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.     

部分响应信道Viterbi算法研究

目前的磁盘存储系统为了满足高数据传输速率和高数据存储密度的要求,造成数字序列之间存在严重的码间干扰,阻碍接收端获得可靠信息。本文基于将磁记录信道均衡为离散时间的部分响应信道模型,接收端采用Viterbi算法对ISI（intersymbol interference）进行检测。通过对PRML检测方案的原理进行理论分析后,给出了磁记录系统中常用的3种部分响应信道模型的计算机仿真。结果表明Viterbi算法能有效地对ISI信道进行检测。     

宽带MIMO-OFDM系统信道估计算法研究

本文提出了MIMO-OFDM系统中基于LS准则的参数化信道估计方法(LSPCE),推导出其MSE性能的下界并给出一种最优导频序列.为了降低复杂度,本文还提出了一种迭代的算法,它利用有限冲击响应信道的抽头之间的相关性从噪声中提取出信道信息并同时估计出多径时延.仿真和分析表明,相比传统的LS信道估计算法,这种基于参数化的信道估计算法可以大大提高信道估计的精度,接收端的检测性能接近理想信道估计的性能.     

固定波形时间保护间隔OFDM系统循环卷积特性研究

针对固定波形时间保护间隔OFDM系统接收端OFDM信息符号和信道冲击响应之间不具有循环卷积特性的系统特点,本文提出一种简单有效的信号处理算法对该系统接收端OFDM信息符号和信道冲击响应之间的循环卷积特性进行恢复。理论分析和计算机仿真表明,该算法能够恢复接收端此循环卷积特性;在时延扩展和AWGN信道条件下,系统误符号性能受到的影响微弱。     

基于PR信道的BCJR检测

为了满足磁盘存储系统的高数据传输速率和高数据存储密度的需求,造成数字序列之间产生的码间干扰成为接收端获得可靠信息的主要阻碍。本文是以部分响应信号作为离散时间的ISI信道模型,采用基于MAP算法的对数域BCJR（log—MAP）算法进行信道检测。文章介绍了PR信道的模型,对算法的检测原理进行理论分析,并给出几种不同的部分响应信道下的计算机仿真。结果表明该算法能有效地对ISI信道进行检测,能应用于磁记录系统。     

LTE OFDMA系统基于最大径选择的信道估计算法

针对3GPP LTE下行链路提出了一种有效可行的信道估计方法,其原理是首先在时域用LS算法估计出信道的冲击响应,然后通过忽略信道响应能量较小的一些径,这样在进一步抑制噪声干扰的同时还有效控制了算法复杂度;最后,将得到的经过径选择的时域信道冲击响应向量变换至频域,得到用于最终信号检测的频域信道响应向量。仿真结果表明,该改进算法与传统的LS算法相比,在保证低复杂度的同时,提高了信道估计精度。     

一种适用于多径信道下DSSS信号检测新方法

针对多径信道下直接序列扩频信号检测的难题,在基于自相关二阶矩的检测算法基础上提出了新的检测参数,从而将加性高斯白噪声信道下的直接序列扩频信号检测算法推广到多径信道。本文算法首先分析了由多径信道导致的能量峰值和由直扩信号的伪码特性导致的自相关峰值的特点,并根据此特点定义了新的检测参数——多径因子,最后将该参数应用到基于自相关二阶矩的直接序列扩频信号检测算法中,实现了对多径信道下的直接序列扩频信号的检测。理论分析和仿真实验表明,本文提出的检测新参数能真实的反映多径信道对信号自相关函数的影响;当信噪比大于-14dB时,本文提出的多径信道下直扩信号检测算法性能与加性高斯白噪声信道下的检测性能相当。      

基于正交多相序列的OFDM信道估计算法

提出了一种基于正交多相序列的OFDM信道估计算法。该算法采用相关性能良好的正交多相序列作为发送信号的循环前缀,在接收端,提取循环前缀,进行相关计算,最终得到系统频域响应的估计值。通过仿真,验证了在多径衰落信道中,提出的算法比频域梳状导频插入的时域滤波算法及采用小m序列作为循环前缀的信道估计算法具有更高的信道估计精度。     

