2,891 research outputs found

    Joint Decision-Directed Channel and Noise-Variance Estimation for MIMO OFDM/SDMA Systems Based on Expectation-Conditional Maximization

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    A joint channel impulse response (CIR) and noise-variance estimation scheme is proposed for multiuser multiple-input–multiple-output (MIMO) orthogonal frequency-division multiplexing/space-division multiple access (OFDM/SDMA) systems, which is based on the expectation-conditional maximization (ECM) algorithm. Multiple users communicating over fading channels exhibiting a range of different characteristics are considered in this paper. Channel estimation becomes quite challenging in this scenario since an increased number of independent transmitter–receiver links having different statistical characteristics have to be simultaneously estimated for each subcarrier. To cope with this scenario, we design an ECM-based joint CIR and noise-variance estimator for multiuser MIMO OFDM/SDMA systems, which is capable of simultaneously estimating diverse CIRs and noise variance. Furthermore, we propose a forward error code (FEC)-aided decision-directed channel estimation scheme based on the ECM algorithm, which further improves the ECM algorithm by exploiting the error correction capability of an FEC decoder for iteratively exchanging information between the decoder and the ECM algorithm

    Differential evolution algorithm aided minimum symbol error rate multi-user detection for multi-user OFDM/SDMA systems

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    A Differential Evolution (DE) algorithm assisted Minimum Symbol Error Ratio (MSER) Multi-User Detection (MUD) scheme is proposed for multi-user Multiple-Input Multiple-Output (MIMO) aided Orthogonal Frequency-Division Multiplexing / Space Division Multiple Access (OFDM/SDMA) systems. Quadrature Amplitude Modulation (QAM) is employed in most wireless standards by virtue of providing a high throughput. The MSER Cost Function (CF) may be deemed to be the most relevant one for QAM, but finding its minimum is challenging. Hence we propose a sophisticated DE assisted MSER-MUD scheme, which directly minimizes the SER CF of multi-user OFDM/SDMA systems employing QAM. Furthermore, the effects of the DE assisted MSER-MUD’s algorithmic parameters, namely those of the population size Ps, of the scaling factor ? and of the crossover probability Cr on the number of DE generations required for attaining convergence were investigated in our simulations. This allowed us to directly quantify their complexity. The simulation results also demonstrate that the proposed DE assisted MSER-MUD scheme significantly outperforms the conventional MMSE-MUD in term of the system’s overall BER and it is capable of narrowing its BER performance discrepancy with respect to the optimal Maximum Likelihood (ML) MUD to about 4dB, while requiring about 200 times less CF evaluations compared to the optimal ML-MUD scheme

    A novel optimization method on logistics operation for warehouse & port enterprises based on game theory

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    Purpose: The following investigation aims to deal with the competitive relationship among different warehouses & ports in the same company. Design/methodology/approach: In this paper, Game Theory is used in carrying out the optimization model. Genetic Algorithm is used to solve the model. Findings: Unnecessary competition will rise up if there is little internal communication among different warehouses & ports in one company. This paper carries out a novel optimization method on warehouse & port logistics operation model. Originality/value: Warehouse logistics business is a combination of warehousing services and terminal services which is provided by port logistics through the existing port infrastructure on the basis of a port. The newly proposed method can help to optimize logistics operation model for warehouse & port enterprises effectively. We set Sinotrans Guangdong Company as an example to illustrate the newly proposed method. Finally, according to the case study, this paper gives some responses and suggestions on logistics operation in Sinotrans Guangdong warehouse & port for its future development.Peer Reviewe

    Design Impedance Mismatch Physical Unclonable Functions for IoT Security

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    We propose a new design, Physical Unclonable Function (PUF) scheme, for the Internet of Things (IoT), which has been suffering from multiple-level security threats. As more and more objects interconnect on IoT networks, the identity of each thing is very important. To authenticate each object, we design an impedance mismatch PUF, which exploits random physical factors of the transmission line to generate a security unique private key. The characteristic impedance of the transmission line and signal transmission theory of the printed circuit board (PCB) are also analyzed in detail. To improve the reliability, current feedback amplifier (CFA) method is applied on the PUF. Finally, the proposed scheme is implemented and tested. The measure results show that impedance mismatch PUF provides better unpredictability and randomness

    Time-periodic solution to nonhomogeneous isentropic compressible Euler equations with time-periodic boundary conditions

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    In this paper, we study one-dimensional nonhomogeneous isentropic compressible Euler equations with time-periodic boundary conditions. With the aid of the energy methods, we prove the existence and uniqueness of the time-periodic supersonic solutions after some certain time

    Efficacy of combined atorvastatin calcium, Salviae miltiorrhizae and ligustrazine hydrochloride injection in cerebral infarction patients

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    Purpose: To study the effect of a combination of atorvastatin calcium with Salviae miltiorrhizae and ligustrazine hydrochloride injection on serum levels of ferritin (SF), C-reactive protein (CRP) and hypoxia-inducible factor 1α(HIF-1α) in cerebral infarction patients.Methods: A total of 60 cerebral infarction patients (confirmed by CT or MRI scan) were randomly assigned to control group and observation group (30 patients/group). Both groups received routine treatments. All patients took atorvastatin calcium, but those in the observation group were treated with Salviae miltiorrhizae and ligustrazine hydrochloride injection, in addition to atorvastatin hydrochloride for 14 days, with 7 days as treatment course. The levels of SF, CRP and HIF-1α were determined before and after treatment, to assess clinical efficacy and safety.Results: In both groups, SF, CRP and HIF-1α levels were lower after treatment than before treatment (p < 0.05). NIHSS score and platelet activation indices were also significantly reduced, relative to control (p < 0.05).Conclusion: The combination of atorvastatin calcium with Salviae miltiorrhizae and ligustrazine hydrochloride injection can control vascular inflammatory reactions by decreasing the levels of SF, CRP and HIF-1α. Thus, it may be beneficial in the clinical management of cerebral infarction.Keyword: Cerebral infarction, Atorvastatin calcium, Salviae miltiorrhizae, Ligustrazine hydrochloride injectio

    Automatic Train Operation Speed Profile Optimization and Tracking with Multi-Objective in Urban Railway

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    Besides energy-efficiency, people also want train operation to be comfortable, punctual and parking precise. In this paper, a multi-objective model for automatic train operation in urban railway is proposed by unifying dimensions of different objectives firstly. This model is built by applying multi-objective decision with the penalty function, based on the analysis of train performance and its operation environment. Then a genetic algorithm is developed to solve this model and obtain the optimal recommended speed profiles. Thirdly, fuzzy controller is designed to achieve track recommended speed profiles. Finally, with the help of Matlab software, control effect is verified based on simulation. From the simulation results, it can be seen this strategy can meet the requirement of multi-objective, which are energy-saving, parking precisely, running punctually and comfort
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