基于Kronecker积的无线通信系统参量分离方法

针对无线通信系统中发射机非线性与多径衰落信道问题,提出了一种根据接收无线信号联合估计无线设备功率放大器(PA)非线性与无线信道单位脉冲响应的方法.首先,根据通信帧训练符号及发射机非线性模型构造卷积矩阵;接着,采用一次最小二乘(LS),根据接收信号估计PA的非线性模型系数与实际发送符号;然后,再采用一次LS,得到无线信道的单位脉冲响应估计;两估计可迭代或直接加取平均进行积累.理论推导与实验结果显示,采用过采样技术,所提方法可应用于单载波或多载波通信,实现PA非线性与无线信道单位脉冲响应的有效分离.新方法在无线通信的物理层射频指纹认证与信号可靠传输中具有应用价值.     

基于Vogler模型的短波OFDM性能仿真

OFDM(正交多载波调制)是一种在无线环境下具有较高频谱利用率的多载波调制技术,它具有较强的对抗多径干扰和消除符号间干扰的能力.基于Vogler模型出发,根据实测的短波信道参数数据进行了OFDM系统仿真,同时,用导频辅助的方法对信道进行估计,并进行信道补偿,克服了短波信道的多径衰落和多普勒频移等因素的影响,有效降低了系统的误码率,提高了整个系统的性能.     

发射分集0FDM系统中基于离散导频的信道估计方法

OFDM技术、空时编码和分集技术的联合可以实现无线数据的高速可靠传输.传统的多天线系统中利用训练序列来实现信道估计.本文给出了一种采用空时编码的发射分集OFDM系统中基于离散导频的信道估计方法,它可以进一步提高系统效率.仿真结果证明该算法具有很好估计性能和鲁棒性.     

正交频分复用系统中的频域插入导频算法

OFDM(正交频分复用)技术是第三代、第四代移动通信的关键技术之一,而移动信道是极为复杂的一种信道,信号通过无线信道时,会遭受各种衰落的影响,信道估计技术就是使得信道对输入信号的影响减至最小化的估计算法.在介绍了OFDM系统相干检测下信道估计方法的基础上,着重讨论和仿真了利用导频插入的方式对OFDM系统进行信道估计的算法.     

一种结合空时编码的导频辅助信道估计方法

多输入多输出-正交频分复用(MIMO-OFDM)作为一种高速率无线通信的有效方式,其信道估计技术具有非常重要的位置。将OFDM技术与基于发射分集的空时格码相结合,构造了一个基于空时格码的OFDM模型。基于MIMO-OFDM系统的导频设计准则及特性,提出了一种空时编码OFDM系统中基于导频的辅助信道估计方法。仿真实验结果表明信道估计的性能接近理想信道情况下的性能。     

一种时频变换OFDM系统的信道估计模型

在OFDM系统中,无线信道的准确估计很大程度上决定了系统的传输性能,提出了一种时频变换信道估计模型,并将它应用于自适应OFDM系统中的信道估计,通过与理想自适应系统相比较,研究了模型的性能以及信道估计的误差对于系统性能的影响。     

OFDM系统基于信道多径时延检测的自适应信道估计

针对宽带正交频分复用(OFDM)系统,提出了一种基于信道多径时延估计的自适应信道估计算法.文章分析了无线信道的特性,随后利用导频频域相关性进行多径时延估计,提出通过动态跟踪信道时延估计参数自适应选择信道估计中适宜的导频数目的方法,同时实现循环前缀(CP)长度的实时调整.仿真结果表明,在时变环境下,本文算法可以有效获知当前信道时延参数的近似统计信息,实现对系统冗余信息的优化.     

CO-OFDM传输系统相位噪声估计

从理论上分析了激光器相位偏移对相干光正交频分复用(CO-OFDM)系统传输性能影响,并指出相位噪声是相干光OFDM主要噪声源。在传统无线OFDM信道估计基础上,提出了一种基于导频子载波的相位噪声估计和补偿方法,在OptiSystem中建立CO-OFDM系统仿真模型,通过仿真证明了该方法可以有效地改善CO-OFDM系统传输性能。     

OFDM-ROF系统中抗非线性方法浅析

未来通信的发展方向将是光通信与无线通信的结合.OFDM光载无线(OFDM-ROF)将无线通信和光纤通信的优点结合起来,具有高速率、高容量和高带宽利用率的优点.非线性是OFDM-ROF系统存在的主要问题之一,降低非线性对系统影响的主要方法有降低峰值功率比(PAPR)、加循环前缀、信道估计、非线性补偿等.     

OFDM移动通信信道估计与仿真

正交频分复用技术（OFDM）可以在条件恶劣信道环境中进行高速数据传播。OFDM是一种多载波传输系统．相对于单载波传输系统具有很多有利条件。移动信号在无线信道中传输时会产生多径时延和多普勒频移,为正确接收信号需要对信遘作出估计并进行补偿。本文重点分析了信道分析与补偿的方法,对信号时域和频域的信道补偿进行详细论述,构建系统进行仿真分析,仿真结果符合理论分析。     

Decoupled compensation of IQ imbalance in MIMO OFDM systems

The direct-conversion architecture is an attractive front-end design for multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. These systems are typically small in size and provide a good flexibility to support growing number of wireless standards. However, direct-conversion based OFDM systems are generally very sensitive to front-end component imperfections. These imperfections are unavoidable especially when cheaper components are used in the manufacturing process and can lead to radio frequency (RF) impairments such as in-phase/quadrature-phase (IQ) imbalance. These RF impairments can result in a severe performance degradation. In this paper, we propose training based efficient compensation schemes for MIMO OFDM systems impaired with transmitter and receiver frequency selective IQ imbalance. The proposed schemes can decouple the compensation of the transmitter and receiver IQ imbalance from the compensation of the channel distortion. It is shown that the proposed schemes result in an overall lower training overhead and a lower computational requirement as compared to a joint estimation/compensation of IQ imbalance and the channel distortion.     

