Power Control for Fading Channels in Cognitive Radio Networks with Outage-Probability Minimization

Cognitive radio allows Secondary Users （SUs） to dynamically use the spectrum resource licensed to Prirmry Users （PUs）, and significantly improves the efficiency of spectrum utilization and is viewed as a promising technology. In cognitive radio networks, the problem of power control is an important issue. In this paper, we mainly focus on the problem of power control for fading channels in cognitive radio networks. The spectrum sharing underlay scenario is considered, where SUs are allowed to coexist with PUs on the condition that the outage probability of PUs is below the maximum outage probability threshold limitation due to the interference caused by SUs. Moreover, besides the outage probability threshold which is defined to protect the performance of PUs, we also consider the maximum transmit power constraints for each SU. With such a setup, we emphasize the problem of power control to minimize the outage probability of each SU in fading channels. Then, based on the statistical information of the fading channel, the closed expression for outage probability is given in fading channels. The Dual-Iteration Power Control （DIPC） algorithm is also proposed to minimize the outage probability based on Perron-Frobenius theory and gradient descent method under the constraint condition. Finally, simulation results are illustrated to demonstrate the performance of the proposed scheme.

Outage Probability Analysis for Modified Decode-and-Forward Model over Nakagami-m Fading Channels

This paper proposes a modified decodeand-forward(DAF) protocol with a three-node model,which contains two users and one destination.Each user can be either the source or the relay in different frames.We analyze the four cooperative cases in the first frame and run simulations to obtain the optimal power allocation coefficients in the second frame.The closed-form expression of outage probability is derived over Nakagami-m fading channels.Furthermore,we show that the proposed model has better performance than the non-cooperation system and traditional DAF strategy based on the derived outage probability.

Iterative static modeling of channelized reservoirs using history-matched facies probability data and rejection of training image

Most inverse reservoir modeling techniques require many forward simulations, and the posterior models cannot preserve geological features of prior models. This study proposes an iterative static modeling approach that utilizes dynamic data for rejecting an unsuitable training image(TI) among a set of TI candidates and for synthesizing history-matched pseudo-soft data. The proposed method is applied to two cases of channelized reservoirs, which have uncertainty in channel geometry such as direction, amplitude, and width. Distance-based clustering is applied to the initial models in total to select the qualified models efficiently. The mean of the qualified models is employed as a history-matched facies probability map in the next iteration of static models. Also, the most plausible TI is determined among TI candidates by rejecting other TIs during the iteration. The posterior models of the proposed method outperform updated models of ensemble Kalman filter(EnKF) and ensemble smoother(ES) because they describe the true facies connectivity with bimodal distribution and predict oil and water production with a reasonable range of uncertainty. In terms of simulation time, it requires 30 times of forward simulation in history matching, while the EnKF and ES need 9000 times and 200 times, respectively.

The feature on the posterior conditional probability of finite state Markov channel

The feature of finite state Markov channel probability distribution is discussed on condition that original I/O are known. The probability is called posterior condition probability. It is also proved by Bayes formula that posterior condition probability forms stationary Markov sequence if channel input is independently and identically distributed. On the contrary, Markov property of posterior condition probability isn’t kept if the input isn’t independently and identically distributed and a numerical example is utilized to explain this case. The properties of posterior condition probability will aid the study of the numerical calculated recurrence formula of finite state Markov channel capacity.

EFFICIENT BIT ERROR PROBABILITY EXPRESSION AND VERY TIGHT BOUND FOR MAXIMAL RATIO COMBINING DIVERSITY SYSTEMS OVER RAYLEIGH FADING CHANNEL

Bit Error Probability (BEP) provides a fundamental performance measure for wireless diversity systems. This paper presents two new exact BEP expressions for Maximal Ratio Combining (MRC) diversity systems. One BEP expression takes a closed form, while the other is derived by treating the squared-sum of Rayleigh random variables as an Erlang variable. Due to the fact that the extant bounds are loose and could not properly characterize the error performance of MRC diversity systems, this paper presents a very tight bound. The numerical analysis shows that the new derived BEP expressions coincide with the extant expressions, and that the new approximation tightly bounds the accurate BEP.

