考虑伪码跟踪误差影响的码片内多径分离研究

本文研究了考虑伪码跟踪误差影响的码片内多径分离技术。首先简要叙述了多径抵消技术的发展 ,然后基于多径监视思想给出了一种开环补偿多径抵消方法 ,随后详细分析了伪码跟踪误差对码片内多径分离结果的影响。仿真结果表明 ,采用这种开环补偿方法后 ,码片内多径分离结果得到不同程度的改善 ,提高了多径参数的估计精度     

CDMA信号码片内多径时延估计算法

针对CDMA信号的特点,提出了低信噪比条件下估计延迟差小于一个码片周期的多径信号时延的有效算法,该文首先建立了一个能够有效抑制噪声影响的多径功率延迟函数,然后推导了建立在此函数基础上的高分辨率时延估计算法,给出了算法的具体步骤,分析了算法的性能,最后通过对比仿真和性能仿真证明了该方法具有低信噪比条件下高频谱分辨率的特点。     

低空多径环境下雷达目标检测性能研究

针对低空多径环境下不同体制雷达目标检测性能展开研究,通过优化配置雷达阵元达到多径环境下的最优检测性能。建立低空多径环境下雷达接收信号模型,引入多径功率传播因子,将经典的Swerling目标起伏模型推广应用于低空多径环境,采用特征函数法推导低空多径环境下不同体制雷达的检测概率。仿真研究了多径功率传播因子对检测性能的影响,比较不同体制雷达的检测性能,结果表明多输入单输出雷达兼具相控阵雷达和多输入多输出雷达的优点,在多径环境下具有稳定的检测性能。     

多径环境下的直扩信号伪码周期估计

针对低信噪比条件下多径直接序列扩频(直扩)信号伪码周期估计的难题,拓展了先前提出的单径环境下基于信号功率谱二次处理的方法,提出了在低信噪比条件下多径环境中直扩信号的伪码周期估计的二次谱算法.该算法首先对多径直扩信号求取功率谱,然后将所得到的功率谱作为一输入信号求其第二次功率谱,所得二次功率谱将在伪码周期整数倍处出现代表信号存在的尖峰脉冲,通过对这些尖峰脉冲闻的距离进行检测就可以获得多径直扩信号伪码周期参数的检测估计.理论分析和计算机仿真结果表明:该算法可以有效地估计出多径环境下直扩信号的伪码周期,且估计性能和多径环境密切相关.     

多径环境下TDDM-BOC信号伪码周期估计

针对低信噪比下存在多径效应的时分数据调制二进制偏移载波( TDDM-BOC )调制信号的伪码周期估计难题,提出了一种基于二次谱的TDDM-BOC信号伪码周期估计算法。该算法首先推导出多径环境下TDDM-BOC信号模型,然后求出多径TDDM-BOC信号的功率谱,再求其二次谱,最后通过检测二次谱的尖峰脉冲间的间距得到多径环境下TDDM-BOC信号的伪码周期。实验过程中采用累加平均的方法可以达到降噪和精确估计的目的。仿真结果表明：该算法能够在多径环境下对TDDM-BOC信号伪码周期进行有效估计,且估计性能与多径环境有密切关系,这为今后我国“北斗冶导航接收设备的开发提供了一定的理论参考。     

WCDMA 移动终端用RAKE接收机结构与实现

针对WCDMAFDD下行链路,提出了一种接收机结构。与传统接收机不同,该结构是根据多径来拉动(延时)输入信号,即根据多径把各径的信号延时对齐,而本地码的相位只需一个,来对多径支路解扩,并直接合并输出。该结构可进一步通过串行方法实现,大大减少硬件资源。由于采用全硬件技术,因此,便于ASIC集成。     

