To improve frame synchronization precision, a scheme named training symbol correlation （TSC） is presented for orthogonal frequency division multiplexing （ OFDM ） system. Based on the solution from Schmidl and Cox,...To improve frame synchronization precision, a scheme named training symbol correlation （TSC） is presented for orthogonal frequency division multiplexing （ OFDM ） system. Based on the solution from Schmidl and Cox, a timing metric related to TSC scheme is put forward and examined. The specific method to select a threshold value provides more precise detection results, which can be shown by performance comparison between the two schemes through Monte Carlo simulation. Taking IEEE 802.1 la WLAN standard as an example, the proposed approach is superior to the most popular Schmidl scheme in terms of BER.展开更多
Multiband orthogonal frequency division multiplexing (MB-OFDM) ultra wide-band (UWB) is a novel wireless communication technology. It has many advantages and is being actively researhed. In this study, we constructed ...Multiband orthogonal frequency division multiplexing (MB-OFDM) ultra wide-band (UWB) is a novel wireless communication technology. It has many advantages and is being actively researhed. In this study, we constructed and implemented a simulation model of UWB communication systems in Simulink. We found the MB-OFDM UWB system has the best performance in distance between 4 m to 10 m without the line-of-sight requirement.展开更多
This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems. The research results show that this method can reduc...This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems. The research results show that this method can reduce the walk- off effect and can therefore equalize the nonlinear impairments effectively. Compared with the only other existing nonlinearity pre-compensation method, the joint nonlinearity and chromatic dispersion pre-compensation method is not only suitable for low-dispersion optical orthogonal frequency-division multiplexing system, but also effective for high- dispersion optical orthogonal frequency-division multiplexing transmission system with higher input power but without optical dispersion compensation. The suggested solution does not increase computation complexity compared with only nonlinearity pre-compensation method. For 40 Gbit/s coherent optical orthogonal frequency-division multiplexing 20 × 80 km standard single-mode fibre system, the suggested method can improve the nonlinear threshold （for Q 〉 10 dB） about 2.7, 1.2 and 1.0 dB, and the maximum Q factor about 1.2, 0.4 and 0.3 dB, for 2, 8 and 16 ps/（nm.km） dispersion coefficients.展开更多
The major constraint on the performance of orthogonal frequency division multiplexing （OFDM） based underwater acoustic （UWA） communication is to keep subcarriers orthogonal. In this paper, Doppler estimation and t...The major constraint on the performance of orthogonal frequency division multiplexing （OFDM） based underwater acoustic （UWA） communication is to keep subcarriers orthogonal. In this paper, Doppler estimation and the respective compensation technique along with various diversity techniques were deliberated for OFDM-based systems best suited for underwater wireless information exchange. In practice, for mobile communication, adjustment and tuning of transducers in order to get spatial diversity is extremely difficult. Considering the relatively low coherence bandwidth in UWA, the frequency diversity design with the Doppler compensation function was elaborated here. The outfield experiments of mobile underwater acoustic communication （UWAC） based on OFDM were carried out with 0.17 bit/（s-Hz） spectral efficiency. The validity and the dependability of the scheme were also analyzed.展开更多
