严格采样FMT系统频域均衡算法

根据滤波多音调制(FMT)系统基本原理推导了严格采样FMT系统的矩阵表示式,并针对严格采样FMT系统符号间干扰(ISI)严重的问题,根据最小均方误差准则提出了一种子信道频域均衡算法,给出了新算法的最小二乘迭代实现.仿真结果表明,新算法能有效均衡FMT信号,相比较于判决反馈均衡(DFE)算法,新算法的实现结构更简单并且误码率性能更好.     

一种基于MSINR的FMT系统频域均衡算法

 针对严格采样FMT系统符号间干扰(ISI)严重的问题,通过推导严格采样FMT系统的矩阵表示式,并对FMT接收信号的组成进行分析,提出了一种以最大化信干噪比(MSINR)为目标的子信道频域均衡算法.仿真结果表明,相比较于先前的判决反馈均衡(DFE)算法和基于最小均方误差准则的频域均衡算法,新算法能获得更好的误码率性能.     

FMT系统中的迭代信道估计和Turbo均衡

在滤波多音调制(FMT)系统中,为了消除由于原型滤波器非理想重构特性和多径信道所导致的符号间干扰,提出了一种联合迭代信道估计和Turbo均衡的FMT系统接收方法,通过对FMT系统中每个子信道的等效冲激响应进行迭代估计,然后采用基于线性滤波器结构的Turbo均衡器来消除符号间干扰.仿真结果表明,不论采用QPSK调制方式还是16QAM调制方式,经过2次以上的迭代后,相比较于传统的判决反馈均衡算法,新算法的误码率性能得到了大大改善.     

一种改进的ISFA信道估计算法

设计了一种基于符号内频域平均(ISFA)的信道估计算法,用于偏振复用光正交频分复用(PDM-O-OFDM)系统的信道估计和传输信道色散损伤的均衡。算法采用凯撒窗函数对基于导频的ISFA算法进行改进,提高了信道估计后处理的精度,改善了长距离PDM-O-OFDM系统的误码率(BER)和光信噪比(OSNR)性能。通过仿真试验,确定了算法的相关参数,分析了算法对长距离系统中色散损伤的均衡性能。仿真结果表明,改进算法对于传输距离超过700km系统的均衡效果优于原算法,其中900km处的OSNR代价比原算法低0.35dB。     

基于符号映射分析的CO-OFDM系统信道估计研究

针对相干光正交频分复用(CO-OFDM)系统中光纤信道快变对系统可靠性和有效性的降低,设计了一种符号映射分析(ASM,analysis of symbols mapping)算法,通过对接收到的OFDM符号星座图进行分析,不断地对由信道估计得到的传递函数进行修正,在不需要大量导频的情况下能快速跟踪信道的变化。仿真结果表明:在40Gb/s的快变光纤信道CO-OFDM系统中,信噪比(SNR)为10dB,在误码率(BER)为10-3时ASM算法比常规的迫零估计(ZFE,zero forcing estima-tion)算法需要的导频间隔减小了1/2;在导频间隔为10、BER为10-3时,ASM算法比常规的ZFE算法有约3.5dB的SNR改善。     

基于粒子滤波的Turbo盲均衡

粒子滤波是一种基于贝叶斯估计的算法,在信道盲辨识和盲均衡问题上具有快收敛、抗深衰信道等优势。Turbo盲均衡在低信噪比条件下有较好的误码性能。为了在深衰信道下使通信具有良好的误码性能,对粒子滤波盲均衡算法进行改进,改进算法的重要性采样函数利用了粒子的先验信息,得到一种软输入软输出的粒子滤波盲均衡算法。依据Turbo盲均衡的框架结构实现了一种基于粒子滤波的Turbo盲均衡算法,该算法利用信道编码带来的编码增益,提高了均衡和信道辨识的性能。仿真结果表明相比粒子滤波盲均衡算法本文提出算法的误码率性能提高1dB左右,误帧率性能则提高了3dB以上,经分析可知在信道系数估计较为准确的条件下,系统数据帧几乎没有误码。      

BICM在差分跳频系统中的应用

将比特交织编码调制(BICM)技术应用于差分跳频(DFH)通信系统,在加性白高斯噪声(AwGN)信道及频率非选择性瑞利慢衰落信道下,对采用无迭代译码及迭代译码的系统比特误码率(BER)上界进行了理论推导及数值仿真验证,并与传统的差分跳频系统的性能进行了比较.其数值仿真结果表明:采用BICM技术的差分跳频系统,可以在不增加跳频带宽及译码复杂度的情况下,利用最优卷积码增大了其G函数网格图的最小自由距离.同时对于可用频率数为16的无迭代译码BICM/DFH,当BER为10-1时,在瑞利信道下相对于CHESS系统而言,其性能改善可达6dB.若采用迭代译码,则当BER为10-1时,其性能相对于无迭代译码可进一步改善3,dB.     

