利用虚拟子载波抑制OFDM系统PAPR及其低复杂度算法

研究了利用虚拟子载波抑制OFDM系统PAPR及其算法简化的问题.通过对虚拟子载波技术迭代过程进行简化,得到了运算量只是系统子载波数量级的低复杂度迭代算法,减小了算法实现的复杂度.计算机仿真表明,通过增大虚拟子载波数量或迭代次数,可使系统PAPR性能在一定范围内得到明显改善.由于不用传输边带信息,系统具有较强的可靠性和抗干扰能力.     

基于虚拟子载波的盲信道估计改进算法

提出了一种改进算法，该算法基于虚拟子载波的子空间算法，利用循环前缀（CP）引入的信息冗余，由于OFDM传输方程不能直接推导子空间算法，故首先给出一种新的方法对OFDM传输方程作矩阵变换，从而得到一个结构简单的新方程，基于这个新方程推导子空间算法。系统分析及仿真结果表明，在信噪比为20dB的条件下，与已有算法相比可以有7dB的性能提高且在收敛速度上和已有算法相比．快500～800个符号。     

一种新的OFDM系统载波频率捕获算法

该文从OFDM信号的特性出发,采用单一训练帧,将OFDM系统的载波频率捕获等效为单载波频差估计。该文提出的算法仅使用一帧辅助数据;具有较高的精度,较少的计算量和较大的捕获范围;且不受多径信道,时偏及帧同步误差的影响。     

一种低复杂度的OFDM子载波分配算法

针对认知无线电中基于OFDM子载波分配ACG算法的计算复杂度高的这一缺点,提出了一种能降低计算复杂度的OFDM子载波分配算法。新的分配算法是通过运用设定方差门限值的方法把一些信道状态变化不大的连续子载波结合成子信道,从而将原来针对每个子载波的分配转变为针对子信道的分配,以此来降低频谱资源的分配次数。仿真分析表明,新的分配算法以牺牲少量频谱效益的代价,较之原有算法,明显地降低了计算复杂度。     

基于天线波束成形的OFDMA系统的自适应资源分配

对正交频分复用接入系统在多用户多天线传输情况下的自适应资源分配策略进行了研究,提出了一种基于天线波束成形的,包括动态子载波分配、自适应调制、比特加载的无线资源分配方案.算法的优化设计目标是在满足总的恒定传输比特数和误比特率性能要求的情况下,使得系统总的发射功率最小.仿真结果表明,由于多天线阵列增益和多用户分集增益,系统整体性能得到了明显的优化.     

多带OFDM-UWB动态子载波分配算法

超宽带系统的传输功率谱密度是严格限制的,发射功率是超宽带系统的主要性能指标之一.为了最小化系统总发射功率,论文在给定用户速率和误比特率限制的前提下提出了一种新的功率最小化的自适应子载波分配算法.该算法采用次优算法,通过基于差值的子载波选择、子载波比特分配和相同比特子载波分配优化三个完整的动态分配,有效避免了衰落严重的子...     

一种基于快跳频技术的多载波CDMA系统

为进一步提高多载波CDMA系统的频带效率与抗干扰能力,提出了一种跳频多址技术结合多载波调制的传输方案,利用跳频技术将部分子载波传输与随机交织引入到多载波传输系统中,给出了系统实现的模型,并对该传输方案的系统带宽和误码性能进行了分析。理论分析与仿真结果表明：与以往的多载波CDMA系统相比,所建议系统的结构简单,性能优异,消除了已有系统中峰均功率比高和远近效应等问题,具有较强的抗多址干扰与窄带干扰的能力,并能有效地抗信道中突发错误的能力。     

多入多出正交频分复用多播波束成形优化

为保证多播服务质量(QoS)要求,建议一种所有组成员满足信号与干扰加噪声比(SINR)门限的功率约束下多输入多输出-正交频分复用(MIMO-OFDM)波束成形优化模型,提出在最大化多播MIMO分集策略下接收波成形算法,并得到发射波成形和接收波成形矢量及满足QoS要求所需最小发射功率。通过仿真与性能分析,证明满足最小SINR要求的波成形优化方法不仅能得到最小发射功率,同时具有改善多播用户间公平性的特性,并得到一些重要结论。     

OFDM自适应子载波功率分配算法

利用误比特率优化的自适应子载波功率分配算法,对发射功率进行合理分配,能够有效地提高正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)系统的频谱效率,但对各子载波采用正交幅度调制(QAM)的OFDM系统,该算法的求解却相当困难。本文研究了一种次优的功率分配算法,利用误差函数(Q函数)的近似值对其进行逼近,从而有效降低了求解难度。通过MATLAB仿真验证了次优分配算法优异的误比特率性能,仿真结果表明,该逼近算法能够很好地解决最优功率分配算法的复杂度问题。     

多用户光OFDM系统自适应子载波与比特分配算法

光OFDM能够方便地应用于现有基于PON的接入网,随着用户业务需求的增加和多样化,在用户间合理地分配资源能够提供更优质的服务。在此,阐述了一种优化的误码率最小化自适应资源分配算法。仿真结果显示,在对系统误码率影响不大的情况下,该算法在原算法的基础上降低了复杂度。     

Optimum beamforming for pre-FFT OFDM adaptive antenna array

It is well known that orthogonal frequency-division multiplexing (OFDM) is robust to frequency-selective fading in wireless channels due to the exploitation of a guard interval that is inserted at the beginning of each OFDM symbol. However, once delayed signals beyond the guard interval are introduced in a channel with a large delay spread, intersymbol interference causes a severe degradation in the transmission performance. In this paper, we propose a novel pre-fast Fourier transform (FFT) OFDM adaptive antenna array, which requires only one FFT processor at a receiver, for suppressing such delayed signals. We derive the optimum weight set for beamformers based on the maximum signal-to-noise-and-interference power ratio (Max-SNIR) and the minimum mean square error (mmse) criteria, respectively. In addition, we propose a novel mmse-criterion-based commutative optimization scheme, which is more robust to the estimation error of the channel state information. Furthermore, we show the equivalence between the Max-SNIR-criterion-based scheme and the proposed commutative optimization scheme. Computer simulation results show its good performance even in channels where directions of arrival of arriving waves are randomly determined.     

