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。     

基于频域波形合成的盲空间分集均衡器设计

针对频率选择性衰落信道下的多天线盲接收问题,本文提出了一种新的"合成器-均衡器"盲空间分集均衡器结构.基于频域波形合成、均衡器与软符号信息的联合处理框架,首先设计了频域BLOCK-SUMPLE迭代算法,对多路信号频域合成权值进行联合估计,实现频率选择性衰落信道下的波形合成.在此基础上,利用均衡器输出软符号信息重构合成参考,对权值相位予以修正,实现对等效合成信道的优化补偿.与传统盲空间分集均衡算法相比,上述算法实现无需训练序列辅助,并且优化了信号分集合并性能,降低了均衡器的设计难度.仿真结果表明,采用新型结构可有效改善衰落信道下的盲接收效果,逼近最佳空间分集均衡器性能.     

单载波频域均衡消除符号间干扰的研究

介绍了单载波频域均衡（SC-FDE）系统以及SC-FDE所常用的频域块最小均方（FBLMS）算法。为了进一步改进单载波频域均衡系统的性能，基于抽头泄漏的思想，通过增加抽头的泄漏进一步优化了FBLMS算法，并对基于优化算法的单载波频域均衡系统进行了计算机仿真模拟。其仿真结果表明：与常用算法相比较，该优化算法能有效提高均衡器的收敛速度和显著改善均衡器消除符号间干扰（ISI）的性能。     

单载波宽带MIMO系统广义近似消息传递Turbo频域均衡

针对编码单载波循环前缀(SC-CP)多输入多输出(MIMO)系统,该文采用消息传递算法研究软输入软输出MIMO频域均衡器(FDE)的设计问题。基于广义近似消息传递(GAMP)算法,该文提出一种新的低复杂度MIMO频域均衡方法。这种消息传递MIMO均衡方法的显著特点是既保留了SC-CP传输所产生的频域均衡的优点,同时又避免了传统MIMO FDE中逐频点MIMO矩阵求逆运算,所以具有随MIMO系统接收天线数增加而线性增长的计算复杂度。计算机仿真结果表明,与传统方案相比,该文提出的MIMO频域均衡算法具有明显的误码率(BER)性能优势。     

基于Rimoldi分解的连续相位调制信号Turbo频域均衡算法

针对高阶部分响应连续相位调制(CPM)信号均衡中存在的复杂度高和性能较差等问题,该文从Rimoldi分解的角度出发,设计了一种新的适用于倾斜相位CPM信号的发射帧结构,并在此基础上结合单载波频域均衡(FDE)和Turbo均衡的思想,提出了一种适用于高阶CPM信号的Turbo频域均衡算法。该算法通过将信号均衡转化到频域进行处理,避免了时域均衡算法在计算均衡器系数时存在的大矩阵求逆问题,同时使用Turbo均衡的软信息迭代处理来改善系统的性能。理论分析和仿真结果表明,对于四阶部分响应CPM信号,在存在严重符号间干扰的多径衰落信道的条件下,该算法与现有的基于符号的频域均衡算法相比,在保持较低复杂度的同时,具有大约1.5 dB的性能增益。     

SC-FDE系统的一种新型判决反馈均衡器

针对单载波频域均衡系统MMSE均衡器存在残留码间干扰的缺点,提出MMSE-RISIC判决反馈均衡器消除残留码间干扰.MMSE-RISIC均衡器采用传统MMSE均衡后的判决数据,对残留码间干扰进行估计并消除.残留码间干扰的估计主要采用FFT和IFFT运算,与其他方法相比计算量较小.对该均衡器在不同信道下进行了计算机仿真,结果表明,在频率选择性衰落信道条件下,系统性能有了较为明显的提高.     

MIMO-CDMA系统的分数间隔空频均衡接收方案

该文提出了两种适用于宽带单载波多用户MIMO-CDMA系统下行链路的分数间隔空频均衡接收方案,并进行了理论推导。第1种接收方案采用分数间隔空频均衡器对MIMO频率选择性衰落信道进行均衡,从而恢复了扩频码的正交性,减小了码间干扰和共道干扰。第2种方案在假设接收端已知各用户扩频码的前提下,将分数间隔空频均衡器与频域并行干扰消除器结合,能够进一步消除天线间干扰,提高系统性能。仿真结果表明,这两种分数间隔空频均衡接收方案都比传统的频域均衡接收方案在性能上有很大的提高,并且复杂度也比较低。     

