A variable-bit-rate characteristic waveform interpolation （VBR-CWI） speech codec with about 1.8 kbit/s average bit rate which integrates phonetic classification into characteristic waveform （CW） decomposition is p...A variable-bit-rate characteristic waveform interpolation （VBR-CWI） speech codec with about 1.8 kbit/s average bit rate which integrates phonetic classification into characteristic waveform （CW） decomposition is proposed. Each input frame is classified into one of 4 phonetic classes. Non-speech frames are represented with Bark-band noise model. The extracted CWs become rapidly evolving waveforms （REWs） or slowly evolving waveforms （SEWs） in the cases of unvoiced or stationary voiced frames respectively, while mixed voiced frames use the same CW decomposition as that in the conventional CWI. Experimental results show that the proposed codec can eliminate most buzzy and noisy artifacts existing in the fixed-bit-rate characteristic waveform interpolation （FBR-CWI） speech codec, the average bit rate can be much lower, and its reconstructed speech quality is much better than FS 1 016 CELP at 4.8 kbit/s and similar to G. 723.1 ACELP at 5.3 kbit/s.展开更多
随着数字化技术和雷达系统的发展,针对合成孔径雷达(Synthetic Aperture Radar,SAR)的干扰对抗技术不断进步,尤其是基于数字射频存储技术(Digital Radio Frequency Memory,DRFM)产生的有源欺骗干扰为SAR成像系统带来了前所未有的考验。...随着数字化技术和雷达系统的发展,针对合成孔径雷达(Synthetic Aperture Radar,SAR)的干扰对抗技术不断进步,尤其是基于数字射频存储技术(Digital Radio Frequency Memory,DRFM)产生的有源欺骗干扰为SAR成像系统带来了前所未有的考验。针对欺骗干扰开展SAR成像抗干扰方法研究,本文基于相位编码波形与带有循环前缀的正交频分复用(Cyclic Prefix Orthogonal Frequency Division Multiplexing,CP-OFDM)波形进行正交波形设计,提出了相位编码CP-OFDM正交波形。基于CP-OFDM波形的循环前缀(Cyclic Prefix,CP)特征,引入基于线性模型的脉冲压缩方法对相位编码CP-OFDM正交波形的SAR成像回波进行距离向处理,能够实现无旁瓣干扰的自相关脉冲压缩。通过对相位编码CP-OFDM波形的时域相位进行编码优化设计,可以实现不同相位编码CP-OFDM波形之间良好的互相关性能。基于线性模型脉冲压缩方法改善了一种p范数多波形加权循环(p-norm Weighted Cyclic Algorithm,p-WeCAN)波形优化算法,采用该算法对相位编码CP-OFDM波形集的相位编码序列进行优化设计,优化后波形的互相关脉冲压缩结果的峰值水平(Peak Sidelobe Level,PSL)相比于随机相位编码CP-OFDM波形的互相关PSL改善了2 dB左右。CP特性赋予了相位编码CP-OFDM波形良好的自相关脉冲压缩结果,相位编码优化设计提供了良好的互相关脉冲压缩结果,采用该正交波形集进行SAR成像,能够实现对欺骗干扰的抑制。进行了点目标、面目标和基于GF-3回波数据反演的半实测数据的抗欺骗干扰SAR成像仿真,与基于线性调频(Linear Frequency Modulation,LFM)波形的欺骗干扰条件下的成像结果进行对比,验证了相位编码CP-OFDM对欺骗干扰的抑制能力。展开更多
Based on the Overlapped Multiplexing Principle[12],a frequency domain OVFDM(Overlapped Frequency Domain Multiplexing)Coding is proposed.By the data weighted shift overlapped version of any band-limited Multiplexing Tr...Based on the Overlapped Multiplexing Principle[12],a frequency domain OVFDM(Overlapped Frequency Domain Multiplexing)Coding is proposed.By the data weighted shift overlapped version of any band-limited Multiplexing Transfer Function H(f)the coding gain and spectral efficiency are both achieved.The heavier the overlap of the data weighted Multiplexing Transfer Function H(f),the higher the coding gain and spectral efficiency as well as the closer the output to the optimum complex Gaussian distribution.The bit error probability performance is estimated.The time domain OVTDM(Overlapped Time Domain Multiplexing)Coding,the dual of OVFDM in time domain is incidentally proposed as well.Both theoretical analysis and testified simulations show that OVFDM(OVTDM)is suitable for high spectral efficiency application and its spectral efficiency is only roughly linear to SNR rather than the well-known logarithm to SNR.展开更多
