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。     

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.     

Frequency domain equalization for single-carrier broadband wirelesssystems

Broadband wireless access systems deployed in residential and business environments are likely to face hostile radio propagation environments, with multipath delay spread extending over tens or hundreds of bit intervals. Orthogonal frequency-division multiplex (OFDM) is a recognized multicarrier solution to combat the effects of such multipath conditions. This article surveys frequency domain equalization (FDE) applied to single-carrier (SC) modulation solutions. SC radio modems with frequency domain equalization have similar performance, efficiency, and low signal processing complexity advantages as OFDM, and in addition are less sensitive than OFDM to RF impairments such as power amplifier nonlinearities. We discuss similarities and differences of SC and OFDM systems and coexistence possibilities, and present examples of SC-FDE performance capabilities     

Maximum multipath diversity with linear equalization in precoded OFDM systems

In wireless communications, the fading multipath channel attenuates and distorts the transmitted signal. To decode the transmitted symbols and take advantage of the full multipath diversity that the channel has to offer, computationally complex maximum-likelihood (ML) decoding is often employed. We show that a linear equalizer followed by a hard decision is capable of benefiting from maximum multipath diversity in linearly precoded orthogonal frequency-division multiplexing (OFDM) systems, where the information symbols are mapped through a matrix transformation before the inverse fast Fourier transform (IFFT) at the OFDM transmitter. As far as we are aware, this is the first proof of a linear equalization scheme achieving maximum multipath diversity over single-input single-output wireless links. We can conclude from this result that at sufficiently high signal-to-noise ratios (SNR), precoded OFDM systems will perform better over channels with more taps even with linear equalization, due to the increase in diversity order.     

IEEE802.16a单载波频域均衡方案的仿真

研究了IEEE802.16a宽带无线接入系统的单载波频域均衡(SC-FDE)方案,建立了完整的802.16a单载波频域均衡系统仿真平台,研究了SC-FDE系统的频域均衡、编码和分集增益.仿真结果表明,将SC-FDE系统与判决反馈均衡、信道编码或发送分集结合都能提高SC-FDE系统抗多径干扰的能力.     

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.     

Iterative Multiuser Detection for Single-Carrier Modulation with Frequency-Domain Equalization

In this letter, we propose a new multiuser detection scheme for single-carrier modulation with frequency-domain equalization (SC-FDE). We first present mathematical formulations of multiuser detection for the SC-FDE system with user- specific interleaving. The proposed structure employs spreader and different interleaver for each user at the transmitter, and re moves multiuser interference with an iterative detection method in the frequency domain at the receiver. Simulation results show that the proposed scheme outperforms the interleave- division multiple-access (IDMA) scheme in the block error rate even for severely frequency-selective channel, while providing considerably lower computational complexity.     

On the design of multidimensional signal sets for OFDM systems

An orthogonal frequency division multiplexing (OFDM) system operating over a wireless communication channel effectively forms a number of parallel frequency-nonselective fading channels, thereby obviating the need for complex equalization and thus greatly simplifying equalization/decoding. However, the OFDM system also exhibits two weaknesses relative to its single-carrier counterparts: (1) the diversity achieved by the OFDM system can be less than a single-carrier system employing the same error control code in a signaling environment rich in diversity and (2) the baseband transmitted signal can exhibit significant amplitude fluctuation over time, thereby precluding efficient transmit amplifier operation. In this paper, nonstandard multidimensional signal sets matched to the OFDM framework are prescribed that address both of these issues. The proposed signal sets are chosen to maximize the diversity achieved by an uncoded system under a constraint to control the peak-to-mean envelope power ratio (PMEPR) of the baseband transmitted waveform. The cost of employing the proposed signal sets is an increase in decoding complexity, as essentially a small amount of controlled equalization has been added to the receiver; thus, the resulting system can be viewed as a hybrid between an OFDM system and a standard single-carrier system. Numerical results are presented which suggest that: (1) the system can provide an attractive alternative to a standard OFDM system in terms of required average transmitted SNR versus receiver complexity and (2) the system yields a modest reduction in PMEPR versus a standard OFDM system     

Cyclic prefixed single carrier transmission in ultra-wideband communications

This letter proposes cyclic prefixed single carrier transmission with frequency domain equalization (SC-FDE) as an alternative physical layer solution for UWB communications. The performance of SC-FDE over IEEE 802.15.3a UWB channel models is analyzed, simulated and compared with that of impulse based single carrier UWB (SC-UWB) and multicarrier UWB employing orthogonal frequency division multiplexing (OFDM-UWB). The impact of channel coding on the performance of OFDM and SC-FDE in UWB is also studied. Our results demonstrate performance advantage of the SC-FDE scheme, especially when implementation issues such as low complexity and low power consumption for UWB are taken into consideration. The performance of SC-FDE with diversity combining using oversampling is also investigated.     

