共查询到20条相似文献,搜索用时 109 毫秒
1.
2.
3.
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
4.
在移动通信环境下,由于Doppler频移以及多径影响,信道是时变的,为了消除信道对传输信号的影响,需要对信道进行估计。文中阐述了一种基于Comb-type导频类型以及IDFT/DFT内插方法的OFDM信道估计方法,分析了对导频个数选取的要求,并结合LS准则给出了16QAM信号在慢衰落Rayleigh多径信道下的误码率曲线和均方差曲线,验证了基于IDFT/DFT内插信道估计方法的准确性和可行性。 相似文献
5.
6.
7.
正交频分复用(OFDM)技术采用多载波传输方式,成为了第四代移动通信核心技术。OFDM系统可采用基于导频的信道估计方法,提高信道传输的准确性。文章在matlab环境下对块状导频进行仿真,对最小乘二算法和最小均方误差估计算法进行了比较,经过实验得出,块状导频更适合于慢衰落信道。 相似文献
8.
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
9.
10.
OFDM/OQAM系统中联合迭代信道估计和信号检测 总被引:1,自引:2,他引:1
与基于复数域空间正交条件的传统正交频分复用系统(OFDM with Cyclic Prefix, CP-OFDM)有所不同,基于交错正交调制的正交频分复用系统(OFDM/Offset QAM, OFDM/OQAM)满足实数域空间严格正交条件。因此在多径衰落信道条件下,CP-OFDM系统中的信道估计方法会导致OFDM/OQAM系统严重的字符间干扰和载波间干扰。该文结合OFDM/OQAM系统结构特点,提出了一种基于迭代信道估计和信号检测算法。该算法通过信道估计器和接收到的信号互相交换信息,消除导频序列中的字符间干扰和载波间干扰,提高信道估计和信号检测的准确度。仿真分析结果表明,经过一定次数迭代处理后,OFDM/OQAM迭代信道估计性能趋近于理想信道估计性能。 相似文献
11.
Abbas Hasan Kattoush Waleed Ameen Mahmoud Al-Jawher Sulaiman M. Abbas Ali Tweij Shaheen 《Wireless Personal Communications》2011,58(4):695-711
In this paper a new method is proposed to perform the N-Radon orthogonal frequency division multiplexing (OFDM), which are equivalent to 4-quadrature amplitude modulation (QAM),
16-QAM, 64-QAM, 256-QAM, ... etc. in spectral efficiency. This non conventional method is proposed in order to reduce the
constellation energy and increase spectral efficiency. The proposed method gives a significant improvement in Bit Error Rate
performance, and keeps bandwidth efficiency and spectrum shape as good as conventional Fast Fourier Transform based OFDM.
The new structure was tested and compared with conventional OFDM for Additive White Gaussian Noise, flat, and multi-path selective
fading channels. Simulation tests were generated for different channels parameters values including multi-path gains vector,
multi-path delay time vector, and maximum Doppler shift. 相似文献
12.
In this paper, we studied the channel estimation problem for the orthogonal frequency division multiplexing (OFDM) system when the statistics of the multi-path fading channel is not known or partial known. A channel estimation approach based on polynomial approximation of the channel response is proposed. The pilot symbols are periodically inserted the channel responses for entire OFDM data sequence for exploiting channel correlation in both time and frequency domain, which is obtained from a time-variant frequency-selective Rayleigh fading channel model. Simulation shows that the method is robust to different channel statistics. Moreover, a window dimension adaptation algorithm is proposed to adapt the channel estimator to the channel statistics which further improves the robustness of the system. 相似文献
13.
14.
基于DET的OFDM信道估计算法及分析 总被引:1,自引:0,他引:1
在高速无线通信中,由于多径衰落和多普勒频移引起的子载波间串扰,严重影响了OFDM系统的性能。因此,接收端的信道估计显得至关重要。基于离散进化变换进行时频分析的方法,可以较完全获得一个受多径衰落、频率选择性衰落干扰的信道的特性。仿真表明,在大多普勒频移影响的时变信道中,采用时频分析的方法比常规信道估计方法的性能有明显提高。 相似文献
15.
16.
Cebrail Çiflikli A. Tuncay Özşahin A. Çağrı Yapici 《Wireless Personal Communications》2009,51(2):221-229
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. 相似文献
17.
Abbas Hasan Kattoush Waleed Ameen Mahmoud Al-Jawher Osama Q. Al-Thahab 《Wireless Personal Communications》2013,71(2):857-871
Finite Radon transform (FRAT) mapper has the ability to increase orthogonality of sub-carriers, it is non sensitive to channel parameters variations, and has a small constellation energy compared with conventional fast Fourier transform (FFT) based orthogonal frequency division multiplexing (OFDM). It is also able to work as a good interleaver which significantly reduces the bit error rate (BER). Due to its good orthogonality, discrete Multiwavelet transform (DMWT) is attractive for implementation in OFDM systems which reduces inter-symbol interference (ISI) and inter-carrier interference (ICI) and eliminates the need for cyclic prefix and increases the spectral efficiency of the design. In this paper both FRAT and DMWT are implemented in a new design for OFDM. The new structure was tested and compared with conventional FFT-based OFDM, Radon-based OFDM, and DMWT-based OFDM for additive white Gaussian noise channel, flat fading channel, and multi-path selective fading channel. Simulation tests were generated for different channels parameters values. The obtained results showed that proposed system has increased spectral efficiency, reduced ISI and ICI, and improved BER performance compared with other systems. 相似文献
18.
19.
通过比较国内外几种LDPC误码平台测试系统,设计了一种基于OFDM的用于测试LDPC解码误码性能的窄带系统,采用了时域同步正交频分复用调制方式,具有抵抗多径干扰和多普勒频移的能力.该系统用FPGA予以实现,不仅可用于实验室测试,也可用于测试真实多径环境下的误码性能,还能作为通用系统用于其他信道纠错码的解码误码测试. 相似文献
20.
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