The most popular and representative classic waveform codes are referred to as orthogonal,bi-orthogonal,simplex,and etc,but the choice of waveform codes is essentially identical in error performance and cross correlati...The most popular and representative classic waveform codes are referred to as orthogonal,bi-orthogonal,simplex,and etc,but the choice of waveform codes is essentially identical in error performance and cross correlation characteristic.Though bi-orthogonal coding requires half the bandwidth of the others,such coding scheme is attractive only when large bandwidth is available.In this paper,a novel finite projective plane（FPP） based waveform coding scheme is proposed,which is with similar error performance and cross correlation.Nevertheless,the bandwidth requirement will grow in a quadratic way,but not in an exponential way with the values of message bit numbers（k）.The proposed scheme takes obvious advantages over the bi-orthogonal scheme when k ≥ 6.展开更多
<div style="text-align:justify;"> A photonics approach to generate a linearly chirped waveform with increased TBWP is proposed and investigated. The time bandwidth product (TBWP) of the linearly chirpe...<div style="text-align:justify;"> A photonics approach to generate a linearly chirped waveform with increased TBWP is proposed and investigated. The time bandwidth product (TBWP) of the linearly chirped waveform is improved based on optical microwave frequency multiplying combined with temporal synthesis. An integrated dual-polarization modulator and an optical filter are utilized to perform frequency doubling operation by generating an orthogonally polarized optical signal, which consists of an optical carrier in one polarization direction and a second-order chirped optical sideband in another. Then the orthogonally polarized optical signal puts into a polarization modulator (PolM) to perform phase coding process. By driving a Pseudorandom (PN) sequence to the PolM, the time duration of the generated bandwidth doubled linearly chirped waveform can be synthesized to arbitrary length. The approach is verified by simulation. A linearly chirped waveform with central frequency of 8.25 GHz, bandwidth of 500 MHz, time duration of 6.4 ns is used to generate a synthesized waveform with central frequency of 16.5 GHz, bandwidth of 1 GHz, time duration of 819.2 ns. The TBWP of the linearly chirped signal is improved from 3.2 to 819.2. The proposed method features arbitrary large TBWP, and it can be used in a radar system to improve its resolution. </div>展开更多
针对现有抗噪声调频干扰相位编码波形设计算法存在计算复杂度高、难以满足实时处理需求的问题,本文提出了一种基于频域坐标下降的高效优化算法。首先,将时域联合优化目标函数转换至频域,建立相位编码波形的频域优化模型。该转换不仅有...针对现有抗噪声调频干扰相位编码波形设计算法存在计算复杂度高、难以满足实时处理需求的问题,本文提出了一种基于频域坐标下降的高效优化算法。首先,将时域联合优化目标函数转换至频域,建立相位编码波形的频域优化模型。该转换不仅有效规避了时域优化过程中大规模矩阵运算带来的高计算代价,还使得优化问题结构更为简洁,便于后续的算法设计。随后,在交替方向乘子法(Alternating Direction Method of Multipliers,ADMM)框架下引入频域坐标下降法(Frequency-domain Coordinate Descent Method,FCDM),形成了ADMMFCDM算法。该算法将复杂的高维优化问题分解为多个可独立并行处理的一维子问题,通过推导波形频域序列元素的闭式解,不仅大幅降低了单次迭代的计算量,还显著提升了全局优化效率。最后,本文引入快速傅里叶变换(Fast Fourier Transform,FFT)技术对ADMM-FCDM进行简化,得到了交替方向乘子法框架下结合快速傅里叶变换的频域坐标下降算法(Frequency-domain Coordinate Descent Method with Fast Fourier Transform under Alternating Direction Method of Multipliers Framework,ADMM-FFT-FCDM)。FFT的引入极大程度地降低了时域与频域之间变换所需的计算时间,进一步提升了算法的运算效率。仿真实验表明,较于现有算法,本文提出的ADMM-FFTFCDM算法在保证雷达抗干扰性能和探测性能的同时,运算速度获得显著提升。展开更多
