/time code has been analyzed by measuring the values of bit error rates and eye diagrams for different number of active users. It is shown that eye opening decreases and BER increases with increase in number of active users. It is also shown that BER further increases with increase in number of active users when number of decoders increases on receiver side. Hence, it is concluded that multiple access interference (MAI) is the dominant source of BER and there is graceful degradation in system performance when number of simultaneously active users increases. The received optical power is also measured at different transmission distance. It has been observed that received optical power decreases with increase in length of fiber due to attenuation. [Copyright &y& Elsevier]

This paper studies the diversity benefit of different interference alignment solutions. While most research about interference alignment was aiming at deriving or realizing the maximum achievable multiplexing gain, the symbol error rate performance, which can be characterized by the diversity gain is of equal importance. Different interference alignment solutions are classified into two categories called diversity interference alignment and zero-forcing interference alignment. Although these two types of solutions are not distinguishable in terms of the multiplexing gain, this paper will show their difference lies in the fact that they have different diversity gains. In this paper, a K-user (M\timesN) interference channel is used, with each user sending 1 degree of freedom of information by using interference alignment precoding and receiving filters but without space-time codes. The feasibility conditions for diversity interference alignment to be achieved are analyzed and the diversity orders different solutions can provide are compared. The results imply that diversity interference alignment solutions offer both multiplexing and diversity gains simultaneously. It also tells us two important rules about the interference alignment precoding filters design: an optimal design has to take both desired and interference channel matrices into consideration and the separation of interference alignment precoding filters design and space-time codes design may not be optimal in general. [ABSTRACT FROM PUBLISHER]

Space-time coding (STC) has been shown to play a key role in the design of MIMO radars with widely spaced antennas: In particular, rank-one coding amounts to using the multiple transmit antennas as power multiplexers, while full-rank coding maximizes the transmit diversity, compromises between the two being possible through rank-deficient coding. In detecting a target at known distance and Doppler frequency, no uniformly optimum transmit policy exists, and diversity maximization turns out to be the way to go only in a (still unspecified) large signal-to-noise ratio region. The aim of this paper is to shed some light on the optimum transmit policy as the radar is to detect a target at an unknown location: To this end, at first the Cramér–Rao bounds as a function of the STC matrix are computed, and then waveform design is stated as a constrained optimization problem, where now the constraint concerns also the accuracy in target ranging, encapsulated in the Fisher Information on the range estimate. Results indicate that such accuracy constraints may visibly modify the required transmit policy and lead to rank-deficient STC also in regions where pure detection would require pursuing full transmit diversity. [ABSTRACT FROM AUTHOR]

This paper focuses on conditional optimization as a decoding primitive for high rate space-time codes that are obtained by multiplexing in the spatial and code domains. The approach is a crystallization of the work of Hottinen et al. which applies to space-time codes that are assisted by quasi-orthogonality. It is independent of implementation and is more general in that it can be applied to space-time codes such as the Golden Code and perfect space-time block codes, that are not assisted by quasi-orthogonality, to derive fast decoders with essentially maximum likelihood (ML) performance. The conditions under which conditional optimization leads to reduced complexity ML decoding are captured in terms of the induced channel at the receiver. These conditions are then translated back to the transmission domain leading to codes that are constructed by multiplexing orthogonal designs. The methods are applied to several block space-time codes obtained by multiplexing Alamouti blocks where it leads to ML decoding with complexity O (N²) where N is the size of the underlying QAM signal constellation. A new code is presented that tests commonly accepted design principles and for which decoding by conditional optimization is both fast and ML. The two design principles for perfect space-time codes are nonvanishing determinant of pairwise differences and cubic shaping, and it is cubic shaping that restricts the possible multiplexing structures. The new code shows that it is possible to give up on cubic shaping without compromising code performance or decoding complexity. [ABSTRACT FROM AUTHOR]

