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He Huang

Publications and source records attributed to He Huang.

126 records · Page 7Linked to original sources
arXiv2017

Performance evaluation of energy detector over generalized non-linear and shadowed composite fading channels using a Mixture Gamma Distribution

The performance of energy detection (ED) for independent and identically distribution (i.i.d.) signal models is analyzed over generalized composite non-linear line-of-sight (LOS) and non-line-of-sight (NLOS) shadowed fading scenarios. The novel expressions for α-\k{appa}-μ/Gamma and α-η-μ/Gamma fading channels have been derived to approximate by using the mixture gamma (MG) distribution under low instantaneous signal-to-noise (SNR) condition. On the basis of the deduced fading distributions, novel, exact and close-form detective models are derived to evaluate the sensing performance with different key fading parameters over generalized non-linear and shadowed composite fading channels.

cs.IT↗
arXiv2017

Cooperative Spectrum Sensing over Generalized Fading Channels Based on Energy Detection

This paper analyzes the unified performance of energy detection (ED) of spectrum sensing (SS) over generalized fading channels in cognitive radio (CR) networks. The detective performance of SS schemes will be obviously affected by fading channel between communication nodes, and ED has the advantages of fast implementation, no requirement of priori received information and low complexity, so it is meaningful to investigate ED that is performed over fading channels such as Nakagami-m channel and Rice channel, or generalized fading channels such as \k{appa}-μ fading distribution and η-μ fading distribution. The α-\k{appa}-μ fading distribution is a generalized fading model that represents the nonlinear and small-scale variation of fading channels. The probability density function (p.d.f.) of instantaneous signal-to-ratio (SNR) of α-\k{appa}-μ distribution is derived from the envelope p.d.f. to evaluate energy efficiency for sensing systems. Next, the probability of detection model with Marcum-Q function has been derived and the close-form detective expressions with moment generating function (MGF) method are deduced to achieve sensing communications over generalized fading channels. Furthermore, novel and exact closed-form analytic expressions for average area under the receiver operating characteristics curve also have been deduced to analyze the performance characteristics of ED over α-\k{appa}-μ fading channels. Besides, cooperative spectrum sensing (CSS) with diversity reception has been applied to improve the detection accuracy and mitigate the shadowed fading features with OR-rule. At last, the results show that the detection capacity can be evidently affected by α-\k{appa}-μ fading conditions, but appropriate channel parameters will improve sensing performance.

cs.IT↗
arXiv2017

Cooperative spectrum sensing with enhanced energy detection under GAUSSIAN noise uncertainty in cognitive radios

This paper presents optimization issues of energy detection (ED) thresholds in cooperative spectrum sensing (CSS) with regard to general Gaussian noise. Enhanced ED thresholds are proposed to overcome sensitivity of multiple noise uncertainty. Two-steps decision pattern and convex samples thresholds have been put forward under Gaussian noise uncertainty. Through deriving the probability of detection (Pd) and the probability of false alarm (Pf ) for independent and identical distribution (i.i.d.) SUs, we obtain lower total error rate (Qe) with proposed ED thresholds at low signal-to-noise-ratio (SNR) condition. Furthermore, simulation results show that proposed schemes outperform most other noise uncertainty plans.

cs.IT↗
arXiv2017

Ergodic Capacity of Composite Fading Channels in Cognitive Radios with the Product of $κ$-$μ$ and $α$-$μ$ Variates

In this study, the product of two independent and non-identically distributed (i.n.i.d.) random variables (RVs) for \k{appa}-μ fading distribution and α-μ fading distribution is considered. The method of the product model of RVs has been widely applied in numerous of communications fields, such as cascaded fading channels, multiple input multiple output (MIMO) systems, radar communications and cognitive radio networks (CRs). The exact series expressions of the product of two i.n.i.d. RVs X for \k{appa}-μ variates and Y for α-μ variates are derived instead of Fox H-function to solve the problem that Fox H-function in the RVs product could not be implemented in popular mathematical software packages as Mathematica and Maple. Novel Exact close-form expressions of probability density function (PDF) and cumulative distribution function (CDF) of proposed models are deduced to present the series expressions of product and generalized composite multipath shadowing models. Furthermore, novel exact expressions of the ergodic channel capacity (ECC) are obtained under optimal rate adaptation with constant transmit power (ORA). At last, these analytical results are confirmed with monte-carlo simulations to evaluate spectrum efficiency over generalized composite shadowing fading scenarios in CRs.

