多进制扩频信号的伪码周期盲估计

针对低信噪比条件下多进制扩频信号伪码周期检测与估计的问题,提出了一种基于多进制扩频信号功率谱二次处理的新方法。该方法首先对多进制扩频信号求取功率谱,接着将所得到的功率谱作为输入信号再求其功率谱,所得到的二次功率谱将在伪码周期整数倍处出现尖锐的脉冲,通过检测这些尖锐脉冲间的距离就可以估计出多进制扩频系统的伪码周期。理论分析和计算机仿真表明,该方法可以有效地估计出多进制扩频信号的伪码周期,且每条伪码传输的信息比特数越少,算法的估计性能就越好。     

基于二次谱的直扩信号伪码周期估计方法研究

文章采用二次功率谱法实现直接序列扩频信号(DS/SS信号)伪码周期的估计,此方法是对接收信号求得一次功率谱后再进行第二次求功率谱处理,最终得到信号的二次谱在信号伪码周期整数倍处出现一系列的尖峰脉冲,脉冲间距即为伪码周期。通过对二次谱法进行仿真实验,结果表明在较低信噪比条件下能够实现直扩信号的伪码周期估计;准确估计时所需的信噪比容限随着伪码周期的增加而逐渐降低。     

负信噪比同步CDMA信号伪码盲估计方法

为了实现对直接序列扩频通信信号的非协作接收，提出了一种新的基于子空间分析和盲信号处理算法的负信噪比同步码分多址（CDMA）信号伪码全盲估计方法。该方法突破了以往直接序列扩频信号伪码估计技术单用户假设的局限，更加贴近实际应用。理论分析和计算机仿真表明了该方法的有效性。     

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。     

一种直扩信号伪码周期及序列的盲估计方法

论述了功率谱二次处理理论和信号子空间分解方法在直接序列扩频(DS/SS)信号的伪码周期估计以及伪码序列盲估计中的应用,提出了利用功率谱二次处理结合信号子空间分解的方法以实现对低信噪比DS/SS信号的完全估计.计算机模拟结果表明,该方法在较低的输入信噪比条件下能良好地工作.     

直扩信号伪码周期的谱检测

针对低信噪比直扩信号（DS／SS信号）的伪码（PC码）周期截获的难题,提出了一类基于信号功率谱二次处理的新方法,理论分析和计算机模拟表明,该类方法在较低的输入信噪比条件下能良好地工作。     

直扩信号伪码的盲估计方法的研究

对直接序列扩频通信的信号检测方法进行了综述,重点讨论了自相关域检测方法、四阶累积量方法、谱分析与信号子空间分解法,其中四阶统积量方法和谱分析与信号子空间分解法的最低检测门限远低于相关算法,谱分析与信号子空间分解法在直接序列扩频(DS/SS)信号的伪码周期估计以及伪码序列盲估计中,利用功率谱二次处理结合信号子空间分解的方法可以实现对低信噪比DS/SS信号的估计。     

BOC信号的伪码周期和组合码盲估计

针对在低信噪比下存在残余频偏的BOC(Binary-Offset-Carrier)调制信号的伪码周期以及组合码(扩频序列和副载波序列的组合)盲估计问题,提出了功率谱二次处理结合矩阵分解的方法。该方法首先对存在残余频偏调制的BOC信号进行二次功率谱运算,所得二次功率谱中会在伪码周期及整数倍出现尖锐的脉冲,通过检测峰值间的距离估计信号的伪码周期,然后对信号采样并按伪码周期分段构成数据向量,计算相关矩阵并进行奇异值分解,最后搜索最大和次大奇异值以及对应的向量估计出组合码序列。仿真分析表明,该方法能够在较大频偏和较低的信噪比下达到较精确的估计性能。相关研究对于从事卫星导航接收机设计的工程技术人员具有一定的参考价值。     

MIMO DS/CDMA系统中基于信号周期平稳特性的频偏盲估计算法

MIMO DS／CDMA通信系统巾,每对收发天线问的载波频偏各不相同,这使得频偏估计变得异常困难。该文基于DS／CDMA信号的周期平稳特性提出了一种适用于该系统的频偏盲估计算法。该算法主要特点在于：（1）它能够分别估计每对收发天线间的载波频偏：（2）综合利用了信号在所有非零周期频率处的周期自棚关函数值,（3）它是一种盲估计算法,不需要专门的训练序列,不会降低系统的带宽利用率。仿真结果表明在FIR信道模型下,该算法能够准确地估计出系统巾各个收发天线对间的载波频偏。     

组合二进制偏移载波信号的伪码周期及组合码序列盲估计

针对在非协作通信以及低信噪比下组合二进制偏移载波(CBOC)信号伪码周期和组合码序列较难估计的问题,该文提出了2次谱算法与基于径向基函数(RBF)神经网络算法。对输入信号进行2次功率谱计算,可以得到CBOC信号的伪码周期。在此基础上,首先对接收的1周期组合码序列进行重叠分段,其次优化筛选出学习系数,对每段数据向量作为RBF神经网络的输入信号并进行有监督地调节,最后对每段数据向量多次输入并反复训练权值向量就可以恢复原组合码序列。仿真结果表明,利用2次谱可以在低信噪比下估计出伪码周期;在误码率低于1%的情况下,所提出的RBF神经网络相比于反向传播(BP)神经网络与Sanger神经网络,信噪比分别提高1 dB和3 dB,并且在同等条件下所需的数据组数较少。

     

短码、周期长码直扩信号伪码序列盲估计

针对短码、周期长码直扩信号在不同的时延下伪码序列估计问题,提出了一种基于奇异值分解的盲解扩算法.在已知信息码元速率和伪码周期条件的前提下,算法首先把接收到的直扩信号按照一定长度进行分段构成相关矩阵并对此矩阵进行奇异值分解得出信号子空间,然后根据信号子空间和伪码序列的模糊关系,利用求解的模糊酉矩阵和特定约束条件(如m序列)去其模糊性,最终估计出伪码序列.仿真结果表明,该算法不仅解决了在不同的时延下估计伪码序列带来的问题,而且具有稳定性高、在低信噪比条件下有良好的估计性能等优点.     