A method is described for verifying video content integrity by checking the continuity of timecodes embedded as digital watermarks. Conventional verification methods using digital signatures and fragile watermarking are unable to distinguish between attacks and regular modifications and thus are unable to protect against threats to content. The proposed verification method distinguishes attacks against video content from regular modifications by detecting timecodes embedded in consecutive frames of the content and then checking their continuity. A prototype implementation showed that the method is more effective than conventional ones and that it can be used by a variety of applications using video content. [ABSTRACT FROM AUTHOR]

Maximum likelihood (ML) receivers for space-time coded multiple-input multiple-output (MIMO) systems with Gaussian channel estimation errors are proposed. Two different cases are considered. In the first case, the conditional probability density function (PDF) of the channel estimate is assumed Gaussian and known. In the second case, the joint PDF of the channel estimate and the true channel gain is assumed Gaussian and known. In addition to ML signal detection for space-time coded MIMO with ML and minimum mean-squared-error channel estimation, ML signal detection without channel estimation is also studied. Two suboptimal structures are derived. The Alamouti space-time codes are used to examine the performances of the new receivers. Simulation results show that the new receivers can reduce the gap between the conventional receiver with channel estimation errors and the receiver with perfect channel knowledge at least by half in some cases. [ABSTRACT FROM AUTHOR]

The goal of combining beamforming and space-time coding is to obtain full-diversity order and to provide additional received power (array gain) compared to conventional space-time codes. In this work, a class of code constellations is proposed, called generalized partly orthogonal designs (PODs) and both high-rate and low-rate feedback information is incorporated with possible feedback errors. A binary symmetric channel (BSC) model characterizes feedback errors. Two cases are studied: first, when the BSC bit error probability is known a priori to the transmission ends, and second, when it is not known exactly. Based on a minimum pairwise error probability (PEP) design criterion, we design a channel optimized vector quantizer (COVQ) for feedback information and a precoder matrix codebook to adjust the transmission codewords. The attractive property of our combining scheme is that it converges to conventional space-time coding with low-rate and erroneous feedback and to directional beamforming with high-rate and error-free feedback. This scheme also shows desirable robustness against feedback channel modeling mismatch. [ABSTRACT FROM AUTHOR]

In this paper, we consider distributed space-time coding for two-way wireless relay networks, where communication between two terminals is assisted by relay nodes. Relaying protocols using two, three, and four time slots are proposed. The protocols using four time slots are the traditional amplify-and-forward (AF) and decode-and-forward (DF) protocols, which do not consider the property of the two-way traffic. A new class of relaying protocols, termed as partial decode-and-forward (PDF), is developed for the two time slots transmission, where each relay first removes part of the noise before sending the signal to the two terminals. Protocols using three time slots are proposed to compensate the fact that the two time slots protocols cannot make use of direct transmission between the two terminals. For all protocols, after processing their received signals, the relays encode the resulting signals using a distributed linear dispersion (LD) code. The proposed AF protocols are shown to achieve the diversity order of min{N, K} (1 - (log log P/log F)), where N is the number of relays, P is the total power of the network, and K is the number of symbols transmitted during each time slot. When random unitary matrix is used for LD code, the proposed PDF protocols resemble random linear network coding, where the former operates on the unitary group and the latter works on the finite field. Moreover, PDF achieves the diversity order of min{N, K} but the conventional DF can only achieve the diversity order of 1. Finally, we find that two time slots protocols also have advantages over four-time-slot protocols in media access control (MAC) layer. [ABSTRACT FROM AUTHOR]

This paper presents serially concatenated trellis coded modulations (SCTCMs) that perform consistently close to the available mutual information for periodic erasure channel (PEC), periodic fading channel (PFC) and the 2 x 2 compound matrix channel. We use both the maximum-likelihood decoding criteria and iterative decoding criteria to design universal SCTCMs for the PEC and the PFC. For the space-time channel, by demultiplexing the symbols across the antennas, the proposed universal SCTCMs for the period-2 PFC deliver consistent performance over the eigenvalue skew of the matrix channel. Within the family of channels having the same eigenvalue skew, a time-varying linear transformation (TVLT) is used to mitigate the performance variation over different eigenvectors. The proposed space-time SCTCMs of 1.0, 2.0 and 3.0 bits per transmission require excess mutual information in the ranges 0.11-0.15, 0.23- 0.26 and 0.35-0.53 bits per antenna, respectively. Because of their consistent performance over all channels, the proposed codes will have good frame-error-rate (FER) performance over any quasi-static fading distribution. In particular, the codes provide competitive FER performance in quasi-static Rayleigh fading. [ABSTRACT FROM AUTHOR]

