单载波频域均衡在地空高速数据链的应用

地空数据链的信道属于低仰角的多径信道,存在较严重的符号间干扰。正交频分复用(OFDM)是得到认可的有效抗多径方案,单载波频域均衡(SC-FDE)采用与OFDM相似的频域均衡方式,具有与OFDM相近的性能和复杂度,并克服了OFDM的一些不足。在比较SC-FDE和OFDM相似性、分析SC-FDE的信道估计与均衡基础上,提出了采用SC-FDE的地空高速数据链解调器结构,该结构在保留单载波处理的优点条件下实现高效的频域均衡。     

Frequency-Domain Channel Estimation for SC-FDE in UWB Communications

Recently, single-carrier block transmission with frequency-domain equalization (SC-FDE) has been shown to be a promising candidate for ultra-wideband (UWB) communications. In this paper, we address the channel estimation problem for SC-FDE transmission over UWB channels. A mean-square error (MSE) lower bound for the frequency-domain linear minimum mean-squared error (LMMSE) channel estimator is derived, and the optimal pilot sequence that achieves this lower bound is obtained. Further simplification leads to a frequency-domain channel estimator with reduced computational complexity. The performance of the simplified estimator for SC-FDE over UWB channels is evaluated and compared with that with perfect channel state information. The effects of nonoptimal and optimal pilot symbols are also investigated. Our results show that the proposed frequency-domain channel estimator performs well over UWB channels with only small performance degradation, compared with that with perfect channel estimation     

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.     

基于散射信道的单载波频域均衡算法仿真

从对流层散射通信信道的特点出发,介绍了单载波频域均衡技术原理与系统结构,研究了可适用于对流层散射通信且易于工程实现的几种频域均衡算法,并创新性地研究了将单载波频域均衡技术与分集接收技术相结合的可行性及系统性能,在理论分析的基础上借助Matlab软件进行了仿真验证,给出了仿真结果,并对其进行了分析。仿真结果验证了算法的有效性以及单载波频域均衡技术与分集接收技术相结合的可行性,为其在散射通信系统中的应用和工程实现提供参考和指导。     

单载波频域均衡系统信道估计的粒子滤波方法

粒子滤波（Particle Filter, PF）是一种有效的参数估计方法。通过对单载波频域均衡（Single Carrier Frequency Domain Equalization, SC-FDE）系统数学模型和粒子滤波原理的分析,将时变信道建模成一阶AR过程,尝试把粒子滤波方法运用到单载波频域均衡系统基于UW的信道估计中去,并给出了算法详细步骤。然后,分别针对三种不同时变程度的信道进行了仿真,并在这三种信道下,分别与LS估计作了误码性能比较。结果表明,在时变条件下,基于粒子滤波的信道估计方法较之线性LS估计能获得良好的误码性能增益,且信道变化越缓慢,这种增益越明显。      

SC-FDE宽带航空数传接收机的设计与实现

为满足航空信道条件下的远距离宽带数据传输需求,基于单载波频域均衡传输(SC-FDE)体制,采用8 PSK调制体制进行了宽带数字接收机的设计,包括传输帧同步、载波同步、定时同步、信道估计和频域均衡.同时,为保证灵活应用的需求,采用数字内插的方式进行了可变传输速率设计.基于Xilinx现场可编程门阵列(FPGA)平台对硬件实现进行优化,最终实现了传输速率能够从112.5 Mbit/s覆盖到900 Mbit/s的数传接收机.仿真分析和硬件测试结果表明,该接收解调设备能够实现很好的性能指标,同时SC-FDE架构具备有效补偿多径传播影响的能力,适合应用于高动态无线宽带航空数据传输系统中.     

Pilot Position Selection and Detection for Channel Estimation of SC-FDE

In this letter, we propose a simple pilot position selection/detection technique for channel estimation of single- carrier frequency domain equalization (SC-FDE). Unlike the conventional channel estimation techniques such as frequency domain superimposed pilot technique (FDSPT), the proposed scheme selects the pilot positions to minimize the distortion of original signals caused by the loss of useful data tones in frequency domain. The corresponding receiver structure is also presented, where the pilot positions are blindly detected and the distorted data symbols are iteratively reconstructed. Simulation results show that the proposed system gives better BER performance than the FDSPT and approaches the lower bound of SC-FDE.     

