A joint iterative channel estimation and symbol detection algorithm for OFDM systems over time-varying channels

针对正交频分复用(OFDM)系统中由于信道快时变导致的子载波间干扰(ICI),基于基扩展模型,提出了一种时变信道下OFDM系统联合迭代信道估计与符号检测算法.该算法将基于基扩展模型的最小均方误差信道估计算法与一种类似于串行干扰抵消的符号检测方式相结合,并利用插值和滤波过程进一步消除噪声影响,进而通过联合迭代获得较为精确的符号检测结果.同时,利用带状矩阵近似降低算法的计算复杂度,在复杂度与算法性能之间取得比较好的折中.理论分析和仿真结果表明,在快时变信道条件下,这种新的联合迭代信道估计与符号检测算法可有效地提高系统性能.     

一种带有CFO补偿的OFDMA上行链路Turbo接收机

提出了一种带有多用户载波频率偏移(CFO)联合补偿功能的迭代(Turbo)接收机,用于频率非同步环境下的正交频分多址(OFDMA)上行信号接收处理。基于频域Turbo均衡原理,该接收机实现了带有软干扰消除(SIC)的CFO补偿、最小均方误差(MMSE)频域均衡和最大后验(MAP)信道译码的联合迭代处理。理论分析和仿真结果均表明:与传统的非迭代接收机相比,文中所提Turbo接收机利用MAP译码器的软判决反馈信息实现了干扰重构和消除,在迭代中获得了更优的频率同步性能和误比特率性能;与现有几种典型的迭代接收机相比,文中所提Turbo接收机具有更优的误比特率性能和更低的实现复杂度。     

基于符号调整的OFDM系统载波间干扰抑制方法

基于组合优化理论,提出了一种通过调整子载波调制符号的正负来抑制正交频分复用(OFDM)系统载波间干扰(ICI)的方法.首先推导出了加性高斯白噪声(AWGN)信道下的最优符号选择算法,并给出了降低其复杂度的简化算法;然后给出了二进制相移键控(BPSK)调制下减少算法码率损失的改进算法,而且在频率选择性衰落信道下对以上算法进行了推广.仿真结果证实,提出方法的误码率低于基于选择映射的载波间干扰抑制方法.     

滤波器组多载波系统的干扰分析和性能验证

分析了多普勒频偏以及多径时延对滤波器组多载波(FBMC)系统的影响,给出了多普勒频偏以及多径时延造成干扰的闭合定量分析式,该分析式对正交频分复用(OFDM)系统同样适用,并据此对无线多径衰落信道场景中的FBMC系统与传统OFDM系统性能进行了对比.研究结果表明,FBMC系统对多普勒频偏的抵抗性优于OFDM系统,但是系统性能会随信道多径时延的增大而降低.在多径时延相对较小的快衰落信道中,符号间干扰并非影响系统性能的主要因素,FBMC系统可以利用简单的频域均衡获得足够好的性能,仿真结果验证了这一点.     

强多径干扰下的水声通信均衡算法研究

水声信道的典型特点为强多径干扰、多普勒频移严重。锁相环-判决反馈均衡器(Phase-Lock Loop-Decision Feedback Equalization,PLL-DFE)是水声相干通信中克服信道多径干扰,消除码间干扰的主要技术手段。对抗多径干扰的判决反馈均衡自适应算法进行了改进,在快速自优化LMS算法的基础上进行了优化,提出了记忆快速自优化均衡(Memory Fast-Optimized LMS,MFOLMS)算法。该算法提高了均衡器的跟踪性能。在二阶锁相环和判决反馈均衡器的联合作用下,按照最小均方误差(Minimum Mean Square Error,MMSE)准则自动调节相应的参数,使均衡器达到最佳的性能。仿真和湖试数据处理结果均表明,该文提出的算法可以抵消多径的影响,提高通信系统的接收性能。     

多径信道下基于频域均衡的超奈奎斯特传输

针对在多径信道下进行超奈奎斯特(FTN)传输时,同时存在由FTN与多径信道引入的双重符号间干扰(ISI)的问题,提出了应用频域均衡与低密度奇偶校验(LDPC)编码相结合的接收机结构来提高系统传输性能。该接收机构在接收端利用频域均衡器对由FTN与多径信道引入的符号间干扰进行频域均衡,均衡后的信号再通过LDPC信道译码器,利用最大后验概率准则(MAP)进行判决,最终恢复出原始信息。仿真实验显示,基于频域均衡的FTN传输系统可改善系统传输的误码性能。     

基于MMSE滤波的虚子载波梳状导频OFDM系统信道估计

分析了带有虚拟子载波并采用梳状导频的正交频分复用通信系统的信道估计过程中,在使用基于离散傅立叶变换的内插的情况下由于频域导频分布不均匀导致的时域信道响应泄漏的表现形式,针对泄漏造成的信道估计结果不精确的问题,提出了一种基于时域最小均方误差(MMSE)滤波的信道估计补偿方法.该方法通过滤波矩阵的作用补偿了时域信道估计结果...     

