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。     

自适应部分干扰抵消多用户接收机

在DS/CDMA系统中,采用多用户检测技术可以有效地克服多址干扰(MAI,MultipleaccessInterference)及远近效应。本文提出了一种自适应部分干扰抵消(APPIC,AdaptivePartialParallelInterferencecancellation)算法,根据匹配滤波器输出的判决统计对多址干扰进行选通抵消,以提高系统性能。同时本文给出了自适应部分干扰抵消接收机的非相干实现方案,并给出了仿真结果。     

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.     

CDMA系统中的多用户干扰抵消

本文介绍在多步检测结构中把干扰对消和利用天线阵的自适应MMSE检测器［1］结合起来,并介绍一种新的基于信号子空间估计的检测器。使用这种新的检测器可以使当子空间的维数减少时,干扰就从接收到的信号中抵消,并用正交投影子空间跟踪估计（OPAST）［2］来自适应的估计检测器和空间特征。与MMSE检测器相比,这种检测器在性能上更优。     

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。     

稀疏多径信道中单载波频域均衡系统的联合干扰抵消和均衡

针对大时延稀疏多径信道条件下的单载波频域均衡系统(SC-FDE),本文提出了一种新的迭代均衡结构,记为IC-FDE-DFE。IC-FDE-DFE可以缩短频域均衡所需的循环前缀(CP)的长度,提高稀疏多径信道下SC-FDE系统的带宽效率和功率效率。与单纯的时频域混合判决反馈均衡器(H-DFE)相比,IC-FDE-DFE能够充分利用信道的‘稀疏’特性,其中的均衡器具有较低的运算复杂度和设计复杂度。仿真结果表明,IC-FDE-DFE能够在迭代过程中逐渐抵消大时延多径的影响,逼近H-DFE的理想性能。     

干扰抵消型多用户检测器性能分析

用模块化的方法描述了 ＳＩＣ、ＭＳＳＩＣ、ＰＩＣ和ＰＳＩＣ干扰抵消多用户检测算法，给出算法的实现结构图，并且在渐近有效性、抗远近效应、系统容量和实现复杂度诸方面进行了性能比较分析。分析表明需要进行功率排序的ＭＳＳＩＣ、ＰＳＩＣ和ＳＩＣ算法比ＰＩＣ算法具有更好的抗远近效应的性能，ＭＳＳＩＣ和 ＰＳＩＣ算法在渐近有效性和系统容量方面要显著强于ＳＩＣ和ＰＩＣ算法。     

基于赛灵思FPGA的数字频域干扰抵消器

在第二届赛灵思开放源码硬件设计大赛举办之际,本文回顾了在第一届大赛中荣获一等奖的项目,即WCDMA系统中的自适应数字频域干扰抵消器。简要介绍了项目背景、系统方案、算法设计、仿真和测试结果等,以期给参赛者们提供一定的经验借鉴。     

一种基于符号级均衡的CDMA接收机

在使用较短扩频码的CDMA系统中,多径干扰会破坏用户扩频码之间的正交性,Rake接收机性能会严重下降.本文提出了一种新的基于Rake的符号级均衡的CDMA接收机,通过分析推导出了基于最小均方误差准则的均衡系数.性能仿真结果表明这种接收机与传统的Rake接收机相比,比特误码率性能有很大的提高,可以有效抑制跨多个符号的多径干扰.     

CDMA移动通信中多址用户干扰抵消技术

本文简要讨论了码分多址移动通信中多址用户干扰的产生和抵消机理,并分别介绍了前向链路和反向链路的多址用户干扰抵消技术。     

Parallel Interference Cancellation in Multiuser CDMA Channel Estimation

Parallel interference cancellation (PIC) based channel parameter estimators for frequency selective fading channels are proposed for the uplink in code-division multiple-access (CDMA) mobile communication systems. The performance of PIC based algorithms depends heavily on the quality of the multiple-access interference estimates, which can be improved by using adaptive channel estimation filters. The performance of two adaptive complex channel coefficient estimation filters has been verified in a fading channel by computer simulations. According to the results, the PIC based adaptive channel estimators outperform clearly conventional, successive interference cancellation, and decorrelation based adaptive channel estimators. The PIC method is also used in delay tracking. By using the principles of sample-correlate-choose-largest (SCCL) delay trackers, a robust algorithm for multiuser delay tracking in fading channels is obtained.     