基于SC-FDE和Turbo码的图像传输技术

分析了单载波频域均衡技术和Turbo编译码技术,研究了基于这两种技术的无线图像传输方案,并对联合SC-FDE和Turbo码图像传输方案进行了数值仿真研究。仿真结果表明,把SC-FDE技术和Turbo码技术结合应用到无线图像传输中可以明显提高接收图像质量,改善信噪比性能。相比较传统无SC-FDE的图像传输方案,在误码率为10-5时有约1.5dB的增益。从而表明,联合SC-FDE和Turbo码可以实现图像的更加可靠的传输,是实现图像的高速传输和高频谱利用率的有效方法。     

单载波频域均衡(SC-FDE)技术浅析

均衡技术是克服多径变参信道衰落的一种有效手段,也是宽带无线通信中对抗多径的一种重要方法。从设计原理出发,进行了单载波频域均衡(SC-FDE)的设计,分析了单载波均衡的技术特点,并与多载波OFDM技术在通信容量、PAPR等方面进行了比较,最后在莱斯信道进行了仿真分析,给出仿真结果,表明单载波频域均衡系统能够获得较好的性能,降低误码率。对系统工程设计有一定的借鉴意义。     

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     

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。     

Frequency-Domain Set-Membership Filtering and Its Applications

Frequency-domain adaptive filtering is appealing in many applications, particularly channel equalization. This paper presents frequency-domain set-membership filtering (F-SMF) and derives adaptive algorithms for F-SMF. The F-SMF is employed to design single-carrier frequency-domain equalizer (SC-FDE). With an unconventional parameter-dependent error-bound specification, an F-SMF algorithm is derived and shown to provide superior performance with sparse updates of parameter estimates. Exploring the feature of sparse updates, we present an innovative parallel adaptive architecture that shares the updating processors and that finds natural appeal in frequency-domain diversity combining and equalization for very dispersive fading channels like those found in broadband wireless communications     

基于滤波器组的单载波频域均衡技术研究

研究了基于滤波器组的单载波频域均衡技术的基本原理和实现方法,通过系统对比基于滤波器组的方法与基于FFT方法的异同之处,从其产生的机理上阐明了基于滤波器组的单载波频域均衡技术能够克服FFT方式的主要缺点的原因。基于滤波器组的均衡技术既有效地抑制频率选择性衰落、避免循环前缀带来的信道开销,又具有良好的带外抑制能力和抗窄带干扰的性能,实现了信号的完全重构,仿真结果进一步验证了理论分析的正确性。     

Frequency-Domain Equalization for Orthogonal and Quasi-Orthogonal STBCs over Frequency-Selective Wireless and Power-Line Channels

In recent years, combination of single-carrier frequency-domain equalization (SC-FDE) and space-time block coding/code (STBC) techniques to exploit the advantages of both, has received a great attention. In this paper we propose new techniques for combining SC-FDE with orthogonal and Quasi-orthogonal STBCs applicable to any number of transmit antennas. For Quasi-orthogonal STBC we first propose a new structure for codes with four transmit antennas and then extend it to higher numbers. We convert Quasi-orthogonal system to two equivalent orthogonal subsystems and equalize and decode these subsystems based on our proposed procedure for orthogonal codes. Finally, we present our simulation results for different frequency-selective wireless and power-line channels and show that a significant SNR gain is achieved when SC-FDE is combined with diversity techniques.     

短波单载波空时分组码的频域均衡研究

短波通信受多径衰落、干扰复杂等影响严重。空时分组码(Space Time Block Code,STBC)技术在无需增加频谱资源和天线发射功率的前提下,可以利用多输入多输出(Multiple-Input Multiple-Output,MIMO)信道提供的分集增益提升传输可靠性。分析短波MIMO研究现状,提出短波单载波STBC频域均衡(Frequency-Domain Equalization,FDE)系统架构,针对短波信道引入的码间干扰研究MIMO MMSE-FDE均衡技术,并将单载波STBC频域均衡与时域均衡及短波现有波形进行仿真对比。仿真结果表明,相较于短波现有波形,单载波STBC频域均衡系统的可靠性有较大幅度提升,且性能与STBC时域均衡接近,但计算复杂度远低于STBC时域均衡。     

Joint Estimation of Carrier-Frequency and Sampling-Frequency Offsets for SC-FDE Systems on Multipath Fading Channels

With single-carrier frequency-domain equalization, the carrier-frequency and sampling-frequency offsets are embedded in the phases of complex frequency-domain signal components. This paper proposes a sub-block processing to extract the phases and applies the least-squares regression to jointly estimate the offsets. The effectiveness of the proposed SC-FDE receiver is demonstrated on multipath fading channels.     

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.     

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。