cs.IT↗
arXiv2017

Perfect codes in Cayley graphs

Given a graph $Γ$, a subset $C$ of $V(Γ)$ is called a perfect code in $Γ$ if every vertex of $Γ$ is at distance no more than one to exactly one vertex in $C$, and a subset $C$ of $V(Γ)$ is called a total perfect code in $Γ$ if every vertex of $Γ$ is adjacent to exactly one vertex in $C$. In this paper we study perfect codes and total perfect codes in Cayley graphs, with a focus on the following themes: when a subgroup of a given group is a (total) perfect code in a Cayley graph of the group; and how to construct new (total) perfect codes in a Cayley graph from known ones using automorphisms of the underlying group. We prove several results around these questions.

math.CO↗
arXiv2017

Calorimetric evidence for enhancement of homogeneity in high performance Sr1-xKxFe2As2 superconductors

We comparatively studied the critical current density, magnetization and specific heat of the rolled and the hot-pressed Sr1-xKxFe2As2 tapes. The Schottky anomaly that is obvious in the specific heat of the rolled tape disappears in the hot-pressed tape. Moreover, the hot-pressed tape has a higher fraction of superconductivity and a narrower distribution of superconducting transition temperature than the rolled tape. Combined with the magnetization data, we conclude that sintering under high pressure provides a better environment for complete chemical reaction and more homogenous dopant distribution, which is beneficial to the global current of a superconductor.

cond-mat.supr-con↗
arXiv2017

High transport current superconductivity in powder-in-tube Ba0.6K0.4Fe2As2 tapes at 27 tesla

The high upper critical field and low anisotropy of iron-based superconductors make them being particularly attractive for high-field applications. However, the current carrying capability needs to be enhanced by overcoming the weak-link effect between misaligned grains inside wire and tape conductors. Here we demonstrate a high transport critical current density (Jc) reaching 1.5x10^5 A/cm^2 (Ic = 437 A) at 4.2 K and 10 T in Ba0.6K0.4Fe2As2 (Ba-122) tapes prepared by a combination of conventional powder-in-tube method and optimized hot-press technique. The transport Jc measured at 4.2 K under high magnetic fields of 27 T is still on the level of 5.5x10^4 A/cm^2, which is much higher than those of low-temperature superconductors. This is the first report of hot-pressed Ba-122 superconducting tapes and these Jc values are by far the highest ever reported for iron-based superconducting wires and tapes. These high-performance tapes exhibit high degree of c-axis texture of Ba-122 grains and low anisotropy of transport Jc, showing great potential for construction of high-field superconducting magnets.

cond-mat.supr-con↗
arXiv2017

Perfect codes in circulant graphs

A perfect code in a graph $Γ= (V, E)$ is a subset $C$ of $V$ that is an independent set such that every vertex in $V \setminus C$ is adjacent to exactly one vertex in $C$. A total perfect code in $Γ$ is a subset $C$ of $V$ such that every vertex of $V$ is adjacent to exactly one vertex in $C$. A perfect code in the Hamming graph $H(n, q)$ agrees with a $q$-ary perfect 1-code of length $n$ in the classical setting. In this paper we give a necessary and sufficient condition for a circulant graph of degree $p-1$ to admit a perfect code, where $p$ is an odd prime. We also obtain a necessary and sufficient condition for a circulant graph of order $n$ and degree $p^l-1$ to have a perfect code, where $p$ is a prime and $p^l$ the largest power of $p$ dividing $n$. Similar results for total perfect codes are also obtained in the paper.

