TDRSS接收机码分多址干扰抑制方案设计

为了在跟踪与数据中继卫星系统( TDRSS)中实现码分多址( CDMA)应用,需要完成多用户检测( MUD)及码分多址干扰( MAI)抑制。采用减性多级迭代对消算法,在数字信号处理芯片中完成信号再生、延时校正、时域相减对消,可以完成至少12通道的多用户检测,并能将多址干扰抑制至最小1 dB以内。该算法可作为通用MUD算法的有效补充,并能应用于各类非最优的CDMA系统中,具有迭代级数可选、通道扩展性强、工程实现性好的优点。     

无线多址接入网络编码中继的信道分配算法

无线多址接入中继网络中,用户可选择是否接入中继,同时中继也可选择所服务的用户。在中继处应用网络编码技术可使单个中继同时服务于2个用户共享同一时频资源进行无干扰信息传输。基站采用联合检测方法恢复原始信息,从而得到传输速率的提升。针对多用户多中继场景,为了进一步提升系统的吞吐量,需要为用户选择合适的中继协助其传输,考虑到多址网络编码中继的中继选择问题是一个复杂的优化问题,为了降低其求解复杂度,分别采用基于贪婪准则和考虑用户公平性的信道分配算法进行求解。仿真结果表明,所提信道分配算法相比于随机信道分配可获得较大的性能增益,并且基于贪婪准则的算法性能优于考虑用户公平性的算法。     

基于最小误码率准则的多载波CDMA系统多用户检测算法

本文介绍了一种将正交频分复用(OFDM)技术和码分多址(CDMA)技术相结合的多载波CDMA (MC-CDMA)系统,分析了MC-CDMA系统的发射端和接收端的结构,建立了MC-CDMA系统的信号模型,详细分析了MC-CDMA中的多址干扰形式,以及针对MC-CDMA系统的多用户检测原理,提出了一种基于最小误码率准则的多用户检测算法。理想的基于最小误码率准则的多用户检测算法在实际中难于实现,本文采用估计概率密度函数的方法,推导出了一种自适应实现的最小误码率多用户检测算法。仿真结果表明,该算法能够有效抑制多址干扰,降低误码率,同时,该算法还具有比基于最小均方误差准则的多用户检测器更低的误码率的优点。      

同步短波差分跳频多址系统单用户及多用户检测的性能

该文讨论同步短波差分跳频在多址通信中的单用户与多用户检测的性能。给出了单用户检测在无背景噪声及有背景噪声的情况下,系统的比特误码率(BER)上界,并对其进行了数值仿真。其结果表明:在无背景噪声的情况下,当总用户数为2时,系统的BER可达10-6;若系统可以得到精确的干扰状态信息(JSI),则多址性能可以得到极大的提升。在此基础上,提出了一种迭代多用户检测算法,在迭代过程中估计各可用频率上的JSI,并利用它对多个用户进行极大似然检测,其仿真结果表明了多用户检测相对于单用户检测,其性能获得了明显的改善。     

码分多址通信系统多用户检测的仿真研究

多用户检测技术利用各个用户的扩频序列、时延、幅度和相位信息对各用户进行联合检测,能有效抑制多址干扰,充分利用上行链路频谱资源,提高系统性能和容量,是码分多址通信系统中的关键技术之一。文章采用基于卷积编码块的串行干扰抵消多用户检测方法,利用MATLAB对多用户检测算法进行仿真,通过研究不同数据速率的三种应用场景,验证多用户检测算法对参考用户误码率的性能改善和提高系统用户容量的有效性。     

频域均衡联合基于能量排序的部分并行干扰删除检测算法

针对频率选择性信道下的DS-CDMA系统,该文提出了一种联合MMSE(最小均方误差)频域均衡与基于能量排序的部分并行干扰删除(MMSE-EOPPIC)的多用户检测算法。该算法首先采用基于重叠剪切法的MMSE频域均衡代替Rake接收机对各用户的数据信息进行初始估计,然后在干扰删除的每个迭代级根据用户能量由强到弱的顺序依次对用户进行部分干扰删除;为了提高每个迭代级检测的可靠性,该文将当前级已经检测出的能量较强用户的硬判决值用于重构当前级能量较弱用户的多址干扰(MAI)。仿真结果表明MMSE-EOPPIC检测算法可以有效提高系统的比特误码率性能。     

Turbo译码原理及其在CDMA多用户检测中的应用

研究了Turbo(并行级联码)译码原理及其在CDMA多用户检测中的应用。文中简述了Turbo译码原理及逐符号最大后验算法(symbol-by-symbol MAP),并将Turbo译码原理应用于CDMA系统的多用户检测,提出了基于Turbo译码原理的多用户检测接收机方案,通过计算机仿真验证该方案的性能。结果表明,本文所提出的方案经过4次迭代之后,其误码率接近单用户界,说明这种接收机可去除多址干扰(MAI)的影响。     

