基于OFDM的DF中继链路能效最优资源分配策略

针对DF模式的OFDM中继链路,将能效最大化资源分配问题转化为在用户最小速率需求和系统总发射功率受约束条的件下,子载波配对和功率分配的联合优化问题,提出一种低复杂度联合最优资源分配策略,并证明速率和功率约束条件下中继链路全局能效最优解的唯一性.仿真结果表明,与固定子载波配对策略相比,当中继节点位于源和目的节点连线中点位置,Rmin=1.5 Mbit/s时,排序子载波配对策略的链路可达速率和系统能效分别提高了2.3%和3.1%;与传统的等功率分配、速率最大化和功率最小化注水算法相比,本文方案能够在保证用户最小速率需求和系统功率约束的同时,自适应分配资源以实现系统能效最优.      

全双工中继选择策略的性能研究

为了提高协同通信系统的频谱效率,对全双工中继通信系统进行了研究.首先,介绍了传统的主动机会中继策略和最优的全双工中继选择策略,并在最优全双工中继选择策略的基础上提出了增强型全双工中继选择策略;其次,分析了主动机会中继选择策略应用在全双工中继网络中的中断性能,推导了3种策略中断概率的闭式精确结果和高信噪比(SNR)下的近似逼近结果;最后,通过数值仿真分析验证了理论推导结果的正确性.研究结果表明:在高SNR范围时,最优全双工中继选择策略和主动机会中继选择策略的中断性能趋于平台效应;增强型全双工中继选择策略的中断性能会随着SNR的增大而一直提高,且增强型全双工中继选择策略的中断性能明显最优,主动机会中继选择策略的性能最差.      

基于层次分析法的频谱资源分配效果综合评价算法

基于AHP的思想提出一种对频谱资源分配效果进行综合评价的算法:将频谱资源分配的效果作为目标层,以认知用户总满意度、频谱分配公平性及系统经济性3个因子为第1准则层,以频谱资源紧张程度、已分配带宽比例、缺口带宽比例等因素为第2准则层,根据准则层各因素的关联关系和重要性程度得出各因素权重,通过虚拟分配及单位化计算各因素的观测值进行综合评价。空闲矩阵、分配矩阵、干扰矩阵等基础数据基于均匀分布进行构造,分别对频谱资源处于充足和紧张的情况进行模拟,采用文中算法对3种频谱分配方案进行仿真。结果显示:系统资源充足时,两级动态分配方案效果最好,多信道联合优化方案次之,次用户协作方案最差;系统资源匮乏时,两级动态分配方案和多信道联合优化方案,均优于次用户协作方案。     

基于OFDM的DFT加扰矢量码分多址接入技术

为解决基于多载波的多址系统在出现子载波深度衰落时系统性能下降的问题,根据矩阵置换原理,提出了一种DFT加扰矢量多载波码分多址接入系统(DFT-VMC-CDMA).该系统利用张量积(Kronecker积)的矩阵分解性,引入矢量正交频分复用(V-OFDM)技术对发射信号进行组合排列,通过对张量积的矩阵向量求解获得分集增益抑制单一子载波上的衰落,并基于r循环信道矩阵的分解特性,加入DFT扩展和加扰前缀,减小系统复杂度和峰平比.通过仿真验证可知,该系统性能与传统的多载波系统相比,在20 d B高信噪比条件下,比上行链路的多载波直接序列码分多址(MC-DS-CDMA)平均提升6 d B,比下行链路的多载波码分多址(MC-CDMA)平均提升0.5 d B,达到了理论上的多径信道分集增益界;此外,新系统还降低了峰平比,提升了频谱效率,如当载波数为64,块长为8,保护间隔为12时,峰平比降低了2 d B,频谱效率提升了10%.     

基于能效的D2D通信系统中资源复用策略研究

针对D2D通信(device-to-device communication)与传统蜂窝通信共存下的能效资源复用问题,联合考虑蜂窝用户和D2D用户对的QoS约束,结合电路消耗功率,提出一种基于能效的D2D用户对与蜂窝用户最优匹配的资源复用和功率分配策略,分析了D2D用户对复用蜂窝用户资源的最优功率的存在性,并用分式规划理论求解了该最优功率的闭合表达式.仿真结果表明,相比已有算法,所提的能效资源复用策略的D2D用户的总能效最优,并且该总能效在低QoS要求下相比最大化和速率算法提高36.25%,高QoS要求下略高于基于节能的功率分配算法,同时还具有1.7~3 Mbit/s的和速率.      

异构网络在高速环境下切换方案中的应用

为提升高速移动环境中列车通信系统在进行越区切换时的无线连接性能、实时业务服务质量等,提出了将异构网络应用于高速环境中以改善系统切换性能.将高铁列车车载移动中继同时连接到两个或多个异构网络中构建多链路软切换方案,使其同时保持多条链路连接,当一条链路进行切换时,其他链路保持通信连接,以此达到信号不中断、无缝切换的目的.分析对比现有的双层网络方案,验证车载移动中继通信性能在切换失败、链路重建过程期间是否恶化.切换性能分析和仿真结果均表明,异构网络中构建的多链路软切换方案可显著降低高速环境中信号切换时无线连接失败率,提高了无线通信性能.     