一种基于STBC的SC-FDE系统双天线联合检测算法

针对双发双收的基于空时分组编码的单载波频域均衡(STBC-SC-FDE)系统,研究了一种双天线联合检测算法,通过信道估计、导频干扰消除、加权联合均衡等过程重构发送的信息。并根据信噪比对频域信号与均衡矩阵进行加权处理,使联合检测算法适用于2路接收信号信噪比不同的情况。仿真结果表明,所提出的双天线联合检测算法在SUI-3信道下最大可获得约8dB的接收分集增益。与时域最大比合并(MRC)算法相比,由于采用联合检测,该算法能有效改善系统在多径衰落信道下的误码率。     

双选择性信道条件下OFDM系统的频域Turbo均衡

未来OFDM系统将工作在高载频、高容量、高移动速率的条件下,传统的单抽头频域均衡器将不再适用。该文基于双选择性信道的ICI分析,提出了一种用于OFDM系统的频域Turbo均衡(Frequency-domain Turbo Equalization, FTE)算法。仿真表明该算法具有BER性能好,计算复杂度低的优点,能够很好地抑制ICI。     

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。     

Frequency domain decision feedback equalizer for time-reversal space-time block coding

In this paper,a frequency domain decision feedback equalizer is proposed for single carrier transmission with time-reversal space-time block coding (TR-STBC).It is shown that the diagonal decision feed...     

多模盲均衡载波同步联合架构及分析

对于QAM体制信号,多模盲均衡算法(MMA)具有优于恒模算法 (CMA)的性能,同时具有矫正固定相位偏差及一定载波频率偏差(CFO)的能力。但在实际通信系统中,MMA对载波频偏的适应能力有限,当系统存在较大CFO时,MMA均衡算法稳态性能大幅下降。为保证MMA算法的稳态性能,同时适应较大载波频率偏差,文中提出了一种均衡载波同步联合结构。该结构将均衡器置于载波同步环路中,在消除载波频偏对均衡器性能影响的同时,提升了系统的载波频偏跟踪能力。文中对联合结构的载波环路跟踪性能进行了详细的理论分析,给出了环路性能指标的计算方法。数值仿真结果验证了理论分析的正确性,同时指出多模盲均衡载波同步联合算法能够在满足较大载波频偏跟踪性能的同时,实现接近无频偏时的均衡效果,很好的解决了大频偏下MMA算法性能损失严重的问题。      

CDMA系统上行链路的分数间隔频域均衡接收方案

提出一种应用于单载波CDMA系统异步上行链路的分数间隔频域均衡接收方案。针对异步上行链路各用户到达基站的信号具有任意随机时延的特性,为了提高CDMA系统上行链路的抗干扰能力,降低接收机检测复杂度。同时与现有单载波系统空中接口兼容,接收方案采用基于重叠截取技术的单载波分数间隔频域均衡器对抗频率选择性衰落所引起的各种干扰;用时域多阶并行干扰消除器减小用户间严重的多址干扰。仿真结果表明,这种分数间隔频域均衡接收方案比传统的码片级均衡接收方案在性能上有很大的提高,并且复杂度也比较低。     

A Hybrid Domain Block Equalizer for Single-Carrier Modulated Systems

Poor performance in the presence of multipath with long delay spread has been considered as one of the main weaknesses of most single carrier modulated systems, including ATSC (advanced television systems committee) system. The introduction of distributed transmission network and single frequency network brings new challenges for the ATSC equalizer design, since the delay spread of a multipath channel under such scenarios becomes significantly longer than the traditional broadcasting practice of using one high power transmitter to cover a wide area, where the multipath distortion is mainly from reflected echoes. An iterative hybrid frequency-time domain equalizer for ATSC system is proposed in this paper based on our block-based interference analysis. The multipath distortion in the received ATSC signal is first tentatively removed with a frequency domain equalizer on a block-by-block basis. However, inter-block and intra-block interferences still exist due to the lack of cyclic structure in the received ATSC signal. A time domain interference cancellation algorithm is then used to cancel the inter-block interference and intra-carrier interference, based on the tentative decisions in time domain after the frequency domain equalization. These two steps are iterated until desired receiver performance is achieved. The proposed equalizer and the subsequent analysis are verified through numerical simulations.     

