Lattice-reduction-aided MMSE precoding for correlated MIMO channels and performance analysis

The lattice-reduction (LR) has been developed to improve the performance of the zero-forcing (ZF) precoder in multiple input multiple output (MIMO) systems. Under the assumptions of uncorrelated flat fading channel model and perfect channel state information at the transmitter (CSIT), an LR-aided ZF precoder is able to collect the full transmit diversity. With the complex LenstraLenstra-Lova′sz (LLL) algorithm and limited feedforward structure, an LR-aided linear minimum-mean-square-error (LMMSE) precoder for spatial correlated MIMO channels and imperfect CSIT is proposed to achieve lower bit error rate (BER). Assuming a time division duplexing (TDD) MIMO system, correlated block flat fading channel and LMMSE uplink channel estimator, it is proved that the proposed LR-aided LMMSE precoder can also obtain the full transmit diversity through an analytical approach. Furthermore, the simulation results show that with the quadrature phase shift keying (QPSK) modulation at the transmitter, the uncoded and coded BERs of the LR-aided LMMSE precoder are lower than that of the traditional LMMSE precoder respectively when E b / N0 is greater than 10 dB and 12 dB at all correlation coefficients.     

A Novel Concatenated Chaotic Communication System

A strategy for a novel concatenated chaotic communication system is presented. The transmitter system comprises chaotic turbo encoder and logistic CSK block in a serially concatenated form. Chaotic turbo code is capable of reducing bit error rate (BER) of the chaotic system in the AWGN channel. Through the chaotic turbo encoder, the coded sequence, which has quasi-chaotic properties, will be transmitted into the logistic CSK block. Having a very sensitive dependence on initial conditions of the map, the logistic CSK block can also be taken as the chaotic authentication method. The receiver, which has logistic demodulation block and chaotic decoder, is a linear asymptotic approximation to the inverse of the transmitter system. A chaotic iterative soft-decision decoding algorithm is also developed based on conventional maximum A posteriori decoding algorithm. At last, a two-step authentication method of this chaotic system is also presented.     

Optimal training sequences for MIMO systems under correlated fading

The optimal design of training sequences for channel estimation in multiple-input multiple-output （MIMO） systems under spatially correlated fading is considered. The channel is assumed to be a block-fading model with spatial correlation known at both the transmitter and the receiver. To minimize the channel estimation error, optimal training sequences are designed to exploit full information of the spatial correlation under the criterion of minimum mean square error （MMSE）. It is investigated that the spatial correlation is helpful to decrease the estimation error and the proposed training sequences have good performance via simulations.     

多天线OFDM系统的线性优化

从Jakes信道模型出发,用KKT优化方法,从信道部分特性已知的情况推导了多天线OFDM系统中发射机与接收机的线性最优化设计问题。仿真比较了多天线OFDM系统的各个子载波之间采用合作的线性优化与非合作的线性优化两种方法在不同最大多普勒频移和反馈时延下发送符号的均方误差。仿真结果表明,当信道特性部分已知时,子载波之间合作的线性优化较之非合作的线性优化有更小的均方误差。可为存在反馈时延的多天线OFDM系统设计提供指导     

基于状态观测器的超混沌同步保密通信系统

提出了一种基于状态观测器的超混沌同步保密通信系统。用超混沌系统的多个状态量对信息信号进行复杂的加密后注入超混沌系统实现混沌调制,同时将加密后的信息信号混沌掩盖后传送出去。用状态观测器思想实现了发送系统和接收系统的同步,并在接收端将信息信号解密。由于用了超混沌系统的多个状态量对信息信号加密,增加了传输信号的复杂性,提高了通信系统的保密性。     

Zero-forcing beamforming with receiver antenna selection in downlink multi-antenna multi-user system

A study on the zero-forcing beamforming （ZFBF） scheme with antenna selection at user terminals in downlink multi-antenna multi-user systems is presented. Simulation results show that the proposed ZFBF scheme with receiver antenna selection （ZFBF-AS） achieves considerable throughput improvement over the ZFBF scheme with single receiver antenna. The results also show that, with multi-user diversity, the ZFBF-AS scheme approaches the throughput performance of the ZFBF scheme using all receiver antennas （ZFBF-WO-AS） when the base station adopts semi-orthogonal user selection （SUS） algorithm, and achieves larger throughput when the base station adopts the Round-robin scheduling algorithm. Compared with ZFBF-WO-AS, the proposed ZFBF-AS scheme can reduce the cost of user equipments and the channel state information requirement at the transmitter （CSIT） as well as the multiuser scheduling complexity at the transmitter.     

