DS/CDMA同步信道中的多用户联合检测和译码

将迭代(Turbo)处理的思想应用于DS/CDMA系统同步信道的多用户检测和译码中,接收机利用信道译码的先验信息进行多用户前端处理,而其输出又作为信道译码器软输入,从而使多用户检测和信道译码联合进行,通过迭代逐渐逼近单用户性能,减少多址干扰的影响。仿真结果给出了迭代处理方法在不同信噪比条件下的比特误码率性能。     

一种频选衰落信道下的Turbo多用户检测算法

联合MAP多用户检测与信道解码的迭代多用户检测(MUD)技术可显著提高宽带移动CDMA系统的容量和性能.在多径时变衰落的编码信道下,提出一种迭代实现干扰抑制、符号估计、信道解码的Turbo多用户检测算法.在每次迭代中,MUD自适应地实现干扰抑制并输出符号估计的软信息,软输入软输出的信道解码器使用LOG MAP方法实现信道解码并反馈符号估计的软信息作为下一次TurboMUD迭代的先验信息.仿真结果证实了该算法在频选衰落信道下经两次迭代就能逼近单用户编码CDMA系统的接收性能.     

编码的多载波CDMA系统中Turbo时空多用户检测

联合MAP多用户检测和信道译码的迭代多用户检测技术可显著提高多载波CDMA系统的容量和性能,本文给出了结合智能天线和迭代MAP多用户检测的Turbo时空多用户检测算法,该方法进一步提高了系统的性能.Turbo时空多用户检测算法不仅极大减小了传统最优MAP多用户检测算法的运算量,而且,此算法性能在AWGN和频率选择性衰落信道中都能逼近单用户编码多载波CDMA系统多天线接收的性能.     

多用户MC DS-CDMA系统中的时频域信道估计方法

该文提出了一种用于多用户MC DS-CDMA系统的信道估计方法,该方法在平均时域估计的基础上迭代一次平均频域信道估计,较好地改善了信道估计的性能。仿真结果表明,经过平均时域信道估计方法能较大程度地滤除多址干扰(MAI)和噪声,提高信道估计的准确性。再经过迭代一次平均频域信道估计,系统的误码率(BER)性能还可进一步改善,经过两次信道估计,系统取得的性能已很接近理想估计的性能。     

MC-CDMA系统迭代检测中的一种基于EM的信道估计算法

该文将多用户检测和译码相结合的迭代检测技术应用于MC-CDMA系统。多用户检测器由串行干扰消除和其后的MMSE滤波器组成。信道估计器采用一种基于期望最大(EM)信道估计算法,该算法降低了信道估计的复杂度,仿真表明其具有良好的性能。     

宇宙通信、星际通信、卫星通信与多址通信

Y98-61483-6 9907938采用迭代译码和软干扰对消的多载频 CDMA=Multi-carrier CDMA with iterative decoding and soft-interfer-ence cancellation[会,英]/Kaiser,S.& Hagenauer,J.//1997 IEEE GLOBECOM,Vol.1.—6～10(MaV)本文提出并研究了在多载频码分多址(CDMA)系统中采用迭代软干扰对消的一种新颖的多用户检测方案。介绍了多载频 CDMA(MC-CDMA)系统模型及所提出的采用软干扰对消的迭代检测和译码方案的基本原理。对于衰落信道验证了所提出方案的性能,并且与采用 MMSE(最小均方误差)均衡的单用户检测及采用 MLSE(最大似然序列估计)的多用户检测进行了性能比较。参12     

MC-CDMA系统迭代检测中的均衡

本文研究在同步MC- CDMA系统中的上行链路中的均衡技术。接收机采用多用户检测和译码相结合的迭代检测技术;其中,串行干扰消除用于多用户检测,一个SISO译码器用于信道译码。仿真给出在不同的均衡策略下如ORC、EGC、MRC、MMSE,迭代检测接收机的性能     

Turbo MUD技术在TD-SCDMA系统中的应用

TD-SCDMA已成为第3代移动通信国际标准之一,它采用联合检测技术来抑制符号间干扰(ISI)和多址干扰(MAI)。介绍了Turbo多用户检测(MUD)技术在TD-SCDMA系统中的应用,该技术将Turbo迭代译码思想引入到联合检测,有机结合多用户检测和信道译码2种技术,通过在软MUD和软信道译码间多次进行迭代并及时交换软信息(如后验概率)来提高系统性能。研究表明,采用TurboMUD可使系统性能显著提高。     