Performance Analysis of UWB Channels for Wireless Personal Area Networks

Ultra-wide band (UWB) communication is one of the most promising technology for high data rate networks over short-range communication. The ultra-wide bandwidth offers pulses with very short duration that provides frequency diversity and multipath resolution. Ultra-wide band (UWB) channels raise new effects in the receiver, the amplitude fading statistics being different compared to the conventional narrow band wireless channels. This review paper focuses on modeling of ultra-wide band channels, especially for simulation of personal area networks and also discusses the benefits, application potential and technical challenges in wideband communication. The concept of Orthogonal Frequency Division Multiplexing (OFDM) has recently been applied in wireless communication systems due to its high data rate transmission capability with high bandwidth efficiency and its robustness to multi-path delay. UWB OFDM communication was proposed for physical layer in the IEEE 802.15.3a standard which covers wideband communication in wireless personal area networks. Since the channel model for multicarrier UWB communication is different from that of plain ultra-wide band channel, a novel modification method in UWB channel model is proposed with specific center frequency and multipath resolution. Moreover, dynamic channel estimation is necessary before demodulation of UWB OFDM signals since the radio channel is time varying and frequency selective for wideband systems. The performance of the proposed method is statistically analyzed using LS and MMSE based channel estimation methods.     

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.     

A low complexity DFT-matrix based pilot allocation algorithm for sparse channel estimation in OFDM systems

The accuracy of channel estimation is very important for Orthogonal Frequency Division Multiplexing (OFDM) systems. In a high speed wideband wireless communication, the channel can be modeled as a sparse one. Therefore, the Compressed Sensing (CS) technique can be used for the estimation of the channel. In this paper, the problem of deterministic pilot allocation in OFDM systems is considered and a new criterion which is based on minimizing the summation of the correlations between the columns of the Discrete Fourier Transform (DFT) sub-matrix is proposed. It will be shown that the proposed criterion is a simple version of the well-known but complex criterion, Restricted Isometry Property (RIP). In addition, the pilot pattern design, using our proposed scheme, indicates better recovery performance than other proposed coherence based criteria in terms of the reconstruction mean square error (MSE) and successful channel recovery percentage. Simulation results confirm our analysis.     

不理想的信道互易性对波束成形技术的影响…

在无线通信系统中,基站可以根据信道互易性使用波束成形(Beam Forming)技术提升系统性能。信道互易性的准确程度对性能是有影响的,因此需要对其分析以指导系统设计。对长期演进(LTE)系统的互易性进行建模,指出了终端发送天线和接收天线数目的不对称性,以及基站信道估计的误差对信道互易性的影响。通过数值仿真验证了不理想的信道互易性使波束成形性能受到损失,并为系统改进提出思路。其结论容易推广到其他应用波束成形的无线通信系统。     

Estimation of time-varying channels for pilot-assisted OFDM systems

Orthogonal frequency division multiplexing (OFDM) systems encounter performance degradations because of the time-varying (TV) channels common in wireless environments. The channel variations within one OFDM symbol introduce intercarrier interference. In this case, the frequency domain channel matrix is no longer diagonal, hence the corresponding channel estimation is challenging. In this article, two novel TV channel estimation approaches are proposed for the pilot-assisted OFDM systems, where the channel is approximated by the high-order linear model or the piece-wise linear model in time domain. The least square estimation is derived for the two kinds of channel approximations. The simulation is performed based on realistic TV channels with a fairly high Doppler spread. The results show the significant decreasing of the estimation mean square error using the proposed approaches.     

一种改进的MIMO OFDM系统信道估计算法

本文对MIMO OFDM系统中基于训练序列的信道估计问题进行了研究，针对信道冲击响应的最大抽头数大于每个OFDM符号中导频数的情况，提出一种有效的结合前后若干训练序列进行信道估计的算法和结合方式。仿真结果表明，在基于无线局域网（WLAN）中打包传送的MIMO OFDM系统里，本文的方法比采用块状训练序列的估计算法有着更小的归一化均方误差。     

AoA-Based Channel Estimation for Massive MIMO OFDM Communication Systems on High Speed Rails

Channel estimation is a well-known challenge for wireless orthogonal frequency division multiplexing(OFDM)communication systems with massive antennas on high speed rails(HSRs).This paper investigates this problem and design two practicable uplink and downlink channel estimators for orthogonal frequency division multiplexing(OFDM)communication systems with massive antenna arrays at base station on HSRs.Specifically,we first use pilots to estimate the initial angle of arrival(AoA)and channel gain information of each uplink path through discrete Fourier transform(DFT),and then refine the estimates via the angle rotation technique and suggested pilot design.Based on the uplink angel estimation,we design a new downlink channel estimator for frequency division duplexing(FDD)systems.Additionally,we derive the Cramér-Rao lower bounds(CRLBs)of the AoA and channel gain estimates.Finally,numerical results are provided to corroborate our proposed studies.