上行空时分组编码多载波码分多址系统的逐级干扰对消接收机算法

针对空时分组编码多载波码分多址系统的上行物理链路,提出了基于QR分解和基于最小均方误差的逐级干扰对消接收机算法。经算法处理后的数据矩阵保持了空时分组编码的正交结构,从而可以通过简单的线性处理实现空时分组编码的次优译码。与传统的置零接收机算法相比,此算法不会对接收机端的白噪声产生放大作用。计算机仿真结果表明,在独立衰落信道或相关衰落信道下,此算法均优于置零接收机算法。在误码率为10-6水平下,此算法比传统算法的信噪比改善约4dB。     

多载波直接序列扩频码分多址系统的性能分析

本文将多载波发送信号技术应用于直接序列扩频码分多址系统中。发射机中直接扩频序列与数据序列相乘,然后调制多个载波;接收机对每个载波进行相关,相关器的输出用最大比值合并。这种发送信号具有很好的窄带干扰压缩性能。文中估计了存在部份带宽干扰下系统的性能,并与单载波直扩码分多址系统进行了比较。     

一种改进的部分并行干扰对消多用户检测接收机

本文研究了部分并行干扰对消(PPIC)多用户检测算法,提出了一种新的PPIC接收机实现结构,这种新的实现结构与经典的PPIC接收机实现结构相比,在不损失接收机抗多址干扰性能的前提下,硬件资源开销降低为经典实现结构的约四分之一,提高了对硬件资源的使用效率.在此新型接收机结构的基础上,设计并实现了PPIC多用户检测接收机,测试结果显示本文设计的PPIC接收机具有显著的抗多址干扰能力,实测多址干扰条件下的误码率性能和抗远近效应性能与计算机仿真结果具有较好的一致性.     

多载波码分多址通信系统中抑制干扰的序列设计

针对多载波码分多址通信系统,该文提出了一种具有优良性能的序列构造方法。此方法基于传统的零相关区序列,通过交织扩展后可以产生互补形式的多子集序列。该类序列具有周期互补特性,从而使系统拥有更强的抗多径干扰和多址干扰的能力。该文证明了所构造序列的周期相关性能,并通过构造举例进一步验证了这种构造方法是互补特性与零相关区特性的有效结合方式。     

一种新的正交多载波CDMA系统

该文提出了一种新的多载波码分多址(MC-CDMA)系统。与传统的MC-CDMA系统相比,其主要区别是要发送的数据比特先串并转换为多个并行分支,每一个分支用一组正交子载波进行调制。在每个分支上,使用相同扩频序列的不同码片调制子载波。这种系统能更有效地利用传输带宽,实现频率分集。由于该系统降低了每个子载波上的数据速率,扩频序列更容易同步。最后给出了在瑞利衰落信道下的性能分析。     

一种部分并行干扰对消因子的计算方法

在CDMA系统中,多用户检测是一种行之有效的方法。而具有部分干扰因子的并行干扰抵消检测器则是目前多用户检测技术中最简单、有效的接收机,但长期以来,部分干扰因子的确定大多根据实验,缺乏理论支持。该文在基于MMSE准则下,给出了一个两级PPIC接收机的部分干扰因子的计算公式。计算机仿真表明它具有良好的干扰消除能力,且对干扰信号功率和噪声估计偏差不敏感。     

PCMA自适应自干扰对消算法与仿真

讨论了成对载波多址(PCMA)自适应自干扰对消原理,分析了参数估计误差对自干扰对消的影响。在频偏误差的影响下对消误差为非平稳过程,传统自适应对消滤波器无法收敛。为了克服频偏误差的影响,提出了一种自适应可变遗忘因子(VFF)RLS算法,同时,给出了具有高精度低运算量的模糊函数参数估计算法。仿真证明了VFF-RLS对消算法具有良好的对消性能和稳健性,且需要的额外功率较低,能满足PCMA系统要求。     

一种时频双选信道下OFDM系统的低复杂度迭代干扰抵消算法

为了消除正交频分复用(OFDM)系统在时频双选信道条件下由于信道快时变带来的载波间干扰,本文提出了一种新的低复杂度迭代干扰抵消方法.为了消除载波间干扰,已经提出了不少方法,但这些方法要么因为矩阵求逆运算带来了高计算复杂度,要么以性能退化为代价换来低计算复杂度.利用并行迭代干扰抵消技术,本文算法可以明显改善系统性能,同时借助带状矩阵近似和最小二乘QR分解(LSQR)迭代计算的特点来降低计算复杂度.仿真结果表明,在高信噪比条件下,随着迭代次数的增加,本文所提出的算法可以有效的减少"地板效应",在系统性能和计算复杂度之间取得更好的折中.     