时间反演UWB通信系统的窄带干扰抑制

超宽带(ultra wide band, UWB)通信系统工作在3.1~10.6 GHz的频谱范围内,与现存的一些通信系统共用频谱资源。为了防止UWB通信系统对其他通信系统造成干扰,美国联邦通信委员会将UWB的室内辐射功率谱密度限制在-41.3 dBm/MHz以下,但UWB通信系统会受到其共存的窄带系统的严重干扰。针对此问题,本文在接收端设计了一种自适应无限脉冲响应陷波器,推导了-3 dB处的自适应带宽,同时结合最速下降算法,找到陷波器的最优带宽,从而抑制UWB中的窄带干扰(narrow band interference, NBI)。最后使用蒙特卡罗仿真验证出自适应陷波器有效抑制了时间反演(time reversal, TR)UWB通信系统中的NBI,提升系统误比特率(bit error rate, BER)。     

非理想信道状态信息下的OFDM比特分配算法

提出一种在非理想信道状态信息条件下,以平均误比特率为目标的正交频分复用(OFDM)比特分配算法.该算法对子信道当前频率响应值进行估计,估计值经延时后反馈至发送端,并以此作为自适应比特分配的依据.仿真结果表明,当信道估计器的均方误差小于-15dB时,信道估计误差对自适应OFDM系统的性能影响不大.采用多个信道估计值来确定比特分配可以减小信道信息延时对系统性能的影响,有效提高系统性能.     

Capacity analysis of transmit beamforming with variable feedback delay

The feedback delay can severely affect the quality of the channel state information at the transmitter (CSIT) which is fed back from the receiver. The outdated CSIT will cause large performance loss in the transmit beamforming systems. The effect of variable feedback delay on the capacity of transmit beamforming systems over Rayleigh fading channels is studied. First, the case of fixed feedback delay is considered and a closed-form expression of system capacity is derived. Based on the results of fixed delay, the delay following certain distributions in variable delay case is assumed and the closed-form expressions of capacities are derived. The closed-form expressions show that the capacity is significantly affected by the statistical characteristics of the feedback delay. The obtained results provide an analytical insight into the effects caused by variable delay on the system capacity.     

发射信号泄露的连续波雷达方程

连续波雷达存在发射信号泄露的现象,泄露的发射信号边带噪声会淹没目标回波信号,使接收机灵敏度降低。而传统连续波雷达方程并没有考虑到这一现象对雷达性能的影响。在分析了传统连续波雷达方程的不足后,通过增加收发通道隔离度和发射信号相位噪声两个参数,对传统连续波雷达方程进行修正,使雷达方程中体现了发射信号泄露对连续波雷达的影响。这种改进的连续波雷达方程可以更切实际地描述出作用距离和雷达参数及目标特性之间的关系。     

Channel capacity of multiple-input multiple-output systems with transmit and receive correlation

In order to investigate the impact of channel model parameters on the channel capacity of a multipleinput multiple-output （MIMO） system, a novel method is proposed to explore the channel capacity under Rayleigh fiat fading with correlated transmit and receive antennas. The optimal transmitting direction which can achieve maximum channel capacity is derived using random matrices theory. In addition, the closed-form expression for the channel capacity of MIMO systems is given by utilizing the properties of Wishart distribution when SNR is high. Computer simulation results show that the channel capacity is maximized when the antenna spacing increases to a certain point, and furthermore, the larger the scattering angle is, the more quickly the channel capacity converges to its maximum. At high SNR （〉12 dB）, the estimation of capacity is close to its true wlue. And, when the same array configuration is adopted both at the transmitter and the receiver, the UCA yields higher channel capacity than ULA.     

Power allocation for MIMO-OFDM systems with multi-user decoupling and scheduling

1 .INTRODUCTIONRecentinformation-theoretic results haveshownthat multi-ple-input multiple-output ( MI MO) channels have a greatpotential to i mprove spectral efficiency in rich scatteringwireless channels[1 ,2].Si multaneously,orthogonal frequen-cy division multiplexing (OFDM) has gained anincreasinginterest as a promisingalternativeforfuture highrate wide-band wireless systems because of its lowcomplexity signalprocessingto counteract frequency selectivity. The combi-nationof MI MOsy…     

发射站/接收站位置误差下无源雷达DOA-TDOA目标定位算法

无源雷达中发射站和接收站位置误差的存在将显著降低目标定位精度。针对这一问题,将发射站和接收站位置误差考虑到基于波达方向和到达时差的无源雷达目标定位模型中,提出了一种目标位置代数解算法。首先,将波达方向和到达时差的测量方程线性化,考虑方程中的各项误差,采用加权最小二乘估计求解,并通过对加权矩阵的迭代更新,得到目标位置最优估计。推导了存在发射站和接收站位置误差条件下目标定位的克拉美罗下界,并从理论上证明了算法的定位精度可以达到克拉美罗下界。仿真结果表明,算法的定位精度优于现有算法,在发射站和接收站位置误差条件下定位精度仍能达到克拉美罗下界。     

全递推型式线性预报法可视化仿真

在数字通信系统中,由于信道的严重非线性失真,使得当发送数据信号通过该信道时,在接收端将产生符号间干扰,导致接收性能的严重衰落,如造成较高的误码率。为了改善系统性能,接收端必须通过信道均衡或序列估计消除信道畸变,因此很多盲均衡算法被相继提出。本文根据基于二阶统计量的盲均衡经典算法构造了全递推型式线性预报算法,利用SIMULINK提供的基本模块库及DSP模块库建立SIMO系统可视化仿真模型。在该系统模型下分别对三种信道情况进行仿真,给出误码率曲线并进行对比,对仿真结果进行分析。     

