MlMO-OFDM系统中基于DFT迭代的导频信道估计的优化方法

从整个系统设计的角度出发，根据最小化MSE（Mean Square Error）准则，推导出一种MIMO-OFDM（Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing）系统中优化的导频值插入方法，并提出一种基于DFT迭代的信道估计算法。与已有的IEEE802.16提出的导频交替传输方法相比，这种优化的导频值能均匀分布于各发射天线所有发射时段，尤其在时变信道中，具有更小的估计误差；在信道估计方法中，提出的基于改进的DFT迭代算法的优化方法，通过仿真，表明这种方法能够更进一步地提高估计的精度。     

MIMO-OFDM系统中基于DFT迭代的导频信道估计的优化方法

从整个系统设计的角度出发,根据最小化MSE(Mean Square Error)准则,推导出一种MIMO-OFDM(Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing)系统中优化的导频值插入方法,并提出一种基于DFT迭代的信道估计算法。与已有的IEEE802.16提出的导频交替传输方法相比,这种优化的导频值能均匀分布于各发射天线所有发射时段,尤其在时变信道中,具有更小的估计误差;在信道估计方法中,提出的基于改进的DFT迭代算法的优化方法,通过仿真,表明这种方法能够更进一步地提高估计的精度。     

基于STBC-SCFDE系统的信道估计算法研究

针对频率选择性衰落信道下2发射天线的空时分组编码-单载波频域均衡(STBC-SCFDE)系统,分别设计了2种新颖的时域多天线导频序列和频域多天线导频序列,相应地提出了一种时域导频信道估计算法和一种频域导频信道估计算法,并分别进行了信道估计的MSE性能分析以及计算复杂度对比.仿真验证表明,相比传统经典多天线信道估计算法,所提2种信道算法在中低信噪比下均能实现良好的信道估计性能,为未来无线通信系统的信道估计开辟了新的解决途径.     

基于天线相关性的信道估计方法

在3D-MIMO系统中,基站端部署的天线数量会大量增加;如果继续按照以往的信道估计方法为每一根发射天线都配置导频,则会带来极大的导频开销问题,导致大量的资源消耗;因此,如何在减少导频开销的前提下完成信道估计就成为3D MIMO系统面临的关键问题。文章在研究现有的信道估计方法基础上,结合阵列天线相关性提出在特定场景下的基于天线相关性的信道估计方法并通过仿真验证了该方法的性能。     

大规模MIMO-OFDM系统结构化压缩感知信道估计中导频优化方法研究

对于FDD模式的大规模MIMO-OFDM系统,本文研究了将结构化压缩感知理论用于该系统的稀疏信道估计。考虑在该系统中将每个发送天线上的导频重叠放置,即每个发送天线可以在相同的时频资源块上发送导频符号,那么此时的系统稀疏信道估计问题可以建模为结构化压缩感知重建问题。为了优化导频位置和导频符号来改进稀疏信道估计的质量,提出了一种最小化完全块间相关值的导频优化准则以及基于此准则的导频搜索算法,完全块间相关值是结构化压缩感知框架下衡量恢复矩阵子块间相关程度的量值。仿真结果表明,与其他导频相比,使用此优化方法获得的导频可以使信道估计误差明显减小,其性能增益大约为2~5 dB。另外,仿真结果还表明,在相同的导频数量前提下,使用优化导频获得的性能增益会随着发送天线数量的增加而变得更加明显。      

基于导频的三维信道估计

对于空间相关的MIMO-OFDM系统,采用基于导频的信道估计(PACE)。导频符号仅插在所选择的发射天线中发射,并且剩余天线的信道响应通过插值得到。通过采用空间插值的方法,使信道估计扩展到第三维,即3D PACE,它在时域、频域和空域三个维度进行。如果在合适的网格结构下,3D PACE可以在不牺牲信道估计精度的前提下大大减少所需的导频开销。     

MIMO-OFDM中一种新的信道估计算法

根据不同发射天线发射的导频移位后应相互正交的原则,运用最小二乘推导出了基于MIMO-OFDM信道估计模型的时域信道估计解。针对该时域信道估计解需要矩阵求逆,运算量大的缺点,研究了基于空时频三维导频符号的设计方法,该方法使得时域信道估计解不需要矩阵求逆,可大大降低信道估计的复杂度,并且可以使信道估计误差最小。仿真结果表明,提出的基于空时频导频的信道估计方法相比传统LS算法和文献算法,MSE和BER性能均有较大的提高。     

正交频分复用信道估计的隐藏导频法

正交频分复用系统具有简单的单抽头频域均衡，在均衡之前需要完成信道估计。本文提出一种基于隐藏导频序列的信道估计方法，只要利用接收信号一阶统计信息就可估计出信道信息。这种半盲的信道估计方法具有简单的信道估计和均衡，而且不占用频谱资源。仿真结果表明本方法能有效进行信道估计，并得到了隐藏序列的最佳能量值。     