基于SDN的数据中心多路径负载均衡算法

为避免两点间某条链路失效而导致的网络拥塞问题,数据中心网络常采用具有多路径特性的胖树拓扑结构,传统路由算法通常只为收发端选择一条路径作为最终路径,没有考虑胖树拓扑的特性,容易造成数据中心网络中链路资源的巨大浪费.基于此,提出一种基于SDN的数据中心多路径负载均衡算法.该算法首先要获取数据中心的全局网络拓扑、链路带宽和时延信息;然后通过寻路算法计算出可用的转发路径;再根据获取的链路带宽及时延信息对可用转发路径进行链路权重评估;最后确定出最佳转发路径.仿真实验结果表明,多路径负载均衡算法在减少平均时延和丢包率方面均优于传统路由算法,能够实现有效的多路径负载均衡.     

大气激光通信中几种调制方式的性能比较

为选择适合大气激光通信的信道调制方式,对湍流信道下的大气激光通信系统中的OOK,PPM,DPPM和DPIM调制方式的包误码率(PER)和带宽性能进行了仿真分析.结果表明,DPIM的PER性能最好,PPM和DPPM次之,OOK最差.当调制参数较小时,PPM的带宽性能较好;当调制参数较大时,DPPM和DPIM的带宽性能较好.除OOK之外的3种调制方式需要的功率都较小.     

无线传感器网络多路径路由算法的研究

在多路径路由算法的研究中,仍然存在着一定的局限性,如没有充分考虑网络中链路的多重特性.因此,文中在定向扩散路由算法的基础上提出了一种多路径路由算法(EDB-MRA).该算法在源节点和目的节点之间建立多条路径,根据网络链路中的3个特征值--能量消耗、延时和带宽,给每条路径赋予一定的选择概率,使得数据总能在链路性能较优的多路径中传输,从而延长了网络的生存周期,提高了传输的可靠性.     

基于CVaR的海运集装箱超订模型

将条件风险价值(CVaR)度量准则应用于集装箱舱位超订的风险管理研究.建立了在CVaR准则下的海运集装箱舱位超订模型,解此模型得到舱位最优超订水平需满足的方程组,并讨论了风险厌恶程度和空箱调运对舱位最优超订水平的影响.分析结果表明,在风险厌恶环境中,集装箱舱位的最优超订水平依赖于需求的分布和风险厌恶程度,不一定小于风险中性时的最优超订水平;与不考虑空箱调运时比较,考虑空箱调运时,最优超订水平会降低.     

Switching between antenna subset selection and quasi-orthogonal space-time block code in presence of correlation

We address the problem of adaptive modulation and coding scheme (AMCS) for a multi-input multioutput (MIMO) system in presence of time-varying transmitting correlation. Antenna subset selection and quasiorthogonal space-time block code (QOSTBC) have different error performances with different signal-to-noise ratios (SNRs) and in different spatial correlation scenarios. The error performance can be improved by selecting an appropriate transmission scheme to adapt to various channel conditions. The maximum distance criterion is the simplest and very effective algorithm for the antenna subset selection without needs of complex calculation and channel state information at transmitter (CSIT). The minimum error performance criteria and the simplified linear decision strategy are developed for constant transmission rate traffic to select the optimal transmission scheme. It can dramatically decrease algorithm complexity for obtaining error probability according to the known quantities comparing with using instant CSIT. Simulation results show that, remarkable performances including low SNR and weak spatial correlation at the expense of simple calculation and almost no bandwidth loss by adopting AMCS can be achieved. The proposed AMCS improves robustness of slowly varying spatial correlated channels.     

基于负载均衡的OFDMA双跳中继网络资源分配策略

为适应蜂窝小区内不同的用户分布,针对基于正交频分多址接入技术的双跳中继网络,提出了一种基于负载均衡的资源分配策略.考虑难以得到联合分配的最优解,在降低计算复杂度的前提下,采用分步式次优化分配.采用比例公平算法对子载波进行分配,并用数学建模的方法解决功率分配问题;根据凸规划和注水算法确定功率分配最优解需满足的条件,在逼近最优解的目标下,求得基站和中继站的发射功率.仿真分析结果表明,与传统的静态资源分配策略相比,提出的基于负载均衡的资源分配策略可以适应不同的用户分布和信道条件,系统吞吐率提高7.8%以上.      

