基于MIMO-OFDM系统的低复杂度LS改进算法

本文建立了MIMO-OFDM系统的Matlab仿真模型,在此基础上研究了STBC(Space Time Block Code)空时编码和基于块状导频的信道估计算法.对基于块状导频的LS(Least Square)信道估计算法做了低复杂度的改进,改进后的算法称为LLS(Low complexity LS)算法.经过计算机仿真显示,在传送大量信息时,该算法的运算复杂度及运算时间相较于其他的信道估计算法都大大降低,并且提高了信道估计的误码率性能.     

非理想信道估计对STBC性能的影响

信道估计误差对空时分组码(STBC)解码性能的影响依然值得进一步的研究,通过讨论STBC在仅有不完整信道估计时的解码性能,首先建立系统分析模型,然后进行理论分析和模拟,并同接收分集的性能作比较.仿真结果表明,在非相关空间衰落的多散射环境中,STBC提供了一种有效的町获得空间分集增益的简单发射分集方案,但信道估计误差对其解码性能有较大的影响.     

空时分组码系统中WL-Kalman均衡算法*

根据空时分组码(STBC)系统的编码特点,提出了一种低复杂度的基于宽线性(WL)处理的Kalman均衡算法。该算法针对STBC系统,利用宽线性处理的思想,采用Kalman均衡算法对接收信号及其复共轭联合进行处理,有效地减轻了由频率选择性衰落信道引起的码间干扰(ISI)。对所提出的均衡算法在不同环境下进行了仿真验证。结果表明,与传统的线性均衡器相比,该算法明显提高了系统的性能,具有实际应用价值。     

MIMO—OFDM系统信道估计技术研究

信道估计是MIMO-OFDM系统中的关键技术之一,信道估计的准确与否直接关系到系统性能的好坏,因此寻求快速、准确、可靠的信道估计算法以提高信道估计精度是一个重要的研究课题。该文通过建立MIMO-OFDM系统信道模型,给出了基于训练序列的LS估计和MMSE估计的基本算法实现原理,并针对算法的不足提出改进算法。通过仿真可知,改进算法比基本算法拥有更好的系统性能。     

一种水声MC-CDMA多用户信道估计仿真研究

研究水声信道优化估计问题,在资源受限的水声环境下,多载波码分多址(MC-CDMA)上行系统信道,由于受到各种干扰,怎样获取多用户的信道准确信息是一个难题。为此提出了一种采用DFT的上行信道估计算法,可以很好的解决了上述问题。算法是在频域上构造不同的导频信号,在时域上估计用户的冲激响应从而得到其信道传输函数。采用改进方案的水声MC-CDMA系统在获得有效频谱效率和分集增益的同时,还能获得很好的误码率性能。首先利用DFT信道估计算法的性能,进行仿真。结果表明,DFT及改进算法较传统的LS信道估计算法,可以使水声系统性能有明显的提高,降低多用户干扰的影响,为水声多用户信道优化估计提供了依据。     

一种大规模MIMO系统中STBC迭代接收机算法

针对大规模MIMO中的空时分组编码(STBC)系统的接收机复杂度随天线数指数增长的问题,提出一种基于EM算法的低计算复杂度的最大似然(ML)接收机。利用STBC和OFMD调制的正交性,避免了矩阵求逆运算;采用步骤E与步骤M迭代处理的方式,极大降低接收机复杂度。基于信道特性提出EM算法初始化方法,达到减少迭代次数进而降低接收机复杂度和提升性能的目的。与之前的决策反馈的非迭代接收机相比,该迭代接收机性能显著提高,在具有快衰落的典型无线信道中,其计算复杂度接近ML接收机,适合实时实现。     

基于信道估计的LDPC仿真算法研究

研究有记忆信道上的LDPC译码算法,对高速数字通信系统具有重要意义.目前运用于有记忆信道上的LDPC迭代译码算法,如基于信道估计的BP迭代译码算法等,都存在算法复杂度较高、运算量较大的问题.针对隐马尔可夫噪声信道,首次将最小和(min-sum)算法引入到基于噪声软判决和信道估计的LDPC迭代译码算法,利用函数特性有效降低算法复杂度、减少运算量.仿真结果表明,此算法的性能不仅优于不考虑信道记忆特性的一般LDPC的迭代译码算法,也优于基于噪声硬判决和信道估计的BP迭代译码算法,在性能损失较小情况下,于译码性能和算法复杂度之间找到了一个很好的折衷,对实时通信系统具有重要意义.     

快衰落信道下改进的STBC解码性能分析

研究无线移动通信优化问题,在分析传统空时分组码(STBC)的解码原理的基础上,针对其在快衰落信道下存在码间干扰问题,从解码方式上进行研究达到解决快衰落信道下受到的码间干扰问题.提出了一种适合快衰落信道环境下改进的STBC线性解码方法可以成功消除了传统STBC存在的码间干扰.通过仿真看出,与采用传统STBC相比,采用新方法的系统性能得到改善.随着多普勒频移和信噪比的增大,系统性能的改善易实现.仿真表明方法的有效性,并有效地消除了码间干扰.     