This paper introduces a new rate-2, full-diversity space-time code for four transmit antennas and one receive antenna. The 4 x 4 codeword matrix consists of four 2 x 2 Alamouti blocks with entries from Q (i, √5), and these blocks can be viewed as quaternions which in turn represent rotations in R3. The Alamouti blocks that appear in a codeword are drawn from the icosian ring consisting of all linear combinations of 120 basic rotations corresponding to symmetries of the icosahedron. This algebraic structure is different from the Golden code, but the complex entries are taken from a common underlying field. The minimum determinant is bounded below by a constant that is independent of the signal constellation, and the new code admits a simple decoding scheme that makes use of a geometric correspondence between the icosian ring and the E8 lattice. [ABSTRACT FROM AUTHOR]

We consider the "one-shot frame synchronization problem," where a decoder wants to locate a sync pattern at the output of a memoryless channel on the basis of sequential observations. The sync pattern of length N starts being emitted at a random time within some interval of size A, where A characterizes the asynchronism level. We show that a sequential decoder can optimally locate the sync pattern, i.e., exactly, without delay, and with probability approaching one as N → ∞, if the asynchronism level grows as O(eN α), with a below the synchronization threshold, a constant that admits a simple expression depending on the channel. If α exceeds the synchronization threshold, any decoder, sequential or nonsequential, locates the sync pattern with an error that tends to one as N → ∞. Hence, a sequential decoder can locate a sync pattern as well as the (nonsequential) maximum-likelihood decoder that operates on the basis of output sequences of maximum length A + N - 1, but with far fewer observations. [ABSTRACT FROM AUTHOR]

Since the standard union bound for space-time codes may diverge in quasi-static fading channels, the limit-before-average (LBA) technique has been exploited to derive tight performance bounds. However, it suffers from the computational burden arising from a multidimensional integral. In this paper, efficient bounding techniques for space-time codes are developed in the framework of Gallager bounds. Two closed-form upper bounds, the ellipsoidal bound and the spherical bound, are proposed that come close to simulation results within a few tenths of a decibel. In addition, two novel methods of weight enumeration operating on a further reduced state diagram are presented, which, in conjunction with the bounding techniques, give a thorough treatment of performance bounds for space-time codes. [ABSTRACT FROM AUTHOR]

1/ f β noise has been revealed in both self-paced and synchronized tapping sequences, without being consistently taken into consideration for the modeling of underlying timing mechanisms. In this study we characterize variability, short-range, and long-range correlation properties of asynchronies and inter-tap intervals collected in a synchronization tapping experiment, attesting statistically the presence of 1/ f β noise in asynchronies. We verify that the linear phase correction model of synchronization tapping in its original formulation cannot account for the empirical long-range correlation properties. On the basis of previous accounts of 1/ f β noise in the literature on self-paced tapping, we propose an extension of the original synchronization model by modeling the timekeeping process as a source of 1/ f β fluctuations. Simulations show that this ‘1/ f-AR synchronization model’ accounts for the statistical properties of empirical series, including long-range correlations, and provides an unifying mechanistic account of 1/ f β noise in self-paced and synchronization tapping. This account opens the original synchronization framework to further investigations of timing mechanisms with regard to the serial correlation properties in performed time intervals. [ABSTRACT FROM AUTHOR]

