硬件损伤下多窃听器NOMA系统平均保密容量分析

研究了非正交多址(Non‑orthogonal‑multiple‑access,NOMA)接入通信系统的物理层安全性能。当基站采用下行NOMA方案发送信息时,由于信道的开放性,信息容易被窃听,而当存在多个随机分布的窃听者时,安全性能会进一步降低。为了增强存在硬件损伤系统的物理层安全性能,本文考虑保护区的方法,针对地面用户与基站之间存在直连链路的情况,采用莱斯衰落来建模小尺度衰落。本文还假设多个窃听者的位置遵循齐次泊松点过程(Homogeneous Poisson point process,HPPP),借助高斯切比雪夫积分公式,推导了平均保密容量的闭式表达式,并给出了在高信噪比情况下的渐近表达式来获得进一步见解。仿真结果验证了保护区方法在增强安全性能方面的有效性,并说明了不同参数对系统保密性能的影响。

Power Allocation for SE Maximization in Uplink Massive MIMO System Under Minimum Rate Constraint

In this paper,we optimize the spectrum efficiency(SE)of uplink massive multiple-input multiple-output(MIMO)system with imperfect channel state information(CSI)over Rayleigh fading channel.The SE optimization problem is formulated under the constraints of maximum power and minimum rate of each user.Then,we develop a near-optimal power allocation(PA)scheme by using the successive convex approximation(SCA)method,Lagrange multiplier method,and block coordinate descent(BCD)method,and it can obtain almost the same SE as the benchmark scheme with lower complexity.Since this scheme needs three-layer iteration,a suboptimal PA scheme is developed to further reduce the complexity,where the characteristic of massive MIMO(i.e.,numerous receive antennas)is utilized for convex reformulation,and the rate constraint is converted to linear constraints.This suboptimal scheme only needs single-layer iteration,thus has lower complexity than the near-optimal scheme.Finally,we joint design the pilot power and data power to further improve the performance,and propose an two-stage algorithm to obtain joint PA.Simulation results verify the effectiveness of the proposed schemes,and superior SE performance is achieved.

面向6G移动通信的可重构智能反射表面技术研究综述

伴随移动通信技术的迅猛发展,复杂多变环境和高能耗将是当前以及未来移动通信面临的主要问题,低能耗、高效通信环境自适应调整将是移动通信技术发展的必经之路。可重构智能反射表面(Reconfigurable intelligent surface,RIS)技术的发展,为移动通信提供了低能耗、通信环境自适应可重构服务,满足了复杂通信场景下多样化设备服务需求。本文首先对RIS技术从原理、特点、优势等方面进行了概述;然后针对RIS具体的应用场景,对RIS技术优势进行总结;最后在现有工作基础上,总结了RIS技术可能面临的技术挑战,并进一步论述与展望RIS技术的发展方向。RIS技术将会进一步推动移动通信技术的变革,助力移动通信技术面向未来复杂、智能化场景应用需求。

蒽醌类化合物用于溃疡性结肠炎治疗的研究进展

根据病变累及的解剖范围,溃疡性结肠炎(ulcerative colitis,UC)通常可分为直肠炎、左半结肠炎(即乙状结肠或不累及降结肠)以及全结肠炎,少数患者还会累及回肠。UC的病因尚不明确,可能与免疫功能障碍、遗传易感性和微生物失衡有关。临床治疗中,常使用美沙拉嗪制剂、皮质类固醇和免疫抑制剂等药物来控制炎症反应,从而缓解症状,促进结肠黏膜愈合。近年来,具有新靶点的生物制剂不断进入临床试验,可通过减轻炎症反应及修复肠黏膜达到治疗目的[1]。然而,仍有部分患者出现药物无应答或停药后复发[2]。近年来,有关UC治疗药物的研究不断取得进展,针对其他单体成分和中药的研究发现,蒽醌类化合物可在UC的治疗中发挥良好的抗炎作用,现进行综述如下。