短波SC-FDE系统中改进的LS信道估计算法

针对短波单载波频域均衡( SC-FDE)系统中最小二乘( LS)信道估计算法受噪声影响大而导致的估计精度低的问题,提出了一种改进的基于小波去噪的LS信道估计算法。改进算法采用基于分块导频的帧结构,首先用LS算法对信道进行初步估计,然后根据小波多分辨率分析( Mallat)理论将LS估计的结果分解,并设置一个合理阈值对分解得到的小波系数处理,从而消除LS估计的残留噪声,提高估计精度。仿真结果表明,在短波信道下,改进算法不仅减小了系统开销,而且提高了LS估计的性能。     

过采样CPM信号的频域均衡

提出了一种直接对过采样的连续相位调制(CPM)信号进行单载波频域均衡的算法,同时提出了一种在插入循环前缀后发送CPM信号的相位仍然连续的方法。仿真结果表明,该单载波频域均衡算法能有效地消除大时延信道冲击响应下的CPM接收信号中的码间串扰。与现有的基于匹配滤波、符号抽样的CPM信号的单载波频域均衡算法相比,其性能和复杂度相当,但是CPM接收机的前端更为简单。     

宽带单载波频域均衡系统设计与FPGA实现

单载波频域均衡(SC-FDE)是数字通信中克服多径衰落的有效技术。宽带通信系统中应用单载波频域均衡系统设计,实现137.5 MHz载波下27.5 Mbps的码元传输速率。同时在系统中添加1/2码率卷积码与(239,223)里德-所罗门(RS)码的级联信道纠错编码,提高系统的可靠性。完成单载波频域均衡系统设计,分析设计系统的关键技术,最终在现场可编程门阵列硬件平台上进行系统实现、调试和验证,完成系统实际误码率的测试。     

The research on channel estimation and signal-noise ratio estimation based on minimum error entropy kalman filter for single carrier frequency domain equalization system

In this paper, the channel estimation and signal-to-noise ratio (SNR) estimation technique of single-carrier frequency domain equalization (SC-FDE) system under low SNR in aeronautical multipath channel are studied, a SNR estimation algorithm which is easy to implement in engineering and an improved LS channel estimation algorithm based on Kalman filter using minimum error entropy (MEE-KF) are proposed. This paper first introduces the SC-FDE system and introduces the principle of MEE-KF, and then, the channel estimation flow based on MEE-KF is obtained by combining it with the traditional LS channel estimation algorithm, which makes the estimation results perform better. Simulation results show that after getting more accurate noise variance, the channel estimation results can better follow the changes of the channel after MEE-KF processing, so as to resist the doppler frequency offset effect and make the channel estimation results more accurate, that is the channel response results of the data part can be closer to the real situation, so that the communication performance of SC-FDE system has also been greatly improved.     

Improved Frequency Domain Channel Estimation and Equalization for MIMO Wireless Communications

This paper introduces an improved frequency domain channel estimation method based on interpolation vectors for single carrier frequency domain equalization (SC-FDE) with the multiple-input multiple-output (MIMO) scheme. The proposed algorithm is derived by employing the least squares (LS) criterion, and a specified application for the wide sense stationary uncorrelated scattering (WSSUS) Rayleigh fading channel is presented. The channel frequency domain responses estimated at two adjacent pilot blocks are used to track the time-variant channel information, which can effectively improve the accuracy of channel estimation without significantly increasing complexity. Maximum mean square error (MMSE) frequency domain equalization based on the estimated channel is employed in the receiver to recover transmitted signals. This paper also investigates a training sequence design method for multiple transmit antennas and a noise variance estimation method. Numerical simulation results show that the proposed methods can perform very well for fading channels with long multipath delay and high Doppler spread.     

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。     

A Technique for Frequency Synchronization in Multi-Band OFDM in Realistic UWB Channel

This paper presents a highly accurate frequency offset estimation algorithm for multi-band orthogonal frequency division multiplexing (MB-OFDM) systems effective for realistic ultra-wideband (UWB) environment. The proposed algorithm derives its estimates based on phase differences in the received subcarrier signals of several successive OFDM symbols in the preamble. We consider different carrier frequency offsets and different channel responses in different bands to keep the analysis and simulation compatible for practical multi-band UWB scenario. Performance of the proposed algorithm is studied by means of bit error rate (BER) performance of MB-OFDM system. In order to compare the variance of the synchronizer to that of the theoretical optimum, we derive the Cramer–Rao lower bound (CRLB) of the estimation error variance and compare it with the simulated error variance both in additive white Gaussian noise and UWB channel model (CM) environments, CM1–CM4. Next, we modify the estimation algorithm by proposing a multi-band averaging frequency offset synchronization (MBAFS) scheme. We establish superior BER performance with MBAFS compared to our first scheme. We calculate modified CRLB for MBAFS and compare it with simulation results for CM1–CM4. Both analysis and simulation show that MBAFS algorithm can estimate the carrier frequency offset effectively and precisely in UWB fading channels for MB-OFDM applications. We also analyze the computational complexity of both the proposed algorithms in order to verify their feasibility of implementation in practical UWB receiver design.     

