一种改进的单载波块迭代判决反馈均衡算法

针对低复杂度的块迭代频域判决反馈均衡算法在迭代过程中对判决误差概率设置不够合理的缺陷,提出一种改进的块迭代频域判决反馈均衡算法,该算法通过在迭代过程中合理的设置判决误差概率,从而提高系统的性能。与低复杂度的块迭代频域判决反馈均衡算法相比,该算法能够获得更好的性能,并且具有较低的复杂度。     

水声通信中基于软判决的块迭代判决反馈均衡器

在单载波频域均衡水声通信系统中,混合结构的时-频域判决反馈均衡器(H-DFE)计算复杂度高,不利于实时实现;而基于硬判决的块迭代判决反馈均衡器(HD-IBDFE)存在错误符号判决造成系统性能下降问题,同时需要估计判决符号和发射数据之间的互相关函数。该文对水声通信中基于软判决的块迭代判决反馈均衡(SD-IBDFE)接收机算法进行了研究,通过对均衡器输出信号进行软判决,并将符号软信息进行反馈,提高了系统性能,同时采用迭代信道估计方法来适应水声信道的时变性。通过仿真比较得出,该方法在水声信道条件下明显优于HD- IBDFE。对湖上试验数据处理结果表明,在浅水1.8 km通信距离下,单通道无编码QPSK调制可实现10-3的误码率并达到3000 bps的有效数据率。     

数字电视接收机中的Block-DFE算法研究

针对地面数字电视传输国家标准(DTMB),研究并提出一种新的数据块判决反馈均衡算法.该算法利用QR因式分解以解决最小二乘方探测问题.通过Matlab仿真对传统判决反馈均衡算法(DFE)、循环构造频域均衡算法(OLA-FDE)和数据块判决反馈均衡算法(Block-DirE)在不同信噪比下的性能作了比较,验证了Block-DFE算法的优越性.     

单载波频域均衡系统中一种简化的IBDFE算法

在单载波频域均衡系统中,线性均衡算法虽然简单易行,但是其抑制噪声干扰和符号间干扰的能力有限,因此需要引入非线性的反馈和迭代机制以进一步提升系统性能.迭代块判决反馈均衡（Iterative Block Decision Feedback Equalization,IBDFE）就是一种行之有效的非线性算法,但其缺点是计算复杂度高.鉴于此,在IBDFE结构的基础上,利用最小均方误差准则,推导出了一种新的简化算法.之后,对简化后算法和现有低复杂度算法的均方误差（Mean Square Error,MSE）性能进行了理论分析和比较,并在两种无线多径衰落信道下对三种不同的算法进行了仿真.结果表明,在所给信道条件下,这种算法在迭代两次后已基本收敛.同时,仿真也验证了MSE分析的结论.最后,对算法复杂度的分析和比较表明,提出的简化算法相比传统IBDFE算法,其误比特率性能有所下降,但能有效地减小计算量.     

基于线性化因子更新的频域迭代判决反馈均衡

迭代块判决反馈均衡(Iterative Block Decision Feedback Equalization,IBDFE)是单载波频域均衡中一种行之有效的非线性均衡算法,但算法计算复杂度随迭代次数增加而增大。本文针对传统IBDFE算法的不足提出一种基于线性因子更新的频域迭代判决反馈均衡算法,利用了线性因子更新来降低均衡器复杂度,并引入修正因子计算反馈滤波器系数以避免性能损失。仿真结果表明,所提出算法性能与传统IBDFE算法相比复杂度降低且在误比特率为10-5时有0.12 dB的性能增益,与已有的低复杂度算法(Low-Complexity IBDFE,LC-IBDFE)相比有0.1 dB的性能增益。      

单通道GMSK混合信号线性联合检测算法

对单通道同频同调制突发高斯最小频移键控(GMSK)混合信号联合检测问题进行了研究。基于混合信号的时延差异性和符号间干扰(ISI)特性,提出了一种分支联合判决反馈检测算法。检测时将每条支路当作单个GMSK信号,并通过其他支路的信息反馈来优化检测性能。理论和仿真表明,与最大似然检测指数复杂度相比,通过分支判决反馈,其复杂度降为线性,检测性能比无判决反馈时的检测带来了约2 dB的增益,并在高信噪比下接近逐幸存路径处理(PSP)算法。仿真分析了时延对分支联合反馈算法的影响:当混合信号的幅度相同,时延为码元整数倍时,混合信号不具有可检测性,并进行了理论推导;当混合信号可分时,相对时延越大,分离性能越好。     

基于判决反馈的CPFSK信号非相干多符号检测算法

针对传统多符号检测算法存在的计算复杂度高、工程实现难度大等问题,提出了基于判决反馈思想的改进算法。该算法利用已判决的码元信息,对观测长度内所有可能发送波形进行筛选,从而减少码元判决时所需的相关器数量,降低算法的检测复杂性。在低信噪比和高信噪比2种情况下推导出改进算法误码性能的联合上边界,并基于网格最小欧氏距离求得其性能下边界,明确界定了改进算法的误码性能。理论分析和仿真结果都表明,与传统算法相比,在不损失检测性能的前提下,改进算法的复杂度随着反馈码元个数的增加呈负指数幂减少。     

