Universal filters of arbitrary order and type employing square-root-domain technique

Novel Single Input Multiple Output (SIMO) and Multiple Input Single Output (MISO) universal filter topologies of arbitrary order and type are introduced in this paper. The proposed topologies have been realised by employing Square-Root Domain (SRD) technique. An offered benefit of the universal filter topologies is that only grounded capacitors are required for their implementations and the resonant frequency of the filters can be electronically controlled by an appropriate dc current. The proposed universal filters simultaneously offer all the five standard filtering functions i.e. Lowpass (LP), Highpass (HP) and Bandpass (BP), Bandstop (BS) and Allpass (AP) frequency responses. In addition, the SIMO topology is generic in the sense that it can yield four different stable filter configurations. Two design examples are provided in each configuration and the correct operation of the corresponding topologies has been evaluated through the PSPICE software with BSIM 0.35-µm CMOS process model parameters.     

Multiple Input Single Output Universal Biquad Filter with Current Feedback Operational Amplifiers

A novel Multiple Input Single Output (MISO) universal biquad filter topology realized using Current Feedback Operational Amplifiers (CFOAs) is introduced in this paper. With regards to the corresponding already published MISO universal biquads with CFOAs, the proposed topology simultaneously offers the benefits of employing only grounded capacitors, absence of any imposed constraint related to the values of input signals, and orthogonal adjustment between the quality factor and resonant frequency of the filter. The operation of the proposed biquad has been verified through experimental results by utilizing the commercially available AD844 CFOA discrete component.     

CFAR Detectors for MIMO Radars

CFAR (Constant False-Alarm Rate) processors are useful for detecting radar targets in a background for which the parameters in the statistical distribution are not known. A variety of CFAR techniques such as CA (Cell Averaging), Go (Greatest Of), SO (Smallest Of), OS (Ordered Statistics) and ACMLD (Automatic Censored Mean-Level Detector) processors have been proposed for SISO (Single Input–Single Output) radars in a non-homogeneous background. In this paper, conventional CFAR algorithms including CA, SO, OS and ACMLD processors are generalized for MIMO (Multiple Input–Multiple Output) radars. The exact expressions for false-alarm probabilities of the proposed algorithms in a homogeneous background are presented. In addition, the detection performance of the proposed detectors is studied by means of simulation in the presence of interfering targets and also colored Gaussian clutter. Besides, the proposed CFAR processors are compared, and it is shown that the ACML-based algorithm is superior to the other investigated methods.     

A Novel Circulant Approximation Method for Frequency Domain LMMSE Equalization

The coefficients of a Linear Minimum Mean Square Error (LMMSE) equalizer for a stationary random signal are defined by a Toeplitz system. The Toeplitz structure can be exploited to reduce computational complexity. In this paper we investigate the Levinson and Schur algorithm, as well as circulant embedding and circulant approximation methods applied to the Preconditioned Conjugate Gradient (PCG) method and Frequency Domain Equalization (FDE). We develop a novel circulant approximation method which improves the performance/complexity tradeoff. We show that the optimal choice of algorithms largely depends on the antenna configuration. Investigated configurations are Single Input Single Output (SISO), Single Input Multiple Output (SIMO) and Multiple Input Multiple Output (MIMO). All considered algorithms are benchmarked in terms of implementation complexity and capacity achieved by a High Speed Downlink Packet Access (HSDPA) receiver in a multipath fading scenario.     

多入单出正交空时分组码系统的调制识别

在现代无线通信系统中,采用正交空时分组码(STBC)的多天线发射技术是提高通信速率和可靠性,并且能够实现简单译码的关键技术。该文针对瑞利信道系统模型,提出一种适用于多入单出正交空时分组码(OSTBC)的调制识别算法。该算法通过对接收到的数据进行重排,将多入单出的系统模型转化为类似多入多出的系统模型,并且根据信源的特殊性用最大似然的思想实现调制类型的识别。仿真结果验证了所提算法的有效性。     

On the use of NSGA-II for multi-objective resource allocation in MIMO-OFDMA systems

This paper investigates the problem of dynamic subcarrier and bit allocation in downlink of Multiple Input Multiple Output (MIMO) Orthogonal Frequency Division Multiple Access (OFDMA) Systems. Using Singular Value Decomposition, the MIMO fading channel of each subcarrier is transformed into an equivalent bank of parallel Single Input Single Output sub-channels. To achieve the capacity bound, one must solve a multiuser subcarrier allocation and the optimal bit allocation jointly. To alleviate the computational complexity of joint subcarrier and bit allocation, several suboptimal solutions have been proposed. These suboptimal solutions handle subcarrier and bits individually. We propose the use of Non-dominated Sorting Genetic Algorithm (NSGA)-II, which is a multi-objective Genetic Algorithm, for joint allocation of bits and subcarriers, in the downlink of MIMO-OFDMA system. NSGA-II is intended for optimization problems involving multiple conflicting objectives. Here the two conflicting objectives are Rate Maximization and Transmit Power Minimization. The simulation results indicate remarkable improvement in terms of convergence over previous approaches involving Evolutionary algorithms. At the same time capacity achieved by the proposed algorithm is found to be comparable with that of previous algorithms.     