基于信号空间对齐的网络编码方案

在多用户协同中继系统中,受共信道干扰的影响,系统性能下降严重。提出了一种融合多源信号空间对齐和网络编码的方案,每个用户通过中继向其他的用户发送不同的信息,同时也通过中继接收其他用户的不同信息。整个过程可分为多址接入信道(MAC)和广播信道(BC)两个阶段。在MAC阶段,利用信号空间对齐技术在中继形成较少的信息量、抑制多用户干扰。在BC阶段,通过中继的网络编码,设计简单的预编码算法,有效降低了用户译码的复杂度。整个系统的完成只需要两个时隙,能有效地抑制干扰和提高系统自由度。     

基于信号空间对齐的网络编码方案北大核心

在多用户协同中继系统中,受共信道干扰的影响,系统性能下降严重。提出了一种融合多源信号空间对齐和网络编码的方案,每个用户通过中继向其他的用户发送不同的信息,同时也通过中继接收其他用户的不同信息。整个过程可分为多址接入信道(MAC)和广播信道(BC)两个阶段。在MAC阶段,利用信号空间对齐技术在中继形成较少的信息量、抑制多用户干扰。在BC阶段,通过中继的网络编码,设计简单的预编码算法,有效降低了用户译码的复杂度。整个系统的完成只需要两个时隙,能有效地抑制干扰和提高系统自由度。     

TDCS大规模分区多址通信方法

针对传统的变换域通信系统多址干扰严重,抑制用户数和误码率性能的问题,提出了一种分区方法降低多址干扰,适用于大规模变换域多址通信.提出多用户的区域划分方法,将用户分为区内用户和干扰较小的区外用户,并推导出误码率计算公式;提出分区向量计算方法,引入CAN算法,提高分区向量的自相关性;从频谱效率和高斯信道下的误码率等角度,分...     

基于IPSO-ICA算法的盲多用户检测

为了有效抑制CDMA通信系统中的多址干扰,提出了一种将新改进的粒子群(IPSO)算法应用到基于独立分量分析(ICA)的盲多用户检测中的方法.首先在IPSO算法中,使用自适应非线性递减惯性权重w降低早熟概率,利用拉伸技术打破早熟现象,从而使最优解更加精确.然后将IPSO算法融合到ICA算法中,得到IPSO-ICA算法来进行盲多用户检测.最后仿真结果表明,在相同通信环境下,该盲多用户检测比已有的基于FastICA和PSO-ICA算法的盲多用户检测的误码率更小,收敛速度更快.     

Multiuser cyclic shift keying spread spectrum underwater acoustic communication

Aiming at the problem of low data rate and high receiver complexity of existing direct sequence spread spectrum code division multiple access (DS-CDMA),a novel code division multiple access (CDMA) using cyclic shift keying (CSK) signaling,namely CSK-CDMA,was proposed for multiuser underwater acoustic communication.The proposed method used the cyclic correlation characteristic of spread spectrum signals with M-ary modulation to provide a higher data rate than conventional.Passive time reversal technology was employed to suppress inter-code interference between users and the co-channel interference.The quasi-orthogonality of spread spectrum code was used to improve the processing gain.Multiuser communications are demonstrated with lake experimental recorded data under the condition of 5.27 km distance and complex multipath interference.The data rate is 39 bit/s/user for 6 users with bit error rate around 10^-2～10^-4.     

Adaptive Multiuser Decision Feedback Detector: A Novel Parallel Interference Canceller

Adaptive decision feedback detector based on the parallel interference cancellation approach (ADFD-PIC) is presented for code division multiple access transmission, which not only combats the intersymbol interference and multiple access interference but also suppresses other-cell interference. For frequency-selective smoothly time-varying channels, the proposed ADFD-PIC structure using the erasure algorithm based soft-slicer and channel estimator (EC-ADFD-PIC) offers performance improvement by mitigating the adverse effects of error propagation. The simulation results are presented to demonstrate the substantial improvement in bit error rate performance of the minimum mean square error EC-ADFD-PIC over other multiuser detection techniques.     

基于改进EASI算法的DS-CDMA信息码与伪码盲估计

针对直扩序列码分多址(DS-CDMA)系统多用户检测的问题,提出了一种基于性能指标(PI)变步长EASI算法信息码与伪码盲估计的算法.该算法在比较盲源分离(BSS)和DS-CDMA系统模型的基础上,用自适应的方法估计混合矩阵进而估计出伪码,并利用分离矩阵分离观测信号从而估计出信息码.另外,该算法利用PI值来调整步长,使算法收敛速度和稳定性能达到一个理想平衡点.实验结果显示,该算法具有很好的抗多址干扰(MAI)的能力,伪码和信息码的误码率分别在-10 dB和0 dB时达到10-2以下;对不同用户数,5dB时所有扩频码被完全正确检测的概率几乎都在80％以上.     

