基于DMF捕获系统频率选择性信道下捕获性能的分析

对基于数字匹配滤波器(DMF)捕获系统在频率选择性信道下的捕获性能进行了深入讨论，利用状态转移图推导出单次驻留判决方式时平均捕获时间的表达式，对平均捕获时间与多径分量的关系进行了数字分析。得出的主要结论是：对于多径分量为非衰落信号时，多径分量之间的能量差别越大，系统捕获性能越好，多径分量的能量相等时，系统捕获性能最差，且随着可以分离的多径路数的增加下降；对于多径分量为慢衰落信号时，多径信道的捕获性能好于单径信道(非频率选择性衰落信道)，且多径分量之间的能量差别越大，系统捕获性能越差，当多径分量的能量相等时，捕获性能最好，这与非衰落信道的情形相反。因此在频率选择性衰落信道中，采用分集接收可以改善系统的捕获性能。     

瑞利衰落信道下基于DMF的伪码捕获性能分析

基于数字匹配滤波器(DMF)的PN码捕获电路具有较快的捕获速度,因此在扩频系统中得到广泛的应用,为了在瑞利衰落信道下进一步提高捕获性能,对影响捕获性能的虚警概率和检测概率进行了推导和分析,进而计算出了平均捕获时间,并且作出了仿真和分析,为改善瑞利衰落信道下捕获性能提供了解决思路和理论依据。     

非衰落信道下基于DMF的伪码捕获性能分析

基于数字匹配滤波器（DMF）的PN码捕获电路具有较快的捕获速度,因此在扩频系统中已得到广泛应用,为了在高斯白噪声环境的非衰落信道下改善DMF捕获性能,对影响捕获性能的虚警概率和检测概率进行了推导和分析,进而计算出了平均捕获时间,最后做出了仿真和分析。     

正交频分复用技术在协作通信下的应用

协作分集技术利用其他用户进行协作传输,可以获得一定的分集增益,但是在频率选择性衰落信道下性能不很乐观。为了对抗频率选择性衰落,采用正交频分复用(ODFM)技术与协作分集技术相结合的方法,研究了基于OFDM技术的协作通信,对在不同调制技术、不同信道估计方法下系统的性能进行了比较,为了进一步提高系统性能,对传统S&C算法进行了改进并应用于该系统中,仿真实验结果表明,改进的定时同步算法性能优于传统的S&C算法。     

多径衰落信道下多载波CDMA信号的频率分集接收

本文研究了多载波码分多址(Multi-Carrier CDMA)扩展频谱系统在多径衰落信道下的频率分集接收技术。文中首先研究了理想载波恢复、频率选择性瑞利衰落信道条件下多载波码分多址系统的性能,然后提出了用时间频率窗平滑来改善载波相位估计的算法,并对该算法在衰落信道下的性能进行了仿真。理论推导和计算机仿真结果说明,多载波码分多址系统的频率分集接收方案与理论上最佳的RAKE分集接收相比,性能略有下降,但接收机结构得到了简化。     

频率选择性衰落信道下的空时分组码技术

空时分组码是一种有效抗衰落的发射分集技术,但是现有的研究大都集中在平坦衰落信道下进行。文章详细分析了频率选择性衰落信道下的空时分组码技术——OFDM-STBC(Orthogonal Frequency Division Multiplexing-Space TimeBlock Coding)的系统结构和编译码方法。仿真结果表明OFDM-STBC的性能可达到甚至优于STBC在非频率选择性信道下的性能。     

