SC-FDE／MIMO技术在宽带无线接入系统中的应用研究

简要介绍了无线宽带接入系统物理层研究的两种重要技术：单载波频域均衡(SC—FDE)技术和多入多出(MIMO)技术。然后，给出SC—FDE MIM0系统的模型结构，并重点讨论了该系统模型的频域均衡系数，以及信道估计和信噪比估计的算法实现。最后，给出SC—FDE MIMO系统的性能仿真结果。     

基于MIMO通信的OFDM／SC～FDE码分多址接人技术研究

为有效克服正交频分复用（OFDM）系统存在的不足,提高系统性能,将OFDM技术及单载波频域均衡（SC—FDE）技术分别与码分多址接入（CDMA）技术相结合,并在多输入多输出（MIMO）空间复用技术的高速率通信基础上,研究了相应的两种基带系统结构,讨论了系统所用的频域均衡算法及系数,最后给出性能仿真结果。结果表明,MIMO—SC—FDE—CDMA技术相结合能够更有效地提高系统性能,降低用户间干扰,有着良好的应用前景。     

单载波宽带无线系统的频域均衡

在住宅或商业环境中开发无线接入系统很容易面临恶劣的无线电传输环境,从而会带来数十或数百比特间隔的多径时延。正交频分复用（OFDM）是一种公认的对付这种多径效应的多载波解决方案。但是由于OFDM本身存在的一些问题,单载波频域均衡越来越受到人们的关注。在3GPP的3G长期演进计划（LTE）中,提出的主要方案之一就是上行采用单载波技术,而下行采用OFDM技术。本文主要讲述应用于单载波（SC）调制方案的频域均衡（FDE）。具有频域均衡功能的单载波无线电调制解调器跟OFDM具有相似的性能,效率以及低信号处理复杂度,另外,它对射频损伤（例如功率放大的非线性）没有OFDM对射频损伤敏感。下面我们主要介绍SC和OFDM系统之间的相同点和不同点以及两者共存的可能性,并且介绍一些把它们进行对比的例子。     

下一代无线通信关键技术及其在遥测中的应用

围绕下一代无线通信中正交频分复用(OFDM)、带频域均衡的单载波(SC/FDE)与多输入多输出(MIMO)技术,首先综述了这些技术的工作原理、发展历程以及关键问题,重点对OFDM的研究热点进行了分析。接下来探讨了这几项技术在遥测领域的应用。最后得出结论,认为:OFDM在航空遥测有着广泛的应用前景;MIMO在很多遥测领域的应用都有很大潜力;单载波频域均衡(SC-FDE)技术可以适应发射功率受限,多径干扰严重的环境,在航空遥测与导弹遥测中是一种新的鲁棒的遥测体制。     

单载波频域均衡技术的研究

介绍了单载波频域均衡技术的原理,在理论上对SC-FDE系统和OFDM系统的峰值平均功率比及对载波频偏和相位噪声的敏感度进行了比较.最后对SC-FDE系统和OFDM系统的性能进行了计算机仿真.     

单载波频域均衡系统的研究

分析比较了正交频分复用(0FDM)系统的优缺点,并在此基础上提出单载波频域均衡(SC／FDE)系统。该系统有效地结合了0FDM和单载波传输系统的优点．克服了0FDM系统中的不足,并且可以和0FDM共存。最后应用最小二乘(Ls)算法对SC／FDE系统简化地进行了系统建模。     

基于Jake信道模型的单载波与OFDM系统性能比较

在介绍正交频分复用(OFDM)系统与单载波频域均衡系统原理基础上,针对第四代移动通信系统中无线传输中由时变多径时延扩展和Doppler频移所引起的符号问干扰ISI,在上行链路中采用单载波调制及频域均衡。依据IEEE WorkingGmup802.20的草案及根据改进的Jake信道模型,选用QPSK、4QAM、64QAM等调制方式对单载波系统进行仿真,并与OFDM系统进行性能比较。结果表明,该方案性能与OFDM系统相当,同时有效地克服了OFDM系统的缺点。     