Super-orthogonal space–time trellis codes (SOSTTC) are full rate, full diversity space–time codes with high coding gains for quasi-static fading channels. In this paper, this design approach is extended to fast fading channels and new SOSTTC are proposed for BPSK and QPSK modulations based on the design criteria valid for this type of channels. The new full rate codes have 4- and 16-state trellises for BPSK and QPSK cases, respectively, to avoid parallel transitions which restrict the error performance. The frame error performances are evaluated through computer simulations and it is shown that the proposed codes have superior performance in the fast fading case compared to their counterparts previously given in the literature for fast and quasi-static fading channels. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

It is a general consensus that an orthogonal space-time block code can achieve full diversity, and due to its orthogonal nature, the multiple-input--multiple-output (MIMO) maximum-likelihood (ML) decoding metrics can be decoupled into single-input-single-output (SISO) ML metrics based on linear processing at the receiver, thus greatly reducing the decoding complexity. In fact, nonorthogonal codes also currently exist that can achieve better symbol-error-rate performance without rate reduction and complexity increase for correlated fading channels. In this paper, we show by detailed derivations that nonorthogonal linear space-time block codes can also be decoded by ML decoupling through receiver linear processing. Our derived expressions for the decoupled ML metrics automatically contain the design information for the receiver linear processors. [ABSTRACT FROM AUTHOR]

A closed-form upper bound is presented for the average pairwise error probabilities (PEP) of space–time codes for a keyhole channel. It is derived from the exact conditional PEP for given fading channel coefficients using a moment generating function-based approach. Simulation results are included for varying numbers of antennas that affirm that the proposed PEP serves as a tight bound for codes in a keyhole channel. [ABSTRACT FROM AUTHOR]

In Karaoke, the displaying of lyrics synchronized with music is the most crucial feature. To synchronize lyrics with music, the time code has been widely used. In general, a huge amount of time codes for one song is required. Thus, the uncompressed time code is a big burden on the mobile device. In this paper, we propose a novel method to compress the time code for Karaoke further. The proposed method uses the correlation between neighboring time codes. In addition, an effective coding method is designed to compress the data of the time code. Experimental results show that the proposed method significantly reduces an amount of data of time codes and is easily applied to other composite contents with time code. [ABSTRACT FROM AUTHOR]

In this paper, a method of correcting both random and systematic timebase errors using measurements of only two quadrature sinusoids made simultaneously with a waveform of interest is described. The authors estimate the fundamental limits to the procedure due to additive noise and sampler jitter and demonstrate the procedure with some actual measurements. [ABSTRACT FROM AUTHOR]

The diversity product and the diversity slim are two very important parameters for a good-performing unitary space-time constellation. A basic question is what the maximal diversity product (or sum) is. In this correspondence, we are going to derive general upper bounds on the diversity sum and the diversity product for unitary constellations of any dimension n and any size m using packing techniques on the compact Lie group U(n). [ABSTRACT FROM AUTHOR]

In this paper, a method is proposed to construct spectrally efficient unitary space-time codes for high-rate differential communications over multiple-antenna channels. Unlike most of the known methods which are designed to maximize the diversity product (the minimum determinant distance), our objective is to increase the spectral efficiency. The simulation results indicate that for high spectral efficiency and for more than one receive antenna, the new method significantly outperforms the existing alternatives. In the special case of two transmit antennas, which is the main focus of this paper, the relation between the proposed code and the Alamouti scheme helps us to provide an efficient maximum-likelihood (ML) decoding algorithm. Also, we demonstrate that similar ideas can be applied to designing codes for more than two transmit antennas. As an example, we present a construction for 4-by-4 unitary constellations which has a good performance, compared with the other known codes. [ABSTRACT FROM AUTHOR]