基于序列检测的块判决辅助Turbo均衡器

该文针对高斯分布假设条件下逐符号检测均衡器的不足,提出了一种基于序列检测的块判决辅助Turbo均衡器(Turbo-BDAE)。新算法利用译码全信息估计发送序列,提高了序列估计的可靠性,引入软判决可以降低硬判决引起的错误扩散,同时结合序列检测为均衡器输出的后验概率(APP)估计提供了更可靠的信息。仿真表明,该均衡器在保持相近复杂度的同时,进一步提升了均衡系统性能,优于逐符号LMMSE均衡器和硬反馈BDFE。     

一种改进的SC-FDE块迭代判决反馈均衡器

单载波频域均衡(SC-FDE)系统能有效地对抗频域选择性衰落信道。块迭代判决反馈均衡(IBDFE)是单载波频域均衡系统中一种有效的非线性均衡算法,但是其计算复杂度较高,且复杂度与迭代次数成正比。鉴于此,提出一种改进算法,在改进算法中,将接收信号经过MMSE均衡得到发送信号估计值作为传统算法反馈支路输出,前馈支路结构保持不变。对比传统IBDFE算法,迭代被取消,故降低了计算复杂度。对传统IBDFE算法和改进IBDFE算法性能进行比较,实验结果证明:改进IBDFE算法性能在与传统IBDFE算法性能相似的条件下降低了计算复杂度。     

一种低复杂度的CPM信号最大似然块检测算法

为了降低连续相位调制(Continuous Phase Modulation,CPM)信号多符号非相干检测的运算复杂度,提出了一种低复杂度的最大似然块检测算法。该算法充分利用已判决输出的符号对检测过程中的符号向量取值进行约束,有效减少判决统计量计算时的运算量,进而降低算法复杂度。另外,该算法引入判决长度变量,通过调整单次检测时判决符号数使算法能够在检测性能与运算量之间灵活折中。仿真结果表明,提出的低复杂度检测算法能够适用于全响应和部分响应CPM信号,相比原最大似然块检测算法能够在不损失检测性能的前提下降低算法运算量至少50〖WT《Times New Roman》〗%〖WTBZ〗,并且能够通过选择不同的判决长度提高算法应用的灵活性。     

Low complexity soft-input soft-output block decision feedback equalization

A low complexity soft-input soft-output (SISO) block decision feedback equalizer (BDFE) is presented for turbo equalization. The proposed method employs a sub-optimum sequence-based detection, where the soft-output of the equalizer is calculated by evaluating an approximation of the sequence-based a posteriori probability (APP) of the data symbol. The sequence-based APP approximation is enabled by the adoption of both soft a priori information and soft decision feedback, and it leads to better performance and faster convergence compared to symbol-based detection methods as used by most other low complexity equalizers. The performance and convergence property of the proposed algorithm is analyzed by using extrinsic information transfer (EXIT) chart. Both analytical and simulation results show that the new equalizer can achieve a performance similar to that of trellis-based equalization algorithms, with a complexity similar to linear SISO minimum mean square error equalizers.     

Blind detection of equalization errors in communication systems

In adaptive channel equalization, transmitted symbol estimates at the equalizer output may be in error because of excessive channel noise, convergence of the equalizer to a “closed-eye” local minimum, or error propagation if the equalizer has a decision feedback structure. This paper is concerned with the detection of equalization errors (i.e., errors in transmitted symbol estimates) in a blindfolded manner whereby no direct access to the channel input is required. The detection problem is cast into a binary hypothesis testing framework. Assuming a linear communication channel that is time-invariant during the test interval, a relationship between the presence of equalization errors and time variations in the underlying linear model taking the transmitted symbol estimates to the equalizer input is established. Based on this relationship, a uniformly most powerful test is constructed to detect the presence of equalization errors in finite-length observations. Finite sample size and asymptotic detection performance of the test is studied. A method for estimating the equalization delay without direct access to the channel input is developed. The effectiveness of the test is illustrated by way of computer simulations     

Evaluation of Decision Feedback Equalization and Viterbi Algorithm Detection for Voiceband Data Transmission--Part II

This paper describes experimental results of simulated 12000 and 14400 bits/s quadrature amplitude-modulated (QAM) systems (which were described in detail in Part I [1] ) operating on real and simulated voiceband channels. These experimental results show that both Viterbi algorithm detection and decision feedback equalization allow digital data transmission at symbol rates exceeding the nominal bandwidth capabilities of typical telephone channels. It is demonstrated in these experiments that the Viterbi algorithm receiver structure tested is less affected by linear distortion than the decision feedback receiver but exhibits greater sensitivity to phase jitter. On conditioned voiceband channels where there may be substantial phase jitter, a reasonable compromise between sensitivity to distortion and noise and sensitivity to phase jitter is made by a modem employing decision feedback equalization and decision-directed carrier phase tracking.     

