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基于OFDM的无线接入技术 总被引:2,自引:0,他引:2
本文首先介绍了正交频分复用技术(OFDM)的原理、技术优点,它在无线局域网中的应用特点.然后分析了在宽带无线接入技术中,三种基于OFDM而发展起来的技术,VOFDM、WOFDM和flash-OFDM的性能特点,最后展望了OFDM在未来移动通信系统中的应用. 相似文献
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MIMO—OFDM技术是当前无线通信中研究的重点课题之一,并被视为是下一代无线局域网的核心技术。本文全面介绍了MIMO—OFDM的技术特点,并对其在下一代无线局域网中的应用做了阐述。 相似文献
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文章首先介绍了OFDM的关键实现技术,然后结合不同无线通信环境的特点,对OFDM在无线局域网和固定无线接入中的应用进行了分析。 相似文献
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OFDM技术是一种多栽波技术,在高速无线数据传输领域有很大的应用前景。本文在分析宽带无线信道性能特点的基础上,介绍了OFDM技术的基本原理和实现方法,并讨论了OFDM的关键技术及其在解决移动信道传输问题上的优势。最后详细给出了OFDM系统收发信机的框图,并展望了OFDM技术在移动通信领域的发展趋势。 相似文献
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LTE下行信道估计算法研究 总被引:4,自引:2,他引:2
近年来,正交频分复用(OFDM)技术以其在高速数据传输中具有的良好的抗多径衰落的特性以及较高的频谱利用率等优点得到了广泛的应用。在OFDM通信系统中,信号在带宽小于信道相干带宽的多个正交子载波上发射和传输,以克服多径衰落信道所带来的信号频率选择性衰落。为了补偿各个子载波上的多径衰落,这就需要一个性能良好的信道估计方案。对LTE中基于导频的下行信道估计算法进行研究,首先在导频子载波处采用LS(最小二乘法)算法估计出信道参数,然后通过内插的方法在数据子载波处内插得到信道参数。频域内插主要采用拉格朗日内插或是LMMSE(线性最小均方误差)内插;时域内插采用拉格朗日内插。 相似文献
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有较长持续时间的正交频分复用符号对频率选择性衰落有更强的承受能力,但是对于时间选择性衰落则较为敏感,因此信道估计在正交频分复用系统中占有重要的地位.文中对正交频分复用的特点进行了概述,并根据正交频分复用本身的特性、WiMAX帧结构,提出了一种基于导频的信道估计的算法.并在SUI1-SUI6信道环境下,用MATLAB对其性能进行了仿真.仿真结果表明,该算法的抗衰落性能有所提高,且具有一定的灵活性. 相似文献
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针对高速移动环境下多普勒频偏造成信道的快衰落和正交频分复用(OFDM)系统中子载波间干扰(ICI)的问题,提出了一种适合快衰落环境的OFDM系统子载波间干扰抑制算法。此算法用线性变化模型来近似一个OFDM符号周期内的信道冲激响应,并以此为基础采用迭代MMSE均衡方法抑制载波间干扰。分析和仿真结果表明,此方法能有效地保证载波间的正交性,从而改善了OFDM系统的误码率(BER)性能。 相似文献
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Orthogonal frequency division multiplexing (OFDM) has become a very popular method for high data rate wireless communications
because of its advantages over single carrier modulation schemes on multipath, frequency selective fading channels. However,
intercarrier interference, due to Doppler frequency shifts, and multipath fading severely degrade the performance of OFDM
systems. Estimation of channel parameters is required at the receiver. In this paper, we present a channel modeling and estimation
method based on the time-frequency representation of the received signal. The discrete evolutionary transform provides a time-frequency
procedure to obtain a complete characterization of the multipath, fading, and frequency selective channels. Simulations are
used to illustrate the performance of the proposed procedure and to compare it with other time-varying channel estimation
techniques. 相似文献
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正交频分复用技术具有较高的频谱效率和好的抗频率选择性衰落性能,被广泛应用于无线通信系统中。但是OFDM信号具有较高的峰均比,当系统采用非线性功放时,OFDM系统需要较大的输入功率回退以避免信号失真。为了研究非线性功放条件下的系统性能,分析了恒包络OFDM系统的实现方式,并以误码率为指标,在加性高斯白噪声信道和多径衰落信道场景下对比了恒包络OFDM系统与采用传统迭代限幅滤波PAPR抑制技术的OFDM系统的性能。 相似文献