以“创新能力教育”为导向的药物制剂专业实践教学体系的构建

大学生创新意识和能力的培养是高等院校改革的重点内容,而实践教学是人才培养体系中的关键环节。在药学专业认证的背景下,对实践教学体系进行改革。以药物制剂专业学生为主体,以创新能力为导向,构建以“创新能力教育”为导向的药物制剂专业实践教学体系,从实践教学体系的模块组成、实施和评价三方面进行分析,为培养高素质创新型人才提供实践基础。

未来移动通信网络中移动边缘计算技术

未来移动通信网络将面临移动数据业务和流量急剧增加,需要低时延和低能耗的高效技术。移动边缘计算(Mobile edge computing,MEC)在网络边缘侧进行计算卸载和资源存储,能极大地降低处理时延和能耗,提高用户服务体验。本文首先概述了MEC的基本原理和技术特点;然后通过具体的MEC的应用场景,进一步总结了MEC技术的优势;最后在现有工作的基础上,给出了MEC可能面临的挑战,并对未来的发展方向进行了论述与展望。MEC将会进一步推动计算和通信的融合,助力5G进入新场景多需求下的多技术融合新阶段。

交互式学习共同体在药剂学教改中的应用

以药剂学课程教学为具体案例,讨论学习共同体在知识的传播过程中起到的具体效用和产生效用的方式,结合交互式教学的相关特点分析可见,学习共同体在不同的学习者之间建构起一个更加便捷和带有互动性的学习网络,不同层次的知识和经验在这个网络下会交叉流动。研究结果有利于教学方式的改革创新及创新性人才的培养。

MATLAB GUI在直接序列扩频通信系统教学中的应用

扩频通信通过扩展信号频带宽度以提高抗干扰能力和保密性,但其概念抽象,内容复杂,为课程的学习带来一定的难度。基于此,利用MATLAB软件中GUI设计一种适用于直接序列扩频系统的仿真实验演示平台,该平台可根据参数设置,给出系统中不同功能模块输出的仿真和测试结果。教学实践结果表明,该平台能够直观地显示系统中信号在时域和频域上的变化,使得学生对直接序列扩频通信系统有着更深入的理解。

移动通信课程教学方法研究与探讨

分析现有移动通信课程教学中存在的问题,提出该课程教学方法上的一些改进。然后阐述授课中应用多媒体教学、讨论式教学、专题式讲座和计算机仿真辅助教学等方法的教学理念,为该课程的教学方法提出新的思路。教学实践结果表明,通过教学方法研究、探讨与实践,可以有效地提高教学质量,获得良好的教学效果。

不完全信道状态信息下非线性波形非正交多址接入系统吞吐量分析

针对目前关于非正交多址接入(NOMA)的研究均局限于线性调制的问题,且考虑到实际系统中不完全的信道状态信息(CSI),基于最小频移键控类(MSK-type)调制,该文提出一种不完全CSI下的非线性波形NOMA系统。首先,分别采用过采样和匹配滤波技术对两用户的上行异步和同步系统进行了建模。进一步,基于矩阵分解理论和连续干扰消除(SIC)机制,分别推导出完全或不完全CSI下系统吞吐量达到最大时的发射功率和归一化时延。最后,数值仿真结果表明了完全与不完全CSI下系统吞吐量与帧长、响应长度、波形以及频率脉冲等系统参数的关系。

Performance Analysis of Uplink Distributed Massive MIMO System with Cross-Layer Design over Rayleigh Fading Channel

The performance of uplink distributed massive multiple-input multiple-output(MIMO)systems with crosslayer design(CLD) is investigated over Rayleigh fading channel, which combines the discrete rate adaptive modulation with truncated automatic repeat request. By means of the performance analysis, the closed-form expressions of average packet error rate(APER)and overall average spectral efficiency(ASE)of distributed massive MIMO systems with CLD are derived based on the conditional probability density function of each user’s approximate effective signal-to-noise ratio(SNR)and the switching thresholds under the target packet loss rate(PLR)constraint.With these results,using the approximation of complementary error functions,the approximate APER and overall ASE are also deduced. Simulation results illustrate that the obtained theoretical ASE and APER can match the corresponding simulations well. Besides,the target PLR requirement is satisfied,and the distributed massive MIMO systems offer an obvious performance gain over the co-located massive MIMO systems.