一种码片内多径参数的最大似然估计算法

针对码分多址卫星移动通信中码片内两径参数估计问题,该文提出了基于最大似然的2维搜索算法。算法对两径时延进行2维搜索,同时对多径复振幅分别采用解相关和线性最小均方误差(LMMSE)算法进行估计,最后通过使似然函数最大化而找出最优的一组时延、复振幅估计值。仿真证明两径时延2维搜索结合采用近似的LMMSE算法进行多径复振幅估计具有良好的性能。     

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。      

多径信号对伪码扩频测距系统性能的影响

分析了多径效应对伪码扩频测距精度的影响,研究了航天测控系统中多径信号的特征,建立了系统的信道模型。利用MATLAB搭建仿真平台,比较了不同环境下多径效应对测距精度的影响。仿真结果表明：测距误差的均值和抖动随着信噪比的增大而减小,莱斯因子越大,测距误差的均值越小;而多径信号的相对延迟越大,多径信号的数量越多,测距误差的抖动越大。     

基于码片延迟的多径信道扩频序列盲估计

针对多径信道下低信噪比直扩信号扩频序列的盲估计问题,提出一种通过码片延迟与相关矩阵分析相结合的方法实现扩频波形估计。该方法首先将接收信号延迟一段时间与原信号相乘,然后代入自相关矩阵中,通过特征值分解求得最大特征值及其对应的特征向量,通过该特征向量中的零点确定同步位置并恢复扩频序列。理论分析和仿真结果表明,本算法在低信噪比条件下能完成对PN码序列的精确估计。     

研究片内多径分离技术在基于RSSI定位中的应用

无线传感器网络中基于接收信号强度指示(RSSI)的定位易受多径干扰。传统的基于RSSI定位方法主要通过增加测距样本来抵抗多径干扰,而在物理层研究抗多径干扰的较少。该文将片内多径分离技术应用于基于RSSI的定位中,通过抽取每个码片的第1个采样点进行相关解扩得到分离多径后的直达径,并求其功率得到抗多径干扰的RSSI值。理论分析其多径的分离能力,信噪比损失情况。最后通过仿真比较了传统方法与该文方法求得的RSSI值方差,该文方法在多径信道下的方差更小。     

Subchip multipath delay estimation for downlink WCDMA system based on Teager-Kaiser operator

Accurate detection and estimation of overlapping fading multipath components is vital for many communication systems, particularly for positioning technologies. Traditional approaches used for channel estimation generally fail in estimating closely-spaced multipath components in code-division multiple access (CDMA) systems. Here, we present a highly efficient technique for asynchronous downlink WCDMA multipath delay estimation with subchip resolution capability based on nonlinear Teager-Kaiser operator concept. The behavior of this technique is influenced considerably by the pulse shape waveform. Both rectangular and root raised cosine pulse shaping filters are considered.     

超宽带Rake接收机在密集多径信道下的性能

超宽带信号在室内环境中将经历密集多径传播,产生严重的时间弥敞。采用Rake接收是提高超宽带接收机性能的重要手段。该文针对采用BPSK调制的超宽带系统,推导出密集多径信道下Rake接收机的误码性能计算公式,揭示了Rake接收机性能与多径信道参数以及脉冲波形自相关系数之间的关系。针对典型信道模型和脉冲给出了计算实例。     

Effect of multipath propagation on the forward link of a CDMA cellular system

In this paper we study the effect of multipath propagation on the performance of the forward link of a CDMA cellular system. We assume that RAKE receivers are used by the mobile terminals to receive the multipath signals and derive signal-to-noise ratios (SNR) for the RAKE receiver output for both orthogonal and non-orthogonal spreading sequences. These SNR expressions are evaluated using real impulse response measurement data obtained in the city of Toronto and comparisons are made between urban and suburban environments. We have found that even though multipath propagation tends to destroy the orthogonality of signals in an orthogonal CDMA system, the system with orthogonal CDMA codes still performs significantly better than a system utilizing random spreading codes in realistic multipath propagation environments.This work was supported in part by Bell Mobility Cellular and in part by the Information Technology Research Center of Ontario (ITRC).     