math.CO↗
arXiv2016

Post-Newtonian parameters and cosmological constant of screened modified gravity

Screened modified gravity (SMG) is a kind of scalar-tensor theories with screening mechanisms, which can generate screening effect to suppress the fifth force in high density environments and pass the solar system tests. Meanwhile, the potential of scalar field in the theories can drive the acceleration of the late universe. In this paper, we calculate the parameterized post-Newtonian (PPN) parameters $γ$ and $β$, the effective gravitational constant $G_{\rm eff}$ and the effective cosmological constant $Λ$ for SMG with a general potential $V$ and coupling function $A$. The dependence of these parameters on the model parameters of SMG and/or the physical properties of the source object are clearly presented. As an application of these results, we focus on three specific theories of SMG (chameleon, symmetron and dilaton models). Using the formulae to calculate their PPN parameters and cosmological constant, we derive the constraints on the model parameters by combining the observations on solar system and cosmological scales.

gr-qc↗
arXiv2016

Vortex pinning and dynamics in high performance Sr0.6K0.4Fe2As2 superconductor

We have studied vortex pinning and dynamics in a Sr0.6K0.4Fe2As2 superconducting tape with critical current density Jc~0.1 MA/cm2 at 4.2 K and 10 T. It is found that grain boundary pinning is dominant in the vortex pinning mechanism. Furthermore, we observe large density of dislocations which can also serve as effective pinning centers. We find that the temperature dependence of critical current density is in agreement with the model of vortices pinned via spatial fluctuation of charge carrier mean free path. Magnetic relaxation measurement indicates that the magnetization depends on time in a logarithmic way. The relaxation rate in the low and intermediate temperature region is small, and it exhibits a weak temperature and field dependence. A crossover from elastic creep to plastic creep regime is observed. Finally, we conclude a vortex phase diagram for the high performance Sr0.6K0.4Fe2As2 superconducting tape.

cond-mat.supr-con↗
arXiv2013

Tricyclic graphs with exactly two main eigenvalues

An eigenvalue of a graph $G$ is called a main eigenvalue if it has an eigenvector the sum of whose entries is not equal to zero. In this paper, all connected tricyclic graphs with exactly two main eigenvalues are determined.

math-ph↗
arXiv2013

PPS: Privacy-Preserving Strategyproof Social-Efficient Spectrum Auction Mechanisms

Many spectrum auction mechanisms have been proposed for spectrum allocation problem, and unfortunately, few of them protect the bid privacy of bidders and achieve good social efficiency. In this paper, we propose PPS, a Privacy Preserving Strategyproof spectrum auction framework. Then, we design two schemes based on PPS separately for 1) the Single-Unit Auction model (SUA), where only single channel to be sold in the spectrum market; and 2) the Multi-Unit Auction model (MUA), where the primary user subleases multi-unit channels to the secondary users and each of the secondary users wants to access multi-unit channels either. Since the social efficiency maximization problem is NP-hard in both auction models, we present allocation mechanisms with approximation factors of $(1+ε)$ and 32 separately for SUA and MUA, and further judiciously design strategyproof auction mechanisms with privacy preserving based on them. Our extensive evaluations show that our mechanisms achieve good social efficiency and with low computation and communication overhead.

cs.NI↗
arXiv2013

Near-Optimal Truthful Auction Mechanisms in Secondary Spectrum Markets

In this work, we study spectrum auction problem where each request from secondary users has spatial, temporal, and spectral features. With the requests of secondary users and the reserve price of the primary user, our goal is to design truthful mechanisms that will either maximize the social efficiency or maximize the revenue of the primary user. As the optimal conflict-free spectrum allocation problem is NP-hard, in this work, we design near optimal spectrum allocation mechanisms separately based on the following techniques: derandomized allocation from integer programming formulation, its linear programming (LP) relaxation, and the dual of the LP. We theoretically prove that 1) our near optimal allocation methods are bid monotone, which implys truthful auction mechanisms; and 2) our near optimal allocation methods can achieve a social efficiency or a revenue that is at least $1-\frac{1}{e}$ times of the optimal respectively. At last, we conduct extensive simulations to study the performances (social efficiency, revenue) of the proposed methods, and the simulation results corroborate our theoretical analysis.

