中、远红外双波段激光器的性能优化

对两根放电管驱动的中、远红外双波段(3～5 μm & 8～12 μm)激光器的输出镜透过率、输出窗口等器件与参数进行了优化, 试验获得了25.5 W的中、远红外双波段激光输出, 两个单波段的输出功率均大于10 W, 中红外波段DF激光为TEM00模, 远红外波段CO2激光为TEM20模.利用Φ8 mm光阑对双波段激光器的横模进行了选择, 试验获得了15.4 W的TEM00基横模双波段激光输出.为红外双/多波段探测器阵列及相关系统的应用研究提供了激光光源.     

电激励DF化学激光器光腔流场荧光光谱测量与分析

 观察并记录了增大D₂流量时DF激光光腔流场可见光荧光的变化现象,对光轴处的可见光荧光进行了光谱测量,使用波长为632.8 nm和543.5 nm的He-Ne激光器对光谱仪进行标定。对激光器光腔内介质成分进行了理论分析,并理论计算了DF高次泛频谱线及D原子谱线,通过比对荧光的实验测量光谱与光腔内介质成分谱线,发现荧光是由F,He,D,N,DF及其它激发态介质共同形成的,对光轴处荧光的颜色构成作出了解释。     

大长宽比矩形有源非稳腔模式的数值模拟

 利用快速傅里叶变换算法和薄层增益近似方法,在Matlab计算平台上,对大长宽比正支共焦有源谐振腔进行了数值模拟。得到了长宽比为3.6∶1的大功率化学激光器输出的近场模式强度和相位分布,以及理想聚焦下的远场光斑的强度分布。给出了由非均匀增益引起的强度分布不均对远场光斑的影响。得到的近场图像结果和实验结果基本一致,表明本方法可以对大长宽比矩形腔的输出模式进行仿真,从而为激光器的光束质量改善提供计算参考。     

Performance analysis of PDMA-based hybrid satellite–terrestrial networks with decode-and-forward relaying

As one of the most promising non-orthogonal multiple access (NOMA) technologies in 5G communication, pattern division multiple access (PDMA) has theoretically higher spectrum utilization and a larger communication capacity than conventional orthogonal multiple access (OMA) technologies. In this letter, PDMA is applied to hybrid satellite–terrestrial networks with decode-and-forward (DF) relaying in the downlink, and an in-depth study on the performance of outage probability (OP), ergodic capacity and system throughput is performed. For a more comprehensive analysis, hybrid satellite–terrestrial relay networks (HSTRNs) with conventional OMA technology are used in the comparative analysis. Analysis and simulation results show that PDMA-based hybrid satellite–terrestrial relay networks outperform the other system in terms of OP and ergodic capacity.     

Effect of correlation on energy of solids

In the present paper we make an attempt to model the lattice energy with the lattice constants through the first-principles calculations. This formalism is designed particularly for application with the self-consistent pseudopotential (PP) method within the density functional (DF) framework and includes exchange and correlation effects. Applying the above formalism we have calculated the lattice energy and correlation energy for a number of solids belonging to groups I–VII and II–VI of the periodic table. The convergence of our results is in the favour of used PP. These results will be helpful in determining various structural and elastic properties of these solids and in the generation of equation of state.     

硅p-n结太阳电池对DF激光的响应

 对硅p-n结太阳电池在DF激光辐照下的响应进行了理论和实验研究。推导了p-n结反向饱和电流随温度的近似变化关系。根据该近似关系，计算了太阳电池在DF激光辐照过程中输出电压的变化曲线。计算结果和实验结果之间取得了比较好的一致性。     

BER analysis of a GMSK system using decision feedback

There are considerable literatures on the Bit Error Rate（BER）evaluation of Differential Detection of Gaussian Minimum Shift Keying（DDGMSK）system using Decision Feedback（DF）,but most of them give the performance based on the Monte Carlo Error Counting（MCEC）technique.From the probability distribution of the phase angle between two vectors perturbed by Gaussian noises,the formulae of BER are derived for the performance analysis of DDGMSK system with DF in this letter.Considering the m-bit dock-tailed sequence,the new formulae of Gaussian Minimum Shift Keying（GMSK）modulated phase and the Time-Varying Signal to Noise Ratio（TVSNR）of the demodulated signal are presented,and it is proved that the relationship between the TVSNR of the demodulated signal and the size of eye opening is not inevitable.Simulation results show that the theoretical investigation gives analogous results with the MCEC technique.The formulae presented are useful for the performance analysis of systems using GMSK as modulating and demodulating method,for instance,the analysis of synchronous performance of frequency-hopping communication system.     

概率译码转发中继系统中的安全极化编码方法

该文针对中继节点依概率辅助译码转发的通信场景,提出一种中继辅助的安全极化编码方法,保证私密信息可靠传输的同时,达到提高安全传输速率的目的。首先,发送端分别进行两层极化编码——中继概率转发行为构成的虚拟二进制删除信道下的极化编码和实际传输信道下的极化编码,并将私密信息分别隐藏在两层码字中,分时隙广播出去。然后,中继依概率译码后提取出合法用户无法直接接收的固定信息再次进行安全极化编码并转发。最后,接收端利用收到的中继转发码字和发端码字依次分层进行译码。理论和仿真分析证明,所提方法下合法用户能够可靠接收私密信息,而窃听者无法获取任何私密信息信息量;安全传输速率随着码长和中继转发概率的增加而增大,且高于一般的安全极化编码方法。     

A smart spectrum utilization approach using multiantenna‐based cognitive relays in cognitive radio network

Efficient spectrum utilization is a promising technique for a prolonged unused radio frequency (RF) spectrum in a wireless network. In this paper, an adaptive spectrum sharing cognitive radio (CR) network has been proposed consisting of a primary user (PU) and secondary user transmitter (SU ? Tx) that communicates with secondary user receiver (SU ? Rx) via multiantenna‐based proactive decode‐and‐forward (DF) relay selection scheme. In our model, strategically an adaptable joint venture on underlay/overlay protocol is defined based on channel occupancy using spectrum sensing technique. Here, secondary transmitters (i.e., source transmitter) continuously sense the PU activities by energy detector and can simultaneously transmit to secondary receivers. Depending on sensing result secondary transmitters automatically switches in underlay mode if PU is active otherwise operates in overlay mode. The advantage of this scheme is that the joint mode of transmission allows the SUs to maximize their transmission rate. The outage performance at SU ? Rx and closed‐form expressions of joint underlay/overlay protocol has been evaluated. The power control policies at different transmitter nodes are taken care of. With the same diversity order, a trade‐off between multiantenna and multirelay is shown. This comparison shows improvement in outage behavior when the count in relays surpasses the number of antennas. Finally, the analytical model of smart efficient spectrum utilization without harming license users in CR is validated by MATLAB simulation.     

基于能效的解码转发中继OFDM链路自适应功率分配方案研究

在能效问题中,设备本身的电路功耗已成为不可忽略的一部分,故将中继引入无线网络之后势必会带来更严重的电路功耗。该文基于解码转发(DF)中继OFDM频率选择性链路,结合电路所耗功率,提出一种最优能效功率分配方法,求得DF中继链路能效上界,同时分析了速率和功率限制对能效的影响。仿真结果表明,该文所提基于能效的功率分配算法可求出最大化能效的最优功率解,并能在保证较高速率的同时获得最好的系统能效。