一种低复杂度的Turbo多用户检测技术

基于Turbo原理,提出了一种适合于同步DS－CDMA系统的迭代多用户接收机结构,它通过在反复迭代的软输入出多用户检测器和一组信道译码之间获得连续的软判决,从而得到一种低复杂度的多用户检测算法－软MMSE干扰消除。     

多码CDMA系统中联合并行干扰抵消与迭代信道估计方法

本文针对多码CDMA系统提出了一种联合并行干扰抵消与迭代信道估计方法。该方法首先通过导频符号对信道进行估计，然后使用RAKE接收机后的软信息对信道参数进行修正，最后通过并行干扰抵消(PIC)去除多码干扰(MCI)。仿真结果表明，经过多次迭代后，该方法可显著地降低多码CDMA系统的误比特率平台。本文同时还给出了信道估计质量、码道数和PIC次数对多码CDMA系统性能的影响。     

OFDM叠加导频联合信道估计和检测方法

针对现有正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)系统信道估计和迭代检测算法中频谱效率低和鲁棒性差等问题,提出了一种基于酉近似消息传递和叠加导频的信道估计与联合检测方法。首先,在软调制/解调中叠加导频对正交幅度调制的星座点进行预处理,检测时将叠加的导频作为频域符号的先验分布,利用置信传播算法进行调制和解调,实现检测模型的简化。然后,应用因子图-消息传递算法对OFDM传输系统和信道进行建模和全局优化,引入酉变换加强信道估计算法的鲁棒性。最后,建立OFDM仿真环境对现有方法进行仿真分析。仿真结果表明,相对于现有的独立导频类算法,所提算法能够以相同复杂度显著提升OFDM系统的频谱效率和鲁棒性。     

Superimposed Pilot Aided Multiuser Channel Estimation for MIMO‐OFDM Uplinks

This letter addresses the superimposed pilot aided multiuser channel estimation for the uplinks of multi‐input multi‐output orthogonal frequency‐division multiplexing systems. To mitigate the embedded‐data effects on the performance of channel estimation, a novel combining algorithm is proposed. Optimal pilot symbols are developed with respect to the least square channel estimate's mean square error. The averaged sum‐capacity lower bound is derived and simulated. Simulation results show that on a low signal‐to‐noise ratio regime, our proposed scheme achieves better performance and higher capacity than the conventional pilot aided approach.     

Iterative receiver for OFDM-SDMA system

An iterative receiver is proposed based on the EM (Expectation-Maximization) algorithm for an OFDM-SDMA (Orthogonal Frequency Division Multiplexing-Space Division Multiple Access) system. By using a few pilots in every OFDM symbol, both channel estimation and multiuser detection can be simultaneously obtained by iteration. The computer simulation results show this receiver can track channel variations and detect multiuser symbols for different number of users under time-varying multipath channels.     

On channel parameter estimation in a space-time bit-interleaved-coded modulation system for multipath DS-CDMA uplink with receive diversity

In this paper, we consider iterative space-time multiuser detection and channel parameter estimation in a bit-interleaved coded modulation scheme for asynchronous direct-sequence code division multiple access (DS-CDMA) transmission over frequency selective, slowly fading channels. Accurate estimation of the channel parameters is critical as it has great impact on the overall BER performance. We present an iterative space-time multiuser (STMU) turbo detection and estimation scheme, based on space alternating generalized expectation maximization (SAGE) algorithm. This algorithm operates on the coded symbols by exchanging soft information between the detector and the estimator. We show through computer simulations that the proposed low complexity STMU receiver considerably outperforms conventional estimation schemes and achieves excellent performance, both in terms of BER and estimation error variance. Finally, we will consider different mapping strategies and investigate their impact on the performance and complexity of the estimator.     

限幅OFDM的一种信道估计优化方法

在OFDM 系统中,限幅常用于抑制信号的峰平比,而限幅会引入额外的限幅噪声,以致干扰数据和导引符号,恶化传输性能.本文针对限幅OFDM系统,提出一种基于导引符号的限幅噪声消除算法.该算法在插入导引符号之前,滤除位于导引位置的限幅噪声,从而改善信道估计性能.在此基础上,本文还提出了利用迭代算法以进一步提高信道估计精确度.本文对所提出的限幅噪声消除算法及迭代算法进行了仿真验证,结果表明,新算法能够明显改善信道估计,优化传输性能.     