Discrete-Rate Adaptive Modulation with Variable Threshold for Distributed Antenna System in the Presence of Imperfect CSI

Discrete-rate adaptive modulation （AM） scheme for distributed antenna system （DAS） with imperfect channel state information （CSI） is developed, and the corresponding performance is investigated in composite Rayleigh channel. Subject to target bit error rate （BER） constraint, an improved fixed switching threshold （FST） for the AM scheme is presented by means of tightly-approximate BER expression, and it can avoid the performance loss fxom conventional FST. Based on the imperfect CSI, the variable switching threshold （VST） is derived by utilizing the maximum a posteriori method. This VST includes the improved FST as a special case, and may lower the impact of estimation error on the performance. By the switching thresholds, the spectrum efficiency （SE） and average BER of the system are respectively derived, and resulting closed- form expressions are attained. With these expressions, the system performance can be effectively evaluated. Simulation results show that the derived theoretical SE and BER can match the simulations well. Moreover, the AM with the presented FST has higher SE than that with the conventional one, and the AM with VST can tolerate the large estimation error while maintaining the target BER.

基于MATLAB GUI的跳频扩频通信系统实验教学平台设计

扩频通信是围绕提高信息传输的可靠性而提出的一种理论和技术。为了便于理解扩频通信的概念,利用MATLAB GUI设计一种频率跳变扩频通信系统的仿真实验演示平台。该平台可通过设置不同参数,展示通信系统中不同阶段的仿真结果,直观显示信号在时域以及频域上的变化,有助于理解跳频扩频通信系统。

Joint Energy-Efficient Power Allocation and Beamforming Design for mm Wave-NOMA System with Imperfect CSI

The joint power allocation(PA)and beamforming(BF)design problem is studied to maximize the energy efficiency of a two-user downlink millimeter-wave system with non-orthogonal multiple access under imperfect channel state information(CSI).By means of block coordinate descent,convex-concave procedure,and successive convex approximate,we propose a suboptimal joint PA and BF design scheme to address this non-convex problem.Simulation results verify that the proposed joint PA and BF design scheme is more effective when compared to some existing schemes.

UPLINK PERFORMANCE OF CWP-MC-CDMA WITH SPACE DIVERSITY COMBINING TECHNIQUE OVER RAYLEIGH FADING CHANNEL

In this paper, a Complex Wavelet Packet （CWP-MC-CDMA） system uplink model is proposed, based Multi-Carrier Code Division Multiple Access based on the analysis of the principle of MC-CDMA and the use of the optimized complex wavelet packet. Considering that the base station can adopt multiple re- ceiver antennas in the uplink, we employ the Space Diversity Combining （SDC） technique to improve the sys- tem pertbrmance via multiple antennas. The uplink performance of proposed CWP-MC-CDMA system with SDC technique is investigated over Rayleigh lading channel, and corresponding bit error rate analysis is given in detail. The system can avoid the decrease of spectrum efficiency of conventional MC-CDMA due to inserting cyclic prefix. Theoretical analysis and simulation result show that the application of SDC technique can improve the CWP-MC-CDMA system ability to combat spatial lading and various interferences effectively. Moreover, the proposed system based on SDC technique has superior Bit Error Rate （BER） performance over the Discrete Fourier Transform （DFT） and SDC based MC-CDMA system and the real wavelet packet and SDC based MC-CDMA system.

Performance Analysis of AF Relaying Aided Space Shift Keying System with Imperfect Channel Estimation

Space shift keying (SSK) is a spectrally efficient and low-complexity technique that only uses antenna index to convey information.Combining SSK with cooperative communication,the transmission reliability of SSK system can be improved effectively.In this paper,considering imperfect channel information,the performance of cooperative SSK system with amplify-and-forward (AF) relaying protocol is investigated,and the effect of estimation error on the performance is analyzed.According to the performance analysis,the probability density function and moment generating function of effective signal-to-noise ratio are derived,respectively.Using these results,the closed-form expression of average bit error rate (BER) can be achieved.Meanwhile,the asymptotically approximated BER and the corresponding diversity order analysis are presented for the performance evaluation.By computer simulations,the validness of the presented theoretical analysis is verified,and the theoretical BERs with different estimation errors are shown to be close to those of the corresponding simulations.

