低轨卫星信道自适应模糊估计算法

针对功率控制,提出一种利用模糊规则的自适应LMS信道估计算法,通过将信道增益大小和前后变化值的大小划分为若干模糊集,建立将自适应算法和经验值相结合的自适应滤波器,使算法具有对低轨信道时变特性一定的适应性。仿真结果表明了算法的有效性。     

一个新的分散定步长功率控制算法

功率控制是CDMA蜂窝移动通信系统的关键技术之一。该文考虑CDMA蜂窝移动系统,在假设系统信道增益时变、有界的情形下,把一个时变系统功率控制问题转化为具有确定信道增益功率控制问题。提出了一个分散定步长反馈调节功率控制算法,并证明了算法的收敛性。仿真结果表明算法是可行的。     

OFDM系统自适应盲信道估计新方法

基于无线通信OFDM系统信道估计,提出了两种时域自适应盲估计方法。这些方法通过对极性(符号)LMS算法（SLMS）进行改进,改进算法有几方面优点,一是继承了极性LMS算法简单易实现的特性;二是解决了极性LMS收敛速度慢的缺点;最后结合自适应可变步长及步长调整策略,有效地提高了算法的估计性能。仿真给出了误差曲线以及归一化均方误差曲线,结果表明,和基于极性LMS盲估计方法相比,修正极性LMS和时变步长修正极性LMS盲估计方法均具有很快的收敛速度。由于采用了变步长技术,时变步长修正极性LMS盲估计方法具有更好的估计性能。      

OFDM调制技术在低压电力线的自适应控制

通过改进传统LMS算法,提出了一种模糊推理的变步长自适应算法。该算法结合模糊推理对LMS算法的步长增益进行了改进,通过模糊推理把输入变量映射为合适的步长增益,从而提高了对信道估计值的精度。通过误差绝对值与均方误差值的比较,表明该算法所测得的信道值比传统的LMS算法信道值更接近真实值,说明该算法具有良好的估计性能。     

一种快速时变自适应信道估计盲方法

提出了一种新的信道估计最小均方(LMS)盲方法--时变步长理想加权判决信道估计盲方法.该方法通过对常规LMS算法进行改进,实现自适应跟踪信道特征变化;同时利用接收机判决误差信息函数作为权系数的理想加权判决,从而解决了常规LMS盲方法收敛速度慢、信道估计性能不高的缺点.仿真证明,对于不同的多普勒频移、时延扩展以及时间,该方法均表现出了比常规LMS方法更优的性能.同时,该方法还可用于航天、雷达等领域估计其他特征参数.     

基于DMB—T标准的数字电视回波抵消技术的研究

以数字电视地面广播国家标准--DMB-T标准为背景,在介绍直放站中回波产生的原因和影响后,设计了回波抵消方案.首先在原有的数字电视信号中添加低功率的PN码,然后采用变换域LMS算法对信道进行估计,利用信道估计的结果生成一路反馈信号,来逼近回波干扰信号,最后从接收信号中除去该反馈信号,最终实现回波抵消的目的.变换域LMS算法通过对输入信号进行预白化处理,来保证能够获得比LMS算法更好的收敛速度.仿真结果表明,该方法具有良好的回波消除性能.     

基于嵌入训练阵列的OTFS信道估计

正交时频空（Orthogonal Time Frequency Space,OTFS）调制在快时变高多普勒信道中展现出良好的频谱利用率和显著的误码率性能优势。然而,传统的OTFS信道估计方法频谱效率较低,且无法应用于低轨卫星等具有高多普勒频偏的通信场景中。文章提出了基于嵌入训练（Training Embedded,TE）阵列的信道估计方法,利用训练阵列的完美自相关特性进行准确的信道估计,并提高了频谱效率。同时,针对低轨卫星通信高多普勒频偏的特性,本文利用快速傅里叶变换对路径的整数倍频偏进行估计,补偿并消除列相关相位偏移干扰,提升了低轨卫星通信场景下信道估计的准确度。仿真结果表明,所提方法在地面、低轨通信场景中均具有较高信道估计精度和频谱效率。     

直扩系统时变单音干扰抑制的新方法

针对直接序列扩频通信系统中的时变单音干扰,提出了一种频域干扰估计时域对消的新方法。在系统中,将干扰信道建模为时变衰落信道。该算法首先在频域对时变单音干扰信号参数进行估计,然后对时变单音干扰进行重构和对消,推导了理论误码率公式。理论分析和仿真结果表明,该算法性能由干扰功率和多普勒频移等因素决定。在频率选择性衰落信道下,当信噪比为20dB,扩频增益为16,干扰信道多普勒频移为100Hz时,该算法可以抑制20dB(干信比)的单音干扰。      

