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In this paper, we present NetQuest, a flexible framework for large-scale network measurement. We apply Bayesian experimental design to select active measurements that maximize the amount of information we gain about the network p...
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In this paper, we present NetQuest, a flexible framework for large-scale network measurement. We apply Bayesian experimental design to select active measurements that maximize the amount of information we gain about the network path properties subject to given resource constraints. We then apply network inference techniques to reconstruct the properties of interest based on the partial, indirect observations we get through these measurements.
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Standard implementation of multiple-model (MM) estimation algorithms may suffer from numerical problems, especially numerical underflows, which occur when the true model is vastly different from one or more models used in the algo...
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Standard implementation of multiple-model (MM) estimation algorithms may suffer from numerical problems, especially numerical underflows, which occur when the true model is vastly different from one or more models used in the algorithm. This may be devastating to the performance of the MM algorithm. Numerical robust implementations of some of the most popular MM algorithms are presented. Simulation results are provided to verify the proposed implementation and to compare with the implementations with a lower bound.
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The paper presents an extension of an earlier paper by the authors (1995), concerned with the development of a single-input single-output (SISO) neural controller for the ship track-keeping problem. Here the single-input parameter...
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The paper presents an extension of an earlier paper by the authors (1995), concerned with the development of a single-input single-output (SISO) neural controller for the ship track-keeping problem. Here the single-input parameter remains as the rudder, but now a multiple output strategy based on the tracking error and heading error (SIMO) is developed and then applied to the same problems investigated by the authors. The differences in the backpropagation-based SISO and SIMO controllers are explained and their relative performances with respect to one another is discussed. In common with earlier reported research, the influence of random wind on the manoeuvring ship and the effect of random noise on the response information supplied to the controller are investigated. In summary, the authors initially review the development of track-keeping strategies since the 1980s.
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Opportunistic scheduling has widely been used in wireless networks to send packet data over fading channels. In the literature, scheduling performance was usually analyzed by assuming a fixed number of active users and infinite p...
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Opportunistic scheduling has widely been used in wireless networks to send packet data over fading channels. In the literature, scheduling performance was usually analyzed by assuming a fixed number of active users and infinite packet buffers. However, the assumption may not be valid due to traffic dynamics in opportunistic packet transmissions. In this paper, we analyze opportunistic scheduling systems with varying number of users and burst packet arrivals. In particular, we define a stability region as the union of a set of convex polyhedral regions. We investigate the tradeoffs between throughput and fairness in terms of stability region. First, the maximal aggregated rate is derived under an optimal scheduling policy, which only depends on the quality-of-service (QoS) requirements without channel-state information (CSI). Second, the perfect fairness limit is defined such that the aggregated rate below the limit can equally be shared among users. Third, the fairness is optimized under a given overall throughput. As a metric to reflect the QoS requirements, we also derive a closed-form average delay for a symmetric system. Theoretical analysis and numerical results demonstrate the advantages of opportunistic scheduling.
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In the reported metrics of the existing literature, the realistic wireless channel situation is generally ignored in selecting the appropriate next-hop relay node during packet forwarding in wireless sensor networks (WSNs). In th...
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In the reported metrics of the existing literature, the realistic wireless channel situation is generally ignored in selecting the appropriate next-hop relay node during packet forwarding in wireless sensor networks (WSNs). In this paper, we propose a new energy-efficient local metric, which is called the efficient advancement metric (EAM), for sensor networks. EAM considers both the maximum forwarding distance and the packet's successful transmission probability by taking into account the wireless channel condition. This will enable the forwarding node to choose the most energy-efficient relay node in the geographic-informed routing protocol. Theoretically, we show the existence of the unique optimal relay node to maximize EAM over a typical Nakagami-$m$ channel of a code-division multiple-access (CDMA)-based WSN. Furthermore, based on the proposed metric EAM, we present a cross-layer packet-forwarding protocol channel-aware geographic-informed forwarding (CAGIF) by optimally selecting the relay nodes. CAGIF only requires that nodes have the knowledge of their own location information and the location information of the source and destination nodes. Numerical examples are presented to show the characteristics of EAM and the optimal distance. Compared with the previous geographic packet-forwarding schemes in WSNs, CAGIF consumes much lower energy and generates a significantly decreased signal overhead.
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This paper proposes a new random-access protocol over $2times M$ multiple-input–multiple-output (MIMO) multiaccess channels, namely, adaptive space–time diversity slotted ALOHA (ASTDSA), to address the issues on collision dive...
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This paper proposes a new random-access protocol over $2times M$ multiple-input–multiple-output (MIMO) multiaccess channels, namely, adaptive space–time diversity slotted ALOHA (ASTDSA), to address the issues on collision diversity while maintaining implementation simplicity. The proposed scheme exploits the advantages of both V-BLAST and Alamouti space–time block coding (STBC). In particular, it adaptively only transmits space–time-coded copies to remediable collisions. The coded replicas contain the same information as the packets involved in collisions and are immediately sent after a colliding slot. Combining the packets received in two consecutive slots, the Alamouti STBC scheme can be reconstructed to linearly resolve the collision without sacrificing the space–time diversity gain. An embedded Markov chain is developed to derive performance metrics with respect to throughput, diversity gain, delay, and stability. The tradeoff among those metrics is investigated. The results demonstrate that ASTDSA significantly outperforms the existing schemes, and simulations are used to validate the analytical model.