An iterative maximum SINR receiver for multicarrier CDMA systems over a multipath fading channel with frequency offset

A robust iterative multicarrier code-division multiple-access (MC-CDMA) receiver with adaptive multiple-access interference (MAI) suppression is proposed for a pilot symbols assisted system over a multipath fading channel with frequency offset. The design of the receiver involves a two-stage procedure. First, an adaptive filter based on the generalized sidelobe canceller (GSC) technique is constructed at each finger to perform despreading and suppression of MAI. Second, pilot symbols assisted frequency offset estimation, channel estimation and a RAKE combining give the estimate of signal symbols. In order to enhance the convergence behavior of the GSC adaptive filters, a decisions-aided scheme is proposed, in which the signal waveform is first reconstructed and then subtracted from the input data of the adaptive filters. With signal subtraction, the proposed MC-CDMA receiver can achieve nearly the performance of the ideal maximum signal-to-interference-plus noise ratio receiver assuming perfect channel and frequency offset information. Finally, a low-complexity partially adaptive (PA) realization of the GSC adaptive filters is presented as an alternative to the conventional multiuser detectors. The new PA receiver is shown to be robust to multiuser channel estimation errors and offer nearly the same performance of the fully adaptive receiver.     

高速场景下基于叠加导频的迭代EKF信道估计方法

针对正交频分复用（Orthogonal Frequency Division Multiplexing,OFDM）系统在高速移动场景下时/频域选择性衰落（双选衰落）和非平稳特性给信道估计带来的技术挑战,本文采用导频与数据叠加的帧结构,提出一种基于基扩展模型（Basis Expansion Model,BEM）的迭代扩展卡尔曼滤波（iterative Extend-Kalman Filter,iEKF）信道估计方法.基于BEM信道模型且采用EKF信道估计方法可以联合估计出信道冲激响应（Channel Impulse Response,CIR）与时变的时域自相关系数,有效消除子载波间干扰（Inter Carrier Interference,ICI）.同时,为了进一步消除叠加导频位置处的数据符号干扰,我们提出将叠加位置处的数据和导频先解耦、后重构再进行迭代EKF的信道估计方法.仿真分析表明,相较传统叠加导频的信道估计方法和导频符号辅助调制（Pilot Symbol Assisted Modulation,PSAM）估计方法,本文提出的信道估计方法在高速场景特别是低信噪比的条件下,具有更高的估计精度,更强的鲁棒性及更大的吞吐量.     

一种基于检测信息可靠度的部分软干扰消除迭代多用户检测算法

该文提出了一种基于检测信息可靠度的部分软干扰消除迭代多用户检测算法。如果由从信道译码器所获得的发送字符的先验信息大于某一预定阈值,则认为对其检测具有较高的可靠度,因而可以考虑将其对应的多址干扰成分从匹配滤波器输出向量中直接消除,相当于减小了干扰用户的数目,从而可以减小迭代多用户检测算法的复杂度。该算法的计算复杂度能够随着多址干扰的减小和信道信噪比的增大而降低。     

一种LDPC编码慢跳频系统迭代信道估计译码算法

低密度奇偶校验码(LDPC, Low Density Parity Check)的和积译码算法(SPA, Sum-product Algorithm)在加性高斯白噪声信道中具有很好的译码性能,但需要已知信道状态信息。提出了一种在部分频带干扰条件下LDPC编码慢跳频(SFH, Slow Frequency Hopping)系统的迭代信道估计译码算法。该算法利用迭代译码过程中产生的比特后验信息作为信道估计器的先验信息辅助信道估计,进而更新下一次译码的初始信息。仿真结果显示,该算法性能逼近已知信道信息时的性能,而且每跳所含的符号数很少,不需要插入导频,增大了传输功率效率。另外,相对于SPA算法运算量增加不大,实现简单。     

Iterative rake receiver with map channel estimation for ds-cdma systems

We propose an iterative rake receiver structure using an optimum semi-blind channel estimation algorithm for ds-cdma mobile communication systems. This receiver performs an iterative estimation of the channel according to the maximum a posteriori criterion, using the expectation-maximization algorithm. This estimation process requires a convenient representation of the discrete multipath fading channel based on the Karhunen-Loève orthogonal expansion theorem. The rake receiver uses pilot as well as unknown control and data symbols optimally for improving channel estimation quality. Moreover, it can take into account the coded structure of all unknown transmitted symbols when channel estimation quality is poor or unsatisfactory. The validity of the proposed method is highlighted by simulation results obtained for the FDD mode of the umts interface.