Research on Improved Low-Energy Adaptive Clustering Hierarchy Protocol in Wireless Sensor Networks

In wireless sensor networks (WSNs), due to the limited battery power of the sensor nodes, the communication energy consumption is the main factor to affect the lifetime of the networks. A reasonable design of the communication protocol can effectively reduce the energy consumption of the network system. Based on low-energy adaptive clustering hierarchy (LEACH), an improved LEACH protocol in WSNs is proposed. In order to optimize the cluster head (CH) election in the cluster setup phase, the improved LEACH takes into account a number of factors, including energy consumption of communication between nodes, remaining energy of the nodes, and the distance between nodes and base station (BS). In the steady phase, one-hop routing and multiple-hop routing are combined to transmit data between CHs to improve energy efficiency. The forward CH is selected as relay node according to the values of path cost. The simulation results show that the proposed algorithm performs better in balancing network energy consumption, and it can effectively improve the data transmission efficiency and prolong the network lifetime, as compared with LEACH, LEACH-C (LEACH-centralized) and NDAPSO-C (an adaptive clustering protocol based on improved particle swarm optimization) algorithms.     

Robust ergodic rate transmission for time division duplex beamforming systems

In time division duplex(TDD)beamforming systems,the base station estimates the channel state information(CSI)at transmitter based on uplink pilots and then uses it to generate the beamforming vector in the downlink transmission.Because of the constraints of the TDD frame structure and the uplink pilot overhead,there inevitably exists CSI delay and channel estimation error between CSI estimation and downlink transmission channel,which would degrade system ergodic rate.In this paper,we propose a robust ergodic rate transmission scheme,in which the uplink pilot time interval(UPTI)of an active user is adaptively adjusted according to the changing channel conditions such as Doppler frequency shift,uplink pilot signal to noise ratio(SNR),to minimize the impact of CSI delay and channel estimation error on the ergodic rate of TDD beamforming systems.In order to get the optimal UPTI,we first derive the average post-processing SNR for TDD beamforming systems with channel estimation error and CSI delay.We then obtain the optimal UPTI,which maximizes the average post-processing SNR,given the normalized pilot overhead(the number of pilot symbols per data symbol).The numerical simulation results validate that the the proposed robust ergodic rate transmission scheme not only maximizes the average post-processing SNR but also maximizes the system ergodic rate.Moreover,the scheme can adapt well to the changing channel environments compared with the current fixed UPTI scheme.Especially our research is valuable for the uplink sounding reference signal design in long term evolution advanced(LTEAdvanced)system.     

基于端到端失真优化的无线视频联合编码方案

在无线视频传输环境端到端失真分析的基础上,针对H.264视频流建立了一种新的端到端失真模型.在使用LDPC信道编码方式与该失真分析模型的基础上,提出了一种基于端到端失真优化的联合信源信道编码方案.该方案根据当前无线信道的信噪比与信道带宽等状态信息,自适应地调节信源编码量化参数和信道编码码率,使端到端失真最小.实验结果表明,与固定码率编码相比,本文提出的联合信源信道编码方案可在不增加带宽的情况下显著提高视频传输质量.     

一种新型级联MZI型不等带宽波长交错滤波器的设计

为了满足在光纤通信系统中不同传输速率对带宽的要求,提出了基于1个3×3和2个2×2光纤耦合器级联组成全光纤马赫-曾德尔干涉仪(MZI)型不等带宽波长交错滤波器的设计方案.运用光纤传输理论和矩阵理论,推得器件输出谱的表达式,对其特性进行数值模拟分析,结果表明:器件将50GHz的输入信号分离成信道间隔为100GHz的奇偶两路输出信号,满足了10Gbit/s+40Gbit/s混合系统中不同传输速率对带宽的要求,实现不等带宽传输;器件中对耦合器的结构参数偏差要求不同而降低了制作难度.该滤波器较等带宽交错滤波器带宽利用率更高,在光纤通信系统中有着潜在的应用价值.     

Joint optimization of spectral and energy efficiency for multi-pair full-duplex two-way relay networks with imperfect channel state information

An iterative algorithm is proposed for jointly optimizing spectral and energy efficiency in a multipair full-duplex (FD) two-way relaying (TWR) system with imperfect channel state information (CSI). Based on Dinkelbach method, a Taylor expansion based approximation method and the Generalized Lagrange Multiplier Method have been applied iteratively to obtain the near optimal relay amplified matrix and power allocation, respectively. And the simulation results illustrate the effectiveness of the proposed algorithm and the algorithm can converge quickly.     

基于分组合并的多信道停等ARQ性能

从信道数、合并方式、分组丢失率、传输延迟等方面,分析了在Rayleigh衰落信道下具有分组合并的多信道停等ARQ性能.分析结果表明:对于多信道停等ARQ,需根据分组传输时间和往返延迟时间合理安排停等ARQ的信道数,以使ARQ系统性能达到最佳;根据信道质量,采用合适的分组合并方式可减少接收处理延迟;为获得恒定分组传输延迟和系统吞吐率,可根据分组丢失率要求和信道质量调整最大传输次数.