3G长期演进系统的导频结构设计

为了进一步提高系统频谱效率并有效对抗无线信道的频率选择性衰落,3G长期演进系统(LTE,Long-Term Evolution)采用了正交频分复用技术(OFDM)和多天线技术(MIMO)。本文给出多种MIMO-OFDM系统中的导频结构设计方案:频分导频、相移导频以及空时码(STC)码分导频,并介绍了相应的信道估计算法。最后,通过仿真比较了不同导频结构下的系统性能。     

基于循环延迟分集的差分酉空时频编码方案

提出了一种应用于MIMO-OFDM系统的基于循环延迟分集的多流差分酉空时频编码方案.该方案利用了差分和酉矩阵技术、结合了正交空时码的分集优势,在不需要信道估计的情况下较大程度地改善了整个MIMO-OFDM系统的误码性能.     

发射分集0FDM系统中基于离散导频的信道估计方法

OFDM技术、空时编码和分集技术的联合可以实现无线数据的高速可靠传输.传统的多天线系统中利用训练序列来实现信道估计.本文给出了一种采用空时编码的发射分集OFDM系统中基于离散导频的信道估计方法,它可以进一步提高系统效率.仿真结果证明该算法具有很好估计性能和鲁棒性.     

OFDM系统中基于导频插入的信道估计技术

介绍了OFDM通信系统中用导频插入来进行信道估计的技术。根据导频插入的方法,信道估计可以分为基于集中式导频插入的信道估计和基于间隔式导频插入的信道估计。在描述OFDM系统信道估计模型的基础上详细阐述这两种方法,并利用多径Rayleigh衰落信道比较它们的性能。     

宽带移动通信系统中基于梳状导频的信道估计

本文主要研究了OFDM系统中基于梳状导频的空时信道估计方法,并提出一种新的信道估计算法,即实现了空时二维信道估计。基于梳状导频的空时信道估计的算法分为两步:第一步是利用导频信号对导频位置的信道进行估计,第二步是信道插值,得到所有频域位置的信道信息。同时还研究了基于LS准则的信号估计以及基于线性插值的信道插值。     

基于分群子载波空时频MIMO-OFDM信道估计

针对空时频编码的MIMO-OFDM系统,根据子信道相关特性确定子载波分群,该文提出了独立子群导频法的信道估计处理策略,并将导频序列由空、频两域扩展到空、时、频域,能进一步提高估计精度。理论分析和计算机仿真表明,在频率选择性衰落信道下,基于空时频的独立子群导频法在较低运算复杂度下可以获得信道估计性能的明显改善。     

单天线OFDM系统的信道估计算法研究

介绍MIMO-OFDM系统中几种基于导频的信道估计方法。首先研究了单天线OFDM系统的信道估计算法。一方面重点关注三种估计准则的原理,仿真表明LMMSE准则具有最佳的性能;另一方面介绍了几种插值的方法用来恢复非导频处的信道信息。     

空时/频编码在OFDM系统中的应用

介绍了空时编码(STBC)和空频编码(SFBC)应用于OFDM系统,实现发射分集,并对基于梳状导频的LS(最小二乘)算法采用正交导频设计方案,把多天线信道估计转化为单天线信道估计,大大简化了运算。仿真结果表明,实现的空时和空频编码OFDM方案不仅误码性能良好,且具有系统实现复杂度低、接收机结构简单等优点。     

空时格码和OFDM系统联合建模及性能分析

发射端分集、编码和调制结合空时格码，可以有效地提高信号在无线衰落信道中传输的有效性和可靠性；在正交频分复用调制OFDM(Omiogonal Frequency Division Multiplexing)系统中应用空时格码可以有效地对抗多径干扰，提高系统容量，适合于在高速无线数据通信中采用。本文详细地说明了它们结合的基础，进而构造了一个基于空时格码的OFDM系统模型，并分析了在高斯信道下的系统性能。     

MIMO-OFDM系统的原理及性能分析

本文简要介绍了MIMO-OFDM系统的发展、原理,详细介绍了MIMO-OFDM中用到的编码技术,空时码OFDM系统,空频码OFDM系统,并且通过仿真,将其性能进行了比较.     

MIMO-OFDM系统信道估计算法研究

正交频分复用(OFDM)技术能有效克服多径带来的不利影响,提高频谱利用率;多输入多输出(MI-MO)技术,可以在不增加系统带宽和发射功率的前提下,成倍提高系统容量和带宽利用率。将两者结合的MIMO-OFDM系统是近年来的研究热点,信道估计在提高该系统性能方面发挥着重要作用。基于此,主要介绍MIMO-OFDM系统结构,在此基础上介绍基于导频的信道估计、半盲信道估计和盲信道估计。     

A road to future broadband wireless access: MIMO-OFDM-Based air interface

Orthogonal frequency-division multiplexing is a popular method for high-data-rate wireless transmission. OFDM may be combined with multiple antennas at both the access point and mobile terminal to increase diversity gain and/or enhance system capacity on a time-varying multipath fading channel, resulting in a multiple-input multiple-output OFDM system. In this article we give a brief technical overview of MIMO-OFDM system design. We focus on various research topics for the MIMO-OFDM-based air interface, including spatial channel modeling, MIMO-OFDM transceiver design, MIMO-OFDM channel estimation, space-time techniques for MIMO-OFDM, and error correction code. The corresponding link-level simulation results are encouraging, and show that MIMO-OFDM is a promising road to future broadband wireless access.     