一种低复杂度的DFT-S-OFDM系统迭代检测算法

针对LTE上行的单载波频分多址系统--离散傅立叶变换扩频的正交频分复用(DFT-S-OFDM)系统,提出了一种低复杂度的迭代检测实现方法.由于传统方法根据发射机与信道级联系统的等效传输矩阵,完成最小均方误差(MMSE)的迭代检测,但非对角矩阵求逆复杂度较高,因此,所提出的新方法对发送端DFT扩频后的信号先进行单点的MMSE检测,然后根据逆离散傅立叶变换(IDFT)解扩后的后验均值和方差等效得到输出外信息比特似然比.仿真结果表明,所提出迭代检测接收算法的性能与传统方法相近,而其实现复杂度则有较大降低.     

OFDM水声通信线性最小均方误差算法信道均衡

正交频分复用在高速水声通信中的应用越来越广泛.水声信道是多径、高噪声的衰落信道.由于信道条件差,容易产生码间干扰,信道均衡技术是提高通信系统性能的重要技术.提出了线性最小均方估计在水声通信系统中应用的方案,研究了实际通信中利用调频信号如何确定信号的平均多径时延、最大多径时延,比较了不同调频信号测量信道的性能.该方案基于导频辅助均衡方法,利用调频信号测量信道,获得的信道统计信息,计算信道的自相关矩阵.从而根据线性最小均方误差算法进行信道均衡.通过仿真和湖试进行验证,结果表明该方案效果较好,对系统性能改善比较明显.     

低复杂度均衡在水声OFDM通信中的应用

由于水声信道特性，传统的用于消除载波间干扰的均衡器计算复杂，难以实现。本文提出了录用一种降低复杂度的均衡方案，通过预处理将信道矩阵简化，然后采用MMSE准则进行均衡。仿真表明，该均衡器町以有效提高OFDM正交频分多路(Orthogonal frequency division multiplexing)符号的平均载干比(SIR)，且运算量有明显降低。     

一种应用于FM IBOC DAB系统的比特交织编码调制方案

提出了一种适用于FM IBOC广播系统的比特交织编码调制方案。此方案结合互补增信删余卷积码(CPPC)和基于迭代译码的比特交织编码调制(BICM-ID)算法。互补增信删余卷积码能有效抵抗FM IBOC系统中面对的第一邻频干扰和无线信道噪声、衰落等干扰。同时,运用基于软判决反馈迭代译码的比特交织编码调制算法,可以不通过扩展频带来提高FM IBOC广播系统在瑞利信道中的编码增益。仿真结果表明,本方案能有效提高FM IBOC广播系统的接收性能。     

A Capacity Improving Scheme in Multi-RSUs Deployed V2I

The communication reliability and system capacity are two of the key performance indicators for Internet of Vehicles (IoV). Existing studies have proposed a variety of technologies to improve reliability and other performance, such as channel selection and power allocation in Vehicle-to-Infrastructure (V2I). However, these researches are mostly applied in a single roadside unit (RSU) scenario without considering inter-cell interference (ICI) of multi-RSUs. In this paper, considering the distribution characteristics of multi-RSUs deployment and corresponding ICI, we propose a reliable uplink transmission scheme to maximize the total capacity and decrease the interference of multi-RSUs (mRSU-DI) in condition of the uplink interruption performance. In the proposed mRSU-DI scheme, ICI is depressed by dynamic channel and power allocation algorithm. A heuristic algorithm based on penalty function is proposed to obtain the optimal power allocation solution of the model. In addition, we realize the scheme in both given conditions of channel state information (CSI) and channel state distribution, respectively. The results show that the proposed scheme can both improve the system capacity and guarantee the reliable transmission in both premises.     

Magnetic resonance brain tissue classification and volume calculation

This study develops a volume sphering analysis (VSA) approach to tissue classification and volume calculation of multispectral magnetic resonance (MR) brain images. It processes all multispectral MR image slices as an image cube while using only one set of training samples obtained from a single multispectral image slice to perform tissue classification as well as to calculate tissue volumes. In order to make a one slice set of training samples fit for all MR image slices a novel multispectral signature-specified extrapolation algorithm is particularly designed for this purpose so that the selected set of training samples can be extrapolated to create new data samples that are also applicable to other MR image slices. As a consequence, it significantly reduces the tremendous burden on radiologists for selection of training samples as well as computational cost. To further resolve instability and inconsistency issues which may be caused by training sample extrapolation, the proposed VSA also includes a support vector machine to refine training samples and develops an iterative Fisher’s linear discriminant analysis (IFLDA) to make VSA robust and insensitive to new generated training samples so as to improve the traditional slice-by-slice MR image classification. Experimental results demonstrate that VSA in conjunction with IFLDA not only performs comparably to approaches using training samples from individual image slices, but also saves significant time in selecting training samples and computational cost.     