复合导频UWB系统信道估计方法

隐藏系统具有估计精度差的缺陷,辅助导频具有占用带宽多的缺陷,针对这种情况提出了复合导频信道估计方法,在隐藏导频中插入极少量的辅助导频,由于UWB信道是慢变信道,所以隐藏导频可以借鉴辅助导频的信道估计。把辅助导频和隐藏导频的信道估计叠加成新的信道估计。仿真结果表明复合导频信道估计继承了两种导频信道估计的优点,提高了信道估计精度,减少了带宽占用率。     

一种新的多天线SC-FDE UWB系统信噪比估计方法

为辅助实现多天线单载波频域均衡超宽带系统相干检测,提出一种新的信噪比估计方法.该方法在不同发射天线传输满足空间复用条件的导频序列,接收端首先获得多天线子信道最小二乘估计,再根据信道共轭对称特性构造噪声采样矢量,然后应用克拉美罗定理获得噪声方差信息,最后联合二者计算系统的信噪比值.仿真结果表明:和传统方法不同,提出方法不仅在高信噪比端大大提高了估计精度,而且可以和简单易执行的最小二乘信道估计器同时使用.     

Pilot Optimization for Structured Compressive Sensing Based Channel Estimation in Large-Scale MIMO Systems with Superimposed Pilot Pattern

Compressive sensing (CS) has attracted much attention in wireless communications due to its ability to attain acceptable channel estimates with a small number of pilots. To further reduce the pilot overhead in multi-input multi-output (MIMO) systems, CS-based channel estimation may employ superimposed pilot pattern. Previous works on superimposed pilot design generally allocate pilots randomly, which may give ill-posed measurement matrices. In this paper, we focus on deterministic pilot allocation for large-scale MIMO systems with superimposed pilot pattern to improve the performance of structured CS based channel estimation. By exploiting the spatial common sparsity and the error bound of block sparse reconstruction, a new criterion is firstly proposed to optimize the pilots in the Hadamard space. The proposed criterion makes full use of the information about the principal angles across the blocks in the measurement matrix, which can enhance the average recovery ability and exclude the worst pilots simultaneously. Secondly, a genetic algorithm is proposed to minimize the merit factor of the proposed criterion efficiently. Simulation results show that the proposed optimized pilots outperform the random pilots in terms of mean-squared error by about 3 dB. Moreover, the proposed criterion is more likely to achieve better measurement matrices than the traditional criteria.     

基于压缩感知的OFDM稀疏信道估计中的导频设计

为了提高基于压缩感知的正交频分复用( Orthogonal Frequency Division Multiplexing,OFDM)稀疏信道估计性能,提出以互相关矩阵元素之间的距离立方和作为新的导频设计准则,更加准确地评价采样矩阵整体互相关性;针对传统导频搜索算法效率慢的问题,提出一种基于树的顺序替换导频间隔搜索( ...     

一种新的OFDM后缀信号-PP

本文提出了一种可用于正交频分复用(OFDM)系统的新型后缀信号-导频后缀(PP:Pilot Postfix),并以此设计了PP-OFDM系统.PP信号由OFDM符号中的导频线性处理生成,它在接收端可以和OFDM符号中的导频相干合并.在此基础上本文给出了PP-OFDM信道估计、以及考虑了信道估值误差的数据符号估计算法.理论分析表明,相对于另外两种OFDM系统中常用的前/后缀信号-循环前缀/补零后缀(CP/ZP),PP信号可以提高信道估计性能.仿真表明,CP/ZP/PP-OFDM分别采用各自的最优导频功率分配参数时,PP-OFDM的误码率最低,这得益于PP-OFDM更好的信道估计性能.PP-OFDM的最优导频功率分配参数应通过二维搜索得到,ZP/PP-OFDM仅有一维参数可优化.     

Robust and consistent pilot designs for frequency offset estimation in MIMO OFDM systems

This paper presents pilot designs for consistent frequency offset estimation of MIMO OFDM systems in frequency selective fading channels. We derive the sufficient consistency condition for the pilots in MIMO OFDM systems to yield unambiguous estimation, and present corresponding consistent pilot designs. We discuss robustness of the frequency offset estimation against outliers at low to moderate SNR values and present an efficient criterion to choose robust and consistent pilots. Furthermore, we develop pilot designs which satisfy both consistency over a limited frequency offset estimation range and the optimal channel estimation condition in MIMO OFDM systems. Simulation results corroborate that both the consistent pilot design condition and the robustness criterion are efficient in choosing pilot patterns yielding better frequency offset estimation performance.     

基于导频辅助的低压电力线通信系统信道估计算法

针对低压电力线信道噪声强、衰减大的问题,基于OFDM技术的电力线通信系统采用时域扩充结构,提高导频数据的可靠性.确定了在OFDM时域扩充结构中应用LMMSE准则时最大多径时延的最优取值.在此基础上提出一种更适合时域扩充系统的信道估计优化算法,通过利用OFDM符号内所有导频参与信道估计从而在低信噪比条件下获得更低的误码率.仿真结果表明提出的改进算法与传统LMMSE算法相比具有更好的信道估计性能,在信噪比低于0dB时改进算法的性能优势更加明显.     