基于空时Turbo网格码的MIMO-OFDM系统

提出了使用空时Turbo网格编码的MIMO-OFDM系统,分析了系统的性能,给出了衰落信道中的性能上界以及编码和分集增益表达式。通过仿真评估了空时Turbo网格码在慢衰落信道中的性能,与传统的STTC方法相比,该系统可以获得更好的分集增益和编码增益。     

MIMO-OFDM系统中的空时/频编码技术

OFDM(正交频分复用)是一种高效的多载波调制技术,可以用来对抗无线环境中的多径衰落,减少码间干扰。空时编码是一种发射分集技术。文中主要研究基于M IMO(多输入多输出)-OFDM的空时分组码和空频分组码的系统结构以及编译码方法。仿真结果表明,将空时编码技术与M IMO-OFDM技术相结合能有效地抵抗频率选择性随机衰落。     

Low complexity channel estimation for space-time coded wideband OFDM systems

In this article, channel estimation for space-time coded orthogonal-frequency division multiplexing (OFDM) systems is considered. By assuming that the channel frequency response is quasi-static over two consecutive OFDM symbols, we develop channel parameter estimators based on the use of space-time block coded (STBC) training blocks. Using an STBC training pattern, a low-rank Wiener filter-based channel estimator with a significant complexity reduction is proposed. A simplified approach for the optimal low-rank estimator is also proposed to further reduce the estimator complexity while retaining an accurate frequency domain channel estimation. Numerical results are provided to demonstrate the performance of the proposed low complexity channel estimators for space-time trellis coded OFDM systems.     

空时Turbo网格码的MIMO-OFDM系统性能研究

分析了OFDM基本原理并构建了MIMO-OFDM系统的模型,接着阐述了空时编码技术在OFDM中的应用,提出了在OFDM系统中采用空时Turbo网格编码的方案,详细分析了ST Turbo TC编码器和译码器原理,最后对系统进行了仿真,并分析了仿真结果。系统仿真结果表明采用Turbo网格编码的系统性能优于采用一般空时编码的MIMO-OFDM系统。     

Artificial Neural Network Channel Estimation Based on Levenberg-Marquardt for OFDM Systems

The many advantages responsible for the widespread application of orthogonal frequency division multiplexing (OFDM) systems are limited by the multipath fading. In OFDM systems, channel estimation is carried out by transmitting pilot symbols generally. In this paper, we propose an artificial neural network (ANN) channel estimation technique based on levenberg-marquardt training algorithm as an alternative to pilot based channel estimation technique for OFDM systems over Rayleigh fading channels. In proposed technique, there are no pilot symbols which added to OFDM. Therefore, this technique is more bandwidth efficient compared to pilot-based channel estimation techniques. Also, this technique is making full use of the learning property of neural network. By using this feature, there is no need of any matrix computation and the proposed technique is less complex than the pilot based techniques. Simulation results show that ANN based channel estimator gives better results compared to the pilot based channel estimator for OFDM systems over Rayleigh fading channel.     

Broadband MIMO-OFDM wireless communications

Orthogonal frequency division multiplexing (OFDM) is a popular method for high data rate wireless transmission. OFDM may be combined with antenna arrays at the transmitter and receiver to increase the diversity gain and/or to enhance the system capacity on time-varying and frequency-selective channels, resulting in a multiple-input multiple-output (MIMO) configuration. The paper explores various physical layer research challenges in MIMO-OFDM system design, including physical channel measurements and modeling, analog beam forming techniques using adaptive antenna arrays, space-time techniques for MIMO-OFDM, error control coding techniques, OFDM preamble and packet design, and signal processing algorithms used to perform time and frequency synchronization, channel estimation, and channel tracking in MIMO-OFDM systems. Finally, the paper considers a software radio implementation of MIMO-OFDM.     

Adaptive Frequency-Domain Channel Estimator in 4$ ,times ,$4 MIMO-OFDM Modems

This work presents an adaptive frequency-domain channel estimator (FD-CE) for equalization of space-time block code multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems in time-varying frequency-selective fading. The proposed adaptive FD-CE ensures the channel estimation accuracy in each set of four MIMO-OFDM symbols. Performance evaluation shows that the proposed method achieved a 10% packet error rate of 64 quadrature amplitude modulation (QAM) at 29.5 dB SNR under 120 km/h (Doppler shift is 266 Hz) in 4 times 4 MIMO-OFDM systems. To decrease complexity, the rich feature of Alamouti-like matrix is exploited to derive an efficient very large-scale integration (VLSI) solution. Finally, this adaptive FD-CE using an in-house 0.13-mu m CMOS library occupies an area of 3 times 3.1 mm², and the 4 times 4 MIMO-OFDM modem consumes about 62.8 mW at 1.2 V supply voltage.