Space-time Systems Research Articles

Cosmological brane systems in warped spacetime

In this paper, we discuss the time-dependent brane solutions in higher-dimensional supergravity theories. We particularly focus on the dynamical extensions of the intersecting brane solutions involving three branes. We also show that in the near-horizon limits, where the time dependence is negligible, these branes describe warped anti--de Sitter spacetimes as in the corresponding static solutions. We finally examine the lower-dimensional cosmological dynamics obtained after compactifications of the higher-dimensional solutions and show the solutions we have found give the four-dimensional universe with power-law expansion.

Riemannian Space-Time, de Donder Conditions and Gravitational Field in Flat Space-Time

Let the coordinate system xi of flat space-time to absorb a second rank tensor field Φij of the flat space-time deforming into a Riemannian space-time, namely, the tensor field Φuv is regarded as a metric tensor with respect to the coordinate system xu. After done this, xu is not the coordinate system of flat space-time anymore, but is the coordinate system of the new Riemannian space-time. The inverse operation also can be done. According to these notions, the concepts of the absorption operation and the desorption operation are proposed. These notions are actually compatible with Einstein’s equivalence principle. By using these concepts, the relationships of the Riemannian space-time, the de Donder conditions and the gravitational field in flat space-time are analyzed and elaborated. The essential significance of the de Donder conditions (the harmonic conditions or gauge) is to desorb the tensor field of gravitation from the Riemannian space-time to the Minkowski space-time with the Cartesian coordinates. Einstein equations with de Donder conditions can be solved in flat space-time. Base on Fock’s works, the equations of gravitational field in flat space-time are obtained, and the tensor expression of the energy-momentum of gravitational field is found. They all satisfy the global Lorentz covariance.

Analytical Evaluation of Space-Time M-QAM Signaling and Time-Delay Estimation in Multipath Terrestrial Communications

This paper presents novel information-theoretic PHY layer performance improvement for combating the system fading effects in wireless terrestrial communication applications. Robust space-time system strategies in cooperation with the high performance unpunctured serially concatenated codes have been jointly employed. The wireless terrestrial system also uses M-ary quadrature amplitude modulation (QAM) signaling to develop a well-established system modeling for multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) analysis. This research also undertakes the analytical evaluation of time-delay estimation in the presence of additive white Gaussian noise (AWGN) in multipath areas. The objective of this investigation is to develop mathematically-oriented estimations intended for suitable employment in terrestrial communications. This model considers the problem of overlapping the terrestrial signals arrival-times estimation from a noisy received waveform in order to develop a system model for terrestrial TDE.

Two-stage constellation partition algorithm for reduced-complexity multiple-input multiple-output–maximum-likelihood detection systems

This study presents the analysis of a constellation partition (CP) algorithm for multiple-input multiple-output–maximum-likelihood detection (MIMO–MLD) systems. The authors consider an Nt by Nr MIMO system, where MLD algorithm is employed at the receiver side for MIMO signal detection. The authors show that for the case of orthogonal space-time block codes and MIMO beamforming (MIMO-BF) systems, the proposed CP algorithm achieves the same error-rate performance as the optimum MLD algorithm while cutting back significantly on the complexity of MIMO–MLD scheme. Thus complexity reduction is not achieved at the expense of the optimum MLD performance in these cases, unlike the existing simplified MLD schemes in the literature. For the case of MIMO-multiplexing system, however, it is observed that the complexity reduction is achieved at the expense of the optimum MLD performance, similar to the existing simplified MLD schemes. Thus the proposed algorithm is especially attractive in real-time implementation of space-time block code and MIMO-BF systems.

Study of the Spatio-Temporal Data Model in Sea Battlefield

An effective analysis of the battlefield situation and spatio-temporal data model in a sea battlefield has great significance for the commander to perceive the battlefield situation and to make the right decisions. Based on the existing spatio-temporal data model, the present paper gives a comprehensive analysis of the characteristics of sea battlefield data, and chooses the object-oriented spatio-temporal data model to modify it; at the same time this paper introduces sea battlefield space-time algebra system to define various data types formally, which lays the foundation for the establishment of the sea battlefield spatio-temporal data model.

