OFDM系统中一种新的迭代信道估计算法

本文提出了OFDM系统中一种新的基于软信息迭代处理的信道估计算法。该算法将面向判决最小二乘估计算法和盲估计算法相结合,在估计器中构造了一种新的置信度量函数,根据解码和软映射重构的反馈信号置信度大小在两种估计算法中自适应选择,这样估计的信道频响可以有效提高软信息迭代接收性能,大大降低信道估计训练开销。仿真结果表明,本文提出的算法能有效跟踪信道时变,限制传统面向判决估计的错误传播,达到好的系统性能。     

时变条件下MIMO-OFDM系统中的信道估计算法

本文设计了时变多径衰落条件下MIMO-OFDM系统中一种新的信道估计算法.该算法结合递归EM算法和Kalman预测对时变信道进行跟踪.借助软球形译码器(List Sphere Decoder,LSD)产生的搜索列表,递归EM算法序贯遍历搜索列表中可能的符号组合来估计各个子载波上的信道频率响应;基于获得的信道频率响应估计,Kalman预测器利用衰落信道的时域二阶统计特性进一步跟踪信道时变.仿真结果表明:本文设计的算法可以有效跟踪信道时变,性能优于传统的软输入Kalman滤波算法.     

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.     

快速生成QAM比特置信度软判决度量的算法

在现代通信系统中,为了保证高的信道解码增益,信道解码器均采用软输入技术。传统的软判决度量大多是基于最小欧氏距离准则生成,该文提出一种基于比特置信度快速生成QAM软判决度量的算法,通过将比特置信度引入到QAM软判决度量的计算中来减少计算的复杂性。相比基于最小欧氏距离的软判决度量生成算法,该文提出的方法在保证信道解码器性能的前提下,减少了生成软判决度量的运算量。应用于中国数字电视地面传输标准DTMB系统的仿真结果表明,该文提出的软判决度量生成算法虽然降低了计算量,但性能几乎没有任何损失,具有良好的性能和可实现性。     

衰落信道下卷积码的软判决译码

本文将交织、信道输出软信息、信道特征软信息相结合,研究Rayleigh衰落信道下卷积码的Viterbi软判决译码,在利用和不利用信道状态信息(CSI)两种情况下给出软判决的支路度量计算公式和性能仿真结果,计算了卷积码的性能上界;研究了解调器输出量化门限(量化级数目、量化间距)对译码性能的影响.结果与硬判决译码及AWGN信道的相关结论进行了比较.     

频选快衰落信道的Turbo均衡算法

针对频选快衰落信道,本文提出卡尔曼滤波信道跟踪、软输出判决反馈均衡及软输入软输出信道解码迭代处理的Turbo均衡算法以充分利用已获得的信息,实现信道估计、信道均衡与信道解码的迭代更新,并克服传统判决反馈均衡器误差传播的缺陷.仿真表明,本算法能有效地跟踪快衰落信道,经两次迭代就可获得较为满意的码间干扰消除效果.     

MIMO—OFDM系统的半盲迭代接收机

针对存在多载波窄带干扰的多输入多输出正交频分复用系统，本文提出了基于马尔可夫链蒙特卡罗方法的迭代接收机．该方法不仅可以精确地估计出信道脉冲响应，还可以估计出噪声方差以及脉冲噪声发生的位置，这样接收机能够对窄带干扰区别对待，从而有效提高系统性能．该方法的另一个优点是，易于和软输入软输出译码结合，从而完成Turbo接收．仿真结果表明，在慢衰落信道下，与理想信道状态信息下的接收算法仅有3dB差别.     

衰落信道下多级编码方案的软判决译码

研究Rayleigh衰落信道下,软判决译码对三种不同映射方案多级编码系统性能的影响.基于信道容量规则,构造卷积码为分量码的8ASK多级编码系统,在多阶段译码中提出利用信道状态信息的软判决支路度量计算公式,并探讨系统的误码传播特性,研究结果可为衰落信道编码调制方案的最佳设计度量提供参考.     

