The purpose of this paper is to survey techniques for constructing effective policies for controlling complex networks, and to extend these techniques to capture special features of wireless communication networks und...
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The purpose of this paper is to survey techniques for constructing effective policies for controlling complex networks, and to extend these techniques to capture special features of wireless communication networks under different networking scenarios. Among the key questions addressed are: The relationship between static network equilibria, and dynamic network control. The effect of coding on control and delay through rate regions. Routing, scheduling, and admission control. These approximations are the basis of a specific formulation of an h-MaxWeight policy for network routing. Simulations show a 50% improvement in average delay performance as compared to methods used in current practice.
Slotted multichannel ALOHA is the access scheme of choice for short messages and for reserving channels for longer ones in many satellite-based networks. This paper proposes schemes for increasing the capacity (maximu...
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Slotted multichannel ALOHA is the access scheme of choice for short messages and for reserving channels for longer ones in many satellite-based networks. This paper proposes schemes for increasing the capacity (maximum attainable throughput) of multichannel slotted ALOHA subject to meeting a user-specified deadline with a (high) required probability, thereby jointly capturing the users' requirements and the system owner's desires. The focus is on short yet multislot messages. A key idea is to achieve a low probability of missing the deadline by permitting a large maximum resource expenditure per message, while holding the mean expenditure low in order to minimize "pollution." For a K-slot message, redundant single-slot fragments are constructed using block erasure-correcting codes., such that any K fragments suffice for message reception. With multiround coding, an optimized number of fragments are transmitted in each round until K are received or the deadline is reached. Even with very strict constraints, capacities that approach the 1/e limit are attained. The coding-reservation scheme raises capacity above 1/e by allowing the hub, upon receipt of any message fragment(s), to grant contention-free slots for the remaining required fragments. Both schemes are also adapted for use with single-transmitter stations at a small performance penalty in most cases. Finally, because capacity is maximized by minimizing the mean per-message transmission resources, the transmission scheme is also energy-efficient.
In many applications, XML documents need to be modelled as graphs. The query processing of graph-structured XML documents brings new challenges. In this paper, we design a method based on labelling scheme for structur...
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In many applications, XML documents need to be modelled as graphs. The query processing of graph-structured XML documents brings new challenges. In this paper, we design a method based on labelling scheme for structural queries processing on graph-structured XML documents. We give each node some labels, the reachability labelling scheme. By extending an interval-based reachability labelling scheme for DAG by Rakesh et al., we design labelling schemes to support the judgements of reachability relationships for general graphs. Based on the labelling schemes, we design graph structural join algorithms to answer the structural queries with only ancestor-descendant relationship efficiently. For the processing of subgraph query, we design a subgraph join algorithm. With efficient data structure, the subgraph join algorithm can process subgraph queries with various structures efficiently. Experimental results show that our algorithms have good performance and scalability.
In this paper, we propose a simple approach to reduce the sensitivity of OFDM system to the carrier frequency offset (CFO). The main idea is to choose a well-known channel code and to rotate each coordinate by a fixed...
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In this paper, we propose a simple approach to reduce the sensitivity of OFDM system to the carrier frequency offset (CFO). The main idea is to choose a well-known channel code and to rotate each coordinate by a fixed phase shift such that the maximum inter-carrier interference (ICI) taken over all sub-carriers is minimized. This approach is based on a geometric interpretation of the peak interference to carrier ratio (PICR) of OFDM signals. Simulation results show that a reduction in PICR of 7 dB can be easily achieved. Furthermore, we addressed the fundamental limit of the proposed technique by providing both an exact and an approximate lower bound of PICR of phase-shifted binary codes. The bounds are applied to some codes: non-redundant binary code, BCH codes, and Reed-Muller codes. Simulation results demonstrated that phase-shift designs approach lower bounds and are resilient to CFO change.
The purpose of this study is to examine the role of Minecraft-based coding activities on computational thinking (CT) of middle school students. In the study, CT was conceptualized so that it encapsulates not only the ...
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The purpose of this study is to examine the role of Minecraft-based coding activities on computational thinking (CT) of middle school students. In the study, CT was conceptualized so that it encapsulates not only the knowledge of computational concepts (e.g., loops and conditionals) but also the use of CT practices (e.g., testing and debugging). Data were collected using a combination of knowledge of computational concepts tests, the Minecraft-based coding artifacts, and one-on-one student interviews focusing on the processes of developing computational artifacts. The participants were 20 fifth-grade middle school students from a low-income public school with very limited (if none) formal computer programming experiences before the study. The Minecraft-based coding activities were designed and implemented as an instructional program to last 6 weeks. The results of the study showed a statistically significant increase in students' knowledge of computational concepts. Based on the analysis of the students' final coding artifacts, we identified that students mostly used the concepts of sequences, events, loops, and parallelism correctly, whereas variables, operators, and conditionals appeared to be the least successfully used concepts. The qualitative analysis of the artifact-based interviews showed that students employed the CT practices of testing and debugging most of the time while developing an artifact through coding. In contrast, the least resorted CT practice appeared to be reusing and remixing.