基于分集的非相干多进制正交调制迭代译码研究

为了解决无线通信系统低速率传输面临的瞬时快衰落明显、归一化多普勒很大、接收信号弱等多种难题,提出了基于分集的非相干多进制正交调制迭代译码体制。首先,构建了非相干多进制正交调制迭代译码模型,给出了基于最大值映射的简化解调译码方法;其次,设计了基于分集的非相干多进制正交调制迭代译码系统方案,分析了信道容量极限关键参数,推算出编码码率与信噪比关系,提出了基于分集合并信号概率密度的性能分析方法;最后,采用蒙特卡洛仿真方法,结合高斯信道与瑞利衰落信道进行了系统仿真验证及性能分析。结果表明:在归一化多普勒0.5的瑞利衰落信道仿真环境下,采用16重分集、32阶正交调制、Turbo/低密度奇偶校验码(LDPC)迭代译码,编码码率为2/3、编码信息长度为384的设计方案,可实现信噪比低至3 dB时的稳定通信。所提出的基于分集的非相干多进制正交调制迭代译码方法,实现了低信噪比高可靠传输,可为低速率无线通信系统设计提供参考。

基于FBMC-chirp的低截获探通一体化信号设计

面对快速发展的先进无源侦察技术,一体化信号除需具备较优的雷达探测和无线通信能力,还需满足抗截获和防窃听的需求,以提高一体化系统的生存能力和作战性能。多载波探通一体化信号的低截获设计已成为目前一体化信号研究的重要问题。针对传统低截获多载波探通一体化信号雷达分辨性能受限且未能同时兼顾通信有效性和可靠性要求的问题,本文在子载波复用的一体化多维信号框架下,研究了一种雷达和通信性能最小损失的低截获多载波探通一体化信号设计方法。首先,从提升时频资源利用率的角度,设计了一种基于滤波器组多载波技术的通信频谱分块功率优化和雷达梳状谱等功率优化的低截获多载波探通一体化信号时频结构。该结构通过分块的方式降低了通信信号的峰均比,提升了通信信号的低截获性能。然后在此基础上,以雷达互信息和通信信道容量为约束条件,以最小化信号总功率为优化目标,建立了雷达子载波功率和通信分块子载波功率联合优化模型。本文将该优化模型转化成一个凸二次规划问题,并采用信赖域方法对该优化问题进行求解。实验结果表明,本文所设计的低截获多载波探通一体化信号不仅具有较优的雷达探测和分辨性能,以及较好的无线通信性能,而且具有较优的低截获性能。

基于双Q学习算法的安全容量的优化

由于无线传播的广播和开放性,车联网通信系统易遭受到窃听者的窃听,这降低了通信系统的安全容量。为此,文中提出基于深度强化学习的安全容量的优化算法(D3QN-RS)。利用随机过程理论将最优转发节点的选举问题转化为马尔可夫决策过程(MDP),并将截获概率融入奖励函数。利用奖励值抑制截获概率,并将选择转发节点的问题转入强化学习框架。最后,利用双Q学习算法(D3QN)求解,产生最优的转发节点,进而提升系统的安全容量。仿真结果表明,与随机选择转发节点的算法相比,D3QN-RS算法的截获概率下降了约15%,系统的安全容量提升了约12%。

基于DSmT证据折扣理论的短波多通道信息融合方法

针对由于短波信道复杂恶劣、通道信息间冲突突出,经典合并方式对短波多通道信息合并效果不佳问题,提出基于DSmT证据折扣理论的短波多通道信息融合方法。以DSmT证据折扣理论作为融合框架,实现对短波多通道信息融合推理判决。首先,归一化OFDM帧的相对包络标准差,并通过相对包络标准差与折扣因子计算得到折扣权重。然后,通过比特软信息提取函数获得比特概率,以比特概率对基本信任分配函数定量赋值来作为证据。最后,以PCR6融合规则对多通道软信息进行融合推理判决。在多种信道条件、多种调制方式下与经典合并方式的对比仿真实验表明,所提方法可以获得明显的误码率增益和误包增益。

混合概率信道下的全双工无人机中继轨迹优化

研究了固定翼无人机作为全双工移动中继,通过混合概率信道为源节点向目标节点转发数据的飞行轨迹优化设计,在满足源与目标通信任务量要求的情况下,最小化无人机飞行能耗。建立了跑道形和混合轨迹的两种最优化问题,该问题是非凸问题,难以求得闭式解,先将混合信道增益用平均信道增益代替,并利用泰勒展开求出中继和目标节点接收数据量的下界,以此化简约束,从而得到原问题的近似问题。利用遗传算法和内点法求解近似问题,给出跑道形和混合轨迹两种无人机轨迹设计。实验结果表明:跑道形轨迹在任何场景下均有较好的节能效果;在大任务量和源与目标距离较远时,混合轨迹节能效果好于直线和圆形轨迹。时间复杂度分析发现,遗传算法的复杂度小于内点法,更加适用于实时性要求高的场景。