Dynamic wavelet-based pilot allocation algorithm for OFDM-based cognitive radio systems

In a cognitive radio system, the goal is to make better use of the radio electric spectrum, allowing non-licensed users access to those currently unused electromagnetic bands assigned to licensed users (LUs). This can be achieved using OFDM, where the non-licensed users must select the temporarily available subcarriers and turn off those subcarriers used by LUs in order to avoid interference. Hence, only a subset of the subcarriers can be used for data or pilot tone transmission. To this end, some pilot allocation algorithms have been proposed for this dynamic scenario, but they are designed in such away that an equispaced pilot placement is respected (as much as possible) while minimizing the mean squared error of the channel estimate. Nevertheless, this equispaced placement can lead to the use of an increased number of pilots in order to achieve a good channel estimation. In this work, a new pilot allocation algorithm based on wavelet transform is presented. The proposed algorithm uses the discrete wavelet transform to analyze the previous channel state information, taking the knowledge of the available subcarriers into account to provide a suboptimal solution for the pilot positions. This solution leads to a non-equispaced pilot placement, which improves the channel estimation and consequently, the system performance. Likewise, the introduced algorithm allows a reduction of the number of necessary pilots, which aids in increasing the data rate. Finally, simulation results corroborate the effectiveness of the algorithm in dynamic channel scenarios.     

Scattered Pilots and Virtual Carriers Based Frequency Offset Tracking for OFDM Systems: Algorithms, Identifiability, and Performance Analysis

In this paper, we propose a novel carrier frequency offset (CFO) tracking algorithm for orthogonal frequency division multiplexing (OFDM) systems by exploiting scattered pilot carriers and virtual carriers embedded in the existing OFDM standards. Assuming that the channel remains constant during two consecutive OFDM blocks and perfect timing, a CFO tracking algorithm is proposed using the limited number of pilot carriers in each OFDM block. Identifiability of this pilot based algorithm is fully discussed under the noise free environment, and a constellation rotation strategy is proposed to eliminate the c-ambiguity for arbitrary constellations. A weighted algorithm is then proposed by considering both scattered pilots and virtual carriers. We find that, the pilots increase the performance accuracy of the algorithm, while the virtual carriers reduce the chance of CFO outlier. Therefore, the proposed tracking algorithm is able to achieve full range CFO estimation, can be used before channel estimation, and could provide improved performance compared to existing algorithms. The asymptotic mean square error (MSE) of the proposed algorithm is derived and simulation results agree with the theoretical analysis.     

基于循环自相关的OFDM时间参数盲估计改进算法研究

在非协作通信领域，传统的基于循环自相关的OFDM（Orthogonal Frequency Division Multiplexing，正交频分复用）时间参数盲估计算法常分析的是无导频OFDM信号，不适用于实际应用场景中含导频OFDM信号的参数盲估计。本文分析了不同导频图案的OFDM信号循环自相关谱特性，针对谱特征变化改进了OFDM信号参数估计算法。改进算法既适用于无导频OFDM信号，也适用于不同导频图案的OFDM信号。仿真结果表明，对于无导频OFDM信号，改进算法比传统算法的时间参数估计误差可降低一个数量级；同时改进算法有效避免了导频引入的二阶周期性谱峰对OFDM时间参数估计的影响，可精确估计含导频OFDM信号的时间参数，具有很好的鲁棒性和应用价值。      

采用BICM-ID的PP-OFDM系统及后缀幅度优化

该文设计了一种用于正交频分复用(OFDM)系统的新型保护间隔信号-导频后缀(Pilot Postfix, PP),并构建了采用比特交织编码调制-迭代解码(BICM-ID)技术的PP-OFDM系统。PP由OFDM符号中的频域导频符号进行逆傅氏变换(IFFT)生成,在接收端可与OFDM符号中的导频相干合并,从而提高信道估计性能。该文给出了相应的信道估计、均衡和BICM-ID算法,并通过研究信道估值误差带来的接收信号有效信噪比变化,给出了PP幅度优化设计方法。仿真表明:选取适当的PP大小后,PP-OFDM比循环前缀/补零后缀-OFDM(CP/ZP-OFDM)的信道估计性能更好,误包率更低。     

基于混合结构导频和FFT低通滤波的OFDM信道估计

精确的估计精度、良好的跟踪能力,以及实现简单是信道估计的三个基本要求.本文提出一种混合结构导频的信道估计新方法,采用块状导频和基于FFT低通滤波的LS算法捕捉准确的信道频域响应,利用少数梳状导频和改进的LS算法跟踪信道变化和修正相位噪声.通过仿真证明,该方法估计精度高,频谱利用高,信道跟踪能力强,实现简单,满足了慢衰落信道环境下的应用要求.