Finding a least-cost path subject to a delay constraint in a network is an NP-complete problem and has been extensively studied. Many works reported in the literature tackle this problem by using ϵ-approximation schemes and scaling techniques, i.e., by mapping link costs into integers or at least discrete numbers, a solution which satisfies the delay constraint and has a cost within a factor of the optimal one, that can be computed with pseudopolynomial computational complexity. In this paper, having observed that the computational complexities of the ϵ-approximation algorithms using the linear scaling technique are linearly proportional to the linear scaling factor, we investigate the issue of finding the optimal (the smallest) linear scaling factor to reduce the computational complexities, and propose two algorithms, the optimal linear scaling algorithm (OLSA) and the transformed OLSA. We analytically show that the computational complexities of our proposed algorithms are very low, as compared with those of ϵ-approximation algorithms. Therefore, incorporating the two algorithms can enhance the ϵ-approximation algorithms by granting them a practically important capability: self-adaptively picking the optimal linear scaling factors in different networks. As such, ϵ-approximation algorithms become more flexible and efficient. [ABSTRACT FROM AUTHOR]

Visual stimuli evoke wave activity in the visual cortex of freshwater turtles. Earlier work from our laboratory showed that information about the positions of stationary visual stimuli is encoded in the spatiotemporal dynamics of the waves and that the waves can be decoded using Bayesian detection theory. This paper extends these results in three ways. First, it shows that flashes of light separated in space and time and stimuli moving with three speeds can be discriminated statistically using the waves generated in a large-scale model of the cortex. Second, it compares the coding capabilities of spike rate and spike time codes. Spike rate codes were obtained by low-pass filtering the activities of individual neurons in the model with filters of different band widths. For the moving targets used in the study, detectability using spike rate codes is immune to the choice of a specific bandwidth, indicating that a coarse filter is able to adequately discriminate targets. Spike timing codes are binary sequences indicating the precise timing of spike activity of individual neurons across the cortex. Spike time codes generally perform better than do spike rate codes. Third, the encoding process is examined in terms of the underlying cellular mechanisms that result in the initiation, propagation and cessation of the wave. The period of peak detectability corresponds to the period in which waves are propagating across the cortex. [ABSTRACT FROM AUTHOR]

Recurrence time of a symbol in a string is defined as the number of symbols that have appeared since the last previous occurrence of the same symbol. It is one of the most fundamental quantities that can be used in universal source coding. If we count only the minimum required number of symbols occurring in the recurrence period, we can reduce some redundancy contained in recurrence time coding. The move-to-front (MTF) scheme is a typical example that shares the idea. In this correspondence, we establish three such schemes, and make a basic comparison with one another from the viewpoint that they can be thought of as different attempts to realize the above idea. [ABSTRACT FROM AUTHOR]

There exist two important design criteria for unitary space time codes. In the situation where the signal-to-noise ratio (SNR) is large the diversity product (DP) of a constellation should be as large as possible. It is less known that the diversity sum (DS) is a very important design criterion for codes working in a low SNR environment. So far, no general method to design good-performing constellations with large diversity for any number of transmit antennas and any transmission rate exists. In this correspondence, we propose constellations with suitable structures, which allow one to construct codes with excellent diversity using geometrical symmetry and numerical methods. The presented design methods work for any dimensional constellation and for any transmission rate. [ABSTRACT FROM AUTHOR]

One approach to designing structured low-density parity-cheek (LDPC) codes with large girth is to shorten codes with small girth in such a manner that the deleted columns of the parity-check matrix contain all the variables involved in short cycles. This approach is especially effective if the parity-check matrix of a code is a matrix composed of blocks of circulant permutation matrices, as is the case for the class of codes known as array codes. We show how to shorten array codes by deleting certain columns of their parity-check matrices so as to increase their girth. The shortening approach is based on the observation that for array codes, and in fact for a slightly more general class of LDPC codes. the cycles in the corresponding Tanner graph are governed by certain homogeneous linear equations with integer coefficients. Consequently, we can selectively eliminate cycles from an array code by only retaining those columns from the parity-check matrix of the original code that are indexed by integer sequences that do not contain solutions to the equations governing those cycles. We provide Ramsey-theoretic estimates for the maximum number of columns that can be retained from the original parity-check matrix with the property that the sequence of their indices avoid solutions to various types of cycle-governing equations. This translates to estimates of the rate penalty incurred in shortening a code to eliminate cycles. Simulation results show that for the codes considered, shortening them to increase the girth can lead to significant gains in signal-to-noise ratio (SNR) in the case of communication over an additive white Gaussian noise (AWGN) channel. [ABSTRACT FROM AUTHOR]

