共查询到18条相似文献,搜索用时 140 毫秒
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提出了一种基于自适应复系数内插的信道估计算法,改善了无线区域网络(WRAN)系统对抗动态多径时延的能力。WRAN是第一个采用认知无线电技术改善频谱效率的宽带接入标准,系统在下行链路中采用了正交频分复用(OFDM)调制技术,而信道估计技术对于采用相干解调的OFDM系统十分重要。传统的OFDM信道频域响应(CFR)估计算法通常采用实系数频域内插的方式,在对抗WRAN系统长多径时延信道时,不能有效地工作。该文在研究实系数FIR内插变换域响应的基础上,提出了一种复系数内插算法。为了同时适用于短时延信道,提出了一种低复杂度、自适应匹配信道最大多径时延的算法。通过仿真,验证了该算法能够对抗更大的多径时延,提高信道估计的精度,改善系统误码性能。 相似文献
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基于Vogler模型的短波OFDM性能仿真 总被引:1,自引:0,他引:1
OFDM(正交多载波调制)是一种在无线环境下具有较高频谱利用率的多载波调制技术,它具有较强的对抗多径干扰和消除符号间干扰的能力.基于Vogler模型出发,根据实测的短波信道参数数据进行了OFDM系统仿真,同时,用导频辅助的方法对信道进行估计,并进行信道补偿,克服了短波信道的多径衰落和多普勒频移等因素的影响,有效降低了系统的误码率,提高了整个系统的性能. 相似文献
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OFDM(正交频分复用)技术是一种多载波数字调制技术,在无线多径衰落信道下具有较好的传输特性,文中设计短波电台系统采用了OFDM技术来对克服多径衰落带来的干扰,并且给出了系统的设计方案。利用Simulink建模,并在瑞利衰落信道和高斯信道下进行了仿真,结果显示出性能上有较大的改进。 相似文献
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5G无线局域网环境下OFDM对无线信道的适应性分析 总被引:1,自引:0,他引:1
建立了基于广义平稳不相关散射假设(WSSUS)下的多径时变信道模型。针对无线局域网(WLAN)的特点,从802.11a协议出发,从全信道和子信道两个角度分别建立信道模型,阐述了OFDM利用循环前缀对抗多径信道码间干扰(ISI)的机理,并仿真了不同多普勒频移对系统误码底板影响,结果表明OFDM系统对WLAN具有强大适应性。 相似文献
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1 OFDM技术简介
OFDM(正交频分复用)是一种无线高速数据传输技术。它能够把一个频率选择性信道转换为并行的平坦衰落信道,使接收机更为简单;它的子载波的时域波形是正交的,而不同子载波的信号频潜在频率上却是重叠的,因此带宽的利用率非常高。OFDM也可以利用AP或者移动终端的多天线结构在一个时变的多径衰落信道中提高分集增益和系统容量。 相似文献
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基于导频符号的信道估计算法研究 总被引:1,自引:1,他引:0
正交频分复用(OFDM)是一种高效的数字传输技术,因其较高的频带利用率以及抗多径衰落的性能,被视为下一代无线通信的核心技术.信道估计技术是实现OFDM系统的关键技术之一.文中主要研究了OFDM无线系统中基于导频的信道估计算法--LS算法和LMMSE算法, 通过仿真其算法的误码率特性和均方误差性能表明,LMMSE的性能明显优于LS. 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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Orthogonal frequency-division multiplexing (OFDM) is a popular transmission format for emerging wireless communication systems, including satellite radio, various wireless local area network (LAN) standards, and digital broadcast television. Single-carrier cyclic-prefixed (SCCP) modulation is similar to OFDM, but with all frequency-domain operations performed at the receiver. Systems employing OFDM and SCCP perform well in the presence of multipath provided that the channel delay spread is shorter than the guard interval between transmitted blocks. If this condition is not met, a channel-shortening equalizer can be used to shorten the channel to the desired length. In modestly time-varying environments, an adaptive channel shortener is of interest. All existing adaptive channel shorteners require renormalization to restrain the channel shortener away from zero. In this paper, we study the use of a unit-tap constraint rather than a unit-norm constraint on the adaptive channel shortener. We use this constraint to manipulate existing algorithms into a framework analogous to the recursive least squares algorithm, and we develop adaptation rules for blind and semiblind frequency domain equalizers for SCCP receivers. Simulations of the proposed algorithms show an order of magnitude improvement in convergence speed, as well as a reduced asymptotic bit error rate 相似文献
