超宽带Pre—Rake接收技术研究

针对当前超宽带系统接收机误码性能较低、复杂度较高的缺点,提出了一种采用DS-PAM调制的Pre-Rake分集合并接收方案.方案基于IEEE802.15.3a的超宽带标准信道模型,首先将DS-PAM调制的发送信号,经信道传输后,在接收端对最强径信号做采样判决.基于蒙特卡罗仿真,对Pre-Arake、Pre-Stake、Pre-Prake等三种不同结构和不同支路数下的接收机性能进行了分析,并比较了不同脉冲传输速率和不同信道环境下的Pre-Rake接收机和Rake接收机的误码率.仿真结果表明,在传输速率较高且多径衰落严重的信道环境里,Pre-Rake接收机的误码率明显低于传统的Rake接收机,即Pre-Rake接收机可以有效的克服码间干扰和多径衰落.     

基于神经网络的超宽带Rake接收机研究

在复杂的超宽带多径传输环境中,利用Rake接收机可以有效的提高接收性能,本文在对现有Rake接收机的原理分析研究的基础上,提出基于神经网络的超宽带Rake接收机,并在IEEE802.15.3a信道模型中对其性能进行了仿真,结果表明能有效的提高接收性能.     

基于空分RAKE接收机的超宽带信号多径性能分析

超宽带信号由于良好的抗多径能力而适用于室内等密集多径场所的高速无线接入。该文研究的就是超宽带信号的多径信道中具体的性能指标，即在一定的信噪比条件和接收机条件下，超宽带系统传输的误码率。文中采用分空RAKE接收机，以最大组合比方式进行接收，在此基础上假设接收信号服从瑞利分布或莱斯分布，推导出了基于接收信号信噪比的不同超宽带多径信号波形及不同天线阵元数量时的误码率计算公式。之后，通过仿真对AWGN信道和多径信道的接收性能、不同UWB波形的接收性能等进行了比较，得出一些重要的具体结论。     

变步长LMS算法的超宽带Rake接收机设计

在无线通信中,超宽带接收机的抗干扰性是接收系统的重要技术,而误码率是抗干扰性重要的评价指标;为了提高超宽带接收机的接收性能和抗干扰能力,设计了变步长LMS算法的超宽带Rake接收机;通过建立系统模型,分析LMS算法基本原理且提出改进思路,将改进的变步长LMS算法应用于Rake接收机,进行建模仿真;结果显示变步长LMS算法的Rake接收机接收性能提高,误码率迅速降低到10-1,有效改善了接收机抗干扰能力。     

超宽带信号室内场强分布

采用了射线跟踪与时域分析相结合的室内超宽带信号仿真模型,用以分析和描述超宽带信号经室内多径环境传播后的时域电场强度。基于仿真模型,计算了超宽带信号的室内场强分布,针对RAKE接收机可利用多径信息的特点,比较了多径接收相对于单径接收的改善效果。结果表明,适当选取接收径数可以取得接收效果与接收机复杂度的综合最优效果,这对超宽带室内通信具有参考意义。     

海上移动信道分析及抗多径接收机设计与仿真

海上舰船之间的通信通常工作在复杂的信道环境下,通信距离可远可近,不仅存在强的敌方恶意干扰,由于受地球弧度和海浪、船只等的遮挡,还存在深衰落和多径效应,因此设计海上通信系统时需要充分考虑这些不利因素的影响.针对海上移动信道的路径衰减特性,提出利用Longley-Rice模型建立海上移动信道模型,并对信道衰减模型进行了数值仿真;分析了多径对扩频系统伪码捕获的影响,提出利用Rake接收技术改善接收机的抗多径性能,并设计了一个Rake接收机结构,最后进行了仿真分析.仿真结果表明所设计的Rake接收机具有良好的抗多径能力,能够满足海上通信的需要.     