Gamma-Gamma信道下基于并行交织极化码的误码性能研究

为了降低大气湍流引起的衰落影响,同时减少长片误码干扰,提出一种基于并行交织极化码(polar code)的编码方法。通过蒙特卡洛模拟Gamma-Gamma分布的随机数构建大气湍流信道,以成对差错概率(pairwise error probability, PEP)和极化谱确定极化信道的误差概率上限,采用乘积距离准则最小化差错概率,建立了并行交织的设计准则。对极化码在湍流信道中的误码率(bit error rate, BER)性能进行了评估,仿真结果表明,基于极化码的并行交织方法获得了一个量级的误码性能提升,在信噪比为5 dB时,误码率从5.11×10-6降低为2.13×10-7,有效缓解了湍流引起的长片误码问题。实验验证了所提准则的可靠性和适用性。

基于逆概率加权法分析急诊救治通道对上消化道出血患者治疗效果的影响

目的通过倾向性评分逆概率加权法(IPTW)探讨上消化道出血急诊救治通道对急性上消化道出血(AUGIB)患者的临床治疗效果。方法采用回顾性研究方法。纳入2018年1月至2021年12月贵阳市第一人民医院收治的299例AUGIB患者的临床信息,选择急诊救治通道建立前(2018年1月至2019年12月)收治的AUGIB患者为常规组(152例),以急诊救治通道建立后(2020年1月至2021年12月)收治的AUGIB患者为通道组(147例)。采用IPTW对多个混杂变量性别、年龄、既往基础疾病、非甾体抗炎药(NSAID)服用史、个人史、格拉斯哥Blatchford评分(GBS)、不同出血病因等进行平衡,经IPTW处理后实现混杂变量在组间的一致分布。比较常规组与通道组临床治疗效果的差异,包括止血时间、出血复发率、输血量、住院时间、住院费用、重症监护病房(ICU)转入率、病死率等。结果经IPTW后,混杂变量在组间均衡效果好。通道组止血时间〔h:7.90(5.36,11.42)比9.92(6.25,18.15)〕、出血复发率〔23.1%(34/147)比40.1%(61/152)〕、住院时间〔d:8.00(7.00,10.34)比9.00(7.00,13.00)〕、ICU转入率〔8.8%(13/147)比17.7%(27/152)〕、病死率〔0.7%(1/147)比4.5%(7/152)〕均明显低于常规组(均P<0.05);通道组和常规组输血量、住院费用比较差异均无统计学意义〔输血量(U):2(0,4)比2(0,4),住院费用(万元):1.35(1.03,2.00)比1.16(0.71,2.29),均P>0.05〕。结论该急诊救治通道能降低AUGIB患者的出血复发率、ICU转入率及病死率,缩短止血时间和住院时间,具有很好的治疗效果。

DESIGN AND PERFORMANCE OF SYMBOL/SEQUENCE TCM FOR DS/SSMA SYSTEM OVER MOBILE RADIO CHANNEL

A novel kind of multidimension symbol/sequence trellis coded modulation (TCM) based on TCM of lower coding rate has been constructed. The redundancy of this new kind of TCM is provided not only by the modulated symbol sequence but also by the PN sequences for spreading spectrum as well. The performance of direct sequence spread spectrum multiple access (DS/SSMA) system with this symbol/sequence TCM over flat Rayleigh fading channel has been investigated by theoretical analysis and numerical simulation. The results obtained in this research demonstrate the performance improvements of this system in comparison with that of the DS/SSMA system with conventional TCM under the same conditions.

一种基于极化码的OFDM水声通信系统

为了降低水声信道强多径效应、大多普勒频移等特性对水声通信系统的影响,提出一种基于极化码的正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)的水声通信系统。选择极化(Polar)码作为信道编码方案,通过量化信道输出直接统计信道转移概率,替代通过信道估计得到的信道冲激响应,再计算转移概率,以降低通信系统的复杂度。在特性随时不变、时变、快时变的3种类型水声信道模型下,分别基于蒙特卡罗算法构造Polar码。仿真结果表明,Polar码在3种信道上的编码增益优于同码长同码率的低密度奇偶校验(Low Density Parity Check,LDPC)码和Turbo码,且信道条件越复杂,取得的编码增益越大,所提系统能够明显降低信道多径效应、多普勒频移对水声通信系统的扰乱,提高系统的可靠性。