针对间歇采样转发干扰产生的假目标和目标高速运动产生的多普勒频移导致雷达脉压性能急剧下降的问题,提出一种高多普勒容限的线性调频离散相位编码(linear frequency modulation-discrete phase coding,LFM-DPC)复合调制相干波形集设计...针对间歇采样转发干扰产生的假目标和目标高速运动产生的多普勒频移导致雷达脉压性能急剧下降的问题,提出一种高多普勒容限的线性调频离散相位编码(linear frequency modulation-discrete phase coding,LFM-DPC)复合调制相干波形集设计方法。在一定多普勒频移范围内,以最小化未转发信号自模糊函数旁瓣能量以及未转发信号与转发信号互模糊函数能量建立优化模型,并设计一种基于KKT(Karush-Kuhn-Tucker)最优性条件的迭代算法对模型求解。仿真实验表明,相比于遗传算法和单一调制的LFM和DPC信号,基于KKT最优性条件的交替迭代优化算法优化的LFM-DPC波形集有更好的抗间歇采样转发干扰性能。展开更多
文摘A variable-bit-rate characteristic waveform interpolation （VBR-CWI） speech codec with about 1.8 kbit/s average bit rate which integrates phonetic classification into characteristic waveform （CW） decomposition is proposed. Each input frame is classified into one of 4 phonetic classes. Non-speech frames are represented with Bark-band noise model. The extracted CWs become rapidly evolving waveforms （REWs） or slowly evolving waveforms （SEWs） in the cases of unvoiced or stationary voiced frames respectively, while mixed voiced frames use the same CW decomposition as that in the conventional CWI. Experimental results show that the proposed codec can eliminate most buzzy and noisy artifacts existing in the fixed-bit-rate characteristic waveform interpolation （FBR-CWI） speech codec, the average bit rate can be much lower, and its reconstructed speech quality is much better than FS 1 016 CELP at 4.8 kbit/s and similar to G. 723.1 ACELP at 5.3 kbit/s.
文摘随着数字化技术和雷达系统的发展,针对合成孔径雷达(Synthetic Aperture Radar,SAR)的干扰对抗技术不断进步,尤其是基于数字射频存储技术(Digital Radio Frequency Memory,DRFM)产生的有源欺骗干扰为SAR成像系统带来了前所未有的考验。针对欺骗干扰开展SAR成像抗干扰方法研究,本文基于相位编码波形与带有循环前缀的正交频分复用(Cyclic Prefix Orthogonal Frequency Division Multiplexing,CP-OFDM)波形进行正交波形设计,提出了相位编码CP-OFDM正交波形。基于CP-OFDM波形的循环前缀(Cyclic Prefix,CP)特征,引入基于线性模型的脉冲压缩方法对相位编码CP-OFDM正交波形的SAR成像回波进行距离向处理,能够实现无旁瓣干扰的自相关脉冲压缩。通过对相位编码CP-OFDM波形的时域相位进行编码优化设计,可以实现不同相位编码CP-OFDM波形之间良好的互相关性能。基于线性模型脉冲压缩方法改善了一种p范数多波形加权循环(p-norm Weighted Cyclic Algorithm,p-WeCAN)波形优化算法,采用该算法对相位编码CP-OFDM波形集的相位编码序列进行优化设计,优化后波形的互相关脉冲压缩结果的峰值水平(Peak Sidelobe Level,PSL)相比于随机相位编码CP-OFDM波形的互相关PSL改善了2 dB左右。CP特性赋予了相位编码CP-OFDM波形良好的自相关脉冲压缩结果,相位编码优化设计提供了良好的互相关脉冲压缩结果,采用该正交波形集进行SAR成像,能够实现对欺骗干扰的抑制。进行了点目标、面目标和基于GF-3回波数据反演的半实测数据的抗欺骗干扰SAR成像仿真,与基于线性调频(Linear Frequency Modulation,LFM)波形的欺骗干扰条件下的成像结果进行对比,验证了相位编码CP-OFDM对欺骗干扰的抑制能力。
基金The NNSF(National Nature Science Foundation)of China for their continuously long term support by key projects
文摘Based on the Overlapped Multiplexing Principle[12],a frequency domain OVFDM(Overlapped Frequency Domain Multiplexing)Coding is proposed.By the data weighted shift overlapped version of any band-limited Multiplexing Transfer Function H(f)the coding gain and spectral efficiency are both achieved.The heavier the overlap of the data weighted Multiplexing Transfer Function H(f),the higher the coding gain and spectral efficiency as well as the closer the output to the optimum complex Gaussian distribution.The bit error probability performance is estimated.The time domain OVTDM(Overlapped Time Domain Multiplexing)Coding,the dual of OVFDM in time domain is incidentally proposed as well.Both theoretical analysis and testified simulations show that OVFDM(OVTDM)is suitable for high spectral efficiency application and its spectral efficiency is only roughly linear to SNR rather than the well-known logarithm to SNR.