超宽带系统中一种新型的MMSE-SRAKE接收机

根据超宽带室内信道多径的特点,阐述了一种新型的MMSE-SRAKE接收机,采用基于遗传(GA)算法的路径选择方法。仿真结果表明,通过合理次数的迭代,该接收机性能达到近似最优,优于传统的MMSE-SRAKE接收机。     

超宽带冲激无线电相关接收器的仿真比较

超宽带相关接收器的设计是超宽带冲激无线电接收机实现信号接收的关键之一,针对使用二阶高斯脉冲的超宽带冲激无线电相关接收器的特点,建立了相应的仿真模型,在Simulink平台下实现了对超宽带冲激无线电相关接收器的模拟,采用了T-R(发送-参考)自相关和互相关三种相关接收机方案,分别通过高斯噪声信道和多径信道进行相关仿真,对比了各种相关接收器的脉冲检测效果,验证了相关检测技术从噪声环境中提取超宽带信号的能力,为超宽带相关接收机系统的优化设计提供了参考.     

多用户混沌扩频通信系统的 Rake 接收误码分析

研究移动通信技术优化传输性能,在扩频通信系统中,针对多径信道的存在而产生了多径衰落问题,为了抗衰落和减少误码率,根据 Rake 接收机则具有良好的对抗多径衰落的效果,提出理论公式的推导,建立正确模型,在理想的信道参数估计器和混沌同步为前提下,假设多径信道的各个路径具有恒定增益.在混沌的多用户 DS-CDMA 扩频通信系统中,采用Rake 接收机,对系统的理论误码率进行了推导,将误码公式以能量分布、多径数目、用户数和混沌序列平均功率的形式给出,并通过 Matlab 对理论值与实际值进行了仿真比较,仿真结果表明实际值和理论值基本吻合,证明了推理过程的正确性.     

多径环境下的BOC信号的通用模型及捕获方法*

针对BOC(binary offset carrier)信号在多径环境下缺乏将各种边峰消除方法统一起来的通用模型以及无法精确捕获的问题,提出了一种基于Rake模型的边峰消除通用精确捕获方法。该方法首先利用Rake接收机将多径BOC信号采用最大比合并的方法得到近似单径信号,然后通过建立泛化的扩频符号波形,得到其边峰消除通用模型,最后通过相关合成运算得到精确的无模糊捕获方法。理论和计算机仿真表明,该方法不仅消除了多径干扰,建立了边峰消除通用模型而且较其他方法有更精确的捕获精度,对于sinBOC(1,1)而言,检测性能比SCPC算法提高了4dB。     

彩色图像有意义水印Rake接收机的设计

利用分集接收能够大幅度地改善系统接收性能的原理，把彩色图像看成是多通道的通信信道，将有意义水印信号进行正弦调制，按照图像信道的特点分别嵌入到彩色图像3个通道的小波域中。在水印检测时，利用小波变换的良好去噪能力和对1/f噪声的良好白化效果，设计了水印的Rake接收机，以达到分集接收的目的。从实验结果看，RAKE接收机的效果十分突出。     

短波软件无线电接收机射频数字化的一种实现方法

本文提出了采用一种电调谐对射频信号直接进行处理,它是一种连续可调的窄带滤波,经过后一级的宽带放大,再采用高性能A/D器件完成模数转换的射频数字化实现方法。该方法实现简单,测试后性能达到了基本的要求,应用于短波软件无线电接收机可大大简化其结构、提高其性能。     

ROPAS: Cross-Layer Cognitive Architecture for Mobile UWB Networks

The allocation of bandwidth to unlicensed users, without significantly increasing the interference on the existing licensed users, is a challenge for Ultra Wideband （UWB） networks. Our research work presents a novel Rake Optimization and Power Aware Scheduling （ROPAS） architecture for UWB networks. Since UWB communication is rich in multipath effects, a Rake receiver is used for path diversity. Our idea of developing an optimized Rake receiver in our ROPAS architecture stems from the intention of reducing the computation complexity in terms of the number of multiplications and additions needed for the weight derivation attached to each finger of the Rake receiver. Our proposed work uses the Cognitive Radio （CR） for dynamic channel allocation among the requesting users while limiting the average power transmitted in each sub-band. In our proposed novel ROPAS architecture, dynamic channel allocation is achieved by a CR-based cross-layer design between the PHY and Medium Access Control （MAC） layers. Additionally, the maximum number of parallel transmissions within a frame interval is formulated as an optimization problem. This optimal decision is based on the distance parameter between a transmitter-receiver pair, bit error rate and frequency of request by a particular application. Moreover, the optimization problem improvises a differentiation technique among the requesting applications by incorporating priority levels among user applications. This provides fairness and higher throughput among services with varying power constraint and data rates required for a UWB network.     