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The effects of time selective multipath fading are investigated for orthogonal frequency-division multiplexing (OFDM) systems in broadband mobile applications. Although in a multipath environment an OFDM system is very robust against frequency selective fading, it is very sensitive to time selective fading characteristics of the mobile channel, causing inter-carrier-interference and degrading system performance. To achieve a signal-to-interference ratio of 20 dB, the OFDM symbol duration must be less than 8% of the channel coherence time 相似文献
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采用空间分集技术可以有效的对抗无线信道中的衰落。协作分集是一种新的空间分集技术,其原理是单天线的无线用户通过协作,811227共享他们的天线和资源从而形成一个虚拟的多天线系统。OFDM是Wimax中的关键技术,其将数据调制到各个子载波上发送。将协作分集引入到Wimax系统中,利用OFDM技术,可以有效地抵抗信道频率选择衰落的影响,使系统性能得到显著提高。 相似文献
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Effects of Power Amplifier Distortion and Carrier Frequency Offset on the Performance of WLAN System
Zi-Wei Zheng 《Wireless Personal Communications》2011,57(4):575-589
Due to the efficiency of mitigation multipath delay spread, orthogonal frequency division multiplexing (OFDM) is extensively
used in the wireless local area network (WLAN) domain, such as the IEEE 802.11a standard defined by the IEEE 802.11 standardization
group and the HIPERLAN/2 defined by the European Telecommunication Standards Institute Project on Broadband Radio Access Networks.
OFDM based WLAN system is very sensitive to the power amplifier distortion and the carrier frequency offset. The performance
of the OFDM based WLAN system in the presence of the power amplifier distortion and the carrier frequency offset under practical
fading channel is researched and analyzed in this paper. A closed form of bit error rate (BER) is derived for the OFDM based
WLAN system in the presence of the power amplifier distortion and the carrier frequency offset under practical fading channel.
The effects of the power amplifier distortion and the carrier frequency offset on the OFDM based WLAN system performance are
comparatively studied by the theoretical method and by the simulation method under practical multipath fading channels. Studies
show that the theoretical and simulated results match well. 相似文献
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协作分集技术利用其他用户进行协作传输,可以获得一定的分集增益,但是在频率选择性衰落信道下性能不很乐观。为了对抗频率选择性衰落,采用正交频分复用(ODFM)技术与协作分集技术相结合的方法,研究了基于OFDM技术的协作通信,对在不同调制技术、不同信道估计方法下系统的性能进行了比较,为了进一步提高系统性能,对传统S&C算法进行了改进并应用于该系统中,仿真实验结果表明,改进的定时同步算法性能优于传统的S&C算法。 相似文献
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In this paper, we derive exact closed form bit error rate (BER) or symbol error rate (SER) expressions for orthogonal frequency division multiplexing (OFDM) systems with carrier frequency offset (CFO). We consider the performance of an OFDM system subject to CFO error in additive white Gaussian noise (AWGN), frequency flat and frequency selective Rayleigh fading channels. The BER/ SER performances of BPSK and QPSK modulation schemes are analyzed for AWGN and frequency-flat Rayleigh fading channels while BPSK is considered for frequency-selective Rayleigh fading channels. Our results can easily be reduced to the respective analytical error rate expressions for the OFDM systems without CFO error. Furthermore, the simulation results are provided to verify the accuracy of the new error rate expressions. 相似文献