基于OFDM的通信系统仿真及性能分析

文章搭建了两种OFDM通信系统模型,采用MATLAB语言仿真了整个系统并得到了相应仿真结果,在此基础上对OFMD系统在八种信道模型、三种信道估计算法下的性能做了更全面而深入地分析,获得的结论有助于我们在面对不同的环境下选择怎样的信道估计算法提高通信系统整体性能时能做出正确而快速判断。     

基于压缩感知的多载波系统信道估计研究

针对多载波系统信道的稀疏特性,提出一种基于压缩感知(CS)的MC-CDMA多载波系统信道估计方法。信号自适应匹配追踪(SAMP)是一种压缩感知算法,详细研究了该算法的设计原理和实现过程。将该算法与传统信道估计方法及基于压缩感知的OMP算法做比较,仿真结果表明,SAMP算法的信道估计均方误差(MSE)和系统误比特率(BER)均更小。对于在稀疏度未知的多载波系统信道中,该算法可以获得很好的信道估计性能,降低系统的复杂度。     

Combined adaptive beamforming with space-time block coding for multi-antenna communications

Aiming at the multi-antenna communication systems, a downlink transmit scheme combining adaptive beamforming （ABF） with space-time block coding （STBC） is first presented, which utilizes the maximization of the output mean signal-to-noise ratio （SNR） and the minimization of the symbol error rate （SER） upper bound of the three widely used modulations as the design criteria. Then, based on the moment generating function （MGF） and the Gauss-Chebyshev integration, a simple and accurate numerical method is presented to analyze the SER performance of the system with the new transmit scheme under the three commonly used modulations. Finally, computer simulation results demonstrate the effectiveness and superiority of the proposed strategy.     

BER analysis of STBC hybrid carrier system based on WFRFT with frequency domain equalization

The inherent characteristic of hybrid carrier (HC) scheme based on the weighted-type fractional Fourier transform (WFRFT) is revealed. The proposed linear combination of single carrier (SC) and multicarrier’s (MC) characteristics is helpful to balance the conflicting requirements and achieve the comparative analysis of SC/MC. As an example, analytical SER/BER expressions of HC system with zero forcing (ZF) and minimum mean square error (MMSE) equalization are derived. In addition, the derived BER expressions are extended to multi-input systems. A unified framework of space time block code (STBC) HC scheme is proposed with two WFRFT modules at the transmitter or receiver, where STBC-SC and STBC-MC systems are the special cases of the novel structure.     

Speech emotion recognition research: an analysis of research focus

This article analyses research in speech emotion recognition (“SER”) from 2006 to 2017 in order to identify the current focus of research, and areas in which research is lacking. The objective is to examine what is being done in this field of research. Searching on selected keywords, we extracted and analysed 260 articles from well-known online databases. The analysis indicates that SER research is an active field of research, dozens of articles being published each year in journals and conference proceedings. The majority of articles concentrate on three critical aspects of SER, namely (1) databases, (2) suitable speech features, and (3) classification techniques to maximize the recognition accuracy of SER systems. Having carried out association analysis of the critical aspects and how they influence the performance of the SER system in term of recognition accuracy, we found that certain combination of databases, speech features and classifiers influence the recognition accuracy of the SER system. We have also suggested aspects of SER that could be taken into consideration in future works based on our review.     

Space–Time Block Coding for Channels with Intersymbol Interference

Stoica, P., and Lindskog, E., Space–Time Block Coding for Channels with Intersymbol Interference, Digital Signal Processing12 (2002) 616–627The downlink of many wireless communication systems can be a MISO channel. An important problem for a MISO channel is how to code across space and time to obtain the same ML receiver as for the corresponding SIMO channel. For flat fading channels, space–time block coding (STBC) is a recent breakthrough solution to this problem. In Lindskog and Paulraj (in Proceedings of ICC'2000, NewOrleans, LA, June 18–22, 2000), STBC has been generalized to channels with intersymbol interference (ISI) for the case of two transmit antennas and one receive antenna. In this paper we first revisit the generalized STBC scheme of Lindskog and Paulraj and show that it has the same appealing properties as the standard STBC for flat fading channels. Then we go on to present an extension of this scheme to ISI channels with any number of transmit and receive antennas.     

