基于导频的光OFDM系统信道估计

为了克服光纤色散和模式的传输时延导致ICI设计了一种基于导频的信道估计器．并分析了LS和LMMSE算法估计原理,通过仿真实验比较了两种算法的误比特率和均方误差性能．实验结果表明LS与LMMSE在光OFDM系统中都有较好的作用但LMMSE算法性能要优于LS算法。     

MIMOHSDPA系统中一种导频抵消迭代码片均衡算法

MIMO HSDPA(High Speed Downlink PacketAccess)系统采用多天线技术,传统的LMMSE码片均衡算法计算复杂度较高,为降低运算量,本文将SMW定理引入LMMSE算法中,并引入导频抵消模块,提出了一种PC-ILMMSE算法.理论分析与仿真结果表明,新算法的性能优于传统的LMMSE,而运算量大大降低.     

认知无线电中基于导频的信道估计研究

介绍了认知无线电NC-OFDM系统中的信道估计技术,着重分析了基于导频的LS信道估计、联合LMMSE信道估计、以及联合SvD—LMMSE信道估计算法。采用频率选择性信道,对各个算法进行了仿真实验,得出不同算法下信道估计的误码率曲线,比较了各算法的性能。仿真结果表明：与LS估计算法及联合LMMSE估计算法相比,联合SVD—LMMSE信道估计算法有效地降低了误码率,并且具有较低的复杂度,但是其性能略于联合LMMSE信道估计的性能：另外,联合SVD—LMMSE信道估计算法的误码率小于分离SVD—LMMSE信道估计算法的误码率。     

基于导频的光OFDM系统信道估计

信道估计是光正交频分复用（OOFDM）系统关键技术之一,为了克服光纤色散和模式的传输时延所产生的载波间干扰（ICI）,设计了一种基于导频的信道估计器,通过分析最小二乘（LS）和线性最小均方误差（LMMSE）算法估计原理,仿真实验比较两种算法的误比特率和均方误差性能,实验结果表明,LS与LMMSE在OOFDM系统中都有较好的作用,但LMMSE算法性能要优于LS算法。     

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.     

基于三级LLR检测的广义零填充三模OFDM索引调制系统研究

本文提出了一种基于对数似然比(LLR)检测算法的广义零填充三模正交频分复用(OFDM)索引调制(GZTM?OFDM?IM)系统,目的在于提高传统ZTM?OFDM?IM系统的频谱效率(SE).在提出的系统发送端,更多的OFDM子载波激活样式有效提高了系统的SE,并且一种新的双模信号星座图被采用.为了降低接收端检测过程的复杂度,设计了基于LLR算法的三级检测器.仿真结果表明:利用设计的低复杂度检测器,GZTM?OFDM?IM在实现了高SE的同时,系统的误比特率(BER)性能在高信噪比(SNR)范围与传统ZTM?OFDM?IM相比没有降低,且BER性能与理论差错性能上边界非常接近.     

基于特殊导频去噪的OFDM信道估计算法

主要研究了正交频分复用(OFDM)系统中基于导频辅助的信道估计算法,分析和比较了2种常用的算法,并提出了一种基于特殊导频序列去噪的信道估计算法。仿真结果表明:提出的基于特殊导频去噪的信道估计算法和LS算法相比,在没有增加LS算法运算复杂度的情况下,有效地抑制噪声的影响,提高了信道估计的准确性;和LMMSE算法相比,信道估计的准确性高于LMMSE算法。     

一种基于LMMSE改进的FBMC信道估计算法

针对滤波器组多载波(Filter Bank Multicarrier,FBMC)系统的信道估计问题,对系统进行了简要介绍并提出一种基于线性最小均方误差(Liner Minimum Mean-Square Error,LMMSE)算法改进的信道估计算法。在原有的LMMSE算法基础上结合离散傅里叶变换(Discrete Fourier Transform,DFT)算法,并进行迭代估计,同时利用奇异值分解(Singular Value Decomposition,SVD)算法降低了计算的复杂度。仿真结果表明,改进的LMMSE算法明显提高了系统的性能。     