The traditional fractional frequency offset(FFO) estimation schemes for orthogonal frequency division multiplexing(OFDM) in non-cooperative communication have the problems of susceptible performance with the frequency...The traditional fractional frequency offset(FFO) estimation schemes for orthogonal frequency division multiplexing(OFDM) in non-cooperative communication have the problems of susceptible performance with the frequency offset values and the number of OFDM symbols,a novel fractional frequency offset blind estimation scheme based on EKF for OFDM systems is conceived.The nonlinear function of the frequency offset is calculated by employing the correlation.And then the frequency offset is estimated by means of the iterative algorithm of EKF.The finally fractional frequency offset is estimated by adopting repeated the above process.Simulation results demonstrate that the proposed scheme is robust to the frequency offset values without any requirements of a prior knowledge.展开更多
针对低空经济通信中导频受限的多输入多输出正交频分复用(Multiple Input and Multiple Output Orthogonal Frequency Division Multiplexing,MIMO-OFDM)存在的信道估计精度低的问题,提出一种适用于低空多径环境的MIMO-OFDM信道估计新...针对低空经济通信中导频受限的多输入多输出正交频分复用(Multiple Input and Multiple Output Orthogonal Frequency Division Multiplexing,MIMO-OFDM)存在的信道估计精度低的问题,提出一种适用于低空多径环境的MIMO-OFDM信道估计新方法。在时频资源平面上,该方法利用信道平滑特征和导频信道系数在子载波和符号维度的关联,根据导频点生成初始的Voronoi图,然后基于插值数据点更新Voronoi图,并将两个Voronoi图叠加。更新Voronoi图中插值数据点所属的Voronoi小区域被初始Voronoi图划分为多块,根据每块面积计算权重,再将多个相邻导频处的信道估计值加权求和,从而得到对应插值数据点的信道估计值。仿真结果表明,与线性插值方法相比,所提方法使得信道估计归一化均方误差降低了50%,误比特率性能提升了1.6 dB。展开更多
正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)调制因其高效的频带利用率和良好的抗多径能力广泛用于合作与非合作通信系统中。合作通信场景下,通常接收机可以利用已知帧结构实现OFDM信号的检测。但在非合作场景下,...正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)调制因其高效的频带利用率和良好的抗多径能力广泛用于合作与非合作通信系统中。合作通信场景下,通常接收机可以利用已知帧结构实现OFDM信号的检测。但在非合作场景下,接收机没有足够的先验信息,导致帧检测难度加大。针对这一问题,提出了一种适合于非合作通信场景的OFDM数据帧的检测算法。所提算法利用快速小波变换将含噪OFDM信号的功率包络进行小波分解与重构,对重构得到的功率包络进行差分运算后,再通过与阈值比较实现OFDM信号的帧检测。相较于混合能量检测算法,所提算法计算预设参数少,复杂度低。仿真结果表明,所提算法在加性高斯白噪声信道和多径衰落信道下带内信噪比分别取-6 dB和3 dB时即可实现零漏报率,且零漏报率的阈值选取范围比混合能量检测算法扩大了约6 dB。展开更多
A closed form expression for the bit error rate (BER) performance of frequency domaindifferential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fadingchannel is derived.The performan...A closed form expression for the bit error rate (BER) performance of frequency domaindifferential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fadingchannel is derived.The performance is evaluated by computer simulation and compared with the timedomain differential demodulation(TDDD).The results indicate that the performance of FDDD is betterthan that of TDDD,and the lower band of BER in the former is lower than that of the latter.展开更多
水声通信中传统宽带多普勒估计方法难以准确跟踪时变多普勒因子,从而导致正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)在变速运动通信场景中补偿性能不佳。针对该问题,文章提出了一种基于空载波的多普勒估计与跟踪...水声通信中传统宽带多普勒估计方法难以准确跟踪时变多普勒因子,从而导致正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)在变速运动通信场景中补偿性能不佳。针对该问题,文章提出了一种基于空载波的多普勒估计与跟踪算法。首先对三频信号做线性调频Z变换(Chirp-Z Transform,CZT)得到多普勒先验值,然后利用OFDM符号中的空载波结合载波频偏(Carrier Frequency Offset,CFO)搜索补偿技术,把估计的最优CFO值转换为宽带多普勒因子,进而计算当前符号的加速度并预测下一符号的速度。通过更新加速度对预测值进行修正,实现每个OFDM符号的多普勒估计。数值仿真和湖试结果表明,文中算法不仅能有效跟踪多普勒的变化,在匀速和变速条件下都有较好的补偿性能,而且对帧结构设计要求低,对先验误差不敏感,有利于水声通信系统的工程实现。展开更多
文摘To improve frame synchronization precision, a scheme named training symbol correlation （TSC） is presented for orthogonal frequency division multiplexing （ OFDM ） system. Based on the solution from Schmidl and Cox, a timing metric related to TSC scheme is put forward and examined. The specific method to select a threshold value provides more precise detection results, which can be shown by performance comparison between the two schemes through Monte Carlo simulation. Taking IEEE 802.1 la WLAN standard as an example, the proposed approach is superior to the most popular Schmidl scheme in terms of BER.
文摘Multiband orthogonal frequency division multiplexing (MB-OFDM) ultra wide-band (UWB) is a novel wireless communication technology. It has many advantages and is being actively researhed. In this study, we constructed and implemented a simulation model of UWB communication systems in Simulink. We found the MB-OFDM UWB system has the best performance in distance between 4 m to 10 m without the line-of-sight requirement.