全速率满分集准正交空时分组码设计研究

自Alamouti提出空时分组码以来,空时分组码的构造得到广泛的研究。研究表明,复正交空时分组码当发射天线数大于3时,它的传输码率小于1。准正交空时分组码虽然能达到全速率,却牺牲了一定的分集增益。根据空时编码秩准则,通过对传统准正交空时分组码进行矩阵旋转处理,得到一种全速率满分集的空时分组码。数值仿真显示,这种全速率满分集空时分组码的性能较传统准正交空时分组码至少有4 dB的提高。     

Cross-layer adaptive modulation and coding design for space-time block coded MIMO–OFDM systems

This paper developed a cross-layer adaptive modulation and coding (AMC) design for space-time block coded (STBC) MIMO–OFDM systems, which combines the AMC at the physical layer with an automatic repeat request (ARQ) protocol at the data link layer, in order to maximize spectral efficiency under specified delay and packet error ratio (PER) constraints. The transmission mode for each subcarrier is updated frame-by-frame to match the time-varying channel conditions, in order to take full advantage of the OFDM systems. The proposed cross-layer AMC design is also incorporated with STBC to further improve the system performance. Numerical results have demonstrated that retransmission at the data link layer alleviate rigorous error-control requirements at the physical layer and thereby allows higher data rate transmission. It is shown that this cross-layer design has achieved considerable spectral efficiency gain in comparison with traditional AMC without cross-layer design. Note that increasing the maximum number of retransmissions beyond one has little effect on spectrum efficiency and will cause longer system delay. This suggests that a desirable trade-off between spectral efficiency and delay in the STBC MIMO–OFDM system is achieved by a small number of retransmission.     

基于STBC的MIMO-OFDM系统中自适应调制技术研究

将自适应比特、功率分配(ABPA)应用在基于空时分组编码(STBC)的MIMO-OFDM系统中,能够进一步提高无线链路的性能,而如何在载波间分配比特、功率是个关键问题。文章提出一种基于ABPA-STBC的MIMO-OFDM系统模型,即根据STBC-MI-MO-OFDM系统的特点,在此系统中采用优化目标为最小化误码率的Fischer算法引入自适应调制技术。仿真结果表明,所提出的系统模型和一般的MIMO-OFDM系统相比可获得更好的误码性能。     

多天线下结合BLAST与STBC算法的HARQ模型研究

提出多天线阵列中基于BLAST和STBC结合的HARQ算法.通过基于不同的空时码发射矩阵,推荐的算法可以分为基于正交发射矩阵的BLAST和STBC结合的HARQ算法以及基于准正交发射矩阵的BLAST和STBC结合的HARQ算法.推荐的算法不是如参照的算法BLAST HARQ那样简单重传同样的信号,而是传输发射矩阵的下一行并联合进行空时码最大似然解码,这样推荐的算法可以获得空时码的分集增益,而在信道条件好和信噪比高时,由于没有重传的发生而可以获得BLAST的复用增益.特别是本算法可以适用于所有接收天线数大干等于发射天线数的多天线阵列中,有很强的实用性.本算法结合了BLAST和STBC以及HARQ的优势,是一个既能够提高系统传输速率也能够提高系统抗干扰性能的HARQ方案.     

Symbol emergence in robotics: a survey

Humans can learn a language through physical interaction with their environment and semiotic communication with other people. It is very important to obtain a computational understanding of how humans can form symbol systems and obtain semiotic skills through their autonomous mental development. Recently, many studies have been conducted regarding the construction of robotic systems and machine learning methods that can learn a language through embodied multimodal interaction with their environment and other systems. Understanding human?-social interactions and developing a robot that can smoothly communicate with human users in the long term require an understanding of the dynamics of symbol systems. The embodied cognition and social interaction of participants gradually alter a symbol system in a constructive manner. In this paper, we introduce a field of research called symbol emergence in robotics (SER). SER represents a constructive approach towards a symbol emergence system. The symbol emergence system is socially self-organized through both semiotic communications and physical interactions with autonomous cognitive developmental agents, i.e. humans and developmental robots. In this paper, specifically, we describe some state-of-art research topics concerning SER, such as multimodal categorization, word discovery, and double articulation analysis. They enable robots to discover words and their embodied meanings from raw sensory-motor information, including visual information, haptic information, auditory information, and acoustic speech signals, in a totally unsupervised manner. Finally, we suggest future directions for research in SER.     

Improved eigenanalysis canceler based on data-independent clutter subspace estimation for space-time adaptive processing

The eigenanalysis canceler(EC)method which is suitable for nonhomogeneous clutter can suppress clutter efectively by discarding the eigenvectors of small eigenvalues,which is a well-known subspace-based space-time adaptive processing(STAP)method.However,the computational complexity of conventional EC STAP method is huge due to the eigenvalue decomposition.Moreover,the corresponding performance would be degraded signifcantly by the subspace leakage phenomenon,since the clutter subspace is not strictly confned to a low-rank subspace any more.Therefore,an improved EC STAP method based on the data-independent clutter subspace estimation is proposed to reduce the computational complexity,where the clutter subspace is rapidly constructed by sampling the prolate spheroidal wave functions(PSWF)non-uniformly.In order to deal with the subspace leakage phenomenon,the proposed EC-PSWF STAP method is modifed based on the covariance matrix taper(CMT)to obtain the covariance matrix by re-establishing the noise floor.The corresponding performance of proposed method is evaluated by using the numerical simulation.