LTE-A物理层下行参考信号的研究

LTE-A（改进的长期演进）OFDM系统接收端采用相干解调技术恢复原始数据信息,相干解调必须利用信道的相关信息,获取信道相关信息接收端需采用先进的信道估计技术实现。LTE-A OFDM系统是基于导频信号的信道估计获取信道的脉冲响应特性。本文主要对LTE-A物理层下行CRS（小区特定参考信号）进行了深入的分析研究。     

新的盲信道估计算法

研究了各种盲信道估计算法.提出一种关于信道的假设,并在此基础上提出一种新的盲信道估计算法.新算法能够同时估计出信号和信道.新算法基于MMSE准则,利用m进制通信系统中,在接收端和发射端都已知信号模式且模式个数有限(K=log2m)的特点,结合预置于算法的信道模型,得到信道模型和信号模式的估计.然后依据MMSE准则得到信道和信号的最佳估计.最后给出仿真结果,仿真表明:新的盲信道估计方法能够精确估计实际信道的等效冲击响应,并能够进行有效通信.     

Combined Equalization and Demodulation of Chaotic Direct Sequence Spread Spectrum Signals for Multipath Channels

Due to the inherent noise-like characteristic of chaotic signals and their sensitivity to the initial value, chaotic direct sequence spread spectrum (CD3S) signals have the advantages of a low probability of intercept (LPI) and a high level of security. Demodulation of non-cooperated CD3S signals is then a challenging issue. If the signal is sent though multipath channels, it is even more difficult for the receiver to demodulate it blindly. Based on the existing theories and methods, we focus more on signals passing through multipath channels. This paper presents an approach to achieve blind equalization and demodulation of CD3S signals through multipath channels. Multiple unscented Kalman filters (UKFs) are used to equalize and demodulate the CD3S signals for the unknown channel. This method can effectively demodulate the signals without any knowledge of the chaotic transmitter’s parameters, initial value, state equation, or the channel coefficients, even when the signal is severely distorted by the multipath channel. Simulation results demonstrate that this method gives faster convergence and better demodulation performance than existing methods for various channel conditions.     

基于稀疏贝叶斯学习的电力线载波通信接收机设计

针对多径信道和脉冲噪声对电力线载波通信系统性能影响的问题,提出了一种能有效对抗多径信道和脉冲噪声影响的电力线通信系统接收机设计方案.该方案将时域上的电力线信道参数和脉冲噪声联合视作稀疏向量,然后利用稀疏贝叶斯理论联合估计电力线信道和脉冲噪声,从而在接收端得以去除脉冲噪声及补偿信道增益.仿真结果表明,与传统将信道估计与脉冲噪声抑制单独考虑的传统接收机相比,本文提出的接收机方案在误符号率和误比特率等性能指标上有较好的提升.     

MIMO协同中继系统中的最大似然合并解调算法

协同中继系统通过合并解调不同路径的信号副本,得到比非协同系统更优的误码性能。传统的合并解调算法将合并解调过程分开处理,性能较差。该文针对多输入多输出（MIMO）放大转发协同中继系统,基于最大似然（ML）准则,提出了在目的节点对来自源节点和中继节点的信号进行合并解调的新算法。该算法首先对来自源节点和中继节点的信号进行ML合并,然后采用传统的MIMO最大似然检测完成信号的解调。分析与仿真结果表明,与最大比合并（MRC）等算法相比,在不同调制方式和信道条件下,所提算法均获得了显著的性能增益,且高阶调制下的复杂度低。      

Multiple-symbol differential detection of GMSK for mobilecommunications

A new multiple differential detection (MDD) sequence estimator is described which uses a decision feedback for the demodulation of a GMSK signal. This technique is based upon a maximum-likelihood sequence estimation of the transmitted phases rather than on a symbol-by-symbol detection. An upper and a lower bound on the bit error probability of the described detector in the case of an AWGN channel and a two-ray Rayleigh fading channel are derived. The performance of the detection algorithm in a mobile radio communication system is obtained through computer simulation. Comparisons with the coherent detection algorithm show that the proposed detection algorithm is quite attractive both in an AWGN and in a multipath channel     