单载波频域均衡技术的Matlab仿真研究

单载波频域均衡技术由于其能有效的对抗频率选择性衰落,成为被多种新兴高速率通信系统所推荐的关键技术之一.利用Matlab/Simulink组件,对单载波频域均衡系统进行了仿真实现.结果显示,单载波频域均衡系统的误码率保持在10-3的数量级上.     

多载波与单载波频域均衡系统的仿真与测量

我国数字电视地面广播传输标准GB20600-2006(以下简称国标)兼容多载波正交频分复用(OFDM)和单载波频域均衡(SC-FDE)2种块传输技术.为了在国标框架下对2种传输技术的抗频率选择性衰落性能进行比较,根据国标的系统参数对采用低密度奇偶校验码(LDPC)的OFDM和SC-FDE传输系统进行了仿真,并对国标实际系统进行了测量.仿真和实测结果均表明:在LDPC编码系统中,OFDM的抗频率选择性衰落性能好于SC-FDE系统,且随着信道频率选择性衰落的恶化和调制级别的提高,这种优势会更加明显.此仿真和实测结果可以为国标系统的实现与优化提供参考.     

单载波频域均衡抗多径码元同步跟踪方法

从信道估计时域冲激响应能量出发,提出了一种运行在2倍采样率上的基于数据分组累积能量的抗多径码元定时同步跟踪方法,适合在全响应和部分响应升余弦脉冲成形QPSK调制的单载波频域均衡系统中应用。在多径信道下对该码元定时同步跟踪方法的跟踪性能进行了仿真,仿真结果表明,该码元定时同步跟踪方法具有良好的跟踪性能和抗多径、抗噪声能力。     

基于宽带突发单载波频域均衡传输的时域精细信道估计方法

单载波频域均衡(SC-FDE)是宽带无线通信系统中一种具有竞争力的解决方案,获得了广泛的关注和研究。SC-FDE方案不仅抗多径能力出色、复杂度低,且具有比正交频分复用(OFDM)信号更低的峰均比值。在突发SC- FDE系统中,接收机需要利用训练序列快速获取信道的特征信息,以避免解调性能损失。传统的基于训练序列的信道估计方法并不适合宽带猝发SC-FDE系统,难以兼顾估计准确性和复杂度。该文提出一种基于时域训练序列的精细信道估计方法。该方法利用时域PN序列得到信道参数的最大似然估计值,并利用信道稀疏的特征,根据信道噪声强度对信道估计值进行噪声抑制处理。仿真表明:与传统信道估计方法相比,该信道估计方法能取得更高的估计精度,且具有较低的实现复杂度。     

Semi-Blind Layered Space-Frequency Equalization for Single-Carrier MIMO Systems with Block Transmission

This letter proposes a novel semi-blind layered space-frequency equalization (LSFE) receiver for single- carrier cyclic-prefix (SC-CP) multiple-input multiple-output (MIMO) systems with block transmission, based on independent component analysis (ICA). Simulation results show that semi- blind LSFE with various Doppler shifts can provide performance close to the case with perfect channel state information (CSI), using a training overhead of only 0.05%. It also significantly outperforms its orthogonal frequency division multiplexing (OFDM) counterpart with perfect CSI and semi-blind linear SC frequency domain equalization (SC-FDE) over a wide range of signal to noise ratios (SNRs).     

基于独特字的单载波频域均衡系统的同步问题研究

介绍了单载波频域均衡系统(single carrier system with frequency domain equalization,SC-FDE)的结构,分析了时偏和频偏对系统性能造成的影响.在指出基于独特字(unique word,UW)和基于循环前缀(cyclic prefix,CP)的系统不同之处后,给出了基于独特字的定时同步和载波同步算法,并对算法进行了仿真.仿真结果表明,定时同步和载波同步算法均很好的解决了同步问题.