基于能量收集的OFDM符号精同步算法

针对OFDM(正交频分复用)符号粗同步定时点会随路径能量变动的缺点,利用信道估计得出的信道脉冲响应,提出一种基于能量收集的精同步算法,不需设定判决门限,得到的最终定时点能有效避免ISI(符号间干扰)和ICI(信道间干扰)的引入.多径信道中的仿真验证了该算法的良好性能.     

基于电力线信道的OFDM盲同步算法

在Takahashi提出的盲同步算法的基础上,提出了一种OFDM多符号联合的差分盲同步算法。同Takahashi的算法一样,该算法利用OFDM符号的循环前缀内不被多径时延扩展所影响的那部分码元提取定时信息,但是为了避免电力线信道中随机的脉冲噪声对符号同步产生的影响,在每个定时时刻,取差值的前后移动平均,并采用多个OFDM符号的联合,以增强同步效果。仿真结果表明,在第一径为最强径或是非最强径的电力线多径衰落信道中,该算法取得了很好的符号同步效果。     

基于电力线信道的OFDM盲同步算法

在Takahashi提出的盲同步算法的基础上,提出了一种正交频分复用（OFDM）多符号联合的差分盲同步算法。同Takahashi的算法一样,该算法利用OFDM符号的循环前缀内不被多径时延扩展所影响的那部分码元提取定时信息,但是为了避免电力线信道中随机的脉冲噪声对符号同步产生的影响,在每个定时时刻,取差值的前后移动平均,并采用多个OFDM符号的联合,以增强同步效果。仿真结果表明,在第一径为最强径或是非最强径的电力线多径衰落信道中,该算法取得了更好的符号同步性能。     

基于Zadoff-Chu序列的OFDM精确定时同步算法

针对OFDM系统在多径衰落环境下通过能量大小定时而产生定时误差的问题,文中提出了一种基于Zadoff-Chu序列的第一径检测算法,利用序列相关性得到信道冲激响应估计值,此外分析了残留频偏对定时同步的影响,并通过改进自适应门限抑制残留频偏来判定准确定时位置。算法在时域完成,实现简单且运算量小。通过仿真对比其他算法可以看出,文中所提算法在高速移动多径环境中第一径检测概率高、均方误差小,特别是低信噪比下仍能准确同步。     

复杂多径环境下的OFDM定时同步改进算法

现有的定时同步算法在第一根径不是最强径的多径信道条件下,易将定时同步位置定在最强径上,而偏移第一根径,导致严重的ISI.文中在基于PN序列的定时同步算法的基础上提出新的算法,进一步引入"和值"计算.仿真结果验证了新算法的正确性,同时表明新算法也同样适用于第一根径是最强径的情况,因而可以广泛适用于多径信道.     

自适应判决门限在超宽带系统中的应用

主要介绍了在超宽带系统中自适应判决门限应用。由于多径信道的影响,超宽带系统相干接收后的最佳判决门限是应随信道时变的。通过判决门限受信道冲击响应影响的分析,提出了根据信道估计结果或直接在信号中加入训练序列脉冲两种得到最佳判决门限的方法,并进行了仿真分析。这两种方法均具有很大的实际应用价值。     

LTE系统时频同步算法及其DSP实现

介绍了LTE—FDD系统主同步序列的产生,给出了一种基于主同步信道的时频同步算法,包括符号定时同步算法和频偏估计算法。定时同步算法引入了多径能量窗,并且根据LTE系统同步信道的特点,对多个同步信道上的相关值进行非相干合并,有效地提高了同步性能。对所给出的算法进行仿真,并采用DSP实现同步算法。仿真和实验结果表明,所给出的算法具有良好的性能,能够满足LTE系统对同步性能的要求。     

多径信道下的OFDM定时同步检测方法

针对多径信道下传统定时同步方法性能较差的问题,提出一种基于2段重复结构前导的OFDM定时同步检测方法。利用一种基于差分相关的定时估计算法获取OFDM接收信号的定时度量,并根据所设计的检测性能评估方法设置满足系统检测概率与虚警概率要求的检测门限,对定时度量的具有2个脉冲峰值进行门限检测获得定时同步。结果表明,在多径信道下,所提出的检测方法通过联合仿真与分析能够准确地评估与设置OFDM定时同步的检测性能与门限,并且具有较低的计算复杂度。     

一种改进的短波高速串行信号检测算法

文章对短波高速串行信号的相关检测进行分析.首先分析了固定门限判决和自适应门限判决,在此基础上综合二者提出固定门限与自适应门限相结合的混合门限判决方法.经过仿真实验表明,该混合门限算法综合了固定门限与自适应门限的优点,在短波信道下低信噪比时综合性能有较大改善.     