块迭代码片均衡算法

为了增强码片均衡器的性能,降低运算量,提出了一种 LMMSE 的改进新算法—BILMMSE 算法。理论分析与计算机模拟结果表明 BILMMSE 码片均衡器性能优于传统的 Rake,以及 Griffith 与 MRLS 码片均衡器,与LMMSE 码片均衡器性能基本保持一致,而运算量却大大降低,非常有利于 FPGA 与 DSP 实现。     

用于 LDPC 码快速译码的改进多比特翻转算法简

为了提高RRWBF算法的译码速度,提出一种多比特翻转机制来加快RRWBF算法的收敛速度。但是,使用该多比特翻转机制的RRWBF算法时,译码过程中出现与单比特翻转类似的循环翻转现象,影响其译码性能。为此,进一步提出一种循环翻转消除机制来破坏多比特翻转译码过程中产生的循环翻转,进而提高其译码性能。仿真结果显示,与单比特翻转算法相比,提出的基于循环翻转消除的多比特RRWBF算法以较小的译码性能损失换来译码速度的较大提升。     

一种低复杂性多级优化智能天线接收机

该文提出了一种适用于无线通信CDMA系统的低复杂性多级优化智能天线接收机的结构与算法。该接收机采用了新颖的正交分级优化方式,每一级的系统参数只需通过简单的循环迭代就可以决定,每一正交级设置一个复加权系数,通过MMSE准则来估算、更新,在各级中独立进行优化。系统级数多少可由信号环境来决定,使系统的运行更为灵活。与其它方法相比,该系统在无线通信环境下,尤其是在有相关性信号存在的情况下,具有更好的性能,而且在系统复杂性方面也有明显的改进。     

Low-Cost Approximate LMMSE Equalizer Based on Krylov Subspace Methods for HSDPA

The throughput of the high speed downlink packet access (HSDPA) sub-system of UMTS suffers significantly from multiple access interference in the wireless channel. A linear minimum mean square error (LMMSE) equalizer at the receiver achieves higher throughput than a conventional RAKE receiver, at the cost of higher complexity. We introduce an iterative algorithm based on Krylov subspace projections, approximating the LMMSE equalizer with negligible loss of performance for the receiver. Slow variations of the channel can be exploited to allow further acceleration of the algorithm. Computational complexity as well as storage requirements are strongly reduced     

一种基于SC-FDMA系统改进的LMMSE信道估计算法

对于LTE上行链路来说,寻求性能优良的信道估计算法是十分必要的。传统的最小平方(LS)和线性最小均方误差(LMMSE)信道估计算法存在许多不足。其中,在研究过程中会发现传统线性最小均方误差(LMMSE)信道估计算法具有计算复杂度大的问题。然而,通过借助于雅克比迭代算法解决线性方程的理念,能够对传统的LMMSE算法做进一步的改进。同时,理论分析和仿真结果表明:该算法在低信噪比下表现出良好的性能,它不仅降低了计算复杂度,而且估计结果更精确。     

Iterative implementation of linear multiuser detection for dynamicasynchronous CDMA systems

Several linear multiuser detectors for code-division multiple access (CDMA) systems can be characterized as an inverse of some form of correlation matrices. If the correlations change, the detectors must be redesigned. An ideal computation of the decorrelating or the linear minimum mean-squared-error (LMMSE) detector requires order K³ flops, where K is the number of users. To alleviate the computational complexity, iterative decorrelating and LMMSE detectors are proposed. The iterative detectors use steepest descent (SD), conjugate gradient (CG), and preconditioned conjugate gradient (PCG) algorithms, and require order K² flops per iteration. Their main advantages are the reduced number of flops and their suitability to highly parallel implementations. The correlation coefficient computation can also be embedded into the CG algorithm, which is an advantage with time-varying signature waveforms. The performance of the iterative algorithms is studied via computer simulations     