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This research investigated the feasibility of stripping CO2 from the digester supernatant to raise the pH, thereby reducing the caustic chemical usage. In this study, a cascade CO2 stripper was first designed and tested, with thre...
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This research investigated the feasibility of stripping CO2 from the digester supernatant to raise the pH, thereby reducing the caustic chemical usage. In this study, a cascade CO2 stripper was first designed and tested, with three different synthetic solutions in a struvite recovery, crystal reactor: (1) tap water saturated with CO2, (2) NaHCO3 solution saturated with CO2, and (3) NaHCO3 + NH4Cl solution saturated with CO2. It was found that the removal efficiency of the CO2 stripper was dependant on several parameters, such as the characteristics of the influent, including total alkalinity, temperature, and initial concentration of dissolved CO2 gas, influent flow rate, effluent recycle rate, aeration rate, and baffle numbers in the stripper. Based on the performance of the stripper on the three synthetic solutions, a CO2 stripping model was developed using these parameters. This model was subsequently tested in a pilot-scale facility, to predict the amount of CO2 removal possible.
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Different noninvasive or minimally invasive therapeutic ablation procedures can produce tissue necrosis associated with local-stiffness increase. Although elastography has been proved as a potential evaluation tool for many kinds ...
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Different noninvasive or minimally invasive therapeutic ablation procedures can produce tissue necrosis associated with local-stiffness increase. Although elastography has been proved as a potential evaluation tool for many kinds of ablation-induced lesions, the application of subtraction technique in elastography to enhance the visualization of the ablation lesions has rarely been reported. In this paper, subtraction elastography is proposed to evaluate the ablation-induced lesions. Three models are constructed to simulate different kinds of ablated inclusions. The simulation results showed that subtraction elastography is superior to conventional elastography in detecting the ablation-induced lesions with higher signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). The artifacts induced by elastographic signal processing algorithms can be largely reduced in subtraction elastography. In addition, subtraction elastography is less influenced by the stiff background and can provide more reliable boundary information about the lesion than conventional elastography. Furthermore, the feasibility of subtraction elastography is validated by an in vitro experiment of ethanol-induced hepatic lesions. The preliminary results of this work suggest that subtraction elastography may be a good option for the evaluation of ablationinduced lesions.
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The missing data problem greatly affects traffic analysis. In this paper, we put forward a new reliable method called probabilistic principal component analysis (PPCA) to impute the missing flow volume data based on historical da...
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The missing data problem greatly affects traffic analysis. In this paper, we put forward a new reliable method called probabilistic principal component analysis (PPCA) to impute the missing flow volume data based on historical data mining. First, we review the current missing data-imputation method and why it may fail to yield acceptable results in many traffic flow applications. Second, we examine the statistical properties of traffic flow volume time series. We show that the fluctuations of traffic flow are Gaussian type and that principal component analysis (PCA) can be used to retrieve the features of traffic flow. Third, we discuss how to use a robust PCA to filter out the abnormal traffic flow data that disturb the imputation process. Finally, we recall the theories of PPCA/Bayesian PCA-based imputation algorithms and compare their performance with some conventional methods, including the nearest/mean historical imputation methods and the local interpolation/regression methods. The experiments prove that the PPCA method provides significantly better performance than the conventional methods, reducing the root-mean-square imputation error by at least 25%.
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The IEEE 802.11 medium-access control (MAC) protocol is usually considered to be a default standard in multihop wireless networks. However, in a multihop network with a large interference range, the request-to-send/clear-to-send ...
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The IEEE 802.11 medium-access control (MAC) protocol is usually considered to be a default standard in multihop wireless networks. However, in a multihop network with a large interference range, the request-to-send/clear-to-send (RTS/CTS) handshake and virtual carrier sensing mechanism may not be able to eliminate interference or solve hidden- and exposed-terminal problems. This paper proposes two new MAC protocols, i.e., the power-fixed dual (PFD) and power-aware dual (PAD) busy-tone schemes, both of which are able to effectively prevent collision of data/acknowledgment (ACK) packets and are applicable in various open-space environments with different path-loss characteristics. Analytical models are developed to evaluate their performance in terms of the blocking area, saturation throughput, and capability of mitigating aggregate interference of simultaneous transmissions. Numerical examples are presented to show the effectiveness of the proposed MAC protocols and the interaction between performance metrics and key parameters. Analysis and simulation results indicate that both PFD and PAD schemes can achieve a much higher throughput and a lower packet-collision ratio than IEEE 802.11 distributed coordination function (DCF), conservative CTS reply (CCR), and dual busy-tone multiple-access (DBTMA) schemes.
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