特征参数自适应盲估计方法

 基于无线移动通信OFDM系统信道估计,提出了三种时域自适应特征参数估计最小均方盲方法——时变步长最小均方法(tvcpblms)、时变步长软判决最小均方法(tvcpsdwlms)、时变步长理想判决最小均方法(tvcpidwlms).这些方法通过对常规LMS算法步长进行自适应的科学设计以便跟踪特征参数变化,从而解决了常规LMS盲方法收敛速度慢、估计性能不高等缺点.仿真证明:对于不同的时延扩展、时间以及多普勒频移,这些方法均表现出了比常规方法更优的估计性能.同时,这些方法不仅可以估计无线移动通信系统信道特征参数,而且还可用于雷达、航天等多种领域估计其他特征参数.     

结构性稀疏阵列多信道联合估计

多信道估计时,如果利用信道的稀疏性和多信道的相关性,可以提高信道估计性能。本文利用阵列信道的结构性稀疏特性,提出了一种多路分组稀疏LMS算法(Group Sparse LMS,GS-LMS)。该算法将多路信道作为一个整体同时进行自适应信道估计,通过引入Ι_2,1范数,将结构性稀疏先验引入到稀疏LMS算法的代价函数中,导出新的滤波器权系数更新公式。仿真结果表明了在不同信道条件下,本文算法的稳态误差性能明显优于若干现有的稀疏LMS算法。      

基于OFDM低压电力线通信的信道估计算法研究

根据工作实验的分析,对低压电力线通信信道模型和信道特性进行了详尽的阐述,对当前应用广泛的几种低压电力线通信信道模型进行了介绍,详细分析了几种基于OFDM低压电力线通信的信道估计算法。同时对多种算法实施比较,分析总结出各自的优缺点,最终得出一种不仅运算量小,而且对信道的利用率很高、实现十分容易的算法。即:基于慢时变信道特性的LMS自适应信道估计算法在信道突变衰减中具有非常高的稳定度特性,非常适合在低压电力线信道中应用。     

Optimum Transmitter/Receiver Design for a Narrowband Overlay in Noncoordinated Subscriber Lines

Analytical Performance of the LMS Algorithm on the Estimation of Wide Sense Stationary Channels The performance of the least mean square (LMS) algorithm on the estimation of time-varying channels is analytically evaluated, using the estimation error-correlation matrix, the mean-square weight error (MSWE), and the mean-square estimation error (MSE) as parameters. Expressions for those parameters are obtained from a set of hypotheses usually adopted in the communication systems context. The channel is modeled as a wide sense stationary (WSS) discrete-time stochastic field with known autocorrelation. The expressions for the steady-state MSWE and MSE are specialized for the class of WSS channel models, and an original analysis of the optimum LMS step-size parameter for usual channel models is addressed. For the sake of comparison with other works, the analytical step-size optimization for random-walk models is also considered. Several estimates of MSWE curves obtained by computer simulation are compared with analytical results for validation purposes. A very good agreement between simulated and analytical results for both the MSWE expressions and the optimum value of the LMS step-size parameter is shown.     

Analytical performance of the LMS algorithm on the estimation of wide sense stationary channels

The performance of the least mean square (LMS) algorithm on the estimation of time-varying channels is analytically evaluated, using the estimation error correlation matrix, the mean-square weight error (MSWE) and the mean-square estimation error (MSE) as parameters. Expressions for those parameters are obtained from a set of hypotheses usually adopted in the communication systems context. The channel is modeled as a wide sense stationary (WSS) discrete time stochastic field with known autocorrelation. The expressions for the steady-state MSWE and MSE are particularized for the class of WSS channel models, and an original analysis of the optimum LMS step-size parameter for usual channel models is addressed. For the sake of comparison with other works, the analytical step-size optimization for random-walk models is also considered. Several estimates of MSWE curves obtained by computer simulation are compared with analytical results for validation purposes. A very good agreement between simulated and analytical results for both the MSWE expressions and the optimum value of the LMS step-size parameter is shown.     