A new lower bound for the distance of cyclic codes is proposed. This bound depends on the defining set of the code, like several other bounds. The proposed bound improves upon the Bose-Chaudhuri-Hocquehghen (BCH) bound and, for some codes, improves upon the Hartmann-Tzeng bound and the Roos bound as well. [ABSTRACT FROM AUTHOR]

Proofs to the conjectures made by Jing and Hassibi on having fully diverse (3 × 3 ) SU(3) and AB unitary space-time codes art, presented in this correspondence. We first prove that the SU(3) codes are fully diverse if and only if the design parameters P, Q, R, and S are all odd integers, and in addition, are relatively prime. For the type I AB codes, it is shown that full diversity can be achieved if and only if the integers P Q, R, and S are relatively prime. Finally, we show that such condition is also sufficient for having fully diverse type II AB codes. [ABSTRACT FROM AUTHOR]

We study the problem of A/D conversion and error-rate dependence of a class of nonbandlimited signals with finite rate of innovation. In particular, we analyze a continuous periodic stream of Diracs, characterized by a finite set of time positions and weights. Previous research has only considered sampling of this type of signals, ignoring the presence of quantization, necessary for any practical implementation. To this end, we first define the concept of consistent reconstruction and introduce corresponding oversampling in both time and frequency. High accuracy in a consistent reconstruction is achieved by enforcing the reconstructed signal to satisfy three sets of constraints, related to low-pass filtering, quantization and the space of continuous periodic streams of Diracs. We provide two schemes to reconstruct the signal. For the first one, we prove that the estimation mean squared error of the time positions is O(1/Rt²Rf³), where Rt and Rf are the oversampling ratios in time and frequency, respectively. For the second scheme, it is experimentally observed that, at the cost of higher complexity, the estimation accuracy lowers to O(1/Rt²Rf5). Our experimental results show a clear advantage of consistent over nonconsistent reconstruction. Regarding the rate, we consider a threshold crossing based scheme where, as opposed to previous research, both oversampling in time and in frequency influence the coding rate. We compare the error-rate behavior resulting, on the one hand, from increasing the oversampling in time and/or frequency, and, on the other hand, from decreasing the quantization stepsize. [ABSTRACT FROM AUTHOR]

In time reversed imaging a pulse is propagated through a medium, the signal is recorded, and then the time reversed signal is back-propagated through the same medium to refocus the energy at the original location of the source. The refocusing is independent of the medium if the medium is the same during back-propagation. If the speed of back-propagation differs from the speed of forward propagation, the waves refocus at a different location. For a single source and single receiver, the shift is proportional to the distance between the source and the receiver and the speed difference. If several receivers are placed along a circle to form an aperture angle, the shift in the location of the refocused pulse increases with increasing aperture angle for a given source-receiver distance and speed difference. If we analyze the problem using ray theory, an increase in the aperture angle would result in a decrease in the shift of the refocused pulse. The explanation for the shift of the refocused pulse with aperture angle is simple from a wave-front point of view. [ABSTRACT FROM AUTHOR]

A high-resolution time-to-digital converter (TDC) implemented in a general purpose field-programmable-gate-array (FPGA) is presented. Dedicated carry lines of an FPGA are used as delay cells to perform time interpolation within the system clock period and to realize the fine time measurement. Two Gray-code counters, working on in-phase and out-of-phase system clocks respectively, are designed to get the stable value of the coarse time measurement. The fine time code and the coarse time counter value, along with the channel identifier, are then written into a first-in first-out (FIFO) buffer. Tests have been done to verify the performance of the TDC. The resolution after calibration can reach 50 Ps. [ABSTRACT FROM AUTHOR]