Random Correlation-Based Receiver for Impulse Radio Communications in UWB Channels

Impulse radio is a low-complexity ultra-wideband system which is suitable for highly dispersive multipath channel. In this paper, we propose a random correlation-based receiver for impulse radio communications. The proposed receiver correlates the received pilot symbols with the randomly generated base functions according to channel statistics and forms the detection template by combining several base functions which have larger correlation coefficients with the pilot symbols. The proposed receiver demodulates the received signal by employing a symbol rate sampling. Computer simulation results have shown that the proposed receiver outperforms the conventional correlator-based receiver, compressive sensing correlator-based receiver, weighted energy detector and autocorrelation receiver.     

A low-complexity combined antenna array and interferencecancellation DS-CDMA receiver in multipath fading channels

A simple direct sequence-code division multiple access receiver that combines adaptive beamforming with parallel interference cancellation in a multipath fading channel is proposed and analyzed. A fast adaptation, conjugate gradient algorithm is used to find the optimum beamformer weights. By beamforming, the desired user's signal is enhanced and the cochannel interference from other directions is reduced. For in-beam multiple access interference reduction, a parallel interference canceller is used in each RAKE finger. In the demodulation process, we propose a new demodulation method in which the incoming signal is correlated with the effecting spreading code rather than the physical spreading code called the effective matched filter. A new combining method called equivalent maximal ratio combining is also proposed and analyzed. The average uncoded bit error rate as a function of the average antenna signal-to-noise ratio and the number of receiving antennas is examined in a frequency selective Rayleigh fading channel for all proposed receiver structures. Both simulation and analysis show an increase in system capacity as a function of the number of antennas and the number of interferers canceled per finger     

一种高动态弱GNSS信号跟踪解调算法研究与实现

在某些高动态弱信号场景中,载波相位难以锁定。为实现对高动态弱全球导航卫星系统(GNSS)信号的跟踪,考虑锁频环较锁相环更为鲁棒,提出了一种基于锁频环(FLL)+差分解调的算法,实现对GNSS信号的跟踪和解调。该算法采用二阶FLL实现对卫星信号的频率进行跟踪,差分解调算法实现对比特数据的解调。工程应用上,算法采用现场可编程门阵列和数字信号处理器(FPGA+DSP)的架构实现,在FPGA中实现信号的跟踪信号的前处理,在DSP中实现跟踪环路算法、位同步和差分解调。本文在Matlab平台中实现算法的仿真,通过模拟器平台和对天接收真实的GNSS信号对算法进行验证。仿真结果与实验结果表明,该算法在高动态弱信号条件下能实现对卫星信号的稳定跟踪和数据的解调,克服了锁相环难以锁定导致数据无法解调的难题,最终实现GNSS信号在该条件下的位置、速度和时间(PVT)解算。     

并行多信道软件无线电接收机仿真

讨论了软件无线电接收机的基本理论:信道划分和解调算法。在此基础上研究了下变频技术和低通滤波技术在并行多信道接收机中的应用,提出了采用软件无线电中的FM和AM解调方式解调信号,并完成了软件无线电接受机的系统仿真。     

Transmit diversity and linear and decision-feedback equalizations for frequency-selective fading channels

Rapid growth and increasing demands for near-ubiquitous high-quality high-data-rate services present the most challenges for wireless system design. As an effective method to provide such services, space-time (ST) coding is gaining more and more attention. The paper extends ST coding, originally designed for known frequency-nonselective fading channels, to unknown frequency-selective channels. An ST transmit diversity wireless time-division multiple-access system, that is equipped with multiple antennas at both transmit and receive sides, is considered. In this system, a novel scheme is presented to suppress intersymbol interference and to demodulate coherently the information symbols with estimated channel state information. The proposed algorithm is powerful and computationally efficient. In addition to the discussion of system identifiability, both theoretical analysis and numerical simulation are presented to illustrate the performance of the proposed estimator and receiver in multipath fading channels.