多址干扰对消及多用户检测技术在CDMA系统中的作用

CDMA系统具有一系列的优点,这些优点使得CDMA技术在移动通信领域中所处的地位越来越重要.但在CDMA已经成为第三代移动通信主流技术的时候,还有许多关键技术要解决,其中最关键的就是要克服CDMA系统中多址干扰（MAI）的技术.本文介绍了多址干扰在CDMA系统中的成因,由此重点阐述了多址干扰对消及多用户检测技术在CDMA系统中的应用,并对他们的性能、局限性和应用环境做了分析和比较.     

CDMA系统下行链路的干扰抵消

CDMA蜂窝移动通信系统是一种采用多址技术的通信系统，即采用不同的地址码来区分用户、基站和信道。然而由于其在多径衰落信道中的自相关和互相关特性的不理想造成了多址干扰。在扩频通信系统的下行链路中，有效地抵消多址干扰是进一步改善系统性能和提高系统容量的重要途径。本文提出一种应用于CDMA下行链路的干扰抵消算法，分析了下行链路接收机的实现原理及过程，并对其中的关键算法进行了详细地分析，仿真结果表明，所选取的下行接收算法能改善系统的性能。     

导频符号辅助干扰删除多用户检测器的研究

根据宽带码分多址（ ＷＣＤＭＡ） 系统的特点,提出并分析了一种导频符号辅助干扰删除多用户检测器（ＰＳＡＩＣ）,分析结果表明,该方法充分利用了ＷＣＤＭＡ系统中的帧结构,在不增加物理信道的情况下,实现接收信号的相干解调,并与多址干扰删除器相连,可以大大提高系统的性能,增加系统的容量,当干扰删除器的级数为２ 时,其性能有较大的改善,复杂度也不高     

Multistage Nonlinear Blind Interference Cancellation for DS-CDMA Systems

In this paper we propose a multistage nonlinear blind interference cancellation (MS-NL-BIC) receiver for direct-sequence code-division multiple-access (DS-CDMA) systems. The receiver uses higher order statistics of the received baseband signal. Specifically, we use the second and fourth moments of the received signal to determine a component of the received vector that has significant mean energy and low variability of the energy, both of which are favorable characteristics for application in an interference cancellation scheme that uses hard decisions. The structure of the receiver is multidimensional and can be viewed as a matrix of receivers. Each row in the matrix consists of receivers that perform (hard decisions) cancellation of successive components that have significant mean energy and low variability of the energy. The columns of the matrix essentially resemble multistage receivers that iteratively refine performance from earlier stages. Simulation results show that unlike linear receivers, the MS-NL-BIC is exceptionally efficient in systems with strong and highly correlated interferers, as may be the case in overloaded DS-CDMA systems.     

Interference cancellation for a multicellular CDMA environment

This paper considers the performance of adaptive interference cancellation applied to a CDMA microcellular environment, by employing a circular cell geometry and a closed form expression for the Bit Error Rate of a CDMA system with interference cancellation to analyze the effect of out-of-cell interference. Results are presented which indicate that out-of-cell interference will severely limit the benefits of interference cancellation in a multicellular system. Attempts to cancel all out-of-cell interference will further degrade performance. However, the use of selective interference cancellation in which only the strongest out-of-cell interferers are cancelled may result in significant performance enhancement. These results agree closely with those obtained using a hexagonal geometry.Portions of this paper have been presented at the PIMRC'95 conference in Toronto, Canada.     

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.     

综合信道估计和卷积码的CDMA同频干扰消除技术

本文提出了一种多级ＣＤＭＡ同频干扰消除算法。算法采用周期性插入书籍码元的方法对反向信道特性进行精确的估计,使得的在反向信道上实现导频符号辅助的相干解调。算法采用Ｖｉｔｒｅｂｉ译码器的输出作为第一级判决结果重建干扰信号而不是常规的解扩以后重建干扰信号,由于综合信道估计和卷积编码提高了干扰信号重建的准确度,从而采用干扰消除技术后剩余干扰大幅度下降,系统时处并没有显著增加。数值结果表明综合信道估计和卷积     

基于重叠变换的CDMA Overlay系统窄带干扰抑制

研究了如何利用既有快速实现算法,又有良好滤波性能的重叠变换来分辨并抑制扩增信号中的窄带干扰。首先分析了重叠变换的工作原理,然后在此基础上设计基于重叠变换的窄带干扰抑制接收机,最后对该收机在CD－MA Overlay系统中抑制干扰的性能进行了仿真分析。     

Effects of Array Weight Errors on Parallel Interference Cancellation Receiver in Uplink Synchronous and Asynchronous DS‐CDMA Systems

This paper investigates the impacts of array weight errors (AWE) in an antenna array (AA) on a parallel interference cancellation (PIC) receiver in uplink synchronous and asynchronous direct sequence code division multiple access (DS‐CDMA) systems. The performance degradation due to an AWE, which is approximated by a Gaussian distributed random variable, is estimated as a function of the variance of the AWE. Theoretical analysis, confirmed by simulation, demonstrates the tradeoffs encountered between system parameters such as the number of antennas and the variance of the AWE in terms of the achievable average bit error rate and the user capacity. Numerical results show that the performance of the PIC with the AA in the DS‐CDMA uplink is sensitive to the AWE. However, either a larger number of antennas or uplink synchronous transmissions have the potential of reducing the overall sensitivity, and thus improving its performance.     

