Performances of BPSK, balanced quaternary modulation, dual quaternary modulation and complex quaternary modulation in direct sequence spectrum spread (DS SS) system are discussed in this paper. Based on the crit...Performances of BPSK, balanced quaternary modulation, dual quaternary modulation and complex quaternary modulation in direct sequence spectrum spread (DS SS) system are discussed in this paper. Based on the criterion the power of original signal is the same, it is shown that complex quaternary modulation has the best performance, and dual quaternary modulation degrades 2dB. Moreover, the frequency efficient of the two modulations is 2bit/Hz. Balanced quaternary has the same performance as BPSK with frequency efficient 1bit/Hz.展开更多
It is a necessary step to estimate the spreading sequence of direct sequence spread spectrum （DSSS） signal for blind despreading and demodulation in non-cooperative communications. Two innovative and effective detec...It is a necessary step to estimate the spreading sequence of direct sequence spread spectrum （DSSS） signal for blind despreading and demodulation in non-cooperative communications. Two innovative and effective detection statistics are proposed to implement the synchronization and spreading sequence estimation procedure. The proposed algorithm also has a low computational complexity with only linear additions and modifications. Theoretical analysis and simulation results show that the algorithm performs quite well in low SNR environment, and is much better than all the existing typical algorithms with a comprehensive consideration both in performance and computational complexity.展开更多
To estimate the spreading sequence of the direct sequence spread spectrum (DSSS) signal, a fast algorithm based on maximum likelihood function is proposed, and the theoretical derivation of the algorithm is provided. ...To estimate the spreading sequence of the direct sequence spread spectrum (DSSS) signal, a fast algorithm based on maximum likelihood function is proposed, and the theoretical derivation of the algorithm is provided. By simplifying the objective function of maximum likelihood estimation, the algorithm can realize sequence synchronization and sequence estimation via adaptive iteration and sliding window. Since it avoids the correlation matrix computation, the algorithm significantly reduces the storage requirement and the computation complexity. Simulations show that it is a fast convergent algorithm, and can perform well in low signal to noise ratio (SNR).展开更多
An approach based on discrete Karhunen-Loeve transformation of the DS/SS signals is proposed to estimate PN sequence in lower S/N ratio DS/SS signals. Characteristics of self-organization and principle components extr...An approach based on discrete Karhunen-Loeve transformation of the DS/SS signals is proposed to estimate PN sequence in lower S/N ratio DS/SS signals. Characteristics of self-organization and principle components extraction of unsupervised neural networks are exploited adequately. Theoretical analysis and experimental results are provided to show that this approach can work well on the lower S/N ratio input signals.展开更多
This paper presents an approach of singular value de- composition plus digital phase lock loop to solve the difficult problem of blind pseudo-noise （PN） sequence estimation in low signal to noise ratios （SNR） dire...This paper presents an approach of singular value de- composition plus digital phase lock loop to solve the difficult problem of blind pseudo-noise （PN） sequence estimation in low signal to noise ratios （SNR） direct sequence spread spectrum （DS-SS） signals with residual carrier. This approach needs some given parameters, such as the period and code rate of PN sequence. The received signal is firstly sampled and divided into non-overlapping signal vectors according to a temporal window, whose duration is two periods of PN sequence. An autocorrelation matrix is then computed and accumulated by those signal vectors one by one. The PN sequence with residual carrier can be estimated by the principal eigenvector of the autocorrelation matrix. Further more, a digital phase lock loop is used to process the estimated PN sequence, it estimates and tracks the residual carrier and removes the residual carrier in the end. Theory analysis and computer simulation results show that this approach can effectively realize the PN sequence blind estimation from the input DS-SS signals with residual carrier in lower SNR.展开更多