发射站/接收站位置误差下无源雷达DOA-TDOA目标定位算法

无源雷达中发射站和接收站位置误差的存在将显著降低目标定位精度。针对这一问题,将发射站和接收站位置误差考虑到基于波达方向和到达时差的无源雷达目标定位模型中,提出了一种目标位置代数解算法。首先,将波达方向和到达时差的测量方程线性化,考虑方程中的各项误差,采用加权最小二乘估计求解,并通过对加权矩阵的迭代更新,得到目标位置最优估计。推导了存在发射站和接收站位置误差条件下目标定位的克拉美罗下界,并从理论上证明了算法的定位精度可以达到克拉美罗下界。仿真结果表明,算法的定位精度优于现有算法,在发射站和接收站位置误差条件下定位精度仍能达到克拉美罗下界。     

多通道分组SFBC-OFDM传输方案

空频分组编码(SFBC)结合正交频分多路复用(OFDM)的发射分集方案(SF-OFDM)利用空间分集可以有效克服快衰落信道造成的不利影响,提高系统性能。对SF-OFDM发射分集方案做了简要分析,提出了一种多通道分组SFBC-OFDM发射分集方案。在发射端采用分组结构的SFBC结合OFDM技术,在接收端利用OFDM中子载波选择矩阵进行分组干扰抑制,然后对每一通道SFBC进行传统的空频分组码解码。这种传输方案克服了发射天线数目较大时传统SFBC编码非常复杂的缺点,极大地降低了编码的复杂度。分析和仿真结果验证了该方法的有效性。     

基于频域互相关序列与峰值检测的空频分组码盲识别算法

针对复杂电磁环境和非协作通信条件下空频分组码(space-frequency block codes, SFBC)信号识别困难、对先验信息要求高的问题, 提出一种基于频域互相关序列与峰值检测的SFBC盲识别方法。首先,通过分析SFBC信号的编码特点, 计算得到发送端的互相关函数。然后,考虑频率选择信道、多径传播和噪声的影响, 推导了接收信号的互相关函数, 并对其进行傅里叶变换得到频域互相关序列。最后,根据频域互相关序列检测其峰值位置识别发射端编码方式。推导和实验结果表明, 该算法在低信噪比下的识别性能较好, 并且对时间偏差和频率偏差等情况的适应性较强, 在复杂电磁环境下具有较好的识别性能, 能够应用在认知无线电和频谱检测等场合。该算法不需要知道信道和噪声的先验信息、正交频分复用(orthogonal frequency division multiplexing, OFDM)块大小以及接收端和发射端的同步信息, 非常适合于电子侦察等非协作通信场合。     

Optimal MMSE successive interference cancellation in group-wise STBC MIMO systems

1.INTRODUCTIONInformationtheoryshowsthat a multiple-input multi-ple-output(MI MO)communication systemcan effi-ciently increase system capacity in rich scatteringwireless channel environment without additional pow-er and frequency spectrumrequirement as traditionaltechniques need[1,2].Transmission schemes based onMI MO typically fall into two categories:data ratemaxi mization schemes and diversity maxi mumschemes.The representative of the first category isBell laboratories layered space…     

双基地MIMO雷达的DOD和DOA联合估计

将收发端各分成两子阵,建立了非均匀线阵下的双基地多输入多输出雷达数学模型。提出了ESPRIT谱搜索法和ESPRIT多项式求根法两种角度估计算法,并利用最大似然估计法实现了参数的正确配对,其优点是当不能提取出收发旋转不变因子时,应用本文算法仍能进行角度估计,放宽了ESPRIT算法对阵元配置的要求。仿真实验表明,低信噪比时,ESPRIT多项式求根法的估计精度优于ESPRIT谱搜索法;高信噪比时,两者的测向精度均接近于克拉美罗下限。同时,ESPRIT多项式求根法避免了谱峰搜索,极大地减少了计算量,在实际应用中更有利于推广。     

基于MCMC的OFDM系统脉冲噪声检测与抑制方法

为解决正交频分复用系统(orthogonal frequency division multiplexing,OFDM)中存在脉冲噪声干扰降低系统链路可靠性的问题,提出基于马尔可夫蒙特卡罗(Markov chain Monte Carlo,MCMC)的turbo迭代均衡检测方法。首先给出OFDM系统发射机和接收机模型;然后分析给出未知变量的先验分布及其在已知接收信号条件下的条件分布,通过MCMC均衡器抽样估计得到信道和脉冲噪声的参数信息;最后给出turbo迭代结构的具体实现过程。仿真结果表明,在加性高斯白噪声(additive white Gaussian noise,AWGN)信道和多径信道中,该方法可以有效降低OFDM系统中脉冲噪声影响,提高系统可靠性