A classical iterative theory based on the Langevin equation for two-dimensional nonlinear terahertz spectroscopy

A classical iterative theory based on the Langevin equation is presented to obtain the nonlinear response of a system and simulate two-dimensional (2D) nonlinear terahertz (THz) spectroscopy (2DTS). Compared with the widely used method of calculating the multi-time correlation function or the Poison brackets, we start from the classical Langevin equation and use an iterative method to obtain any order of nonlinear response. The anharmonic potential (AHP) and nonlinear coordinates dependence of the dipole moment (NDM) are two types of nonlinear sources introduced here. Results are derived for general three-pulse processes with nonlinear sources, AHP or NDM, separately and with the combination of both. Only the simulative 2DTS results for the single mode case with impulsive incident THz fields are presented.     

桥梁动态称重迭代算法的理论与试验研究

桥梁动态称重(bridge weigh-in-motion,BWIM)能够以桥梁作为载体识别过往车辆的轴重。商用BWIM系统通常基于Moses算法,以桥梁的实测影响线对车桥实测动力响应进行轴重识别。然而,该算法的轴重求解方程是病态方程,在特定情况下轴重识别精度偏低。为解决这一问题,该研究提出桥梁动态称重迭代算法,通过Moses算法和实测影响线算法之间的反复迭代,修正病态的轴重求解方程。该研究介绍了桥梁动态称重迭代算法的原理,并进行了相关公式推导;基于怀化舞水五桥引桥的车桥动力试验,对比分析商用BWIM算法和桥梁动态称重迭代算法的轴重识别精度;并深入探讨影响线的选取对轴重识别精度的影响。研究表明,桥梁动态称重迭代算法能够在一定程度上提高轴重识别的精度,其最佳的基准影响线是实测均值影响线。     

DS-UWB接收机双陷波器抑制窄带干扰研究

针对直接扩频序列超宽带(DS-UWB)通信系统中常见的窄带干扰问题, 提出了一种采用陷波技术的窄带干扰抑制新方法.理论分析表明,传统的只使用接收陷波器的窄带干扰抑制方法在滤出窄带干扰信号的同时,也导致了有用信号和模板信号相关函数峰值的损失,劣化了系统误码性能,而该方法同时对接收信号和模板信号进行相同的陷波处理可补偿这种损失,提高系统性能.对DS-UWB接收机的仿真结果表明,当信干比(SIR)为-20dB时,采用该方法后误码率(BER)曲线与没有干扰时的曲线基本重合;当Eb/n0=8dB时,对应BER＝1E-3,该方法较没有陷波器时抗窄带干扰能力提高了26dB;较只有接收陷波器时提高了17dB.以上结果说明该方法是DS-UWB接收机窄带干扰抑制的有效方法.     

超宽带对塔康系统的干扰分析

针对超宽带(UWB)对窄带无线通信系统的潜在干扰分析,使用基于物理层模型的方法分析了脉冲无线电(IR)和多带(MB)等不同技术体制的超宽带系统对塔康(TACAN)系统的影响.在充分考虑了系统的物理特性的情况下, 利用Matlab的可视化仿真工具Simulink建立系统的物理层仿真模型, 根据塔康系统误码率(BER)和接收机灵敏度的要求, 得出了超宽带在塔康系统工作频段(962～1213MHz)的发射功率限制参考值.通过与基于干噪比(I/N)的链路预算干扰分析方法的比较分析,本文的方法更能反映实际系统的影响状况,因此这个结果能够为规划超宽带在塔康系统工作频段的频谱提供参考.     

Efficient Algorithms for Cache-Throughput Analysis in Cellular-D2D 5G Networks

In this paper, we propose a two-tiered segment-based Device-to-Device (S-D2D) caching approach to decrease the startup and playback delay experienced by Video-on-Demand (VoD) users in a cellular network. In the S-D2D caching approach cache space of each mobile device is divided into two cache-blocks. The first cache-block reserve for caching and delivering the beginning portion of the most popular video files and the second cache-block caches the latter portion of the requested video files ‘fully or partially’ depending on the users’ video watching behaviour and popularity of videos. In this approach before caching, video is divided and grouped in a sequence of fixed-sized fragments called segments. To control the admission to both cache-blocks and improve the system throughput, we further propose and evaluate three cache admission control algorithms. We also propose a video segment access protocol to elaborate on how to cache and share the video segments in a segmentation based D2D caching architecture. We formulate an optimisation problem and find the optimal cache probability and beginning-segment size that maximise the cache-throughput probability of beginning-segments. To solve the non-convex cache-throughout maximisation problem, we derive an iterative algorithm, where the optimal solution is derived in each step. We used extensive simulations to evaluate the performance of our proposed S-D2D caching system.