用于WCDMA上行系统的并行干扰对消算法

为了利用多用户检测和并行干扰对消克服WCOMA系统的多址干扰和远近效应,文中建立了WCDMA系统模型并由此推导了一种用于WCDMA上行系统的并行干扰对消算法,并在E-DPDCH信道验证了算法的性能。将干扰用户发射信噪比固定为14dB,当两个用户到达同一吞吐量时,采用PIC有1．5dB的信噪比增益。最后针对基于CCSS平台的仿真结果提出了几种优化方案。     

基于混合载波系统的载波间干扰抑制算法

针对双选信道下信号传输受到严重的载波间干扰(Inter Carrier Interference,ICI)的问题,首先利用部分FFT解调技术对局部干扰进行了分析,进一步在基于加权分数傅里叶变换的混合载波系统的抗干扰理论的基础上,提出了基于混合载波-部分FFT解调的信道ICI抑制算法,设计了这种算法的实现结构,最终将这种新的算法应用到双选信道下。仿真表明,相比较于传统单载波和OFDM系统,该算法具有误码率性能上的明显优势。     

一种基于组信息的并行干涉消除技术研究

为了克服多址干扰（MAD对光码分多址（OCDMA）通信系统性能的影响，针对提出的二维地址码MPC／OOC，研究了一种基于组信息的并行干扰消除（PIC）技术。考虑MA1、背景光（APD）噪声、热噪声和接收机噪声，详细分析了采用该PIC技术的OCDMA通信系统的性能。结果表明，基于组信息的PIC技术，可以有效地消除采用MPC／OOC作为地址码的OCDMA通信系统的MAI，提高该系统的系统容量和误码率性能。     

Reference Symbol Assisted Multi-Stage Successive Interference Cancellation for CDMA Wireless Communication: Robustness to Parameter Imperfections with Biphase and Quadriphase spreading

This paper investigates the sensitivity to system imperfections of a reference symbol assisted multi-stage successive interference cancelling (RAMSIC) receiver. Reverse link of a CDMA system with binary antipodal modulation and coherent detection is considered. Performance of systems using either biphase and quadriphase spreading is compared under different operating conditions. Analysis of a conventional matched filter receiver operating on an AWGN channel reveals that when the number of users is small (such that the multiple access interference cannot be accurately modelled as Gaussian), quadriphase spreading has a significant advantage over biphase spreading. This advantage, however, disappears when the number of users per sector is large (of the order necessary for the multiple access interference to be considered Gaussian). Results for the RAMSIC receiver with quadriphase spreading, on the other hand, show that for hexagonal cell geometry with path loss exponent of 4 and without any forward error correction coding, the traffic capacity is between 1.17 and 1.67 times that of the IS-95. These numbers represent a significant increase over those obtained with biphase spreading. Further investigation with nonidealized cell geometries and other path loss exponents also shows substantial capacity improvement over that of conventional correlator receivers. Performance losses due to nonideal transmitter power amplifier gating, imperfect power control and synchronization errors in the RAKE receiver are also determined. The results for biphase spreading show that for path loss exponent of 4, imperfect amplifier gating causes relatively minor decrease in the traffic capacity, while no such effect is observed for path loss exponents of 2 and 3. As expected, relaxing of power control for both biphase and quadriphase spreading has a similar capacity reducing effect. In spite of these two effects the resultant capacity is still significantly higher than that with the conventional matched filter receiver. Capacity increase with quadriphase over biphase spreading is between 1.4 and 2.0 times. Chip synchronization errors of the order to be expected in a properly designed conventional CDMA system have only minimal effect on performance. Therefore, we conclude that conventional synchronization algorithms should perform adequately with successive interference cancelling receivers considered in the paper.     

基于纠错编码联合迭代的多址干扰消除方法

在链路资源受限条件下的扩频通信应用中,多址干扰成为限制系统多用户服务能力和通信质量的最主要因素。针对多址干扰问题,提出了一种基于纠错译码联合迭代的并行多址干扰消除方法,显著改善了在多址干扰恶劣条件下,传统并行干扰消除算法多址干扰抑制性能不佳的情况,解决了传统算法难以应用于异步扩频通信系统的问题。仿真实验结果表明相比经典的部分并行干扰消除(PPIC)算法可带来7 dB以上的解调性能增益,同等链路资源可以支持更多用户数量进行通信,有效提高了扩频通信系统多用户信息传输能力。     

Linear Interference Cancellation of Asynchronous CDMA Systems by Preconditioned CG Method

It is well known that the iterative method is used for solving a set of linear equations corresponding to linear interference cancellation structures. An ideal computation of the decorrelating or the linear minimum mean-squared-error (LMMSE) detector requires order K ³ flops, where K is the number of users. To alleviate the computational complexity, iterative decorrelating and the LMMSE detectors are proposed. In this paper, the symmetric successive over relaxation (SSOR) preconditioning scheme is applied to the conjugate gradient (CG) method. The performance of the detectors is investigated and it is found that the SSOR preconditioned CG (PCG) method can provide significantly faster convergence than CG method.     