A reduction in the track width in disc-recording systems results in a desirable increase in areal density, but also in the undesirable appearance of inter-track interference (ITI) and loss of signal-to-noise ratio (SN...
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A reduction in the track width in disc-recording systems results in a desirable increase in areal density, but also in the undesirable appearance of inter-track interference (ITI) and loss of signal-to-noise ratio (SNR), One way the effects of ITI may be alleviated is through the use of multiple-head systems simultaneously writing and reading a number of adjacent tracks, In this paper we investigate the performance of two-track detectors, and design codes that combat two-dimensional interference patterns, ISI in the axial dimension, and ITI in the radial dimension, and recover the loss in SNR due to track-narrowing Sliding-block decoders and reduced-complexity Viterbi detectors are also designed for these codes, which are seen to more than compensate for the performance loss for a large range of ITI levels.
This paper studies the tradeoff between channel coding and ARQ (automatic repeat request) in Rayleigh block-fading channels. A heavily coded system corresponds to a low transmission rate with few ARQ re-transmissions,...
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This paper studies the tradeoff between channel coding and ARQ (automatic repeat request) in Rayleigh block-fading channels. A heavily coded system corresponds to a low transmission rate with few ARQ re-transmissions, whereas lighter coding corresponds to a higher transmitted rate but more retransmissions. The optimum packet error probability, where optimum refers to the maximization of the average successful throughput, is derived and is shown to be a decreasing function of the average signal-to-noise ratio and of the channel diversity order. A general conclusion of the work is that the optimum error probability is quite large (e.g., 10% or larger) for reasonable channel parameters, and that operating at a very small error probability can lead to a significantly reduced throughput. This conclusion holds even when a number of practical ARQ considerations, such as delay constraints and acknowledgement feedback errors, are taken into account.
coding metasurfaces, based on the combination of two basic unit cells with out-of-phase responses, have been the subject of many recent studies aimed at achieving diffuse scattering, with potential applications to div...
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coding metasurfaces, based on the combination of two basic unit cells with out-of-phase responses, have been the subject of many recent studies aimed at achieving diffuse scattering, with potential applications to diverse fields ranging from radar-signature control to computational imaging. Here, via a theoretical study of the relevant scaling-laws, the physical mechanism underlying the scattering-signature reduction is elucidated, and some absolute and realistic bounds are analytically derived. Moreover, a simple, deterministic suboptimal design strategy is introduced that yields results comparable with those typically obtained by approaches based on brute-force numerical optimization, at a negligible fraction of their computational burden, thereby paving the way to the design of structures with arbitrarily large electrical size. Results are corroborated by rigorous full-wave numerical simulations and microwave experiments, and may be of interest in a variety of application fields, such as the design of low-scattering targets and illumination apertures for computational imaging, not necessarily restricted to electromagnetic scenarios.
Ambient backscatter technology has attracted much attention recently, because it enables battery-free devices, such as tags or sensors, to communicate through wireless energy harvesting and radio backscattering. Exist...
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Ambient backscatter technology has attracted much attention recently, because it enables battery-free devices, such as tags or sensors, to communicate through wireless energy harvesting and radio backscattering. Existing studies about ambient backscatter assume that the tags have only two states: backscatter or non-backscatter. Actually, some references have shown that the tags can readily realize three states: positive and negative phase backscatter, and non-backscatter. In this paper, we propose a new coding scheme for these tags with three states to improve the throughput of the ambient backscatter communication system. We then design a maximum a posteriori (MAP) detector for the reader to extract binary information from ternary coded signals. We also analyze the detection performance in terms of closed-form bit error rate (BER) expressions. It is found that the proposed coding scheme can improve the throughput of an ambient backscatter system, and there exists an error floor for the BER curve. Finally, simulation results are provided to corroborate our theoretical studies.
Although spiking neural network (SNN) has the advantages of strong brain-likeness and low energy consumption due to the use of discrete spikes for information representation and transmission, its performance still nee...
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Although spiking neural network (SNN) has the advantages of strong brain-likeness and low energy consumption due to the use of discrete spikes for information representation and transmission, its performance still needs to be improved. This article improves SNN in terms of the coding process and the spike response function by invoking fuzzy sets. In terms of coding, a new fuzzy C-means coding (FCMC) method is proposed, which breaks the limitation of uniformly distributed receptive fields of existing coding methods and automatically determines suitable receptive fields that reflect the density distribution of the input data for encoding through the fuzzy C-means clustering. In terms of spike response function, triangular fuzzy numbers instead of the commonly used alpha-type function are used as the spike response function. Different from other functions of fixed shape, width parameters of the proposed function are learnt in the iterative way like weights of synapses do. Experimental results obtained on seven benchmark datasets and two real-world datasets with eleven approaches demonstrate that SNN with triangular spike response functions (abbreviated as T-SNN) combining FCMC can achieve improved performance in terms of accuracy, F-measure, AUC, required epochs, running time, and stability.
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