Trellis-Coded Non-Orthogonal Multiple Access

In this letter, we propose a trellis-coded non-orthogonal multiple access (NOMA) scheme. The signals for different users are produced by trellis coded modulation (TCM) and then superimposed on different power levels. By interpreting the encoding process via the tensor product of trellises, we introduce a joint detection method based on the Viterbi algorithm. Then, we determine the optimal power allocation between the two users by maximizing the free distance of the tensor product trellis. Finally, we manifest that the trellis-coded NOMA outperforms the uncoded NOMA at high signal-to-noise ratio (SNR)

Time-and event-driven communication process for networked control systems: A survey

Copyright © 2014 Lei Zou et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.In recent years, theoretical and practical research topics on networked control systems (NCSs) have gained an increasing interest from many researchers in a variety of disciplines owing to the extensive applications of NCSs in practice. In particular, an urgent need has arisen to understand the effects of communication processes on system performances. Sampling and protocol are two fundamental aspects of a communication process which have attracted a great deal of research attention. Most research focus has been on the analysis and control of dynamical behaviors under certain sampling procedures and communication protocols. In this paper, we aim to survey some recent advances on the analysis and synthesis issues of NCSs with different sampling procedures (time-and event-driven sampling) and protocols (static and dynamic protocols). First, these sampling procedures and protocols are introduced in detail according to their engineering backgrounds as well as dynamic natures. Then, the developments of the stabilization, control, and filtering problems are systematically reviewed and discussed in great detail. Finally, we conclude the paper by outlining future research challenges for analysis and synthesis problems of NCSs with different communication processes.This work was supported in part by the National Natural Science Foundation of China under Grants 61329301, 61374127, and 61374010, the Royal Society of the UK, and the Alexander von Humboldt Foundation of Germany

Dynamical formation of stable irregular transients in discontinuous map systems

Stable chaos refers to the long irregular transients, with a negative largest Lyapunov exponent, which is usually observed in certain high-dimensional dynamical systems. The mechanism underlying this phenomenon has not been well studied so far. In this paper, we investigate the dynamical formation of stable irregular transients in coupled discontinuous map systems. Interestingly, it is found that the transient dynamics has a hidden pattern in the phase space: it repeatedly approaches a basin boundary and then jumps from the bundary to a remote region in the phase space. This pattern can be clearly visualized by measuring the distance sequences between the trajectory and the basin boundary. The dynamical formation of stable chaos originates from the intersection points of the discontinuous boundaries and their images. We carry out numerical experiments to verify this mechanism.Comment: 5 pages, 5 figure

Reply to "Comment on 'Semiquantum-key distribution using less than four quantum states' "

Recently Boyer and Mor pointed out the first conclusion of Lemma 1 in our original paper is not correct, and therefore, the proof of Theorem 5 based on Lemma 1 is wrong. Furthermore, they gave a direct proof for Theorem 5 and affirmed the conclusions in our original paper. In this reply, we admit the first conclusion of Lemma 1 is not correct, but we need to point out the second conclusion of Lemma 1 is correct. Accordingly, all the proofs for Lemma 2, Lemma 3, and Theorems 3--6 are only based on the the second conclusion of Lemma 1 and therefore are correct.Comment: 1 pag

Nonparametric Detection of Geometric Structures over Networks

Nonparametric detection of existence of an anomalous structure over a network is investigated. Nodes corresponding to the anomalous structure (if one exists) receive samples generated by a distribution q, which is different from a distribution p generating samples for other nodes. If an anomalous structure does not exist, all nodes receive samples generated by p. It is assumed that the distributions p and q are arbitrary and unknown. The goal is to design statistically consistent tests with probability of errors converging to zero as the network size becomes asymptotically large. Kernel-based tests are proposed based on maximum mean discrepancy that measures the distance between mean embeddings of distributions into a reproducing kernel Hilbert space. Detection of an anomalous interval over a line network is first studied. Sufficient conditions on minimum and maximum sizes of candidate anomalous intervals are characterized in order to guarantee the proposed test to be consistent. It is also shown that certain necessary conditions must hold to guarantee any test to be universally consistent. Comparison of sufficient and necessary conditions yields that the proposed test is order-level optimal and nearly optimal respectively in terms of minimum and maximum sizes of candidate anomalous intervals. Generalization of the results to other networks is further developed. Numerical results are provided to demonstrate the performance of the proposed tests.Comment: Submitted for journal publication in November 2015. arXiv admin note: text overlap with arXiv:1404.029