Performance Analysis of a QR Decomposition Algorithm Employing Rearrangement of Antenna Layers on V-BLAST Systems

In a Rayleigh fading environment, the paper firstly introduces system model and the vertical Bell laboratories layered space-time (V-BLAST) systems structure. Several popular decoding algorithms for V-BLAST are carried on the analysis comparison, such as zero-foring (ZF), minimum mean squared error (MMSE), QR decomposition, and maximum likelihood (ML) etc. On this basis, the paper focuses on QR decomposition research, analyzes and summarizes the QR decomposition algorithm and iterative algorithm. We draw a conclusion that the key of improving QR scheme performance is to choose the upper triangular matrix R. From intuitionistic point of view, three selection criterions are given, such as rearrangeing matrix H according to row vectors, the maximum element r(Nt, Nt) of the matrix R, and the maximum diagonal squared Frobenius norms (SFN) in R. The simulation results indicate that the selection rule of the maximum r(Nt, Nt) can obviously improve the performance of the first decoded layer. For a 4Tx4Rx MIMO V-BALST system, the simulation results show that the V-BALST system performance is to be improved further when we combined the maximum r(4,4) criterion with the iterative algorithm.

Computationally efficient near-optimal combined antenna selection algorithms for V-BLAST systems

The Vertical Bell Laboratories Layer Space-Time (V-BLAST) system using ordered successive interference cancellation (OSIC) detection is a popular system architecture featuring high data rate and moderate computational complexity. The performance of the V-BLAST system can be further improved by exploiting the diversity and closed-loop gain provided by the technique of combined antenna selection (CAS). In this paper, we investigate the design of CAS algorithms with a goal to minimize the system@?s error rate. As the error rate of a system varies dramatically with the transceiver architecture, the proposed CAS algorithms explicitly take the VBLAST detection structure into account. Despite the optimal CAS can be achieved by exhaustively searching all the transmit and receive antenna subsets, the applicability of this brute-force approach is excessively limited due to its huge computational complexity. To this end, we propose two computationally efficient CAS algorithms by implementing a greedy strategy incrementally or decrementally to fully exploit the recursive structure of mean-square-error matrices between consecutive V-BLAST detection stages. Near optimal error rate performance can therefore be obtained with significantly lower complexity as verified by the extensive computer simulations.

Comparison of Enzootic Risk Measures for Predicting West Nile Disease, Los Angeles, California, USA, 2004–2010

In Los Angeles, California, USA, 2 epidemics of West Nile virus (WNV) disease have occurred since WNV was recognized in 2003. To assess which measure of risk was most predictive of human cases, we compared 3 measures: the California Mosquito-Borne Virus Surveillance and Response Plan Assessment, the vector index, and the Dynamic Continuous-Area Space-Time system. A case-crossover study was performed by using symptom onset dates from 384 persons with WNV infection to determine their relative environmental exposure to high-risk conditions as measured by each method. Receiver-operating characteristic plots determined thresholds for each model, and the area under the curve was used to compare methods. We found that the best risk assessment model for human WNV cases included surveillance data from avian, mosquito, and climate sources.

Virtual Receive Antenna for Overloaded MIMO Layered Space-Time System

Layered space time processing in spatial multiplexing systems requires the number of receive antennas to be equal to or larger than the number of transmit antennas. However, it is impractical for small-sized mobile units to accommodate a large number of antennas. To loosen this stringent requirement, a novel concept of virtual receive antennas (VRA) for overloaded MIMO system is presented. The VRA system architecture consists of two major parts: fractional timing offset in the transmitter and oversampling at the receive matched filter. This procedure expands the received signal dimension and thus creates virtual receive antennas. Due to these created virtual receive antennas, the minimum number of physical receive antennas could be reduced. In order to explore the potential of VRA, this paper evaluates its system capacity and performance bound. Results show that the VRA system can achieve higher ergodic capacity and outage rate than conventional overloaded MIMO system. Performance analysis also suggests a potential performance gain for the VRA system. To eliminate the created inter-symbol interference in the VRA, time domain and frequency domain equalization are utilized and evaluated.

Pseudo-unitary dynamics of free relativistic quantum mechanical twofold systems

A finite-dimensional pseudo-unitary framework is set up for describing the dynamics of free elementary particles in a purely relativistic quantum mechanical way. States of any individual particles or antiparticles are defined as suitably normalized vectors belonging to the two-complex-dimensional spaces that occur in local orthogonal decompositions of isomorphic copies of Cartan’s space. The corresponding dynamical variables thus show up as bounded pseudo-Hermitian operator restrictions that possess real discrete spectra. Any measurement processes have to be performed locally in orthocronous proper Lorentz frames, but typical observational correlations are expressed in terms of symbolic configurations which come from the covariant action on spaces of state vectors of the Poincaré subgroup of an adequate realization of SU(2,2). The overall approach turns out to supply a supposedly natural description of the dynamics of free twofold systems in flat spacetime. One of the main outlooks devised here brings forward the possibility of carrying out methodically the construction of a background to a new relativistic theory of quantum information.