cs.NI↗
arXiv2012

On the Main Signless Laplacian Eigenvalues of a Graph

A signless Laplacian eigenvalue of a graph $G$ is called a main signless Laplacian eigenvalue if it has an eigenvector the sum of whose entries is not equal to zero. In this paper, we first give the necessary and sufficient conditions for a graph with one main signless Laplacian eigenvalue or two main signless Laplacian eigenvalues, and then characterize the trees and unicyclic graphs with exactly two main signless Laplacian eigenvalues, respectively.

math.CO↗
arXiv2012

True-MCSA: A Framework for Truthful Double Multi-Channel Spectrum Auctions

We design a framework for truthful double multi-channel spectrum auctions where each seller (or buyer) can sell (or buy) multiple spectrum channels based on their individual needs. Open, market-based spectrum trading motivates existing spectrum owners (as sellers) to lease their selected idle spectrum channels to new spectrum users (as buyers) who need the spectrum desperately. The most significant requirement is how to make the auction economic-robust (truthful in particular) while enabling spectrum reuse to improve spectrum utilization. Additionally, in practice, both sellers and buyers would require to trade multiple channels at one time, while guaranteeing their individual profitability. Unfortunately, none of the existing designs can meet all these requirements simultaneously. We address these requirements by proposing True-MCSA, a framework for truthful double multi-channel spectrum auctions. True-MCSA takes as input any reusability-driven spectrum allocation algorithm, introduces novel virtual buyer group (VBG) splitting and bidding algorithms, and applies a winner determination and pricing mechanism to achieve truthfulness and other economic properties while improving spectrum utilization and successfully dealing with multi-channel requests from both buyers and sellers. Our results show that the auction efficiency is impacted by the economic factors with efficiency degradations within 30%, under different experimental settings. Furthermore, the experimental results indicate that we can improve the auction efficiency by choosing a proper bidding algorithm and using a base bid. True-MCSA makes an important contribution on enabling spectrum reuse to improve auction efficiency in multi-channel cases.

cs.NI↗
arXiv2012

Truthful Auction Mechanism for Heterogeneous Spectrum Allocation in Wireless Networks

Secondary spectrum auction is widely applied in wireless networks for mitigating the spectrum scarcity. In a realistic spectrum trading market, the requests from secondary users often specify the usage of a fixed spectrum frequency band in a certain geographical region and require a duration time in a fixed available time interval. Considering the selfish behaviors of secondary users, it is imperative to design a truthful auction which matches the available spectrums and requests of secondary users optimally. Unfortunately, existing designs either do not consider spectrum heterogeneity or ignore the differences of required time among secondary users. In this paper, we address this problem by investigating how to use auction mechanisms to allocate and price spectrum resources so that the social efficiency can be maximized. We begin by classifying the spectrums and requests from secondary users into different local markets which ensures there is no interference between local markets, and then we can focus on the auction in a single local market. We first design an optimal auction based on the Vickrey-Clarke-Groves (VCG) mechanism to maximize the social efficiency while enforcing truthfulness. To reduce the computational complexity, we further propose a truthful sub-optimal auction with polynomial time complexity, which yields an approximation factor 6+4\surd2. Our extensive simulation results using real spectrum availability data show that the social efficiency ratio of the sub-optimal auction is always above 70% compared with the optimal auction.

cs.GT↗
arXiv2007

An algorithm for detecting oscillatory behavior in discretized data: the damped-oscillator oscillator detector

We present a simple algorithm for detecting oscillatory behavior in discrete data. The data is used as an input driving force acting on a set of simulated damped oscillators. By monitoring the energy of the simulated oscillators, we can detect oscillatory behavior in data. In application to in vivo deep brain basal ganglia recordings, we found sharp peaks in the spectrum at 20 and 70 Hz. The algorithm is also compared to the conventional fast Fourier transform and circular statistics techniques using computer generated model data, and is found to be comparable to or better than fast Fourier transform in test cases. Circular statistics performed poorly in our tests.

q-bio.QM↗