LDPC coded MIMO multiple access with iterative joint decoding

An efficient scheme for the multiple-access multiple-input multiple-output (MIMO) channel is proposed, which operates well also in the single user regime, as well as in a direct-sequence spread-spectrum (DS-CDMA) setting. The design features scalability and is of limited complexity. The system employs optimized low-density parity-check (LDPC) codes and an efficient iterative (belief propagation-BP) detection which combines linear minimum mean-square error (LMMSE) detection and iterative interference cancellation (IC). This combination is found to be necessary for efficient operation in high system loads /spl alpha/>1. An asymptotic density evolution (DE) is used to optimize the degree polynomials of the underlining LDPC code, and thresholds as close as 0.77 dB to the channel capacity are evident for a system load of 2. Replacing the LMMSE with the complex individually optimal multiuser detector (IO-MUD) further improves the performance up to 0.14 dB from the capacity. Comparing the thresholds of a good single-user LDPC code to the multiuser optimized LDPC code, both over the above multiuser channel, reveals a surprising 8-dB difference, emphasizing thus the necessity of optimizing the code. The asymptotic analysis of the proposed scheme is verified by simulations of finite systems, which reveal meaningful differences between the performances of MIMO systems with single and multiple users and demonstrate performance similar to previously reported techniques, but with higher system loads, and significantly lower receiver complexity.     

伪叠加Zadoff-Chu序列的LTE下行信道估计

分析了正交频分复用系统中基于叠加训练序列的最小二乘和线性最小均方误差信道估计算法,在此基础上针对LTE信道的结构特征,提出了一种利用伪叠加Zadoff-Chu序列进行信道估计的最小二乘算法。该方法可以大大降低算法复杂度,并且不需要信道先验信息、不占用带宽资源。仿真结果验证了该方法的有效性,其性能比频域的离散傅里叶变换算法和线性最小均方误差算法性能更优。     

Space-time turbo multiuser detection for coded MC-CDMA

The system capacity and performance of multicarrier code-division multiple-access (MC-CDMA) communication systems can be significantly enhanced by jointly employing MAP-based multiuser detection (MUD) and channel decoding techniques. In this paper, a group-oriented soft iterative MUD based on the combination of smart antennas and iterative MAP-based MUD is presented. The proposed method is featured as a novel technique for further increasing the system capacity and performance. In this method, all the users are first grouped into several groups according to their impinging direction of arrivals (DOAs). All users with similar DOAs are classified into the same group and then low-complexity MAP-based iterative MUD is employed in each group. Because spatial filtering cannot suppress all the interference between the groups, interference cancellation among the groups is used prior to MUD within each group. It is shown that the proposed group-oriented soft iterative MUD algorithm can significantly reduce the computational complexity compared with the conventional optimal MAP-based MUD schemes. It is also demonstrated that the performance of the proposed algorithm can approach that of a single-user coded MC-CDMA system with an antenna array in additive white Gaussian noise and frequency selective fading channels.     

Capacity regions and optimal power allocation for groupwise multiuser detection

In this letter, optimal power allocation and capacity regions are derived for groupwise successive interference cancellation (GSIC) systems operating in multipath fading channels, under imperfect channel estimation conditions. It is shown that the impact of channel estimation errors on the system capacity is two-fold: It affects the receiver performance within a group of users, as well as the cancellation performance (through cancellation errors). An iterative power allocation algorithm is derived, based on which it can be shown that that the total required received power is minimized when the groups are ordered according to their cancellation errors, and the first detected group has the smallest cancellation error. Performance/complexity tradeoff issues are also discussed by directly comparing the system capacity for different implementations: GSIC with linear minimum-mean-square error (LMMSE) receivers within the detection groups; GSIC with matched filter (MF) receivers; multicode LMMSE systems; and simple all MF receivers systems.     

基于联合迭代算法的多层编码超宽带通信系统

该文提出一种多层编码的超宽带通信系统,给出接收端脉冲解映射器和译码器之间联合迭代处理算法。三层编码的超宽带系统的误码性能仿真表明:比较未编码系统,误码性能得到明显的改善;AWGN信道下,多级迭代算法和并行迭代算法分别需要3次和4次迭代收敛到最佳性能;而在室内信道环境中,多级迭代算法和并行迭代算法各自需要2次和3次迭代收敛到最佳性能;最佳迭代次数下,两种算法的性能相当,但并行迭代算法的时延约为多级迭代算法时延的1/3。