基金supported by MOST under Grant MOST 103-2633-E-242-002
文摘The most popular and representative classic waveform codes are referred to as orthogonal,bi-orthogonal,simplex,and etc,but the choice of waveform codes is essentially identical in error performance and cross correlation characteristic.Though bi-orthogonal coding requires half the bandwidth of the others,such coding scheme is attractive only when large bandwidth is available.In this paper,a novel finite projective plane（FPP） based waveform coding scheme is proposed,which is with similar error performance and cross correlation.Nevertheless,the bandwidth requirement will grow in a quadratic way,but not in an exponential way with the values of message bit numbers（k）.The proposed scheme takes obvious advantages over the bi-orthogonal scheme when k ≥ 6.
文摘<div style="text-align:justify;"> A photonics approach to generate a linearly chirped waveform with increased TBWP is proposed and investigated. The time bandwidth product (TBWP) of the linearly chirped waveform is improved based on optical microwave frequency multiplying combined with temporal synthesis. An integrated dual-polarization modulator and an optical filter are utilized to perform frequency doubling operation by generating an orthogonally polarized optical signal, which consists of an optical carrier in one polarization direction and a second-order chirped optical sideband in another. Then the orthogonally polarized optical signal puts into a polarization modulator (PolM) to perform phase coding process. By driving a Pseudorandom (PN) sequence to the PolM, the time duration of the generated bandwidth doubled linearly chirped waveform can be synthesized to arbitrary length. The approach is verified by simulation. A linearly chirped waveform with central frequency of 8.25 GHz, bandwidth of 500 MHz, time duration of 6.4 ns is used to generate a synthesized waveform with central frequency of 16.5 GHz, bandwidth of 1 GHz, time duration of 819.2 ns. The TBWP of the linearly chirped signal is improved from 3.2 to 819.2. The proposed method features arbitrary large TBWP, and it can be used in a radar system to improve its resolution. </div>
文摘针对现有抗噪声调频干扰相位编码波形设计算法存在计算复杂度高、难以满足实时处理需求的问题,本文提出了一种基于频域坐标下降的高效优化算法。首先,将时域联合优化目标函数转换至频域,建立相位编码波形的频域优化模型。该转换不仅有效规避了时域优化过程中大规模矩阵运算带来的高计算代价,还使得优化问题结构更为简洁,便于后续的算法设计。随后,在交替方向乘子法(Alternating Direction Method of Multipliers,ADMM)框架下引入频域坐标下降法(Frequency-domain Coordinate Descent Method,FCDM),形成了ADMMFCDM算法。该算法将复杂的高维优化问题分解为多个可独立并行处理的一维子问题,通过推导波形频域序列元素的闭式解,不仅大幅降低了单次迭代的计算量,还显著提升了全局优化效率。最后,本文引入快速傅里叶变换(Fast Fourier Transform,FFT)技术对ADMM-FCDM进行简化,得到了交替方向乘子法框架下结合快速傅里叶变换的频域坐标下降算法(Frequency-domain Coordinate Descent Method with Fast Fourier Transform under Alternating Direction Method of Multipliers Framework,ADMM-FFT-FCDM)。FFT的引入极大程度地降低了时域与频域之间变换所需的计算时间,进一步提升了算法的运算效率。仿真实验表明,较于现有算法,本文提出的ADMM-FFTFCDM算法在保证雷达抗干扰性能和探测性能的同时,运算速度获得显著提升。
文摘针对间歇采样转发干扰产生的假目标和目标高速运动产生的多普勒频移导致雷达脉压性能急剧下降的问题,提出一种高多普勒容限的线性调频离散相位编码(linear frequency modulation-discrete phase coding,LFM-DPC)复合调制相干波形集设计方法。在一定多普勒频移范围内,以最小化未转发信号自模糊函数旁瓣能量以及未转发信号与转发信号互模糊函数能量建立优化模型,并设计一种基于KKT(Karush-Kuhn-Tucker)最优性条件的迭代算法对模型求解。仿真实验表明,相比于遗传算法和单一调制的LFM和DPC信号,基于KKT最优性条件的交替迭代优化算法优化的LFM-DPC波形集有更好的抗间歇采样转发干扰性能。