非同步扩频系统中空时分组码的阵列处理

针对非同步DS-CDMA系统提出了一种基于空时分组码的阵列处理干扰对消的技术。通过对发射信号进行空时分组编码,可以使发射信号在瑞利衰落信道中传输时信息不会畸变,并取得最大分集增益和码增益。利用空时分组码的性质有效抑制干扰的同时,大大简化了空时分组码的解码。仿真结果表明,这里提出的方法与传统的抑制干扰的方法相比具有更低的误比特率,并且有更快的解码速率。     

Iterative Soft Parallel Interference Cancellation for Convolutional-coded DS-CDMA System

We propose the use of soft feedback estimates for the PIC detector in aDS-CDMA system with FEC. The soft estimates are computed by the a posterioriof the log-MAP decoder. We compare this method with the conventional methodof using tentative hard decisions to perform interference cancellation at eachstage. Simulations under AWGN and multipath asynchronous channels areperformed for comparison. We supply a suitable a posteriori for the log-MAPdecoder, and obtain a suitable soft feedback from the decoder.     

一种低复杂度空-时选择性干扰消除方法

提出了一种行之有效的将智能天线技术同多用户检测技术结合的空-时接收方法,并对其参数进行了优化。它根据误码率信息有选择地实施干扰消除,先并行消除低误码率用户信号的影响,再检测高误码率用户信号。它复杂度低,计算效率高,易于实时实现,具有很好的应用价值。蒙特卡洛仿真实验表明,该方法可以显著改善码分多址移动通信系统的性能。     

非理想定时跟踪下CDMA并行干扰消除检测器的性能

以异步码分多址(DS-CDMA)系统硬判并行干扰消除检测器为模型,在定时同步错误情况下.由于并行干扰消除(PIC)分析的复杂性,以前的工作主要是依靠仿真方法.文献[5]分析了软判决PIC在定时跟踪错误下的性能,给出了封闭形式的误码率表达式.本文则分析了硬判决PIC残余多址干扰的结构及统计特性,导出了定时跟踪错误下封闭形式的误码率表达式.通过仿真与数值计算,分析了定时跟踪错误对硬判决并行干扰消除算法的影响.     

小扩频比的CDMA2000下行链路中Viterbi均衡算法的研究

针对CDMA2000—1X系统中存在的双小扩频比码道提出了Viterbi均衡和联合干扰抵消与Viterbi均衡两种算法，并比较了它们之间的性能差异。仿真结果表明，两种算法都能在计算复杂度增加不多的情况下，有效地克服蜂窝CDMA2000—1X系统中传输高速数据业务时所存在的多径干扰和多址干扰的影响，显著地提高了接收机的性能。     

Performance of Multiuser Detection in Multirate CDMA Systems

Multiuser detectors for asynchronous multirate code-division multiple-access (CDMA) systems are considered. A multirate CDMA system model able to fit several system concepts in the same framework is presented. The performance of the multi-code (MC) system with one processing gain and the multiple processing gain (MPG) system is compared. Upper bounds for the expected value of the asymptotic multiuser efficiency of the decorrelating detector for a synchronous multirate CDMA system with three effective users are derived for a system with one and two processing gains. The numerical results show that the performance of the decorrelating detector for MC and MPG systems do not differ significantly. The bit error rates (BER) of the decorrelating, parallel interference canceler (PIC) and groupwise serial interference canceler (GSIC) with either PIC or decorrelator within the group are compared. The results show that the decorrelating and the GSIC detectors yield the best performance. For all interference cancellation schemes the BER saturates at high SNRs due to decision errors degrading the multiple-access interference (MAI) estimates.     

扩频通信的干扰抵消算法

本文分析了非理想信道环境下递归部分并行干扰抵消(PPIC)接收机的性能及收敛特性，推导了其接收机结构，给出了计算机仿真结果。     

A Beamspace-Time Blind RAKE Receiver for Sectored CDMA Systems

A beamspace-time (BT) RAKE receiver is proposed for multiple accessinterference (MAI) suppression and multipath diversity reception insectored wireless CDMA communications. The scheme involves three stages.First, a set of adaptive beamformers encompassing a prescribed angular sectoris constructed on an antenna array, each providing effective suppression ofout-of-sector MAI and reception of in-sector signal. Second, a set of adaptivecorrelators is attached to each beam to combat in-sector MAI. Finally, thebeamspace correlator output data are combined to capture the signal multipathscoherently.The above three-stage operation is performed in a blind mode inthat no training signal is needed. The only information required is the signature,timing and a rough estimate of the angle of arrival (AOA) of the desired signal.     

Inter-Cell Interference Cancellation Algorithm for Reverse Link TDD-CDMA Systems

1IntroductionThe Ti me Division Duplex-Code Division MultipleAccess(TDD-CDMA)system makes use of TDD syn-chronous CDMA technology and offers several opera-tional advantages.First,it is based upon TDD-modewith flexible forward link and reverse link switchi…     

自适应干扰对消系统中的时延匹配

分析了模拟实现的自适应干扰对消系统中存在时延失配情况下系统的性能.通过理论计算求解了时延条件下的周期时变微分方程组,得到时延增大与系统收敛速度降低的结论,分析得到系统稳定性的判断标准.通过对系统模型的简化分析,得到时延与稳态权值的关系式,并求解得到时延与稳态误差的量化关系,以及干扰对消比随时延变化的规律.最后通过仿真和...     

基于并行干扰消除算法的信道估计

为降低TD-SCDMA系统同频组网时同频邻区对终端信道估计造成的同频干扰,提出了一种时域的平行干扰消除算法,相对于串行干扰消除算法,在有多个强同频邻区干扰的条件下,表现出了更好的性能。