Full-diversity high-rate space-time block-coded systems using estimated channel state information for symbol detection

In this paper, the frame-error-rate (FER) performance of full-diversity high-rate space-time block-coded (STBC) system is presented for quadrature phase-shift keying (QPSK) digital modulation technique, which is using the numeric-variable-forgetting-factor (NVFF) least-squares (LS) algorithm based channel estimator. The STBC transmission data-rates with two-transmitter antennas and with four-transmitter antennas are achieved by maximizing the coding gain and by minimizing the peak-to-minimum-power-ratio while using the selective power scaling of the information symbols, which also guarantees full-diversity in case of the two-transmitter antennas. The imperfect channel estimation leads to degradation in the FER performance of the low complexity maximum likelihood decoding algorithms, though the optimum power scaling factor is incorporated along with the constellation rotation scheme. Simulation results are presented to demonstrate that the FER performance of high-rate STBC system under idealistic conditions is quite different from its performance under realistic wireless environment due to the channel estimation errors. Therefore, the tracking performance of the pilot channel estimator is found to play significant role in the overall performance evaluation of the proposed wireless systems under slowly time-varying channels also in case of the general M-ary phase-shift keying (M-PSK) constellations. Key words: Space-time block-code, coding gain, peak-to-minimum-power-ratio, numeric-variable-forgetting-factor, variable-forgetting-factor, least-squares algorithm.

Combining GA and iterative MVDR for DOA estimation in space-time CDMA systems

This paper deals with direction-of-arrival (DOA) estimation of minimum variance distortionless response (MVDR) approach based on iterative searching technique for space-time code-division multiple access (CDMA) systems. It has been shown that the iterative searching technique is more likely to converge to a local maximum, causing errors in DOA estimation. In conjunction with a genetic algorithm for selecting initial search angle, an efficient approach is presented to achieve the advantages of iterative DOA estimation with fast convergence and less computational load over existing conventional spectral searching MVDR estimator. Simulation results are provided for illustrating the effectiveness of the proposed approach.

Generalised Spatial Modulation System with Multiple Active Transmit Antennas and Low Complexity Detection Scheme

A generalised spatial modulation (SM) scheme with multiple active transmit antennas, named as multiple active-spatial modulation (MA-SM), is proposed in this paper. By allowing multiple transmitting antennas in the SM system to transmit different symbols at the same time instant, MA-SM takes advantages of the low complexity of SM and high multiplexing gain of Vertical-Bell Lab Layered Space-Time (V-BLAST) system. In the MA-SM system, the transmitted symbols are mapped into a high dimensional constellation space including the spatial dimension. The general principle for designing the efficient MA-SM for arbitrary number of transmit antennas and modulation scheme is presented. Moreover, a near-optimal detection scheme with low complexity for MA-SM is also proposed and analyzed. A closed form bound for the bit error probability (BEP) of the proposed detection scheme is also derived in this paper. Numerical results with the comparison among the existing multiple-input multiple-output (MIMO) systems such as space time block code (STBC) and V-BLAST demonstrate the efficiency of MA-SM.

Space–time compressive imaging

Compressive imaging systems typically exploit the spatial correlation of the scene to facilitate a lower dimensional measurement relative to a conventional imaging system. In natural time-varying scenes there is a high degree of temporal correlation that may also be exploited to further reduce the number of measurements. In this work we analyze space-time compressive imaging using Karhunen-Loève (KL) projections for the read-noise-limited measurement case. Based on a comprehensive simulation study, we show that a KL-based space-time compressive imager offers higher compression relative to space-only compressive imaging. For a relative noise strength of 10% and reconstruction error of 10%, we find that space-time compressive imaging with 8×8×16 spatiotemporal blocks yields about 292× compression compared to a conventional imager, while space-only compressive imaging provides only 32× compression. Additionally, under high read-noise conditions, a space-time compressive imaging system yields lower reconstruction error than a conventional imaging system due to the multiplexing advantage. We also discuss three electro-optic space-time compressive imaging architecture classes, including charge-domain processing by a smart focal plane array (FPA). Space-time compressive imaging using a smart FPA provides an alternative method to capture the nonredundant portions of time-varying scenes.