On Multirate DS-CDMA Schemes with Interference Cancellation

This paper investigates interference cancellation (IC) in direct-sequence code-division multiple access (DS-CDMA) systems that support multiple data rates. Two methods for implementing multiple data rates are considered. One is the use of mixed modulation and the other is the use of multicodes. We introduce and analyze a new approach that combines these multiple data rate systems with IC. The cancellation in the receiver is performed successively on each user, starting with the user received with the highest power. This procedure can in turn be iterated, forming a multistage scheme, with the number of iterations set as a design parameter. Our analysis employs a Gaussian approximation for the distribution of the interference, and it includes both the AWGN and the flat Rayleigh fading channel. The systems are also evaluated via computer simulations. Our analysis and simulations indicate that the IC schemes used in mixed modulation or multicode systems yield a performance close to the single BPSK user bound and, consequently, give a prospect of a considerable improvement in performance compared to systems employing matched filter detectors.     

An Ordered Successive Interference Cancellation Scheme in UWB MIMO Systems

In this letter, an ordered successive interference cancellation (OSIC) scheme is applied for multiple‐input multiple‐output (MIMO) detection in ultra‐wideband (UWB) communication systems. The error rate expression of an OSIC receiver on a log‐normal multipath fading channel is theoretically derived in a closed form solution. Its bit error rate performance is analytically compared with that of a zero forcing receiver in the UWB MIMO detection scheme followed by RAKE combining.     

Multiuser Detection in MC-CDMA Communication Systems Using MPEM Algorithm

In this paper, we propose a sub-optimum multiuser detection technique in multicarrier code division multiple access (MC-CDMA) communication systems based on missing parameter expectation maximization (MPEM) algorithm. In the proposed detection procedure, first initial values for the bits of all users are estimated from received signal. Then, the proposed MPEM based algorithm uses outputs of carries’ demodulators to improve the accuracy of the initial estimates of the bits. In this paper, the expectation and maximization steps’ functions of the MPEM algorithm for MC-CDMA multiuser detection are derived and the performance of the proposed algorithm is analyzed. Our presented numerical results demonstrate the efficiency of the proposed detection algorithm both in bit error rate performance and computational complexity points of view. Paeiz Azmi was born in Tehran, Iran, on April 17, 1974. He received the B.Sc., M.Sc., and Ph.D. degrees in electrical engineering from Sharif University of Technology (SUT), Tehran, Iran, in 1996, 1998, and 2002, respectively. Since September 2002, he has been with the Electrical and Computers Engineering Department of Tarbiat Modarres University, Tehran, Iran. From 1999 to 2001, he was with Advanced Communication Science Research Laboratory at Iran Telecommunication Research Center (ITRC), Tehran, Iran. From 2002 to 2005, he was with Signal Processing Research Group at ITRC. His current research interests include modulation and coding techniques, digital signal processing, and optical CDMA communications.     

Analytical Methods for CDMA Systems with Parallel Interference Cancellation: The Large Deviation Approach

For a simple CDMA system, we compute the bit-error probability (BEP)with soft-decisionparallel-interference-cancellation (SD-PIC). Instead of approximatingthe signal-to-noise ratio, we use a different measure to calculateperformance. This measure is the exponential rate of the BEP, i.e., thelimit of n^–1 log(BEP) = –I, for the processinggain n , where I depends only on the number of users. Weshow, using the rate as a measure, that SD-PIC improves the performance.The values of I follow as the solution of an optimization problem whichcan be calculated numerically. We use these results to derive theasymptotic behaviour of the rate for large k. We also derive results forthe second order asymptotics of the BEP. Inclusion of second orderasymptotics leads to excellent approximations.     

无源相干定位系统直达波干扰对消研究

无源相干定位系统中的主要问题之一就是接收机接收到的目标信号回波中的直达波干扰。传统的解决办法是采用自适应天线零陷对准直达波干扰,但广播信号的无源相干定位系统的天线零陷不够低。因此,文中提出了采用双通道对消的办法来抑制直达波,给出了所有的数学推导以及推导过程中的问题,最后给出了实验对消的结果。