自适应相关性消除算法下的非线性盲均衡

针对现代宽带软件无线电接收机的动态性能受到接收器件非线性效应影响而恶化的问题,本文提出基于Wiener接收模型的自适应相关性消除算法实现对非线性信道的盲均衡。该算法以正交频分复用技术（Orthogonal frequency division multiplexing,OFDM）信号为例,利用接收信号间和数据间的独立不相关性,先对宽带信号与残余谐波进行相关性检测,再根据相关性进行自适应更新补偿模型权重,消除相关性,从而抑制系统非线性。仿真结果表明,相比于过去的算法,该算法在存在大信号干扰的情况下,能大大抑制信号的非线性,使得微弱信号误码率下降,大幅提高了接收系统的灵敏度,且计算复杂度较低。     

Augmented Hammerstein model for the calibration of six‐port based dual band wireless receivers

Two architectures of concurrent dual‐band six‐port‐based receiver (SPR), which are modeled and calibrated using the augmented Hammerstein model (AHM) are proposed for the first time in this article. The receivers are based on six‐port junctions with one or two local oscillators (LO). The proposed single step calibration algorithms achieve the recovery of the two in‐phase (I₁ and I₂) and quadrature (Q₁ and Q₂) components of an RF signal with two frequency components (RF₁ and RF₂). Experimental validations have been performed to verify the performance of the proposed concurrent dual‐band receivers and to test the efficiency of the AHM based calibration algorithms. As a performance metric, the Error Vector Magnitude (EVM) has been measured to compare the transmitted and recovered baseband signals and to evaluate the performance and efficiency of the proposed calibration algorithms for the two receiver topologies. The IQ data has been recovered with EVMs no higher than 2% for the two LOs based receiver excited with a QAM modulated dual‐band RF signal. The single LO based receiver has been tested with a dual‐band LTE signal and the recovered IQ data exhibited EVMs no higher than 4%.     

一种基于分形结构的超宽带天线研究

基于微带天线和分形天线的基本理论,采用正方形和圆形交替的方法设计了用于超宽带（UWB）通信的分形天线。利用电磁仿真软件CST软件对所设计的天线进行仿真、优化,并分析了影响天线阻抗特性和辐射特性的关键参数。从仿真实验结果可以看出,所设计的天线有较好的全向辐射特性和宽的阻抗带宽,能够满足超宽带通信需求。     

DS-CDMA downlink systems with fading channel employing the generalized receiver

In this paper, we investigate a generalized receiver (GR) constructed on the basis of the generalized approach to signal processing (GASP) in noise employing by direct-sequence code-division multiple access (DS-CDMA) downlink wireless communication system with multipath fading. Transmitted signaling technique is based on using the orthogonal unified complex Hadamard transform spreading sequences. The use of GR allows us to maintain the orthogonality between users and reduce the multipath fading effect and interference from other users. A general multipath-fading model is assumed. Bit-error rate (BER) performance of system is evaluated by means of the signal-to-interference-plus-noise ratio (SINR) at the output of GR employed by DS-CDMA downlink wireless communication system. Using the orthogonal unified complex Hadamard transform spreading sequences as the transmitted signaling technique, we obtain that SINR at the GR output is independent of the phase offsets between different paths. If the Walsh–Hadamard (WH) spreading sequences are used as the transmitted signaling technique, the SINR at the output of GR employed by the same system is a function of squared cosine of path phase offsets. As a result, the BER performance of the last DS-CDMA downlink wireless communication system is worse in comparison with that of the first system. Comparative analysis between the BER performance of DS-CDMA downlink wireless communication systems employing both the GR and the Rake receiver, which consists of a bank of correlation receivers, with each individual receiver correlating with a different arriving multipath component, shows us a superiority of the first system over the second one both at high and low SINRs.     

超宽带传输参考接收机研究

针对超宽带传输参考接收机模板信号包含噪声的问题,引入了一种新型的超宽带传输参考接收机结构,重点分析了该接收机的原理及性能。通过仿真验证,该新型的超宽带传输参考接收机性能相比平均超宽带传输参考接收机有很大提升。