Adaptive Spatial Mode Of Space–Time And Spacefrequency OFDM System Over Fading Channels

Dalam kertas kerja ini kami membentangkan skema mod ruang (ASM) adaptif 2 menghantar 1 menerima (2 Tx : 1 Rx) menggunakan kaedah ruang–masa (ST) dan ruang frekuensi (SF) multiplekskan pembahagian frekuensi ortogonal (OFDM). Pada nilai nisbah isyarat ke hingar yang rendah kami menggunakan ST–OFDM dan menukar kepada mod SF–OFDM pada nilai ambang yang telah ditentukan. Nilai ini ditentukan berdasarkan titik silang antara lengkuk prestasi kedua–dua mod. Keputusan simulasi menunjukkan gandaan banyak 9 dB (pada kadar ralat bit 10–3) diperolehi dengan menggunakan mod ruang adaptif (ASM) berbanding dengan ST–OFDM tanpa kod, lebih kurang 6 dB berbanding SF–OFDM, 4 dB berbanding ST–OFDM terkod dan gandaan sebanyak 2 dB berbanding SF–OFDM terkod, pada rebak lengah 700 ns. Kata kunci: OFDM, ruang–masa, ruang–frekuensi, pengekodan saluran dan saluran pemudaran berbilang laluan In this paper we present a 2 transmit 1 receive (1 Tx : 1 Rx) adaptive spatial mode (ASM) of space–time (ST) and space–frequency (SF) orthogonal frequency division multiplexing (OFDM). At low signal to noise ratio (SNR) we employ ST–OFDM and switch to SF–OFDM at a certain SNR threshold. We determine this threshold from the intersection of individual performance curves. Results show a gain of 9 dB (at a bit error rate of 10–3) is achieved by employing adaptive spatial mode compared to a fixed ST–OFDM, almost 6 dB to fixed SF–OFDM, 4 dB to Coded ST–OFDM and 2 dB to a fixed coded SF–OFDM, at a delay spread of 700 ns. Key words: OFDM, space–time, space–frequency, channel coding and multipath fading channels

A 6D space framework for the description of distributed systems

This paper proposes a six-dimensional (6D) space framework and an appropriate reference entity for the description of organizations and realization of identifiable matter. The aim was to compose and present a new differentiable and well-structured syntactic reference entity on the basis of a general 4D space-time system. The entity should be visual, capable of providing people who develop, integrate or analyse distributed motional applications with basic means for navigation and adequate comprehension of motion. The common length, width and height dimensions determine the 3D subspace for definition of the geographic points of the motional concept. Time and the newly- founded content and merit dimensions together form a 3D realization space that inherently describes existence of motion outside the geographic points. The content dimension is used to declare the quantitative values of the quantities and properties of motion. The merit dimension is used to declare the qualities of quantities and properties. The transformation in the dynamic realization space is defined by the named quantities and properties. The time dimension is used to define the dynamic channels for the valuable content of a named quantity or a property of motion. The temporal content values of the named quantities and properties of matter are defined at the geographic points. Symbolic names of the axes of the new 6D axis system are: length, width, height, time, and the newly introduced content and merit. An ontology is proposed by the author to define the hierarchy of the merital names. The content axis uses the basic hierarchy with Arabic numerals to define the quantitative values of the quantities (properties). The 6D axis system that is semantically interpreted as a syntactic reference item is universally usable to describe the motion of a distributed concept, a model or a real entity, including transformation between different qualities of motion. Potential usage of the new 6D axis system together with the ontology is described. An example in the field of electrical engineering and industrial automation technology is presented. A visual user interface is discussed.

Complex Generalized Basis Reduction Assisted Successive Interference Cancellation Detection for SCBLAST Systems

Complex generalized basis reduction assisted successive interference cancellation is proposed for mitigating multi-stream interference of transmitted signals in single code Bell Laboratories layered space-time systems. Generalized basis reduction method is modified to better the complex channel matrix, which leads to the extended generalized reduction basis channel matrix with shorter and roughly orthogonal basis vectors in polynomial-time. This distinguished property guarantees the concatenated successive interference cancellation detector, based on the MMSE criterion, converges to the approximately global optimum estimation points. Emulation results have shown that the proposed detection scheme is superior to other suboptimum detection schemes considered in this paper in terms of two points. They are the mitigation of multi-stream interference and the diversity gain. Its performance is close to the sphere decoder but with a lower complexity.