DialogDesigner is an integrated design and development environment that supports dialogue designers in creating an electronic dialogue model, writing dialogue snippets, running and analysing simulation sessions, getting graphical views of the model, making automatic evaluation regarding dialogue model well-formedness, compiling the model into run-time code, and extracting different presentations. DialogDesigner has been used for research purposes as well as in commercial projects. Its primary focus is on providing support for the development process. We explain underlying ideas, illustrate the functionality of DialogDesigner and discuss its strengths. [ABSTRACT FROM AUTHOR]

In this paper, we study the performance of a bandwidth efficient space-frequency turbo encoding scheme over wideband channels. Results are presented for simulated wideband MIMO channels consisting of two transmit antennas and up to two receive antennas. In addition, wideband channel measurements undertaken with practical multi-element antenna structures at both the access point (AP) and mobile terminal (MT) are presented. Analysis is in terms of channel capacity, 10% channel outage capacity and space frequency iterative decoding for an IEEE802.11a physical layer complaint modem. It is shown when operating with a spectral efficiency of 1.2 hits/s/Hz. the iterative decoded space time codes comes within approximately 4.7 dB of 10 outage capacity over Rayleigh fading wideband channels with two transmit and two receive antennas. Over measured channels the iterative decoding scheme performs within 7.7 dB 10% of outage capacity. Losses due to channel state information estimation are also investigated. [ABSTRACT FROM AUTHOR]

The potential promised by multiple transmit antennas has raised considerable interest in space-time coding for wireless communications. In this paper, we propose a systematic approach for designing space-time trellis codes over flat fading channels with full antenna diversity and good coding advantage. It is suitable for an arbitrary number of transmit antennas with arbitrary signal constellations. The key to this approach is to separate the traditional space-time trellis code design into two parts. It first encodes the information symbols using a one-dimensional (M, 1) nonbinary block code, with M being the number of transmit antennas, and then transmits the coded symbols diagonally across the space-time grid. We show that regardless of channel time-selectivity, this new class of space-time codes always achieves a transmit diversity of order M with a minimum number of trellis states and a coding advantage equal to the minimum product distance of the employed block code. Traditional delay diversity codes can be viewed as a special case of this coding scheme in which the repetition block code is employed. To maximize the coding advantage, we introduce an optimal construction of the nonbinary block code for a given modulation scheme. In particular, an efficient suboptimal solution for multilevel phase-shift-keying (PSK) modulation is proposed. Some code examples with 2-6 bits/s/Hz and two to six transmit antennas are provided, and they demonstrate excellent performance via computer simulations. Although it is proposed for flat fading channels, this coding scheme can be easily extended to frequency-selective fading channels. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the equalization and channel identification for space-time block coded signals over a frequency-selective multiple-input multiple-output (MIMO) channel. The equalization has been considered by taking into account the cyclostationarity of space-time block coded signals. The minimum mean square error (MMSE) solutions have been derived for the linear and decision feedback (DF) equalizers. The channel estimation is required for the equalization. With known symbols (as pilot symbols), MIMO channels can be estimated. In addition, due to the redundancy induced by space-time block code, it is possible to identify MIMO channels blindly using the subspace method. We consider both blind and semi-blind channel estimation for MIMO channels. It is shown that the semi-blind channel estimate has fewer estimation errors, and it results in less (bit error rate) performance degradation of the MMSE linear and DF equalizers. [ABSTRACT FROM AUTHOR]

Some important properties are derived for the diversity gain and the coding gain of space-time codes (STCs) for frequency-selective channels. It is proven that the diversity gain of a STC that provides maximum diversity gain for channels with a given number of taps is robust to a decrease in the number of taps. For coding gain analysis, we categorize the possible types of correlation matrices into several classes based on the type of power delay profile, spatial correlation, and tap correlation. It is proven that optimum STCs found for spatially independent and frequency-selective channels with uncorrelated taps and uniform power delay profile have coding gains that are robust against a mismatch in correlation structure if the number of taps is fixed. Thereafter, a systematic design procedure is applied to search for the best space-time trellis codes (STTCs) for frequency-selective channels. At a frame error rate (FER) of 0.01, our example 16-state binary phase-shift keying (BPSK) STTC outperforms the delay diversity code by 3.4 dB for a channel with three uncorrelated uniform taps. Further, the example STC designed for a channel with a given number of taps is shown to provide good performance for channels with fewer taps. [ABSTRACT FROM AUTHOR]