基于MIMO通信的OFDM／SC～FDE码分多址接人技术研究

为有效克服正交频分复用（OFDM）系统存在的不足,提高系统性能,将OFDM技术及单载波频域均衡（SC—FDE）技术分别与码分多址接入（CDMA）技术相结合,并在多输入多输出（MIMO）空间复用技术的高速率通信基础上,研究了相应的两种基带系统结构,讨论了系统所用的频域均衡算法及系数,最后给出性能仿真结果。结果表明,MIMO—SC—FDE—CDMA技术相结合能够更有效地提高系统性能,降低用户间干扰,有着良好的应用前景。     

Designing Fast Fourier Transform Accelerators for Orthogonal Frequency-Division Multiplexing Systems

Designing accelerators for the real-time computation of Fast Fourier Transform (FFT) algorithms for state-of-the-art Orthogonal Frequency-Division Multiplexing (OFDM) demodulators has always been challenging. We have scaled-up a template-based Coarse-Grain Reconfigurable Array device for faster FFT processing that generates special purpose accelerators based on the user input. Using a basic and a scaled-up version, we have generated a radix-4 and mixed-radix (2, 4) FFT accelerator to process different length and types of algorithms. Our implementation results show that these accelerators satisfy not only the execution time requirements of FFT processing for Single Input Single Output (SISO) wireless standards that are IEEE-802.11 a/g and 3GPP-LTE but also for Multiple Input Multiple Output (MIMO) IEEE-802.11n standard.     

基于MWF的非线性Volterra滤波

结合Volterra滤波的多人单出(MISO)模型,本文将多级维纳滤波(MWF)应用于非线性Volterra滤波,提出三种实现结构及其降秩滤波算法.MWF将期望信号连续投影到正交的低维子空间,利用嵌套的一组标量维纳滤波器实现滤波,避免求解观测矢量的自相关矩阵及其逆;而基于MWF的降秩滤波算法不需要进行计算复杂的特征值分解.结合中继卫星信道的非线性均衡对算法进行仿真,仿真结果表明三种结构均可以很好地收敛;降秩算法在减小运算量的同时,性能接近全秩算法.     

Space Diversity Knotted with WiMAX- A Way for Undistorted and Anti-Corruptive Channel

The principal aim of this research article is to develop an apt transmission scheme which will completely accomplish the goal of eliminating channel distortion. The effort on this work signifies and delivers a combined transmit diversity scheme that scatters the transmitter signal in multi dimension to comprehend the need to improve noise immunity. Extrapolating the diversity combining techniques, it is possible to perceive the same in the case of receivers. Space diversity is intertwined with WiMAX and the benefits have been demonstrated by incorporating various space diversity techniques and the analysis is done with respect to Bit Error Rate. Performance comparison is presented for Multiple Input Single Output and Multiple Input Multiple Output configurations.     

A High Resolution Wide Swath SAR method based on intra-pulse null steering and MIMO

High Resolution Wide Swath （HRWS） Synthetic Aperture Radar （SAR） often suffers from low Signal-to-Noise Ratio （SNR） due to small transmitting antenna, especially in phased array antenna systems. Digital Beam Forming （DBF） based on Single Input and Multiple Output （SIMO） achieves receiving array gain at the cost of increasing data rate. This letter proposes a new HRWS SAR method, which employs intra-pulse null steering to get receiving gain in elevation and decrease the data rate, and Multiple Input and Multiple Output （MIMO） using Space-Time Block Coding （STBC） in azimuth to get transmitting gain and receiving array gain simultaneously. The feasibility is verified by deduction and simulations.     

一种空时相关信道下的鲁棒SLNR预编码算法

为了改善存在信道误差、空时相关条件下多用户多入多出（MIMO）系统的性能,给出了一种基于信漏噪声比（SLNR）的鲁棒预编码算法.通过推导空时相关信道环境下信道向量的条件均值和协方差,分别建立了发送端信道状态信息（CSIT）和接收端信道状态信息（CSIR）模型.在此模型基础上,推导了收发两端信道状态信息（CSI）均不理想情况下的鲁棒SLNR 预编码以及相应的接收滤波矩阵.仿真结果表明,该算法对空间相关性、时间相关性以及信道误差均具备一定的鲁棒性.     