单载波频域均衡信道估计分析

针对高速率信息传输系统中多径衰落对单载波频域均衡(SC-FDE)信道估计造成的影响,在SC-FDE原理基础上,将无线通信中信噪比估计和SC-FDE中信道估计结合起来,对现有信噪比估计算法进行优化。分析和仿真结果表明,此方法能有效地改善多径衰落信道中信道估计的有效性,提高了频域均衡的效果,从而改善了SC-FDE系统的误码率(BER)性能。     

低莱斯因子下的时频联合MMSE均衡算法

针对低莱斯因子的慢衰落时变多径信道条件下,难以有效利用信号能量,导致系统误码性能差,单纯的基于最小均方误差准则均衡（Minimum Mean Squared Error, MMSE）技术不能够有效降低误码率的实际问题。在构建信道等效模型的基础上,提出了一种利用硬判决符号重构信道,在两个信道长度内比较改判信号误差信息的时频联合判决两轮次MMSE均衡算法。仿真结果表明:通过均衡处理后的低莱斯因子信道能逼近高莱斯因子的误码特性,当信噪比为20dB时,不同莱斯因子下QPSK信号的误码率均降低至10^(-4)以下,且在一个数量级内。当信噪比为2~6dB时,系统误码率分布在10^(-1)~10^(-3)之间,要低于信号在自由空间传播的误码率,说明MMSE均衡充分利用了多径分量的能量,获得了信噪比增益。      

大气湍流影响下基于自适应判决门限的逆向调制自由空间光通信系统误码率性能分析

推导了最优误码率(BER)性能对应的判决门限计算公式,并在此判决门限基础上,推导出大气湍流影响下基于自适应判决门限的逆向调制(MRR)自由空间光通信(FSOC)系统BER解析表达式,推导过程考虑了判决门限本身的干扰和探测器噪声的影响。根据所推导的表达式,仿真研究自适应判决门限参数和调制消光比对BER的影响,仿真结果表明:自适应判决门限系统BER性能优于固定判决门限17.5dB(误码率为10-5,弱湍流),并且当训练数据比特位数大于3时,自适应判决门限系统的BER性能与根据瞬时信道状态信息计算判决门限系统的BER性能相近。     

Efficient image transmission scheme in FMT system

An efficient image transmission scheme is proposed based on byte partition and adaptive sub-channel distribution technique in Filtered MultiTone (FMT) system over frequency selective slow fading channel. According to the simulation results and analysis of a typical image with matlab, improvement in Peak Signal to Noise Ratio (PSNR) of the received image and low complexity for equalization is demonstrated remarkably. Comparing with no adaptive and no actual channel equalization scheme, the proposed scheme saves over 6 dB when PSNR=40 dB.     

基于粒子群优化的MIMO系统判决反馈均衡研究

为了更好地消除多输入多输出(MIMO)系统中的码间干扰(ISI),提出了一种基于粒子群优化(PSO)的判决反馈均衡(DFE)算法;将该算法与基于最小均方(LMS)算法的判决反馈均衡进行了比较.仿真结果表明,PSO DFE的误码率性能明显优于LMS DFE,且收敛速度快.     

宽带自适应MIMO-DFE空时接收机

设计了频率选择信道基于RLS算法的自适应判决反馈均衡MIMO-DFE空时接收机,由于这种接收机不需要信道识别,从而降低了接收机的复杂度。通过蒙特卡罗仿真评估了接收机在频率选择信道下的误符号率性能。仿真结果表明,在不加信道编码的情况下,该接收机在信噪比为 14dB时误符号率达到 10-3以下。     

Equalization methods in OFDM and FMT systems for broadband wireless communications

Multicarrier systems are adopted in several standards for their ability to achieve optimal performance in very dispersive channels. In particular, orthogonal-frequency division multiplexing (OFDM) and filtered multitone (FMT) systems are two examples where the modulation filter has an ideal rectangular amplitude characteristic in time and frequency domains, respectively. In this letter, we propose new equalization schemes for FMT and compare their performances with OFDM. In general, FMT has a greater spectral efficiency than OFDM, due to the absence of the cyclic prefix and a reduced number of virtual carriers. However, it exhibits a higher distortion per subchannel, due to the imperfect equalization of the transmit filters. As a performance comparison, we considered both the achievable bit rate (ABR) and the bit error rate (BER) in a multipath Rayleigh fading channel. We note that while ABR gives a theoretical bound on the system bit rate, assuming the knowledge of the channel at the transmit side, the BER refers to an uncoiled system with a fixed modulation. Although FMT requires a fixed structure with a higher computational complexity than OFDM, it turns out that FMT, even with the simplest one tap per subchannel adaptive equalizer, yields a better performance than OFDM, both in terms of ABR and BER. Hence, FMT can be a valid alternative to OFDM for broadband wireless applications, also.     