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本文结合正交频分复用(OFDM)、格形编码调制(TCM)与差分编码,提出一种使用子信道交织技术的差分TC—OFDM系统,并在此基础上将信道估计引入系统接收机,提出了与解码相联合的SEWRLS自适应信道估计方法。计算机仿真结果表明,本文提出的联合系统能有效地克服宽带无线通信中的多径衰落,并在快衰落环境中具有很强的抗信道干扰能力。 相似文献
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OFDM技术是一种无线环境下的高速多载波传输技术,抗频率选择性衰落或窄带干扰能力较强,同时又有很高的频谱利用率,适合在多径传播的无线移动信道中传输高速数据。论文分析了OFDM的基本原理,论述了其关键技术及优缺点。OFDM技术将成为未来无线通信中的核心技术,在认知无线电、4G移动通信和无线宽带接入等领域得到广泛的应用。 相似文献
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正交频分复用(OFDM)技术是下一代移动通信的核心技术之一。其最突出的优点是频谱利用率高和抗多径时延能力强,适合未来高速宽带无线通信的应用。OFDM技术通过将频率选择性多径衰落信道在频域内转换为平坦信道,减小了多径衰落的影响。根据OFDM基本原理特构建了一个OFDM通信系统仿真模型,分析了在不同调制方式、不同信道下信道编码对系统性能的影响。仿真结果表明,采用信道编码可有效的降低OFDM系统的误码率。 相似文献
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单载波频域均衡在地空高速数据链的应用 总被引:1,自引:0,他引:1
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。 相似文献
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正交频分复用技术(OFDM)由于其对抗多径能力强和频谱利用率高而被视为下一代无线通信的核心技术。多输入输出(MIMO)技术和OFDM技术已经或者即将应用于各种高速宽带通信系统中,对于MIMO-OFDM系统关键技术的研究至关重要。MIMO-OFDM与SISO-OFDM相似,对定时同步错误和频率偏移敏感,定时和频率不同步都可能会破坏帧结构,因此准确的符号定时和精确的载波频偏估计是系统正常工作的前提。本中首先用CAZAC序列构建出共轭交错结构作为训练序列,然后应用门限值方法改进定时同步估计并基于交错结构进行载波频率偏移估计,最后结合仿真结果确定影响门限值性能的参数值。仿真数据显示,在多径信道条件下,该方法可以使得系统的误码率相对传统方法得到进一步减小,有效地提高同步性能。 相似文献
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Ultra-wide band (UWB) communication is one of the most promising technology for high data rate networks over short-range communication.
The ultra-wide bandwidth offers pulses with very short duration that provides frequency diversity and multipath resolution.
Ultra-wide band (UWB) channels raise new effects in the receiver, the amplitude fading statistics being different compared
to the conventional narrow band wireless channels. This review paper focuses on modeling of ultra-wide band channels, especially
for simulation of personal area networks and also discusses the benefits, application potential and technical challenges in
wideband communication. The concept of Orthogonal Frequency Division Multiplexing (OFDM) has recently been applied in wireless
communication systems due to its high data rate transmission capability with high bandwidth efficiency and its robustness
to multi-path delay. UWB OFDM communication was proposed for physical layer in the IEEE 802.15.3a standard which covers wideband
communication in wireless personal area networks. Since the channel model for multicarrier UWB communication is different
from that of plain ultra-wide band channel, a novel modification method in UWB channel model is proposed with specific center
frequency and multipath resolution. Moreover, dynamic channel estimation is necessary before demodulation of UWB OFDM signals
since the radio channel is time varying and frequency selective for wideband systems. The performance of the proposed method
is statistically analyzed using LS and MMSE based channel estimation methods. 相似文献