基金supported by the National High Technology Research and Development Program of China(Grant No.2009AA01A345)the National Basic Research Program of China(Grant No.2011CB302702)the National Natural Science Foundation of China(Grant No.60932004)
文摘This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems. The research results show that this method can reduce the walk- off effect and can therefore equalize the nonlinear impairments effectively. Compared with the only other existing nonlinearity pre-compensation method, the joint nonlinearity and chromatic dispersion pre-compensation method is not only suitable for low-dispersion optical orthogonal frequency-division multiplexing system, but also effective for high- dispersion optical orthogonal frequency-division multiplexing transmission system with higher input power but without optical dispersion compensation. The suggested solution does not increase computation complexity compared with only nonlinearity pre-compensation method. For 40 Gbit/s coherent optical orthogonal frequency-division multiplexing 20 × 80 km standard single-mode fibre system, the suggested method can improve the nonlinear threshold （for Q 〉 10 dB） about 2.7, 1.2 and 1.0 dB, and the maximum Q factor about 1.2, 0.4 and 0.3 dB, for 2, 8 and 16 ps/（nm.km） dispersion coefficients.
基金Supported by the National High Technology Research and Development Program of China (2009AA093601-2)the National Defense Foundation Research (B2420110007)
文摘The major constraint on the performance of orthogonal frequency division multiplexing （OFDM） based underwater acoustic （UWA） communication is to keep subcarriers orthogonal. In this paper, Doppler estimation and the respective compensation technique along with various diversity techniques were deliberated for OFDM-based systems best suited for underwater wireless information exchange. In practice, for mobile communication, adjustment and tuning of transducers in order to get spatial diversity is extremely difficult. Considering the relatively low coherence bandwidth in UWA, the frequency diversity design with the Doppler compensation function was elaborated here. The outfield experiments of mobile underwater acoustic communication （UWAC） based on OFDM were carried out with 0.17 bit/（s-Hz） spectral efficiency. The validity and the dependability of the scheme were also analyzed.
基金supported by the National Natural Science Foundation of China under Grant No.61501348 and 61271299China Postdoctoral Science Foundation funded project under Grant No.2014M562372+1 种基金Natural Science Basic Research Plan in Shaanxi Province of China under Grant No.2016JQ6039the 111 Project under Grant No.B08038
文摘The traditional fractional frequency offset(FFO) estimation schemes for orthogonal frequency division multiplexing(OFDM) in non-cooperative communication have the problems of susceptible performance with the frequency offset values and the number of OFDM symbols,a novel fractional frequency offset blind estimation scheme based on EKF for OFDM systems is conceived.The nonlinear function of the frequency offset is calculated by employing the correlation.And then the frequency offset is estimated by means of the iterative algorithm of EKF.The finally fractional frequency offset is estimated by adopting repeated the above process.Simulation results demonstrate that the proposed scheme is robust to the frequency offset values without any requirements of a prior knowledge.
文摘针对低空经济通信中导频受限的多输入多输出正交频分复用(Multiple Input and Multiple Output Orthogonal Frequency Division Multiplexing,MIMO-OFDM)存在的信道估计精度低的问题,提出一种适用于低空多径环境的MIMO-OFDM信道估计新方法。在时频资源平面上,该方法利用信道平滑特征和导频信道系数在子载波和符号维度的关联,根据导频点生成初始的Voronoi图,然后基于插值数据点更新Voronoi图,并将两个Voronoi图叠加。更新Voronoi图中插值数据点所属的Voronoi小区域被初始Voronoi图划分为多块,根据每块面积计算权重,再将多个相邻导频处的信道估计值加权求和,从而得到对应插值数据点的信道估计值。仿真结果表明,与线性插值方法相比,所提方法使得信道估计归一化均方误差降低了50%,误比特率性能提升了1.6 dB。
基金Supported by National Natural Science Foundation of China(No.60272009)and National 863 Plan Project(NO.2001AA1230131)
文摘A closed form expression for the bit error rate (BER) performance of frequency domaindifferential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fadingchannel is derived.The performance is evaluated by computer simulation and compared with the timedomain differential demodulation(TDDD).The results indicate that the performance of FDDD is betterthan that of TDDD,and the lower band of BER in the former is lower than that of the latter.
文摘水声通信中传统宽带多普勒估计方法难以准确跟踪时变多普勒因子,从而导致正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)在变速运动通信场景中补偿性能不佳。针对该问题,文章提出了一种基于空载波的多普勒估计与跟踪算法。首先对三频信号做线性调频Z变换(Chirp-Z Transform,CZT)得到多普勒先验值,然后利用OFDM符号中的空载波结合载波频偏(Carrier Frequency Offset,CFO)搜索补偿技术,把估计的最优CFO值转换为宽带多普勒因子,进而计算当前符号的加速度并预测下一符号的速度。通过更新加速度对预测值进行修正,实现每个OFDM符号的多普勒估计。数值仿真和湖试结果表明,文中算法不仅能有效跟踪多普勒的变化,在匀速和变速条件下都有较好的补偿性能,而且对帧结构设计要求低,对先验误差不敏感,有利于水声通信系统的工程实现。
