共查询到20条相似文献,搜索用时 156 毫秒
1.
在正交频分复用(OFDM)系统中,频率偏移会破坏子载波间的正交性,降低整个系统的性能。在研究传统频偏估计算法的基础上,利用简单的实数训练序列,进行OFDM系统的载波频偏估计,只需要一个训练序列,就可以有效地在时域内同时对小数倍和整数倍的频率偏移进行估计。仿真结果表明,基于实数训练序列的载波频偏估计算法不仅方法简单,易于实现,而且可提高频偏估计精度。 相似文献
2.
协作OFDM系统中,由于OFDM技术的引入,使协作通信系统对载波频率偏移非常敏感,很小的频偏就会引起子载波间的干扰.提出了协作OFDM系统中基于前导符号改进的载波频偏估计算法,设计了一种用PN序列调制指数序列得到的前导符号.仿真结果表明,该算法对协作OFDM系统的载波频偏估计性能明显优于传统算法. 相似文献
3.
4.
同步系统是 DAB 接收机的关键之一,针对其中的载波同步算法进行了分析。在理论分析载波频率偏差对 DAB 系统性能影响的基础上,介绍了2种分别用于载波粗频偏估计和细频偏估计的算法。粗频偏估计算法基于 DAB 信号所特有的相位参考符号(PRS),细频偏估计算法基于 OFDM 信号所特有的循环前缀(CP),对其它采用 OFDM 技术的系统具有很好的通用性。仿真结果表明这2种算法估计性能良好。 相似文献
5.
由于多输入多输出-正交频分复用(MIMO-OFDM)系统对频偏很敏感,很小的频偏就能引起系统性能的大幅下降.为了提高MIMO-OFDM系统频偏估计的精度和频谱的利用率,采用一种基于新训练序列的小数倍频偏估计算法.该算法利用构造的新训练序列获得比传统算法更精准的频偏估计,可有效地对小数倍频偏进行估计,同时提出的算法减少训练序列的数量,提高系统频谱利用率.仿真结果表明,在加性高斯白噪声信道环境下,所提出的方法在载波频偏估计中能有很好的性能. 相似文献
6.
7.
由于多输入多输出-正交频分复用(MIMO-OFDM)系统对频偏很敏感,很小的频偏就能引起系统性能的大幅下降。为了提高MIMO-OFDM系统频偏估计的精度和频谱的利用率,采用一种基于新训练序列的小数倍频偏估计算法。该算法利用构造的新训练序列获得比传统算法更精准的频偏估计,可有效地对小数倍频偏进行估计,同时提出的算法减少训练序列的数量,提高系统频谱利用率。仿真结果表明,在加性高斯白噪声信道环境下,所提出的方法在载波频偏估计中能有很好的性能。 相似文献
8.
9.
10.
针对QAM相干光传输系统中载波频偏估计算法存在估计范围小、计算复杂度高的问题,提出一种基于训练符号的FFT频偏估计算法.利用训练符号相位信息消除部分采样信号调制相位,取该部分信号的幅角进行FFT变换,最终得到频偏估计值.消除了原频偏估计算法中除以4的运算,从而扩大了频偏估计范围,同时由于减少了FFT长度进而降低计算复杂度.仿真结果表明,改进后的算法在QAM相干检测系统保持较高精度的频偏估计情况下,其估计范围可以达到±50%符号速率. 相似文献
11.
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
12.
针对电气与电子工程师协会802.11正交频分复用通信系统研究了一种利用导频间隔优化导频位置的方法,进而提出了一种利用导频序列更好的对频偏进行估计和补偿的算法。在电气与电子工程师协会802.11标准规定的帧格式基础上,利用数值仿真方法对提出方法所确定的导频位置和所提出的频偏估计补偿算法进行了性能分析。数值仿真结果表明,所提出的导频位置确定方法和频偏估计和补偿算法,在不提高系统复杂度的情况下,所提算法能够显著改善系统性能。 相似文献
13.
14.
CAO Xue-hong Department of Information Engineering Nanjing University of Posts Telecommunications Nanjing P.R. China 《中国邮电高校学报(英文版)》2005,12(2)
1Introduction Orthogonal Frequency Division Multiplexing(OFDM) has become a popular technique for transmis-sion of signals over wireless channels . OFDMhas beenadoptedinseveral wireless standards such as Digital Au-dio Broadcasting ( DAB) , Digital Video Broadcasting(DVB-T) ,the IEEE 802 .11a[1]Local Area Network(LAN) standard and high performance LAN type 2(HIPERLAN/2)[2]standard. OFDMis also being pur-sued for Dedicated Short-Range Communications(DSRC) for road side to … 相似文献
15.