MAP selection-diversity DFE for indoor wireless data communications

Indoor high-speed wireless data networks encounter signal fading and delay-spread multipath propagation. Hence, the realization of low error rate transmission requires measures to combat the performance degradation due to both signal fading and intersymbol interference (ISI). Receiver diversity has been known to be an efficient way of coping with the former problem, while adaptive equalization could be used to mitigate the effects of the latter. Incorporation of receiver diversity with adaptive equalization is therefore desirable. We propose a novel selection-diversity approach with an adaptive decision-feedback equalizer (DFE). In this method, selection is done on a symbol-by-symbol basis such that the output of the branch with the lowest estimated a posteriori probability of error is used as the final decision. This final (and hence more reliable) decision is used to adapt the DFE for all diversity branches. It is shown in this paper that the proposed selection rule is optimal for selection-diversity in the maximum a posteriori probability (MAP) sense. A very simple selection metric can be derived from this selection rule and practical ways of computing the selection metric are also presented. Simulation results show that the proposed method is very efficient. It is capable of achieving almost the same performance as an optimal [least squares (LS)], but computationally intensive, combining diversity approach. Furthermore, at an average bit error rate (BER) of 10^-4, a gain of approximately 1.25 dB can be achieved over a previously proposed selection-diversity equalization approach     

Performance analysis of error propagation effects in the DFE for ATSC DTV receivers

The paper analyzes the error propagation phenomenon in the decision feedback equalizer (DFE) for the receivers of Advanced Television Systems Committee (ATSC) digital television (DTV) and presents the performance upper-limits of the DFE by comparing various error propagation cases and the no-error propagation case. As one approach to the performance limit, we consider a blind DFE, adopting a trellis decoder with a trace-back depth of 1 as a decision device. Through simulation, we show how much the DFE performance in ATSC DTV receivers is affected by error propagation. We found that while blind equalization is preferable to decision-directed (DD) equalization at signal-to-noise ratio (SNR) values less than 18 dB, DD equalization is superior to blind equalization at SNR values greater than 18 dB. In addition, symbol error rate curves quantitatively show that the performance difference in the DFE caused by error propagation becomes clearer at the trellis decoder following the DFE. The analysis results presented are very informative for developing equalization algorithms for ATSC DTV receivers.     

Adaptive decision feedback equalization for digital satellitechannels using multilayer neural networks

This paper introduces an adaptive derision feedback equalization using the multilayer perceptron structure of an M-ary PSK signal through a TDMA satellite radio channel. The transmission is disturbed not only by intersymbol interference (ISI) and additive white Gaussian noise, but also by the nonlinearity of transmitter amplifiers. The conventional decision feedback equalizer (DFE) is not well-suited to detect the transmitted sequence, whereas the neural-based DFE is able to take into account the nonlinearities and therefore to detect the signal much better. Nevertheless, the applications of the traditional multilayer neural networks have been limited to real-valued signals. To overcome this difficulty, a neural-based DFE is proposed to deal with the complex PSK signal over the complex-valued nonlinear MPSK satellite channel without performing time-consuming complex-valued back-propagation training algorithms, while maintaining almost the same computational complexity as the original real-valued training algorithm. Moreover, a modified back-propagation algorithm with better convergence properties is derived on the basis of delta-bar-delta rule. Simulation results for the equalization of QPSK satellite channels show that the neural-based DFE provides a superior bit error rate performance relative to the conventional mean square DFE, especially in poor signal-to-noise ratio conditions     

Sequence estimation techniques for digital subscriber looptransmission with crosstalk interference

The use of reduced-state sequence estimation techniques in a digital subscriber loop receiver is discussed. These techniques offer a potential performance improvement over conventional equalization techniques such as decision feedback equalization (DFE). Stationary and cyclostationary NEXT noise models are described. The theoretical performance obtainable from a Viterbi algorithm receiver with stationary white Gaussian noise, stationary NEXT, and cyclostationary NEXT noise models is estimated, and the reduced-state decision feedback sequence estimation and M algorithms are reviewed. It is shown that the improvement can be especially significant in the presence of cyclostationary crosstalk because of the freedom that sequence estimation receivers afford in the choice of receiver sampling phase. This advantage is evaluated for Viterbi algorithm receivers. By simulation of two practical reduced-state sequence estimation receivers, it is demonstrated that, in the presence of cyclostationary crosstalk, a substantial increase in maximum loop range (or equivalently, maximum bit rate) may be achievable compared to conventional DFE equalization     

短波宽带波形迭代均衡技术

短波宽带波形是现代短波通信的最新研究成果,短波信道时变多径传播效应会产生严重的码间干扰(ISI),必须采用均衡技术消除ISI。迭代均衡技术(Turbo均衡)将信号检测技术和译码技术结合起来,比传统判决反馈均衡(DFE)技术具有更强抗ISI能力。研究了短波宽带波形Turbo均衡技术,提出了一种低复杂度的迭代检测方法用于短波宽带波形,仿真结果表明,在短波差信道条件下,Turbo均衡比DFE均衡的性能增益超过1.5 dB。