一种用于IEEE802.16d的联合信道估计算法

针对IEEE802.16d帧结构提出一种结合前导训练序列和导频的信道估计算法。算法通过前导完成初始精确的信道估计,再使用判决反馈方式提高导频估计准确度,并根据前后符号导频估计结果得到反映信道变化的时变因子,利用它来调整前导估计和导频估计比例,联合完成信道估计。仿真结果表明,与传统的信道估计方法相比,此算法能够更有效的对抗频率选择性衰落和更大的多普勒频移,改善系统的性能。     

高精度无线移动通信信道盲估计方法

基于多载波OFDM系统,提出了一种新的时变步长修正软加权判决递归二乘信道估计盲方法(TVCPMSDWRLS).该法通过对常规算法步长进行自适应的科学设计以便跟踪信道特征变化,同时利用接收机判决信息函数修正权系数,解决了常规RLS盲方法收敛速度慢、信道估计性能不高的缺点.仿真证明:对于不同的时延扩展、时间以及信噪比(SNR),该法均表现出比常规方法更优的性能.同时,该法亦可用于估计通信、雷达、航天等领域的其他特征参数.     

Performance Bounds for Convolutional Codes with Digital Viterbi Decoders in Gaussian Noise

With digital implementations of the Viterbi decoding algorithm for convolutional codes, soft quantization is preferred over hard quantization because it generally yields superior performance. Since the decoder needs to know the signal energy and channel noise variance with soft quantization, inaccurate information can result in a mismatch between the channel and decoder. Bounds which are tight for high signal-to-noise ratios are obtained on the bit error probability using the generating function approach. Automatic gain control level inaccuracies, imperfect carrier phase, symbol timing synchronization error, and path metric digitization are discussed in the context of a mismatch between the channel and decoder.     

Performance analysis of Viterbi decoder using channel stateinformation in COFDM system

This paper relates to the application method of channel state information (CSI) to the Viterbi (maximum likelihood) decoder in the digital terrestrial television broadcasting system. The proposed Viterbi decoder uses the CSI derived from the pilots inserted in the transmitter of the COFDM (coded orthogonal frequency division multiplexing) system. The CSI is calculated by interpolation using the pilots in the receiver. The active real (I) and imaginary (Q) data after equalization are transferred to the branch metric calculation block that decides the euclidean distance for soft decision decoding and also the estimated CSI values are transferred to the same block. After calculating the euclidean distance for the soft decision decoding, the euclidean distance of the branch metric is multiplied by CSI. To do so, new branch metric values that consider each carrier state information are obtained. We simulated this method in Rayleigh fading defined in the ETSI standard. From the simulation, this method has better performance of about 0.15 dB to 0.7 dB and 2.2 dB to 2.9 dB in the Rayleigh channel than that of conventional soft decision Viterbi decoding with or without a bit interleaver where the constellation is QPSK, l6-QAM and 64-QAM     

Performance of LDPC coded FMT systems over frequency selective fading channel

This paper proposes the Low Density Parity Check （LDPC） coded Filtered MultiTone （FMT） systems with high-order modulation for the high data rate reliable transmission over frequency selective fading channel. For the purpose of accomplishing soft input soft output iterative decoding of LDPC codes, a new soft decision metric generation method is proposed, which obviates the need of the noise variance estimation, for M-PSK/M-QAM-type high-order modulation over frequency selective fading channel. Computer simulation indicates that, there is no performance loss with our new metric, but the complexity of implementation is reduced, and that the LDPC codes are effective to improve the Bit Error Rate （BER） of FMT in frequency selective fading channel.     

Analysis of an adaptive rate convolutionally coded multicarrierDS/CDMA system

The analysis of an adaptive rate convolutionally coded multicarrier direct sequence code division multiple-access (DS/CDMA) system is considered. In order to accommodate a number of coding rates easily and make the encoder and decoder structure simple, we use the rate-compatible punctured convolutional (RCPC) code. We obtain data throughputs at several coding rates, and choose the coding rate that has the highest data throughput in the signal-to-interference and noise ratio (SINR) sense. To achieve maximum data throughput, a rate adaptive system is proposed based on the channel state information (the SINR estimate). The SINR estimate is obtained by the soft decision Viterbi decoding metric. We show that the proposed rate adaptive convolutionally coded multicarrier DS/CDMA system can enhance the spectral efficiency and provide frequency diversity     