A Broadband Mid-infrared Metasurface for Polarisation Manipulation and Utilisation

A pair of enantiomers are distinct from each other due to chiral structural arrangement which leads to selective interaction with chiral light. Vibrational circular dichroism spectroscopy in mid-infrared region provide a powerful label-free method to distinguish chiral enantiomers. Besides, mid-infrared sensing also significantly benefit from resolving compositional information of molecules due to molecular vibrational fingerprints which holds promising application in biological and medical sensing. However, the low signal-to-noise ratio associated with weak light-matter interaction is a continuing obstacle hindering the practical application. Recent demonstrations of chiral metamaterials have shown that due to the chirality of structure, local superchiral field can be produced in the vicinity of structure to interact with molecules and enhance vibrational circular dichroism response. However, a limitation factor in development of chiral structure is the narrow effective working bandwidth and the requirement of circular polarization excitation. This thesis introduces an achiral nanorod-based metausrface that enable to overcome these limitations. First, the nanorod-based metasurface is present to achieve high efficient linear-to-circular polarization conversion in a broadband mid-infrared wavelength range in reflection mode. The model was firstly studied and optimised through simulation tool based on Finite Difference Time Domain method. The device was fabricated in a top-down approach based on electron beam lithography and characterised using Fourier transform infrared spectroscopy. We identified two distinct resonances originated from gap-plasmon mode at 3.4μm and Fabry-Perot mode at 7.9μm. The demonstration of polarization state based on the measured Stokes parameters within off-resonance range from 4-7μm show that the reflected beam has converted into circular polarization state. For practical application of vibrational circular dichroism spectroscopy, we numerically demonstrate the induced chirality in near-field under excitation of linear polarization with various polarization angles. These analysis suggest that superchiral field can be produced by nanorod-based metasurface and distributed spatially under linear polarization excitation. When polarization is parallel or orthogonal to rod, namely the symmetry exist in the combination of rod and incident polarization, the absolute chirality is zero due to the fact that same amount of optical chirality density with opposite handedness offset by each other. However it is showed that one handedness of the optical chirality density is dominant when the symmetry is broken, hence, holds potential for circular dichroism spectroscopy sensing. In an experimental feasibility study, we measured the polarization states of light in far-field and demonstrate that the absolute chirality in the far-field show similar behaviour as that in near-field. Finally, we conduct a molecular sensing measurement based on the rod-shape metausrface for enantiomers (alanine) identification through circular dichroism spectroscopy. This thesis demonstrates with FDTD simulations that the metasurface can generate superchiral fields which enable to enhance interaction with molecules upon linear polarization excitation. By simply rotating sample with 90 degree, molecules can then interact with superchiral field with opposite handedness. The circular dichroism is to record the intensity of reflected beam and characterise the differential intensity between the two. Despite the measured data do not show inverse pattern for L- and D-alanine, we confirmed that metausrface enable to enhance the light-matter interaction

Evidence for spin-flip scattering and local moments in dilute fluorinated graphene

The issue of whether local magnetic moments can be formed by introducing adatoms into graphene is of intense research interest because it opens the window to fundamental studies of magnetism in graphene, as well as of its potential spintronics applications. To investigate this question we measure, by exploiting the well-established weak localization physics, the phase coherence length L_phi in dilute fluorinated graphene. L_phi reveals an unusual saturation below ~ 10 K, which cannot be explained by non-magnetic origins. The corresponding phase breaking rate increases with decreasing carrier density and increases with increasing fluorine density. These results provide strong evidence for spin-flip scattering and points to the existence of adatom-induced local magnetic moment in fluorinated graphene. Our results will stimulate further investigations of magnetism and spintronics applications in adatom-engineered graphene.Comment: 9 pages, 4 figures, and supplementary materials; Phys. Rev. Lett. in pres