双选择性信道下发射分集MISO OFDM系统基于BEM的低复杂度信道均衡

在高速移动环境下,无线信道会同时经历时间选择性和频率选择性衰落,即所谓的快速时变信道,也称之为双选择性信道。最初的发射分集Alamouti编码方案是针对时不变平坦信道提出的,不能直接应用于快速时变信道。此外,OFDM 系统在双选信道下遭受的载波间干扰(ICI)不可忽视。因此,发射分集MISO OFDM系统在双选择性信道下既节能又有效的信号恢复是有挑战的。本文基于双选择性信道的基扩展模型(BEM)表示,研究了一种有效的可动态分组的混合干扰消除(HIC)信道均衡方案。仿真结果表明,提出的方案,与传统的MMSE均衡相比,计算复杂度大大降低的同时性能显著提高,计算量的降低减少了能量消耗,达到节能的目的;与现有的关于发射分集的信道均衡方案相比,表现出性能和复杂度的较好折中;此外,在信道信息完美已知的假设下,随着移动速度的提高,误码性能没有损失。      

分布式天线系统混合SC/MRC分集中断概率性能

在频率选择性复合Nakagami/lognormal衰落信道条件下,研究了层叠分布式天线系统(Cascade Distributed Antenna System--CDAS)采用混合SC/MRC分集的中断概率性能.针对中断概率性能,分析了多径密度函数(Multipath Intensity Profile MIP)衰减因子、空时分集维数、活动用户数、每比特平均接收信噪比以及衰落因子对系统性能的影响.仿真表明CDAS系统可以有效对抗衰落,提高系统容量,削弱对数正态阴影衰落影响.     

多径衰落信道下多功波CDMA信号的频率分集接收

本文研究了多载波码分多址（Ｍｕｌｔｉ－ＣａｒｒｉｅｒＣＤＭＡ）扩展频谱在系统在多径衰落信道下的频率分集接收技术，文中首先研究了理想载波恢复，频率选择性瑞利衰落信道条件下多功波码分址系统的性能，然后提出了用时间频率窗有来改善载波相位估计的算法，并对该算法在衰落信道下的性能进行了仿真，理论推导和计算机仿真结果表明，多载波码分多址系统的频率分集接收方案与理论上最佳的ＲＡＫＥ分集接收相比，性能略有下降，但     

FFH/BFSK选择分集合并接收机在部分频带干扰Nakagami-m信道下的性能分析

快速跳频通信系统选择分集合并接收机可以有效减轻干扰及衰落对系统带来的性能损伤。该文给出了快速跳频BFSK系统在部分频带干扰下的选择分集合并接收机模型,并对该接收机在同时存在部分频带干扰以及加性高斯白噪声的非频率选择性Nakagami-m衰落信道下的性能进行了推导,给出了误码率的闭合表达式。最后进行了仿真验证,仿真结果与理论分析结果完全一致。分析表明:具有高分集度的选择分集合并接收机受干扰影响较小;在干扰功率较大时,其性能要好于其它几种分集合并接收机;在一定的信道条件下,存在一个最佳分集度。最后针对选择分集合并接收机在弱干扰信号下的性能不足,提出相应的改进措施。     

DS-CDMA移动通信系统的捕获技术

PN (PseudoNoise)码捕获技术是DS CDMA (DirectSequence CodeDivisionMultipleAccess)蜂窝移动通信系统的关键技术。文中提出了一种基于能量窗的捕获技术 ,有效地利用了CDMA系统固有的多径分集能力 ,捕获对象是多径信号 ,研究结果表明 :对有效多径成分进行捕获有比单径捕获和跟踪有更好的性能。     

Serial acquisition performance of single-carrier and multicarrier DS-CDMA over Nakagami-m fading channels

We investigate the issue of pseudo noise (PN) code acquisition in single-carrier and multicarrier (MC) direct-sequence code-division multiple-access (DS-CDMA) systems, when the channel is modeled by frequency-selective Nakagami-m (1960) fading. The PN code acquisition performance of single-carrier and MC DS-CDMA systems is analyzed and compared when communicating over Nakagami-m fading channels under the hypothesis of multiple synchronous states (H/sub 1/ cells) in the uncertainty region of the PN code. In the context of MC DS-CDMA, the code acquisition performance is evaluated, when the correlator outputs of the subcarriers associated with the same phase of the local PN code replica are noncoherently combined by using equal gain combining (EGC) or selection combining (SC) schemes. The performance comparison of the above mentioned schemes shows that the code acquisition performance of the MC DS-CDMA scheme, especially when using the EGC scheme, is more robust, than that of single-carrier DS-CDMA schemes communicating over the multipath Nakagami-m fading channels encountered. However, our code acquisition performance comparison also shows that if the detection threshold was set inappropriately, the performance might be degraded, even if the channel fading becomes less severe.     