大气相干激光通信的中断概率和信道容量研究

针对大气相干激光通信常受到信道衰减、大气湍流和指向误差等效应影响的问题,分析在这些复合效应下的大气信道的衰落分布模型,求出中断概率和信道容量的闭合解。研究得出,一方面,虽然指向误差恶化了相干激光通信系统的中断性能和信道容量,但是通过将指向精度控制在ξ=1.4量级可明显降低其影响;另一方面,虽然高阶数的自适应光学补偿能更好地抑制大气湍流引入的光相位畸变,但是较低阶数(J=3)的自适应光学补偿可明显改善中断概率和信道容量。为了实现高可靠、大容量的大气相干激光通信,在系统设计时需联合考虑低阶自适应光学补偿和高精度光束指向、跟踪。

二连盆地巴音都兰凹陷B51井区白垩系阿四段扇三角洲前缘沉积特征

在岩心观察和粒度分析的基础上,结合录井、测井、地震等资料,对二连盆地巴音都兰凹陷B51井区下白垩统阿四段扇三角洲前缘沉积特征、分布规律与发育模式进行了研究。研究结果表明:(1)巴音都兰凹陷B51井区阿四段发育砂砾岩相、砂岩相、粉砂岩相、泥岩相等四大类,可进一步划分为13个小类,粒度概率累计曲线表现为悬浮一段式、低斜两段式、高斜两段式、滚动-跳跃-悬浮三段式4种类型,具有箱形、钟形、漏斗形、指形、平直形5种测井相标志,发育前积、丘状、杂乱状、亚平行状4种地震相。(2)研究区阿四段扇三角洲前缘发育水下分流主河道、水下分流河道、河口坝、水下分流间湾、席状砂和远砂坝6种沉积微相,纵向上可分为Ⅰ,Ⅱ,Ⅲ共3个砂组,Ⅱ砂组和Ⅲ砂组沉积时期,扇三角洲前缘砂体分布广泛,水下分流主河道和水下分流河道发育;Ⅰ砂组沉积时期,湖盆范围最大,砂体变细、变薄。(3)研究区阿四段自下而上表现为水进沉积序列,发育退积型扇三角洲前缘,预测B51-71井区和B51-74井区发育的水下分流主河道和水下分流河道为利储集相带,B51-19井区发育的河口坝为较有利的储集相带。

考虑共因失效的列控系统定量安全分析研究

列车运行控制系统(简称“列控系统”)作为保障列车安全运营的安全相关系统,因采用多通道冗余设计而较易引发共因失效,因此对列控系统进行共因失效分析和防护是很有必要的。文章根据系统安全理论,结合β因子和独立性分析方法对系统可能出现的共因失效情况进行分析评估,通过共因失效检查表识别分析系统设计过程中的薄弱环节,并提出相应的安全防御措施;同时结合β因子模型对共因失效进行定量评估,判定系统危险侧失效率是否在可接受的范围并达到规定的安全目标。文章以计算机联锁系统作为研究对象,定量计算结果表明,β因子越小,共因失效影响越小。因此为了最大限度地减少共因失效发生的概率,在系统设计中应采用适当的安全防御措施,减小在估算因为共因失效而引发系统失效时使用的β因子数值,进而提升系统的安全性。

Channel Modeling and Performance Analysis for UAV Relay Systems

In this paper, a multi-hop relay channel model based on unmanned aerial vehicles(UAVs) is established by taking into account of the propagation loss, shadowing, and multi-path fading. Based on the proposed channel model, the cascaded propagation loss of relay link and the cascaded probability density function(PDF) of channel fading are derived. Moreover, the theoretical performance of the UAV-based relay system, i.e., the outage probability, bit error rate(BER), and channel capacity, is also analysed and derived. Simulation results show agreement with theoretical results for the hill, mountain, and sea scenarios, indicating the accuracy of both the simulations and derivations.

Entanglement-enhanced classical communication through an amplitude-damping channel

We consider the problem of trying to send a single classical bit through an amplitude-damping channel when two transmissions through the channel are available as a resource. It is demonstrated that two entangled transmissions can enhance the receiver＇s capability of making a correct inference under certain conditions compared with two product-state transmissions.

OPTIMUM FRAME SYNCHRONIZATION AND PERFORMANCE OVER BINARY SYMMETRIC CHANNEL

The fixed frame length maximum correlation method which is the optimum methodover the binary symmetric channel has been proved.With Poisson distribution,the frame syncacquisition probability is obtained and followed by computer simulation.By Markov modelingtechniques,the probability and the mean time into lock mode are given.Finally,it is shown thatthe optimum frame sync method is far superior to conventional,and it is very useful in practice.