多径信道下TD-LTE系统中定时同步算法的研究

多径传播是无线信道所固有的特性,信道时延的存在将会导致符号间干扰(ISI),严重影响接收端信号的解调.本文重点研究了多径信道下TD-LTE系统中的定时同步模块,并对基于循环前缀(CP)的能量差分算法加以改进,联合主同步信号(PSS)精确估计定时同步位置.仿真结果表明,该算法在多径衰落信道下能获得较好的定时同步性能,即使在信道时延较大的情况下也能够稳定地工作.     

Performance based on selective multipath reception

As wireless data rate requirements increase, multipath delay spread becomes an increasingly significant limitation on the performance of wireless systems. Techniques such as RAKE reception combat time dispersion by combining multipath components. Alternative implementations of RAKE receivers isolate the strongest multipath components and then shift each component to a common timing reference. The optimal timing reference in frequency-selective fading channels remains an open problem. This paper examines the impact pulse shaping and multipath delay spread on both signal-to-noise ratio (SNR) and bit-error rate performance. The receiver being considered achieves symbol synchronization to the strongest multipath component. The performance when synchronization is achieved based on the first multipath component arrival is also found and used to illustrate performance differences. Multipath delay distributions used on the performance calculations are derived from indoor measurements. Pulse shapes considered in the analysis include root-raised cosine, raised cosine, and Gaussian filters. SNR losses are shown to range between 1-6 dB for bit rates of 10 Mb/s. Results show that synchronization of the receiver to the strongest multipath component gives a 1-3 dB advantage over synchronization to the first arriving multipath component.     

A robust timing and frequency synchronization for OFDM systems

A robust symbol-timing and carrier-frequency synchronization scheme applicable to orthogonal frequency-division-multiplexing systems is presented. The proposed method is based on a training symbol specifically designed to have a steep rolloff timing metric. The proposed timing metric also provides a robust sync detection capability. Both time domain training and frequency domain (FD) training are investigated. For FD training, maintaining a low peak-to-average power ratio of the training symbol was taken into consideration. The channel estimation scheme based on the designed training symbol was also incorporated in the system in order to give both fine-timing and frequency-offset estimates. For fine frequency estimation, two approaches are presented. The first one is based on the suppression of the interference introduced in the frequency estimation process by the training symbol pattern in the context of multipath dispersive channels. The second one is based on the maximum likelihood principle and does not suffer from any interference. A new performance measure is introduced for timing estimation, which is based on the plot of signal to timing-error-induced average interference power ratio against the timing estimate shift. A simple approach for finding the optimal setting of the timing estimator is presented. Finally, the sync detection, timing estimation, frequency estimation, and bit-error-rate performance of the proposed method are presented in a multipath Rayleigh fading channel.     

Fast Synchronization and Channel Estimation for OFDM Systems

A joint synchronization and channel estimation scheme is proposed for orthogonal frequency division multiplexing (OFDM) system. In the proposed scheme, the integer frequency offset, fine timing offset and channel estimation are estimated based on the characteristics of the chirp signals. The main contributions of the paper are: the more robust ability to find the actual first path instead of the strongest path on the assumption of repeated chirp waveforms in the timing synchronization approach, and the lower computational complexity with high performance in the channel estimation approach. Moreover, we analyze the performance of the proposed method and check it via Monte Carlo simulations. The simulation results show that the proposed method can achieve good performance for both synchronization and channel estimation in frequency selective channels.     

战术自组网下非平稳信道测量与建模

为研究城市战场环境下战术自组织网络（tactical mobile ad hoc network,TacMAN）通信节点间的信道特性,针对城区场景超短波频段展开信道测量与建模。测量结果表明,TacMAN通信场景下,多径信号存在明显的非平稳性和生灭现象。针对信道非平稳性,首先设计了一种多径识别与跟踪算法,有效地估计出多径信号的存在概率。其次,使用基于马尔科夫链的改进型抽头延迟线（tapped delay line,TDL）模型对实测数据的非平稳过程进行建模。最后基于赤池信息准则（akaike information criterion,AIC）给出了小尺度衰落的统计模型,分析表明双高斯混合分布（bimodal Gaussian mixture distribution,BGMD）和Ricean分布分别是描述模型首径与最强径幅度分布的最佳模型。论文建立的非平稳信道模型可以较好地描述TacMAN场景下信道特性,为提高相关军事通信场景下通信系统的性能提供参考。     

基于门限判决的OFDM时间同步算法

在基于共轭对称序列前导的正交频分复用（OFDM）系统中,定时函数解决了峰值平台和重复共轭对称序列引入的副峰值问题。但由于循环前缀的存在以及共轭对称序列的特殊结构,定时函数仍存在另一个副峰值。为消除该副峰值的影响,采用了改进的定时度量函数以及区间门限判决捕获算法。理论分析以及在多径信道下的仿真表明,改进算法不受循环前缀长度的影响,时间同步准确率高于已有算法。