Pilot HI survey of Planck Galactic Cold Clumps with FAST

We present a pilot HI survey of 17 Planck Galactic Cold Clumps(PGCCs)with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).HI Narrow Self-Absorption(HINSA)is an effective method to detect cold HI being mixed with molecular hydrogen H2 and improves our understanding of the atomic to molecular transition in the interstellar medium.HINSA was found in 58%PGCCs that we observed.The column density of HINSA was found to have an intermediate correlation with that of 13CO,following log(N(HINSA))=(0.52±0.26)log(N13CO)+(10±4.1).HI abundance relative to total hydrogen[HI]/[H]has an average value of 4.4×10-3,which is about 2.8 times of the average value of previous HINSA surveys toward molecular clouds.For clouds with total column density NH>5×1020 cm-2,an inverse correlation between HINSA abundance and total hydrogen column density is found,confirming the depletion of cold HI gas during molecular gas formation in more massive clouds.Nonthermal line width of 13CO is about 0-0.5 kms-1 larger than that of HINSA.One possible explanation of narrower non-thermal width of HINSA is that HINSA region is smaller than that of 13CO.Based on an analytic model of H2 formation and H2 dissociation by cosmic ray,we found the cloud ages to be within 106.7-107.0 yr for five sources.

The fundamental performance of FAST with 19-beam receiver at L band

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) has passed national acceptance and finished one pilot cycle of ‘Shared-Risk’ observations. It will start formal operation soon. In this context, this paper describes testing results of key fundamental parameters for FAST, aiming to provide basic support for observation and data reduction of FAST for scientific researchers. The 19-beam receiver covering 1.05–1.45 GHz was utilized for most of these observations. The fluctuation in electronic gain of the system is better than 1% over 3.5 hours, enabling enough stability for observations. Pointing accuracy,aperture efficiency and system temperature are three key parameters for FAST. The measured standard deviation of pointing accuracy is 7.9′′, which satisfies the initial design of FAST. When zenith angle is less than 26.4°, the aperture efficiency and system temperature around 1.4 GHz are ~0.63 and less than 24 K for central beam, respectively. The sensitivity and stability of the 19-beam backend are confirmed to satisfy expectation by spectral HI observations toward NGC 672 and polarization observations toward 3 C 286. The performance allows FAST to take sensitive observations for various scientific goals, from studies of pulsars to galaxy evolution.

Ergodic secrecy capacity of MRC/SC in single-input multiple-output wiretap systems with imperfect channel state information

在物理层中,本文研究了存在信道估计误差的最大比合并/选择合并的保密容量性能。在一个单输入多输出窃密信道中,信源向一个装备M根接收天线并采用最大比合并/选择合并技术处理多径信号的信宿发送保密信息。与此同时,一个窃密者装备N根接收天线并采用最大比合并/选择合并技术来提高窃密的成功率。我们分别推导了两种情况下遍历保密容量的精确和近似闭式表达式:(1)最大比合并带有信道估计误差;(2)选择合并带有信道延迟。此外,本文得到了高信噪比斜率和高信噪比功率补偿两个重要的参数,它们在高信噪比条件下决定了遍历保密容量。最后,本文通过仿真分析验证了所得到的闭式表达式的准确性。

Secrecy performance analysis of single-input multiple-output generalized-K fading channels

该文研究了基于generalizedK信道的单发多收系统的物理层安全性能。分别考虑源节点在有和没有窃听信道的信道状态信息的两种情况,将generalizedK分布近似为伽马分布和混合伽马分布,分别推导出系统的保密中断概率和平均保密容量的解析表达式。最后通过蒙特卡罗仿真验证了分析结果。

Physical layer security of underlay cognitive radio using maximal ratio combining

We investigate the secrecy outage performance of maximal ratio combining(MRC) in cognitive radio networks over Rayleigh fading channels. In a single-input multiple-output wiretap system, we consider a secondary user(SU-TX) that transmits confidential messages to another secondary user(SU-RX) equipped with M(M ≥ 1)antennas where the MRC technique is adopted to improve its received signal-to-noise ratio. Meanwhile, an eavesdropper equipped with N(N ≥ 1) antennas adopts the MRC scheme to overhear the information between SU-TX and SU-RX. SU-TX adopts the underlay strategy to guarantee the service quality of the primary user without spectrum sensing. We derive the closed-form expressions for an exact and asymptotic secrecy outage probability.

Secrecy outage performance for wireless-powered relaying systems with nonlinear energy harvesters

本文考虑了一个包含单一信源、单一信宿、N(N>1)个无线充电中继和单一窃听者的协作系统。本文假设每个中继都拥有一个非线性的能量收集器,且该能量收集器存在一个饱和阈值以限制收集能量的大小。在考虑解码转发和功率分配接收器的场景中,本文选择第K个最优中继来协助信源-中继-信宿链路的传输。同时,本文还推导了保密中断概率的解析表达式,并用通过仿真验证了分析结果。