WCDMA中联合迭代信道估计与解码的研究

首先介绍了基于WCDMA系统中RAKE接收机的信道估计方法，然后将Turbo原理引入信道估计，针对WCDMA系统提出两种迭代信道的估计方法。通过使用RAKE接收机或解码之后的软信息来改善整个WCDMA系统的性能，对WCDMA系统中联合运用信道估计与解码技术进行了研究。由于联合信道估计与解码技术可以利用通信系统不同模块之间的“软信息”交换，从而有效地提高了信道估计准确程度和解码器的性能。仿真结果表明，利用解码之后的软信息来修正信道估计的方法较传统的RAKE接收机中的信道估计方法性能有较大改善，在误码率为10^-2左右时，提高大约1dB。     

Code-aided iterative carrier phase estimation using selective soft decision feedback

A code-aided iterative carrier phase estimator using selective soft decision feedback is proposed. Based on the reliability metric defined, soft decisions provided by the soft-in/soft-out channel decoder with higher reliabilities are selected to perform carrier phase estimation iteratively. Simulation results demonstrate the performance improvement of the proposed algorithm in both the unbiased estimation range and the estimation precision. The overall bit error rate performance of the coded systems with different phase estimators is also compared.     

Iterative channel estimation and decoding for convolutionally codedanti-jam FH signals

An iterative algorithm for joint decoding and channel estimation in frequency-hopping (FH) networks is proposed. In the proposed algorithm, soft decoder outputs are used in the iterative estimation of the time-varying variance of the additive interference resulting from the sum of the thermal noise, partial-band noise jamming, and other-user interference. The soft outputs are also used in the estimation of the independent random carrier phases and multiplicative Rayleigh fading coefficients in different frequency dwells. The estimation process is further enhanced through the insertion of known symbols in the transmitted data stream. The proposed iterative symbol-aided demodulation scheme is compared with the coherent scenario, where the channel state information is assumed to be known a priori at the receiver, for both convolutionally coded and turbo coded FH systems. The proposed iterative channel estimation approach is suited for slow FH systems where the channel dynamics are much slower than the hopping rate. This observation motivates the consideration of another robust approach for generating the log-likelihood ratios for fast hopping systems in additive white Gaussian noise channels. Simulation results that demonstrate the excellent performance of the proposed algorithms in various scenarios are also presented     

EM‐based iterative receiver for coded MIMO systems in unknown spatially correlated noise

We present iterative channel estimation and decoding schemes for multi‐input multi‐output (MIMO) Rayleigh block fading channels in spatially correlated noise. An expectation‐maximization (EM) algorithm is utilized to find the maximum likelihood (ML) estimates of the channel and spatial noise covariance matrices, and to compute soft information of coded symbols which is sent to an error‐control decoder. The extrinsic information produced by the decoder is then used to refine channel estimation. Several iterations are performed between the above channel estimation and decoding steps. We derive modified Cramer–Rao Bound (MCRB) for the unknown channel and noise parameters, and show that the proposed EM‐based channel estimation scheme achieves the MCRB at medium and high SNRs. For a bit error rate of 10⁻⁶ and long frame length, there is negligible performance difference between the proposed scheme and the ideal coherent detector that utilizes the true channel and noise covariance matrices. Copyright © 2006 John Wiley & Sons, Ltd.     

Particle filtering based channel estimation in OFDM power line communication

Particle filtering （PF） algorithm has the powerful potential for coping with difficult non-linear and non-Gaussian problems. Aiming at non-linear, non-Gaussian and time-varying characteristics of power line channel, a time-varying channel estimation scheme combined PF algorithm with decision feedback method is proposed. In the proposed scheme, firstly the indoor power line channel is measured using the pseudo-noise （PN） correlation method, and a first-order dynamic autoregressive （AR） model is set up to describe the measured channel, then, the channel states are estimated dynamically from the received signals by exploiting the proposed scheme. Meanwhile, due to the complex noise distribution of power line channel, the performance of channel estimation based on the proposed scheme under the Middleton class A impulsive noise environment is analyzed. Comparisons are made with the channel estimation scheme respectively based on least square （LS）, Kalman filtering （KF） and the proposed algorithm. Simulation indicates that PF algorithm dealing with this power line channel estimation difficult non-linear and non-Gaussian problems performance is superior to those of LS and KF respectively, so the proposed scheme achieves higher estimation accuracy. Therefore, it is confirmed that PF algorithm has its own unique advantage for power line channel estimation.