上行链路MC-CDMA系统并行干扰抵消接收机的改进

介绍了上行链路MC-CDMA系统的一种初级采用线性MMSE检测的PIC多用户接收机。为了减小初级判决不精确带来的误差传播,提出了一种新的基于部分并行干扰抵消的多级PIC接收机结构,他是通过每级乘以一个不同的部分相消因子实现的。在不考虑信道估计误差的情况下,仿真了上行信道不同用户数、不同部分相消因子对改进的接收机性能的影响。仿真结果表明改进的接收机具有更好的误码率性能。     

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.     

Robust Multiuser Interference Cancellation for OFDM Systems With Frequency Offset

In orthogonal frequency division multiple access systems clusters of subcarriers are assigned to different users for parallel data transmissions. The subcarriers are overlapped, but orthogonal to each other such that there is no intercarrier interference (ICI). However, synchronization errors among users cause the loss of the orthogonality and introduce ICI resulting in multiple-access interference. Synchronization between users is particularly difficult in the uplink channel where the user signals are potentially asynchronous and affected by different frequency offsets due to misalignment in carrier frequencies and Doppler shifts. This paper proposes a method to lower the effects of different frequency offsets among user signals in an OFDMA uplink system. The multiple access interference due to the user frequency misalignments is reduced by reconstructing and removing the interfering signals in the frequency domain. An approach based on the selective cancellation method, is proposed and its performance is analyzed by means of theoretical analysis and computer simulations. The effectiveness of the proposed system has been evaluated in the case of ideal and no-ideal frequency offset estimation and has been compared with that of the classical successive and parallel cancellation schemes. Simulation results show that the proposed approach allows performance close to the ideal case, i.e., with ideal frequency synchronization among users, with a low increase of the implementation complexity. Moreover, it is also highlighted here, that the successive cancellation method slightly outperforms the selective scheme, at the expense of a higher computational complexity and processing delay     

Alternating Multiuser Detection with Soft Interference Cancellation for Heterogeneous-Signaling MIMO CDMA Systems

This paper presents an effective alternating multiuser detector for the uplink of heterogeneous-signaling multiple-input multiple-output code division multiple access systems over multipath fading channels, where the data are transmitted using either spatially multiplexing for high transmission rate or space-time block code for transmit diversity gains. The new MUD first separates users into two groups according to their transmission signaling schemes and then detects the transmitted symbols in each group alternately with the removal of iteratively refined soft information-assisted multiple access interference to enhance the interference cancellation capability. Moreover, for practical low-complexity implementations, the users in each group are further partitioned into smaller subgroups based on their effective channel correlations and then detected in parallel by a bank of minimum mean-squared error soft detectors to further reduce the computational load. Conducted simulations show that the proposed MUD can render superior performance compared with previous approaches, especially in highly loaded scenarios.     

利用频域检索的单音干扰消除算法

在正交频分复用（OFDM,Orthogonal Frequency Division Multiplexing）系统中,当每次处理的OFDM符号较少时,OFDM数据子载波上的调制符号将严重影响单音干扰的参数估计。针对这个问题,本文提出一种利用频域检索的单音干扰消除算法。该算法首先利用离散傅里叶变换（DFT,Discrete Fourier Transform）粗估计单音干扰频点,然后通过检索干扰频点附近子载波的调制符号,消除其对单音干扰频域主瓣的影响,提高干扰参数估计精度,从而实现精确的单音干扰重构与消除。仿真结果表明,新算法可以有效地提高单音干扰参数估计精度,并可以降低OFDM系统误码率。      

A Multiuser Detection Receiver Using Blind Antenna Array and Adaptive Parallel Interference Cancellation

In this paper, the problem of multiuser detection for synchronous code division multiple access systems in both additive white Gaussian noise and multipath channels is addressed. A new multiuser detection receiver that uses an adaptive blind array along with an adaptive parallel interference canceler is proposed. The replacement of a conventional antenna array with a two-dimensional RAKE receiver is also considered for frequency selective Rayleigh fading channels. By using a constrained optimization criterion along with the gradient-projection algorithm, a blind algorithm for the adaptation of the array response vector is proposed. The new algorithm is superior to a few typical blind algorithms in the literature in terms of both performance and computational complexity. The proposed receiver has the ability to cancel very strong multiple access interference coming from the same direction as the desired signal. Simulation results are presented to show the excellent performance of the proposed combination scheme in comparison to that of using either a multiuser detection or adaptive antenna arrays in a severe near-far situation.