PN sequence blind estimation in multiuser DS‐CDMA systems with multipath channels based on successive subspace scheme

In this paper, we proposed a new method based on expanding subspace algorithm and finite alphabet characteristics, for blind estimation of the users' spreading sequences in the multiuser direct sequence code division multiple access system in the presence of the multipath channels. In the proposed scheme, we show that the estimation of the users' overall channels in the direct sequence code division multiple access system is equivalent to the impulse response estimation of the multi‐input multi‐output finite impulse response channels. Our proposed approach is based on the successive estimation of the columns of the equivalent multi‐input multi‐output finite impulse response channels from the lowest degree columns to the highest degree ones. Accordingly, each user's overall channel that is the convolution of the original multipath channel and the spreading sequence is estimated. Then we extract PN sequences from the overall channel using finite alphabet characteristics of the spreading sequence chips for each user. According to simulation results, our proposed scheme outperforms the conventional methods in that it does not require symbol synchronization and does not have channel constraints (for example, AWGN and single user system) in the multipath channels.     

基于Fast-ICA的CDMA信号扩频序列盲估计及性能分析

DS-CDMA分为长码和短码扩频2种扩频方式,已有的扩频序列盲估计算法只适用于短码扩频信号,不能完成长码扩频信号的扩频序列估计。对长码扩频CDMA信号的数学模型进行分析,提出了一种的新的基于Fast-ICA的多用户扩频序列盲估计方法并推导了算法的理论性能。该方法不仅能适用于长码扩频CDMA信号,而且对同步短码扩频CDMA信号也同样适用。理论分析和仿真结果验证了该方法的有效性。     

A novel tracking algorithm based on gravity of energy windows for DS/CDMA system

PN (Pseudo-Noise) code tracking is the most challenging task in a Direct Sequence Spread Code Division Multiplex Access (DS-CDMA) for celluar mobile communication systems. In this paper, the gravity of energy windows (GEW) tracking loop of the time and frequency uncertainty of the received signal is investigated, and the GEW's analytical results in a multi-path fading channel are introduced. GEW tracking loop exploits the inherent multi-path diversity of the channel, and has better performance than single-path one when working in multi-path fading environment.     

Blind Multiuser Detection in Multirate CDMA Based on Cyclic LMS Adaptation

The problem of blind adaptive multiuser detection in multirateCDMA systems is considered. Indeed, since symboldetection in multirate CDMA systems requires periodicallytime-varying processing of the observables, classical LMS and RLSadaptive algorithms, which assume that the solution to be trackedis time-invariant or slowly time-varying, are not suited for blindadaptive multiuser detection in a multirate system. While a cyclicRLS algorithm has recently appeared in the literature, thispaper focuses on the development of LMS-based cyclic filteringalgorithms. In particular, cyclic versions of the standard LMSalgorithm, of the LMS algorithm with iterate averaging and of theLMS algorithm with adaptive step-size are derived. Interestingly,the last two algorithms are shown to exhibit a convergence speed close to thatof the cyclicRLS procedure, but with an order of magnitude lower computationalcomplexity.An adaptive procedure for the automatic selection ofthe algorithm periodicity is also presented, which is based on aminimum mean-output-energy criterion, and that obviates theneed for knowledge of the transmitted data-rates from theinterfering signals.Moreover, the case of known multipathfading channels is also examined. In particular, it is shown that theproposed cyclic LMS algorithms can be used to achieve RLS-likeperformance also in the presence of multipath distortion.Extensive computer simulation results, along with some analyticalconvergence results, confirmthat the proposed algorithms are effective and achieve very satisfactoryperformance.     

DS/CDMA多用户检测盲自适应梯度算法的改进

本文在直接序列/码分多址(DS/CDMA)系统盲检测自适应梯度算法(BAG)的基础上,提出了一种多用户检测盲自适应梯度算法的改进算法(IBAG).BAG算法包括自适应梯度算法(TBAG)和时变自适应梯度算法(TIBAG),TBAG算法的跟踪特性较好,但起始收敛特性不好;TIBAG算法的收敛特性较好,但跟踪特性较差,几乎不具备跟踪能力.本改进算法结合了这两种自适应梯度算法的优点,在不增加算法复杂度的前提下,使其收敛性和跟踪特性较BAG算法有所提高.     

Blind Channel Estimation for Multi-Rate Multicarrier DS/CDMA Communications

Multi-rate multicarrier DS/CDMA is a potentially attractive multiple access method for future wireless communications networks that must support multimedia, and thus multi-rate, traffic. Several receiver structures exist for single-rate multicarrier systems, but little has been reported on multi-rate multicarrier systems. Considering that high-performance detection such as coherent demodulation needs the explicit knowledge of the channel, based on the finite-length chip waveform truncation, this paper proposes a subspace-based scheme for timing and channel estimation in multi-rate multicarrier DS/CDMA systems, which is applicable to both multicode and variable spreading factor systems. The performance of the proposed scheme for these two multi-rate systems is validated via numerical simulations. The effects of the finite-length chip waveform truncation on the performance of the proposed scheme is also analyzed theoretically.