同步是OFDM系统中至关重要的一个环节,目前已有很多针对OFDM系统的同步算法,大致可以分为3类:基于嵌入符号中的导频、基于前导序列和基于循环前缀。提出了具体针对IEEE802.11a帧结构的同步算法(包括时间定时和频偏估计及纠正)。详细阐述了该算法各个模块FPGA的具体实现,具有复杂度低,便于工程实现的特点。 相似文献
16.
Aki Silvennoinen Michael Hall Sven-Gustav Häggman 《Wireless Personal Communications》2007,41(4):487-505
The effect of terminal movement on the performance of the IEEE 802.11 g wireless LAN (WLAN) system is evaluated using a measurement
set-up including a radio channel simulator. The evaluation is based on laboratory measurements of WLAN PC cards in different
simulated radio environments. In the measurements, two different radio channel models are used; the exponential channel model
and the UMTS vehicular channel model. The measurement results indicate promising operation of IEEE 802.11 g WLAN systems as
such. However, the use of different packet sizes has a significant effect on the system behaviour. With large packets the
terminal is more likely to experience channel estimation errors than with small packets. This is due to the fact that the
IEEE 802.11 g receiver estimates the channel only once per frame, and uses this estimation over the entire frame. Based on
the measurement results we suggest a modification to the medium access control (MAC) layer operation that overcomes this problem:
the use of optimized fragmentation. 相似文献
17.
OFDM系统中的联合同步和信道估计 总被引:1,自引:0,他引:1
在OFDM系统中,由于定时恢复、频率同步和信道估计之间存在密切联系,时延和频偏的估计误差会影响信道响应估计的准确性.本文采用IEEE802.11a无线局域网系统标准定义的训练序列进行联合估计.考虑系统性能优化和算法简化,将处理过程分成两步,首先得到粗的同步和信道响应估计,再利用得到的结果进行细同步和信道估计.实验结果显示信道估计精度高,系统误码率低. 相似文献
18.
Estimation of carrier frequency offset (CFO) is an important issue in the design of a wireless receiver that employs orthogonal
frequency division multiplexing (OFDM) techniques. In this paper, using the ten short training symbols specified in the signal
format of the IEEE 802.11a WLAN, we investigate the performance of a coarse CFO estimation scheme for OFDM signals with multiple
preamble symbols. This scheme, which we call DC-ML, employs the maximum likelihood (ML) method with delayed correlation (DC).
For AWGN channels under moderate signal to noise ratio (SNR) conditions, we develop an analysis to evaluate the variance of
estimation error (VEER). The analysis is corroborated in light of simulations, and compared with the formulated Cramer-Rao
lower bound (CRLB). VEER of the DC-ML in a multipath environment is studied via simulations. Numerical results show that a
certain parameter combination can result in minimum VEER. Simulation results justify that the probability of estimation error
(PEER) approximates Gaussian distribution in both AWGN and multipath scenarios. We also present a Two-Branch DC-ML (TBDC-ML)
scheme, which comprises two correlation branches of DC-ML, and an associative ambiguity resolution algorithm. Numerical examples
reveal that TBDC-ML outperforms DC-ML in both VEER and PEER. Assuming that the estimation error resulting from the two branches
is jointly Gaussian, we derive the joint probability density function (pdf) and validate it via simulations. 相似文献
19.
Yik-Chung Wu Kun-Wah Yip Tung-Sang Ng Serpedin E. 《Wireless Communications, IEEE Transactions on》2005,4(6):2751-2763
Based on the maximum-likelihood principle and the preamble structure of IEEE 802.11a wireless local area network (WLAN) standard, this paper proposes a new symbol synchronization algorithm for IEEE 802.11a WLANs over frequency-selective fading channels. In addition to the physical channel, the effects of filtering and unknown sampling phase offset are also considered. Loss in system performance due to synchronization error is used as a performance criterion. Computer simulations show that the proposed algorithm exhibits better performances than the simple correlation-based algorithms. When compared to the algorithm based on the generalized Akaike information criterion, the proposed algorithm presents comparable performance and exhibits reduced complexity. 相似文献