Adaptive Energy Efficient Power Allocation Scheme for DAS with Multiple Receive Antennas

Energy efficiency(EE)of downlink distributed antenna system(DAS)with multiple receive antennas is investigated over composite Rayleigh fading channel that takes the path loss and lognormal shadow fading into account.Our aim is to maximize EE which is defined as the ratio of the transmission rate to the total consumed power under the constraints of the maximum transmit power of each remote antenna.According to the definition of EE,the optimized objective function is formulated with the help of Lagrangian method.By using the Karush-KuhnTucker(KKT)conditions and numerical calculation,considering both the static and dynamic circuit power consumptions,an adaptive energy efficient power allocation(PA)scheme is derived.This scheme is different from the conventional iterative PA schemes based on EE maximization since it can provide closed-form expression of PA coefficients.Moreover,it can obtain the EE performance close to the conventional iterative scheme and exhaustive search method while reducing the computation complexity greatly.Simulation results verify the effectiveness of the proposed scheme.

Capacity Analysis on Distributed Antenna System with Imperfect CSI over Rayleigh Fading Channel

Considering that perfect channel state information(CSI)is hard to obtain in practice,the capacity of downlink distributed antennas system(DAS)with imperfect CSI is analyzed over Rayleigh fading channel.Based on the performance analysis,using the probability density function and numerical calculation,an accurate closedform expression of ergodic capacity of downlink DAS under imperfect CSI is derived.It includes the one under perfect CSI as a special case.This theoretical expression can provide good performance evaluation for downlink DAS for both perfect and imperfect CSI due to its accuracy.Simulation results indicate that the theoretical analysis agrees well with the corresponding simulation,and the capacity can be increased effectively by decreasing the estimation error and/or path loss.

Performance Analysis and Power Allocation for Cooperative SSK System with Receive Correlation in Rayleigh Fading Channel

In this paper,the performance analysis of cooperative space shift keying(SSK)system with dual hop amplify and forward(AF)in receive correlated Rayleigh channel is presented.By means of the performance analysis,a closed form approximate expression of the average bit error rate(BER)is derived for the performance evaluation.With this expression,in a high signal to noise ratio(SNR)region,a tight closed form asymptotic BER of the system is also derived.It can simplify the calculation of average BER and provide effective evaluation for asymptotic performance.By minimizing this asymptotic BER expression,a suboptimum power allocation(PA)scheme is developed,and the closed form PA coefficients are obtained.Simulation indicates that the suboptimal PA scheme outperforms the conventional equal PA scheme,and its performance is very close to that of the exhaustive search based optimal PA scheme but with low complexity.Moreover,the system performance under the spatially correlated channel is worse than that in spatially independent channel due to the effect of spatial correlation.

UNIT-RATE COMPLEX ORTHOGONAL SPACE-TIME BLOCK CODE CONCATENATED WITH TURBO CODING

Space-Time Block (STB) code has been an effective transmit diversity technique for combating fading due to its orthogonal design, simple decoding and high diversity gains. In this paper, a unit-rate complex orthogonal STB code for multiple antennas in Time Division Duplex (TDD) mode is proposed. Meanwhile, Turbo Coding (TC) is employed to improve the performance of proposed STB code further by utilizing its good ability to combat the burst error of fading channel. Compared with full-diversity multiple antennas STB codes, the proposed code can implement unit rate and partial diversity; and it has much smaller computational complexity under the same system throughput. Moreover, the application of TC can effectively make up for the performance loss due to partial diversity. Simulation results show that on the condition of same system throughput and concatenation of TC, the proposed code has lower Bit Error Rate (BER) than those full-diversity codes.