Computationally efficient equalization for asynchronous cooperative communications with multiple frequency offsets

In cooperative communications, time and frequency synchronization is an important issue needed to be addressed in practice. Due to the nature of cooperative communications, multiple frequency offsets may occur and the traditional frequency offset compensations may not apply. For this problem, equalization for the time-varying channel has been used in the literature, where the equalization matrix inverse needs to be retaken every symbol. In this paper, we propose computationally efficient minimum mean square error (MMSE) and MMSE decision feedback equalizers (MMSE-DFE) when multiple frequency offsets are present, where the equalization matrix inverses do not need to be retaken every symbol. Our proposed equalization methods apply to linear convolutively coded cooperative systems, where linear convolutive space-time coding is used to achieve the full cooperative diversity when there are timing errors from the cooperative users or relay nodes, i.e., asynchronous cooperative communication systems.     

Iterative nonlinear detection for SFBC SC–FDMA uplink MIMO transmission systems

Single‐carrier frequency division multiple access (SC‐FDMA) systems with space frequency block coding (SFBC) transmissions achieve both spatial and frequency diversity gains in wireless communications. However, SFBC SC‐FDMA schemes using linear detectors suffer from severe performance deterioration because of noise enhancement propagation and additive noise presence in the detected output. Both issues are similar to inter‐symbol‐interference (ISI). Traditionally, SC‐FDMA system decision feedback equalizer (DFE) is often used to eliminate ISI caused by multipath propagation. This article proposes frequency domain turbo equalization based on nonlinear multiuser detection for uplink SFBC SC‐FDMA transmission systems. The presented iterative receiver performs equalization with soft decisions feedback for ISI mitigation. Its coefficients are derived using minimum mean squared error criteria. The receiver configuration study is Alamouti's SFBC with two transmit and two receive antennas. New receiver approach is compared with the recently proposed suboptimal linear detector for SFBC SC‐FDMA systems. Simulation results confirm that the performance of the proposed iterative detection outperforms conventional detection techniques. After a few iterations, bit‐error‐rate performance of the proposed receiver design is closely to the matched filter bound. Copyright © 2016 John Wiley & Sons, Ltd.     

Evaluation of Decision Feedback Equalization and Viterbi Algorithm Detection for Voiceband Data Transmission--Part I

The application of QAM receivers employing passband decision feedback equalization or Viterbi algorithm detection is considered for high-speed data transmission in voiceband telephone channels. Analytical results for the Viterbi receiver indicate that it can permit digital data transmission with symbol rates exceeding the nominal bandwidth capabilities of the channel. However, it is also shown that the minimum distance of partial response-type impulse responses can substantially decrease due to small demodulation phase errors. Thus, decision feedback receivers may offer more robust performance on channels with phase jitter.     

Upper bounds to the error probability of decision feedbackequalization

The exact computation of the symbol error probability of systems using decision feedback equalization is difficult due to the propagation of errors. New upper bounds to the error probability of decision feedback equalization, which take error propagation into account, are developed. The derivations of the bounds assume a causal channel response, independent data symbols, and independent noise samples. The bounds are valid for any noise process that has a symmetric and unimodal probability density function. In some cases, the new bounds are significantly tighter than a well-known upper bound of D.L. Duttweiler et al. (1974)     

应用于窄脉冲超宽带通信的均衡算法及其实现

由于高传输速率及多径效应的影响,在窄脉冲超宽带(IR-UWB)通信系统中,基于传统横向滤波器的时域均衡技术已无法对抗严重的码间干扰。通过收发两端联合设计,提出了一种以数据块为基础的基于码元的频域均衡技术,同时介绍了其应用前提和算法实现。仿真结果表明,所提方法能有效对抗超宽带通信系统中存在的码间干扰,是窄脉冲超宽带通信系统中更为现实的技术选择。     

室内可见光通信中的线性均衡与判决反馈均衡

信道均衡是光通信的关键技术之一。信道均衡能有效地克服信息传输中的多径干扰和消除码间串扰,适合于数据传输。本文针对室内可见光通信系统中由信道失真引起的严重的码间串扰（ISI）情况,研究迫零均衡（ZFE）、最小均方误差（MMSE）均衡、判决反馈均衡（DFE）3种均衡技术,并利用计算机仿真对3种均衡技术的性能进行评估。仿真结果表明,判决反馈均衡器具有明显的优越性。     

Joint equalization and decoding for QAM block transmissions

A method of joint equalization and decoding for block transmission with coding across blocks is presented. It is well suited for bandwidth efficient QAM transmission using large transmit symbol alphabets, whereby the blocking structure can be arbitrary in principle. The method consists in multiple iterations of equalization and decoding, whereby information is exchanged back and forth between the decoder and the equalizer. The equalizer is based on Cholesky factorization of the equivalent discrete-time channel matrix (Eur. Trans. Telecommun 10 (1999) 351; Grundlagen der Kommunikationstechnik, Springer, Berlin, 2004). The convergence behavior of the iterative equalization and decoding method is analyzed by means of an upper bound on the extrinsic information transfer. It is shown that the method has improved bit error performance versus separate equalization and decoding without decoder feedback and, thus, yields superior power efficiency.