基于叠加训练序列和低复杂度频域Turbo均衡的时变水声信道估计和均衡

针对时变水声信道估计和均衡问题,该文提出基于叠加训练序列(ST)和低复杂度频域Turbo均衡(LTE)的时变水声信道估计和均衡(ST-LTE)算法。基于叠加训练序列方案,将训练序列和符号线性叠加,使得训练序列和符号信道信息一致;基于最小二乘算法,进行信道估计。基于频域训练序列干扰消除技术,在频域消除训练序列对符号的干扰;基于频域线性最小均方误差(LMMSE)均衡算法,通过先验、后验、外均值和方差的计算,实现低复杂度信道均衡(符号估计);基于Turbo均衡算法,软重构叠加训练序列和更新信道估计,进行均衡器和译码器的信息交换,利用编码冗余信息,大幅度提升信道均衡性能。进行仿真、水池静态通信试验(通信频率12 kHz,带宽6 kHz,采样频率96 kHz,符号传输速率4.8 ksym/s,训练序列和符号的功率比为0.25:1)和胶州湾运动通信试验(通信频率12 kHz,带宽6 kHz,采样频率96 kHz,符号传输速率3 ksym/s,训练序列和符号的功率比为0.25:1),仿真和试验结果验证了所提算法的有效性。     

Performance evaluation of OFDM and single‐carrier systems using frequency domain equalization and phase modulation

In this paper, we study the performance of the continuous phase modulation (CPM)‐based orthogonal frequency division multiplexing (CPM‐OFDM) system. Also, we propose a CPM‐based single‐carrier frequency domain equalization (CPM‐SC‐FDE) structure for broadband wireless communication systems. The proposed structure combines the advantages of the low complexity of SC‐FDE, in addition to exploiting the channel frequency diversity and the power efficiency of CPM. Both the CPM‐OFDM system and the proposed system are implemented with FDE to avoid the complexity of the equalization. Two types of frequency domain equalizers are considered and compared for performance evaluation of both systems; the zero forcing (ZF) equalizer and the minimum mean square error (MMSE) equalizer. Simulation experiments are performed for a variety of multipath fading channels. Simulation results show that the performance of the CPM‐based systems with multipath fading is better than their performance with single path fading. The performance over a multipath channel is at least 5 and 12 dB better than the performance over a single path channel, for the CPM‐OFDM system and the proposed CPM‐SC‐FDE system, respectively. The results also show that, when CPM is utilized in SC‐FDE systems, they can outperform CPM‐OFDM systems by about 5 dB. Copyright © 2010 John Wiley & Sons, Ltd.     

Joint Frequency-Domain Multiuser Turbo Equalization with Successive Interference Cancellation for Doubly-Selective Fading Channels

A novel multiuser separation and equalization scheme is proposed for single carrier wireless communication systems integrating frequency-domain (FD) multiuser turbo equalization (MUTE) and successive interference cancellation (SIC). The proposed iterative structure consists of multiple layers of detection, and at each layer the user with strongest power is processed by a frequency-domain multiuser equalizer to yield the soft extrinsic information on the coded bits of that user, which is delivered to a channel decoder after deinterleaving. The extrinsic information gleaned by the decoder is fed back to both the current and previous multiuser equalizers for the next iteration as a-priori information. The soft symbols of the current user are evaluated by the a-posteriori information of coded bits provided by the multiuser equalizer, and the interference reconstructed by the current user’s soft symbols is canceled out from the received signals in frequency domain. The interference-canceled signals are fed forward to subsequent layers for detection of other users. The proposed scheme effectively mitigates multiple access interference and intersymbol interference by an iterative (turbo) detection method. Numerical simulation examples demonstrate that the proposed FD MUTE with SIC outperforms the traditional MMSE multiuser equalizer over the severely doubly-selective channels, and the bit-error-rate performance tends to be better with the increase of iterations.     

部分更新块LMS均衡算法分析及应用

采用部分更新最小均方(LMS)算法和重叠保留的块信号频域处理结构,针对现场可编程门阵列(FPGA)的硬件实现平台,提出了时频混合部分更新块LMS和周期性块部分更新LMS均衡算法结构。2种新结构均能有效降低均衡算法的实现复杂度。步长收敛条件分析和数值仿真结果表明,新结构能够在适当调整更新步长的情况下,有效跟踪缓变信道的变化,实现与完整块LMS算法相当的性能,能够有效解决高速数据传输中的均衡复杂度过高的问题。