De la bifurcation des flux psychiques en pathologie mentale. Étude clinique, informatique et modélisation calculable

The objective of this survey is to show the important role of the bifurcations of the psychic flux in the starting up of the mental troubles. However, the role of bifurcations is not usually revealed by the classic observation. This one tackles troubles with a descriptive manner from their appearances, while associating symptoms, pathogenic and evolving factors. It is notably the case for the contemporary works founded on criteria allowing a computerized treatment. That is different on the qualitative studies of individual cases that incite, beyond the descriptive aspects of the troubles, to penetrate into their effective structuring. Of this fact, they imply new logical investigations, associating to the classical logic founded on the third excluded logic of third inclusive allowing to virtually studying the trouble from psychic real-life experiences. To this effect, the method we adopt, named the systemal method, uses an operative architecture of the psychic system. It considers a conceptual mold expressing the sets and the subsets that constitute the thought. So it transposes the virtual psychic system into a specific space-time system made up of several levels of organizations, which are going to constitute an operative grid. This one includes various levels like somato-instinctive, emotional, affective and intellectual, this last one being subdivided into mental representations, automatic devices and mental syntheses. In the paper, the observed facts supporting this research concern the young woman's observation that has been in treatment during 10 consecutive years. She exposes to us the ambivalences, simultaneously affirming and invalidating the same events she has lived. The evolution will show several episodes of confusion and dissociation that answer, according to the DSM criteria, to a schizophrenic pathology. However, the analysis of the various psychic organization levels underlines that during this long evolution, the existence of bifurcations that concern as well the real-life experiences that her own representations of facts, the significance of her matters, the language, the emotive and emotional charges, and even psychomotric behavior. The inventory of clinics data incites to conclude to the probable existence of sets of bifurcations in the determinism of troubles. Besides, the clinic shows that this property appears under the effect of pathogenic attractors that weakens regulations of each of these levels. These same phenomena of bifurcations, attractors and regulators, appear in the new systems of artificial consciousness. The model generating artificial consciousness is founded on the calculable and uses many artificial processes with their evolving relations. Its architecture is based on the Freudian topics of no conscious, preconscious and conscious, linked with a systemic organizational loop. The model expresses the functioning of an autonomous system based on an organizational memory representing real-life experiences, using in real-time an artificial embodiment, and using many elements of control as regulator or attractors to intentionally generate and feel complex forms equivalent to artificial thoughts. The model manages weak and strong bifurcations into the regulation of organization of its dynamic components to express the qualities of the emergences felt. The bifurcation presumably appears as an essential property of the evolutionary systems using memory, whether they are living or of computer nature. It concerns the modeling of qualitative and quantitative order, implying to have recourse to interdisciplinary studies to refine the knowledge of the mental troubles.

Two efficient and stable MMSE detection algorithms for the V-BLAST system

For practical consideration, efficient and stable implementation of the promising vertical Bell Labs Layered Space-Time system is highly desirable. The original square-root algorithm SRA, proposed by Hassibi, for the minimum mean square error detection, is composed of three stages, that is, initialization, ordering, and nulling. Unlike the original SRA whose initialization stage is not completely based on unitary transformations, the three stages of our proposed algorithm #1 are all based on unitary transformations. The average number of multiplications required by our proposed algorithm #1 is about 29i¾?10M3, where both the numbers of transmit and receive antennas are equal to M. In the meantime, the average number of multiplications required by the original SRA is 17i¾?3M3. In addition to the stable initialization, ordering, and nulling considered by the proposed algorithm #1, our proposed algorithm #2 considers stable detection. Our proposed algorithm #2 is completely based on Givens rotations, which is to be implemented by COordinate Rotation DIgital Computer-based hardwares. Copyright © 2011 John Wiley & Sons, Ltd.

Frequency domain equalization space-time block-coded CDMA transmission system

In this work we propose a space-time block-coded (STBF) CDMA transmission system suitable for use with frequency domain equalization (FDE) algorithms. We illustrate the FDE by implementing the maximal ratio combining, the zero forcing and the minimum mean squared error single user detection algorithms. A diversity gain analysis is developed and some interesting results are pointed out. It is shown through computer simulations that the proposed transmission system exhibits good performance in terms of bit error rate when compared to previously proposed STBC CDMA transmission systems.