基于叠加训练序列和低复杂度频域Turbo均衡的时变水声信道估计和均衡

针对时变水声信道估计和均衡问题,该文提出基于叠加训练序列(ST)和低复杂度频域Turbo均衡(LTE)的时变水声信道估计和均衡(ST-LTE)算法。基于叠加训练序列方案,将训练序列和符号线性叠加,使得训练序列和符号信道信息一致;基于最小二乘算法,进行信道估计。基于频域训练序列干扰消除技术,在频域消除训练序列对符号的干扰;基于频域线性最小均方误差(LMMSE)均衡算法,通过先验、后验、外均值和方差的计算,实现低复杂度信道均衡(符号估计);基于Turbo均衡算法,软重构叠加训练序列和更新信道估计,进行均衡器和译码器的信息交换,利用编码冗余信息,大幅度提升信道均衡性能。进行仿真、水池静态通信试验(通信频率12 kHz,带宽6 kHz,采样频率96 kHz,符号传输速率4.8 ksym/s,训练序列和符号的功率比为0.25:1)和胶州湾运动通信试验(通信频率12 kHz,带宽6 kHz,采样频率96 kHz,符号传输速率3 ksym/s,训练序列和符号的功率比为0.25:1),仿真和试验结果验证了所提算法的有效性。     

可重构全息超表面辅助卫星通信关键技术

超密集低地球轨道卫星通信网络能弥补传统地面网络频谱资源稀缺、覆盖范围有限的不足,有潜力提供全球大规模接入的高速率服务。由于卫星的高速移动性,卫星通信对天线性能,如波束控制能力和天线增益等,也提出了更为严苛的要求。因此,对一种新型的超材料天线——可重构全息超表面（reconfigurable holographic surface,RHS）辅助卫星通信展开了研究。RHS采用全息原理对超材料单元进行电控,从而实现波束成形。基于 RHS 的硬件结构和全息工作原理,提出了一种 RHS 辅助多卫星通信方案,该方案同时考虑卫星跟踪和数据传输。同时,设计了全息波束成形优化算法以最大化和速率。仿真结果验证了所提方案的有效性并表明了相较于传统相控阵天线,RHS提供了一种成本效益更高的卫星通信支持方式。     

Evaluation of handover mechanisms in shadowed low earth orbit land mobile satellite systems

This paper presents a quantitative analysis by computer simulation of the active set update (ASU) handover algorithm for a shadowed low earth orbit (LEO) land mobile satellite (LMS) environment. As a precursor to the handover analysis, the mutual visibility statistics for a 66 satellite polar and 48 satellite rosette-type constellation are presented. These results show the statistical nature of the levels of satellite diversity and mobile-to-satellite elevation angles (to the highest satellite) within each network and also indicate the influence of the channel characteristics on the handover strategy. A two-state Markov modulated channel model is assumed in the handover analysis, and this enables the assessment of increased levels of power and time hysteresis on the quality of service and network signalling load in a shadowed land mobile satellite environment. In particular, attention is given to the different modes of ASU operation for hard handover, switch diversity and soft handover.     

多场景卫星通信信道动态建模与仿真实现

面向智慧海洋、智慧农业等垂直行业场景的广覆盖无线接入需求,低轨卫星通信因其可靠的连接性、更宽广的覆盖能力以及超大带宽连接的巨大潜力而成为了下一代移动通信技术的重要组成部分.目前,针对低轨卫星通信的系统性信道建模流程与仿真方法仍相对匮乏,对于低轨卫星信道的高动态特性仍缺乏有效的建模方法,且大多模型仅能支持单场景通信环境.基于此,本文提出了一种模块化、高动态的多场景卫星通信信道建模机制,并据此设计实现了一套动态卫星信道建模仿真系统.该系统实现了流程化的建模思路,并引入了基于卫星信道高动态特性的动态参数更新方法.所设计的卫星通信信道建模与仿真机制能够生成卫星通信的信道大、小尺度参数与信道冲激响应,且对不同场景具有较好的适用性.     

Study on application of CMA to land mobile LEO satellite communication systems based on a deterministic channel model

This paper studies the application of the constant modulus algorithm (CMA) in land mobile low earth orbit (LEO) satellite communication systems. Two propagation phenomena prevail in narrow band land mobile LEO satellite channel, namely, adjacent channel interference (ACI) and frequency‐non‐selective fading. The performance of CMA for ACI cancellation and the behaviours of CMA in frequency‐non‐selective fading channels are evaluated using a digital beamforming (DBF) array antenna simulation scheme. All these evaluations are based on a simple but efficient channel model which provides a good and fast simulation method for land mobile LEO satellite channels. The restricted Jakes Doppler power spectral density (psd) function is incorporated into the model to ensure that it will be appropriate for the evaluation of a DBF antenna. Our results reveal that CMA can reject ACI and work well in frequency‐non‐selective fading channels. Copyright © 2002 John Wiley & Sons, Ltd.     

A channel estimation using sliding window approach and tuningalgorithm for MLSE

A simultaneous sliding window channel estimation and timing adjustment method is proposed for adaptive maximum-likelihood sequence equalizer (MLSE) in the global system for mobile communication (GSM) system, and also a tuning scheme based on least mean squared (LMS) algorithm is presented in order to improve the performance of equalizer. Simulation results show that the proposed channel estimation technique is effective for channel estimation of the adaptive equalizer