Multiuser detection for cooperative networks and performance analysis

We investigate strategies for user cooperation in the uplink of a synchronous direct-sequence code-division multiple-access (DS/CDMA) network employing nonorthogonal spreading codes and analyze their performance. We consider two repetition-based relay schemes: decode-and-forward (DAF) and amplify-and-forward (AAF). Focusing on the use of linear multiuser detectors, we first present cooperation strategies, i.e., signal processing at both the relay nodes and the base station (BS), under the assumption of perfectly known channel conditions of all links; then, we consider the more practical scenario where relays and BS have only partial information about the system parameters, which requires blind multiuser detection methods. We provide performance analysis of the proposed detection strategies in terms of the (asymptotic) signal-to-(interference plus noise) ratio and the bit error rate, and we show that AAF achieves a full second-order diversity when a minimum mean-square-error detector is employed at both the relay side and the BS. A simple, yet effective, partner selection algorithm is also presented. Finally, a thorough performance assessment is undertaken to study the impact of the multiple-access interference on the proposed cooperative strategies under different scenarios and system assumptions.     

基于量子计算方法的多址DCSK通信系统的研究

为了降低多用户之间的干扰问题,提出了一种新的混沌多址通信系统（多比特MA-DCSK）,并设计了该系统的多用户检测算法。通过仿真实验,比较了该多比特MA-DCSK系统与可变延时MA-DCSK系统的误码率性能,证明了该系统具有更低的误码率。利用量子并行运算的特性,采用Grover量子算法解决多用户检测算法的计算复杂度,这种算法可以将复杂度从 降低到 。仿真结果表明,在不影响系统性能的同时,量子算法可以有效地降低计算复杂度。     

互信息量最大化和低复杂度的全双工中继网络自干扰消除和干扰对齐算法

该文针对多用户全双工中继干扰信道,同时考虑全双工中继自干扰消除及用户端干扰消除问题。首先,提出了基于最大化全局互信息量的自干扰消除和干扰对齐算法,并具体给出了自干扰消除矩阵的具体求解算法和方案。进一步,给出了信号对齐和干扰抑制的可行性条件,并分析了系统的互信息量和所受干扰噪声功率,以及系统的自由度。理论分析和仿真结果显示,与现有的典型全双工中继方案相比,该文算法可以提高系统互信息量和自由度,并有较低误码率;另外,该文算法的中继只需进行简单的功率约束,不需做复杂的信号处理,降低了整个系统的信号处理复杂度。     

An Adaline Neural Network-Based Multi-User Detector Improved by Particle Swarm Optimization in CDMA Systems

The detector applied to each single user based on adaline neural network (ANN) is presented in this paper, which is equivalent to the joint one applied to all users in eliminating the multiple access interference in CDMA systems. Then, particle swarm optimization (PSO) algorithm combined with least mean square scheme is employed in the training procedure of the ANN, which can effectively remove the shortcoming of the poor dynamic adaptive behavior of conventional neural network, i.e. during the convergence procedure of the weights in conventional neural network, the training samples are usually required to be trained iteratively. However, in the improved detector, each training sample can be trained repeatedly, so that the converging speed is getting much faster. Simulation results show that, in the ANN based multi-user detector improved by PSO, the dynamic adaptive behavior has been remarkably improved.     

FD-MC-CDMA: A Frequency-Based Multiple Access Architecture for High Performance Wireless Communication

Multi-carrier code division multiple access (MC-CDMA) demonstrates good probability of error performances in frequency selective fading channels, a direct result of its ability to resolve the available frequency diversity. However, MC-CDMA performances may be limited by degradation due to large multiple-access interference (MAI). Frequency division multi-carrier code division multiple access (FD-MC-CDMA), a novel multiple access architecture proposed in this paper, exploits the available frequency diversity benefits while reducing MAI. Specifically, instead of transmitting all users' information bits over all carriers, FD-MC-CDMA employs a subset of carriers to support a subset of users (while maintaining the same overall system capacity and throughput as in MC-CDMA). By careful selection of each subset of carriers, the available frequency diversity benefits are fully exploited, while the MAI experienced by each user is reduced. Furthermore, since the number of carriers employed by each user is significantly reduced, the complexity of the truly optimal multiuser detection (MUD) receiver for FD-MC-CDMA is low. An optimal MUD based on the maximum likelihood (ML) criteria is employed to optimize the system performance of FD-MC-CDMA. The proposed FD-MC-CDMA (with MUD) provides significantly better bit error rate (BER) performances than traditional MC-CDMA systems with little increase in system complexity.