无线信道中的单载波频域均衡技术研究

介绍了单载波频域均衡技术的原理,与单载波时域均衡以及多载波OFDM系统进行了比较。该技术结合了两者的优点:能有效对抗多径信道,且具有较低的复杂度;降低了峰均比和对载波频偏、相位噪声的敏感性,因而在无线通信领域具有广阔的应用前景。     

一种无循环前缀迭代单载波频域均衡算法

单载波频域均衡（SC—FDE）技术可以有效消除符号间干扰（ISI）,相对于正交频分复用（OFDM）,具有较低的峰均比,因此成为宽带无线通信关键技术之一。传统的SC-FDE系统需要在发送帧前加入循环前缀（CP）,且CP长度要大于信道最大多径时延,这就降低了频带利用率,使得发射机功率增加。本文在取消CP情况下,提出一种辅助补零算法,恢复发送信号和信道的循环卷积,并通过迭代处理消除干扰。仿真结果表明,在信噪比大于3dB后,所提算法误码率更接近相同信噪比条件下的高斯白噪声信道,性能也较为理想。     

载波干涉OFDM系统的辨析

将载波干涉码引入OFDM系统,可以提高误码性能,并消除峰均功率比问题。该文从数学角度证明了载波干涉OFDM系统与现有的单载波频域均衡系统其实等同。     

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.     

OFDM和SC/FDE在宽带通信中的应用

在宽带无线通信中，传统的单载波时域均衡的方法由于计算的复杂度已很难适应。本文的叙述了的SC／FDE和OFDM系统结构、关键技术和算法，详细的比较了它们在结构和性能上的差异和共同点。最后给出了双模结构的可能性。     

频域均衡的单载波传输方案研究

无线信道的信道干扰主要表现为多径衰落和多普勒衰落对信道的影响。我们可以采用均衡技术来补偿信道中由于多径效应产生的码间干扰（ISI）。现引入频域均衡的单栽波传输（SC／FDE）方案，探讨了其实现机理，并对采用SC／FDE的高速率无线通讯系统实例进行系统整体建模和仿真计算。     

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     

A Reduced-CP Approach to SC/FDE Block Transmission for Broadband Wireless Communications

For conventional cyclic prefix (CP)-assisted single-carrier/frequency-domain equalization (SC/FDE) implementations, as well as for orthogonal frequency-division multiplexing (OFDM) implementations, the CP length is known to be selected on the basis of the expected maximum delay spread. Next, the data block size can be chosen to be large enough to minimize the CP overhead, yet small enough to make the channel variation over the block negligible. This paper considers the possibility of reducing the overall CP assistance, when transmitting sequences of SC blocks, while avoiding an excessively long fast Fourier transform window for FDE purposes and keeping good FDE performances through low-complexity, noniterative receiver techniques. These techniques, which take advantage of specially designed frame structures, rely on a basic algorithm for decision-directed correction (DDC) of the FDE inputs when the CP is not long enough to cope with the time-dispersive channel effects. More specifically, we present and evaluate a novel class of reduced-CP SC/FDE schemes, which takes advantage of a special frame structure for replacing "useless" CP redundancy by fully useful channel coding redundancy, with the help of the DDC algorithm. When using the DDC-FDE technique with these especially designed frame structures, the impact of previous decisions, which are not error-free, is shown to be rather small, thereby allowing a power-efficiency advantage (in addition to the obvious bandwidth-efficiency advantage) over conventional block transmission implementations under full-length CP. Additionally, the DDC algorithm is also shown to be useful to improve the power efficiency of these conventional implementations     

Layered space-frequency equalization in a single-carrier MIMO system for frequency-selective channels