分布式孔径相参雷达预警探测技术

分布式孔径相参雷达是指空间分置的多部雷达在统一的控制和调度下,实现对目标信号级相参探测,具有探测威力大、测量精度高等优势,可应用于防空反导、预警探测、精密跟踪和空间目标监视等领域。本文针对分布式孔径雷达相参探测在预警领域的应用开展技术研究,首先分别给出了一发多收和多发多收相参合成预警探测工作原理;然后从探测威力和检测概率两方面对相参合成预警探测性能进行了分析,结果表明,相参合成对探测威力和检测概率改善效果明显;在此基础上,构建了低频段一发两收相参合成预警探测试验系统,通过对飞机目标相参探测试验验证了分布式孔径雷达相参合成预警探测的性能优势。      

The Capacity Performance of ASTC-MIMO-OFDM System in a Correlated Rayleigh Frequency-Selective Channel

Algebraic Space-Time Codes (ASTC) for Multiple Input Multiple Output (MIMO) systems are based on quaternion algebras. Thanks to their algebraic construction, the ASTC codes are full-rank, full-rate and have the non-vanishing determinant property. These codes have been proposed for MIMO flat fading channels in order to increase the spectral efficiency and to maximize the coding gain. The purpose of this work is to analyze the performance of the ASTC in a frequency selective Rayleigh channel. To deal with the frequency selectivity, we use the OFDM modulation. The capacity performances of an ASTC-MIMO-OFDM system, under correlated Rayleigh frequency-selective channel, have been evaluated.     

分布式MIMO-OFDM系统的同步捕获算法

该文提出了一种分布式多输入多输出正交频分复用(MIMO-OFDM)系统初始信号检测和同步捕获算法。该算法设计了导频符号,采用谱分析方法实现可靠的初始信号检测、粗定时和粗频偏估计,并在快速傅里叶变换(FFT)之后进行精确地频偏和定时估计。仿真结果表明,该算法在低信噪比多径瑞利信道条件下具有很好的性能。     

基于门限控制的新型矢量扰动预编码方法

以下行多用户多输入单输出系统为例,分析了在发送端采用矢量扰动预编码时,信道矩阵的条件数大小对算法复杂度及其系统性能的影响。通过蒙特卡洛仿真发现,当信道矩阵的条件数较小时,硬性采用矢量扰动预编码所寻找出来的扰动矢量大多是零矢量,此时不恰当的扰动甚至可能增大信号发送功率,导致不必要的浪费。当信道矩阵的条件数较大时,采用格基约缩的方法可以降低搜索扰动矢量的复杂度。在此基础上,提出了一种基于门限控制的新型矢量扰动预编码方法,该方法相对于传统的完全不考虑信道特性的矢量扰动预编码,可以极小的性能损失换取计算复杂度的显著降低。     

一种广义分布式多小区架构--群小区

为了更好地适应如空时码、联合发送、多入多出等未来移动通信系统核心技术的应用，满足第三代移动通信系统（3G）的多媒体业务对通信链路质量越来越高的要求。需要探讨全新的移动通信小区与网络拓扑结构。广义分布式多小区架构可以适应先进的多天线技术，并有效地解决由于载频提高导致的频繁切换问题。基于该架构的新型切换策略——群切换可以消除小区边缘效应，而进一步将群切换思想应用于3G系统的快速小区组选择方案可以大幅度地提高小区边缘用户的数据速率。     

MIMO广播系统中基于有限反馈的多用户选择新算法

在基于有限反馈多输入多输出(MIMO)广播系统的多用户选择研究中,目前已有的用户信噪干扰比(SINR)估计存在较大误差,这使得整个系统的性能受到制约。该文利用推导出的上下界来联合估计用户接收到的有用信号功率,得到了一种误差较小的SINR估计式,并基于该式给出了一种用户选择新算法。仿真结果表明,新的用户选择算法可以在低信噪比和高信噪比下同时达到较优性能,且复杂度较低。     

Orthogonal Discrete Frequency-Coding Waveform design for MIMO radar

Design of orthogonal code sets with ideal correlation properties is crucial for orthogonal Multiple Input Multiple Output（MIMO）radar.A modified Genetic Algorithm（GA）is proposed to numerically design orthogonal Discrete Frequency-Coding Waveforms（DFCWs）with good correlation properties for MIMO radar.Some of the designed results are presented,and their correlation properties are better than those presented in literatures.The effect of Doppler frequency shift on the performance of these signals is simply investigated.Simulation results and comparisons show that the proposed algorithm is more effective for the design of DFCWs with superior aperiodic correlation properties.     

基于网格搜索的同步损伤和信道联合估计算法

为了实现多输入多输出(MIMO)正交频分复用(OFDM)系统中同步损伤和信道的联合估计,提出了一种基于网格搜索的联合估计算法。首先通过构建起一个以反映同步损伤和信道响应影响的系统模型,然后将各损伤参数估计的多维优化问题简化为二维网格和一维网格搜索,从而实现对载波频率偏移、采样频率偏移和符号定时误差的联合估计;数值仿真结果表明,本文提出的联合估计算法相比于非联合估计算法具有更好的估计性能。