DS／CDMA移动通信系统的同步技术

PN码捕获技术是DS -CDMA蜂窝移动通信系统的关键技术。这里提出了一种基于能量窗的捕获技术 ,基于能量窗的捕获技术有效地利用了CDMA系统固有的多径分集能力 ,捕获对象是多径信号。研究结果表明对有效多径成分进行捕获有比单径捕获和跟踪更好的性能。     

Noncoherent hybrid parallel PN code acquisition for CDMA mobilecommunications

This paper proposes a noncoherent hybrid parallel pseudonoise (PN) code acquisition scheme for code-division multiple access (CDMA) mobile communication systems and analyzes the effect of multiple access interference (MAI) on the code acquisition performance for Rayleigh and Rician fading channels. The hybrid acquisition scheme combines parallel search with serial search to cover the whole uncertainty region of the input code phase. It has a much simpler acquisition hardware structure than the total parallel acquisition and can achieve the mean acquisition time slightly inferior to that of the total parallel acquisition in the case of severe MAI; on the other hand, it provides the flexibility in the tradeoff between the mean acquisition time and system complexity if no MAI is considered. The closed-form expressions of the detection and false-alarm probabilities and mean acquisition time are derived. Numerical analysis quantifies the severe performance degradation of code acquisition due to both MAI and channel fading, and demonstrates the dependence of the increase of mean acquisition time (due to MAI) on the number of users in the CDMA system, system design parameters, and channel fading statistics     

基于DMF直扩系统捕获性能的研究

对以数字匹配滤波器（DMF）为核心的捕获电路的性能进行了深入研究，推导出单次、两次驻留判决方式的平均捕获时间的表达式，并进行了数值分析。得出的结论是：基于DMF的捕获电路具有很快的捕获速度，适合于猝发通信；低信噪比下，捕获速度对门限更多敏感，且两次驻留判决在低信噪比下略好于单次驻留判决。     

Single-dwell and multidwell PN code acquisition in multipath Rayleigh fading channels

Traditional analysis on PN code acquisition was based on either AWGN or single-ray Rician/Rayleigh fading channels. In this paper, we analyze single-dwell and multidwell code acquisition schemes based on a two-ray Rayleigh fading channel model which is more appropriate to represent the real situations in mobile (personal) communication. Through the analytical and numerical results, we may figure out the performance of typical PN code acquisition schemes and the corresponding penalty in multipath fading channels when the second ray has much smaller power and the processing gain is not large. Otherwise, the second ray may be useful in communication and thus improves the acquisition performance as introducing a new correct acquisition state.     

Performance of antenna diversity multiuser receivers in CDMA channels with imperfect fading estimation

The performance of antenna diversity coherent and differentially coherent linear multiuser receivers is analyzed in frequency-nonselective Rayleigh fading CDMA channels with memory. The estimates of the complex fading processes are utilized for maximal-ratio combining and carrier recovery of the coherent multiuser receiver. To analyze the impact of channel estimation errors on the receiver performance, error probability is assessed directly in terms of the fading rate and the number of active users, showing the penalty imposed by imperfect channel estimation as well as the fading-induced error probability floor. The impact of fading dynamics on the differentially coherent decorrelating receiver with equal-gain combining is quantified. While performance of multiuser receivers at lower SNR is determined by both the fading dynamics and the number of active CDMA users, performance at higher SNR is given by an error probability floor which is due to fading only and has the same value as in a single-user case. The comparison of the two receiver structures indicates that the coherent decorrelating receiver with diversity reception may be preferable to the differentially coherent one in nonselective fading CDMA channels with memory.