On the capacity of UWB over multipath channels

In this work we compute the information theoretic capacity C of binary orthogonal pulse position modulated (PPM) signals for ultra wideband (UWB) communications over multipath channels. We consider binary PPM signals with random energy and correlation values. Numerical examples are given to illustrate the capacity results.     

A lens antenna array with adaptive optical processing

This paper presents an X band smart antenna array in which adaptive processing of the received signals is performed by dynamic holographic optical circuitry. The optical circuitry adaptively extracts the principal component of the received signal space, that is the strongest first-order independent temporal component of the ensemble of received signals. The adaptive receiver system can be used, for example, to mitigate multipath interference effects and can separate one received signal from another even though their power spectra may entirely overlap. A prototype two-channel system is designed to fit in a standard-size briefcase and consume less than 50 W of power. The input to the system are modulated waves with a carrier in X band and the output is an electronic demodulated signal. Three major components of this system are described in detail: (1) the quasi-optical lens antenna array front end with angle-of-arrival preprocessing and downconversion, (2) the two-channel electrooptic modulation and optical carrier suppression stage, and (3) the smart optical processor (auto-tuning filter). Component and end-to-end system measurements give quantitative indicators for the usefulness of optical processing in wireless communications     

Joint angle and delay estimation (JADE) for multipath signalsarriving at an antenna array

In wireless communications, mobiles emit signals that arrive at a base station via multiple paths. Estimating each path's angle-of-arrival (AOA) and propagation delay is necessary for several applications, such as mobile localization for emergency services. We propose a novel subspace approach to estimate the AOA and delays of multipath signals from digitally modulated sources arriving at an antenna array. Our method uses a collection of estimates of a space-time vector channel. The Cramer-Rao bound (CRB) and simulations are provided     

On Time-of-arrival Positioning in a Multipath Environment

Wireless geolocation in a multipath environment is of particular interest for wideband communications and fast-developing ultrawideband (UWB) technologies. Conventional methods are solely based on first arriving signals. In this paper, it is investigated whether and under what conditions processing delay estimates of multipath components in addition to first arrivals can enhance the positioning accuracy. It is shown that the enhancement depends on two principal factors: strength of multipath components and variance of nonline-of-sight (NLOS) delays. Analytical results, which are derived as an extension of a single-path propagation case (IEEE Trans. Wireless Commun., Feb. 2006), are presented first. Their practical implications are then discussed by examining several numerical examples. Finally, modified schemes of practical interest in a multipath environment are proposed.     

基于FDTD的罗兰-C信号地波传播特性的时域分析

罗兰-C信号为载波调制的高斯脉冲,而传统方法对其传播特性预测均是基于100 kHz单频信号结果。文章采用FDTD方法计算了实际罗兰信号的时域特性,并和100 kHz连续单频信号结果进行了比较。结果显示:对于地形起伏不大的传播路径,两种信号结果吻合得很好,而对于地形起伏较大路径,脉冲信号结果与单频信号结果存在较大差异。该结果对地波传播特性工程测量与分析具有一定指导意义。     

A prediction model for multipath propagation of pulse signals at VHF and UHF over irregular terrain

A prediction model is presented that permits calculation of the probability of occurrence of distinct multipath propagation of pulse signals at VHF and UHF over irregular terrain. The model applies to terrain characterized by an irregular distribution of obstacles such as hills, buildings, trees, etc., so as to make it impractical to calculate the effect of multipath propagation by diffraction or bistatic-reflection theory. Statistical data on wave propagation over irregular terrain form the basis for the empirical model developed. Generally, the model predicts that 1) for constant transmitter-receiver separation, the amplitudes of the received echoes decrease with increasing echo delay, and 2) for constant echo delay, the occurrence of echo pulses increases as the transmitter-receiver distance increases. The results obtained from the model for rural, hilly terrain, and for a built-up metropolitan area are compared with available measured data.