基于自适应拟牛顿法的CDMA天线阵列波束形成

针对于CDMA系统自适应天线阵列,提出了一种新的盲自适应MSINR(Maximum Signal-to-Interference plus noise ratio)波束形成算法.首先,将MSINR准则转化为一种新的无约束损失函数,并且从理论上分析该损失函数的性质.然后,应用自适应拟牛顿方法得到在线迭代波束形成算法.该算法无需训练序,而是利用CDMA信号自身的结构特点,结合空间处理提高了系统性能.最后,给出了仿真结果,表明算法具有较快的收敛速度和良好的动态跟踪能力.     

A novel adaptive beamforming algorithm for antenna array CDMA systems with strong interferers

Blind beamforming based on the maximum signal-to-noise ratio (MSNR) can improve the performance of an array system only when the processing gain of the given code-division multiple-access (CDMA) system is high enough such that the desired signal can become dominant after despreading (see Choi, S. and Shim, D., IEEE Trans. Veh. Technol., vol.49, p.1793-1806, 2000; Choi, S. and Yun, D., IEEE Trans. Antennas Propagat., vol.45, p.1393-1404, 1997). We consider a maximum signal-to-interference-plus-noise ratio (MSINR) beamforming. The MSINR performance criterion is chosen to deal with strong interferers effectively. It is shown that blind MSINR beamforming is possible by directly utilizing the input and output signals of correlators of the CDMA systems. In addition, we propose an adaptive beamforming algorithm at a lower computational complexity - about O(7.5N) - where N is the number of antenna elements of the array system. Simulation results are presented in various signal environments to show the performance of the proposed adaptive algorithm.     

Fast adaptive blind beamforming algorithm for antenna array in CDMA systems

In this paper, the maximum signal-to-interference-plus-noise ratio (MSINR) beamforming problem in antenna-array CDMA systems is considered. In this paper, a modified MSINR criterion presented in a previous paper is interpreted as an unconstrained scalar cost function. By applying recursive least squares (RLS) to minimize the cost function, a novel blind adaptive beamforming algorithm to estimate the beamforming vector, which optimally combines the desired signal contributions from different antenna elements while suppressing noise and interference, is derived. Neither the knowledge of the channel conditions (fading coefficients, signature sequences and timing of interferers, statistics of other noises, etc.) nor training sequence is required. Compared with previously published adaptive beamforming algorithms based on the stochastic-gradient method, it has faster convergence and better tracking capability in the time-varying environment. Simulation results in various signal environments are presented to show the performance of the proposed algorithm.     

基于EIRP最优的智能天线阵赋型算法研究

在实际天线阵列中,由于互耦的影响会使得单天线阵元辐射方向图畸变,导致传统的波束赋形算法性能恶化甚至失效。针对这个问题,文中提出了基于等效全向功率约束条件的粒子群算法,避免了传统的波束赋形算法的失效,提升了系统的等效全向功率。同时,为了减弱干扰方向的影响,文中进一步提出了零陷生成方案。仿真结果显示本文提出的算法不仅能够提升波束的等效全向功率,而且可以有效地生成干扰方向的零陷。     

一种基于OFDM系统的自适应加载算法

提出一种适用于OFDM系统的自适应加载算法。此算法与现有的已知算法相比，方法简单，运算量小。计算机仿真表明，采用此算法在系统性能增益基本不变的条件下，可以大大降低计算量。     

Modified pre-FFT OFDM adaptive antenna array with beam-space channel estimation

A modified pre-FFT OFDM adaptive antenna array with max-SNIR criterion is proposed, in which the CSI estimation is made on the beam-space. Simulation results show that the proposed scheme can outperform the element-space scheme, especially when strong cochannel interference is present.     

Simple -steering OFDM adaptive array antenna for Doppler-shifted signal suppression

A new -steering method to suppress Doppler-shifted signals is proposed for orthogonal frequency-division multiplexing adaptive array antenna. The proposed array antenna has a simple structure and can steer s for interfering signals even with small Doppler shifts by forcing virtual subcarrier outputs to be zero. A multistep recursive least-square algorithm is proposed to control the array weights and the bit-error rate and antenna pattern are evaluated by computer simulation.     

一种基于无偏协方差估计RLS的自适应阵列天线抗干扰算法

RLS是自适应阵列天线抗干扰的主要算法之一。为提高RLS算法对遗忘因子选择健壮性,避免因遗忘因子选择不当所造成的算法不收敛问题,本文针对自适应阵列天线的多路接收信号,基于其无偏协方差矩阵模型,推导设计出了一种新的RLS算法,相比于常规RLS,在该算法中遗忘因子可以更加精确地控制RLS迭代过程项,降低因遗忘因子设置不当而造成的算法不收敛风险。通过仿真验证了算法的有效性。     

基于定点LMS算法的自适应天线阵技术及其FPGA实现

如何在满足实时性及精度的前提下实现LMS算法一直是工程上的难点。根据SINR（信干噪比）对天线阵元的输入信号进行了建模,提出一种适合于FPGA（现场可编程门阵列）实现的定点数制,并在满足算法实时性的前提下在FPGA上实现了LMS（最小均方）算法。测试结果表明采用这种定点数制的算法所形成的天线阵方向图具有较好的性能。