A digital carrier recovery (CR) loop with an adaptive loop bandwidth for rapid carrier frequency offset acquisition and low steady-state jitter is proposed in this paper In addition to the traditional CR functional blocks, the presented carrier synchronizer consists of a tracking-status detector and a loop bandwidth controller. The tracking-status detector monitors the frequency-estimate signals output from the frequency-tracking (integral) branch of the loop filter, detecting whether the frequency offset is locked or not. Then, by adjusting the loop bandwidth in response to the detected result, the convergence time of the acquisition-state and the carrier jitter in the steady-state can be reduced. The new scheme, implemented by FPGAs, has been successfully applied to a 256-QAM baseband digital receiver and also inter-operated with a commercial CMTS. The SNR performance can be improved up to 3 dB only at the expense of 3% hardware area of a Virtex-II-2000 FPGA for this proposed architecture. [ABSTRACT FROM AUTHOR]

Digital television (DTV) receiver architecture with an antenna array is proposed to improve the reception performance in multipath fading conditions. The proposed DTV receiver uses diversity combining and equalization techniques in the beam-space. Two separate beamformers are forming separate beam patterns to two different signal arriving angles by utilizing a channel estimation technique. Then the outputs of the beamformers are combined with a proper time adjustment. Simulation results show the convergence speed of the proposed architecture is three times faster than that of the receiver using only one branch beamformer. [ABSTRACT FROM AUTHOR]

Investigates the importance of microsecond interaural time difference coding in localizing low-frequency sounds in space. Role of glycine-controlled inhibition in interaural time difference coding; Response of coincidence-detector neuron with bilateral excitatory inputs; Observation of neuronal processing with temporal acuity in mammalian central nervous system.

The Bifurcating Neuron (BN), a chaotic integrate-and-fire neuron, is a model of a neuron augmented by coherent modulation from its environment. The BN is mathematically equivalent to the sine-circle map, and this equivalence relationship allowed us to apply the mathematics of one-dimensional maps to the design of a BN network. The study of the bifurcating diagram of the BN revealed that the BN, under a suitable condition, can function as an amplitude-to-phase converter. Also, being an integrate-and-fire neuron, it has an inherent capability to function as a coincidence detector. These two observations led us to the design of the BN Network 2 (BNN-2), a pulse-coupled neural network that exhibits associative memory of multiple analog patterns. In addition to the usual dynamical properties as an associative memory, the BNN-2 was shown to exhibit volume-holographic memory: it switches to different pages of its memory space as the frequency of the coherent modulation changes, meaning context-sensitive memory. [Copyright &y& Elsevier]

Reports that Ormia ochracea can behaviorally localize a salient sound source with a precision equal to that of humans. Measurement of auditory directional acuity; Details of how information is represented in the auditory system with hyperacute timecoding; Finding that nanoscale/microscale directional microphones patterned after the fly have the potential for highly accurate directional sensitivity, independent of their size; Mentions of coding strategy employed by the nervous system.

The auditory and electrosensory systems contain circuits that are specialized for the encoding and processing of microsecond time differences. Analysis of these circuits in two specialists, weakly electric fish and barn owls, has uncovered common design principles and illuminated some aspects of their evolution. [ABSTRACT FROM AUTHOR]

We describe a fluorescent detection technique for a lab-on-a-chip flow cytometer. Fluorescent emission is encoded into a time-dependent signal as a fluorescent cell or bead traverses a waveguide array with integrated spatial filters and color filters. Different from conventional colored filters with well-defined transmission spectral window, the integrated color filters are designed to have broad transmission characteristics, similar to the red-green-blue photoreceptors in the retina of human eye. This unique design allows us to detect multiple fluorescent colors with only three color filters based on the technique of color-space-time coding using only one single photomultiplier tube or avalanche photodetector. [ABSTRACT FROM AUTHOR]