Frequency-domain equalization (FDE) has been shown to be an effective approach to combat frequency-selective wireless channels. In this letter, we propose a layered space-frequency equalization (LSFE) architecture for a single-carrier (SC) multiple-input multiple-output (MIMO) system, where MIMO FDE is employed at each stage or (layer) of detection. At a particular stage, a group of the best data streams in the minimum mean square error sense are detected and are canceled from the received signals. Simulation results show that our proposed LSFE structures can outperform layered space-time equalization (LSTE) structures and uncoded orthogonal frequency division multiplex (OFDM), especially at a higher delay spread. Performance is enhanced further, by incorporating the FDE with time-domain decision feedback at each stage of LSFE. We also provide performance analysis for LSFE, in comparison with OFDM.     

一种基于空时分组编码的MIMO-SC/FDE系统的接收空间分集方案

该文提出了一种基于空时分组编码的多输入多输出频域均衡单载波分组传输(MIMO-SC/FDE)系统的空间分集接收方案,通过在Huang(2004)提出的分集结构中引入使用空时分组编码的发射分集,弥补了因减少DFT块数目而造成的性能损失,同时在接收端进一步减少了IDFT块的数目;通过适当设计空时分组编码,还可以进一步提高数据传输速率。该文详细推导了使用空时分组编码后的处理过程,并对使用空时编码后的MIMO-SC/FDE系统和相应的MIMO-OFDM系统性能进行了仿真比较。仿真结果表明,MIMO-SC/FDE系统的性能从总体上优于MIMO-OFDM系统。     

A Comparison of Frequency-Domain Block MIMO Transmission Systems

Block transmission techniques, with appropriate cyclic prefix and frequency-domain processing schemes, have been shown to be excellent candidates for digital transmission over severely time-dispersive channels, allowing good performance with implementation complexity that is much lower than traditional time-domain processing schemes. Orthogonal frequency-division multiplexing (OFDM) modulation is the most popular block transmission technique. Single-carrier (SC) modulation using frequency-domain equalization (FDE) is an attractive alternative approach based on this principle. In this paper, we propose two new receiver structures for multiple-input-multiple-output (MIMO) channels employing SC (MIMO-SC) modulation and FDE schemes. These receivers have a hybrid structure with frequency-domain feedforward and time-domain feedback filters for intersymbol interference (ISI) and interference cancellation. The proposed schemes are compared with different MIMO systems employing OFDM modulation (MIMO-OFDM) receivers in terms of performance [bit error rate (BER) and throughput] and complexity. Our performance results show the superiority of MIMO-SC approaches relative to MIMO-OFDM in terms of the BER performance for the simulated scenarios. Also, the simulation results show that the proposed hybrid MIMO-SC receivers yield a higher throughput than a MIMO-OFDM system.     

Selected mapping with symbol re‐mapping for OFDM/TDM using MMSE‐FDE

Orthogonal frequency division multiplexing (OFDM) signals have a problem with a high peak‐to‐average power ratio (PAPR). A distortionless selected mapping (SLM) has been proposed to reduce the PAPR, but a high computational complexity prohibits its application to an OFDM system with a large number of subcarriers. Recently, we proposed OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency‐domain equalization (MMSE‐FDE) to improve the bit error rate (BER) performance of conventional OFDM with a lower PAPR. The PAPR problem, however, cannot be completely eliminated. In this paper, we present an SLM combined with symbol re‐mapping for OFDM/TDM using MMSE‐FDE. Unlike the conventional OFDM, where SLM is applied over subcarriers in the frequency domain, we exploit both time and frequency dimensions of OFDM/TDM signal to improve the performance with respect to PAPR and BER. A mathematical model for PAPR distribution of OFDM/TDM with SLM is presented to complement the computer simulation results. It is shown that proposed SLM can further reduce the PAPR without sacrificing the BER performance with the same or reduced computational complexity. Copyright © 2010 John Wiley & Sons, Ltd.