The key to narrow-band interference excision in frequency domain is to determine the excision thresh- old in direct-sequence spread-spectrum （DS-SS） systems. The excision threshold is a non-linear function related t...The key to narrow-band interference excision in frequency domain is to determine the excision thresh- old in direct-sequence spread-spectrum （DS-SS） systems. The excision threshold is a non-linear function related to the number and the power of interference, and attempting to get the exact relation of threshold related to the number and the power of interference is almost impossible. The N-sigma algorithm determines the excision threshold using subsection function; however, the excision threshold determined by this method is not exact. A new method to determine the threshold of N-sigma algorithm is proposed. The new method modifies the scale factor N by use of the membership function. The threshold determined by this method is consecutive and smooth, and it is closer to the fact than that of the initial N-sigma algorithm. The GPS signal and single-tone （CW） interference （that is, typical narrow-band interference） are implemented in the simulation, and the results are presented to demonstrate the validity of the new algorithm.展开更多
短码扩频长码加扰的直扩信号可视为特殊的长码直扩信号,将其短扩频码和长扰码作为复合码。首先通过特征值分解和酉矩阵去位置模糊实现复合码的盲估计;然后利用m序列的三阶相关函数特性识别短扩频码的类型;最后根据识别结果采用三阶相关...短码扩频长码加扰的直扩信号可视为特殊的长码直扩信号,将其短扩频码和长扰码作为复合码。首先通过特征值分解和酉矩阵去位置模糊实现复合码的盲估计;然后利用m序列的三阶相关函数特性识别短扩频码的类型;最后根据识别结果采用三阶相关法或延迟三阶相关法实现长短伪码的盲估计。仿真表明,复合码估计在信噪比-7.5 d B以上可达到1%以下的误码率;当信噪比高于-6 d B时,三阶相关法估计长短伪码本原多项式的正确率可以达到90%以上;当信噪比高于-4 d B时,延迟三阶相关法估计长短伪码序列的误码率低于1%。展开更多
正交时频空(Orthogonal Time Frequency Space,OTFS)调制技术因其在多普勒频偏和时延条件下的适应能力,正逐渐应用于高动态场景中。作为一种多载波调制方式,尽管OTFS技术在高速移动通信中表现出色,但其高峰均比(Peak-to-Average Power R...正交时频空(Orthogonal Time Frequency Space,OTFS)调制技术因其在多普勒频偏和时延条件下的适应能力,正逐渐应用于高动态场景中。作为一种多载波调制方式,尽管OTFS技术在高速移动通信中表现出色,但其高峰均比(Peak-to-Average Power Ratio,PAPR)问题依然亟待解决。高峰均比问题容易导致OTFS信号出现非线性失真,降低信号质量,进而影响通信系统的整体性能。为了有效降低OTFS系统信号波形的峰均比并提升系统的整体传输性能,本文提出了一种基于扩频的OTFS系统峰均比抑制方案。具体而言,通过软扩频和直接序列扩频的方式在时延-多普勒域内对OTFS信息符号进行扩展,利用Zadoff-Chu(ZC)序列良好的自相关性和恒模特性以及m序列良好的自相关性,能够显著抑制系统信号的峰均比,从而减少信号非线性失真,提升系统传输能力。进一步通过理论推导,本文说明了在相移键控(Phase Shift Keying,PSK)调制条件下,当OTFS系统符号数大于扩频因子且为其2的整数次幂倍数时,发射信号波形的峰均比更高。仿真结果表明,相较于原始OTFS系统,提出的扩频OTFS系统在峰均比方面表现出显著改善,尤其基于ZC序列的软扩频OTFS系统,其发射信号呈现出恒模特性,极大降低了对功率放大器线性度的要求。同时,基于m序列的直接序列扩频方案亦在发射信号峰均比方面实现了约8.5 dB的改善。仿真结果验证了理论分析的正确性,并且表明提出的扩频OTFS系统具有更优的传输性能。展开更多
基金ThisprojectwassupportedbytheKeyProjectoftheNaturalScienceFoundationofChina (No .6 98310 30 )
文摘Performances of BPSK, balanced quaternary modulation, dual quaternary modulation and complex quaternary modulation in direct sequence spectrum spread (DS SS) system are discussed in this paper. Based on the criterion the power of original signal is the same, it is shown that complex quaternary modulation has the best performance, and dual quaternary modulation degrades 2dB. Moreover, the frequency efficient of the two modulations is 2bit/Hz. Balanced quaternary has the same performance as BPSK with frequency efficient 1bit/Hz.
基金supported by the Specialized Research Fund for the Doctoral Program of Higher Education (20060003032)
文摘It is a necessary step to estimate the spreading sequence of direct sequence spread spectrum （DSSS） signal for blind despreading and demodulation in non-cooperative communications. Two innovative and effective detection statistics are proposed to implement the synchronization and spreading sequence estimation procedure. The proposed algorithm also has a low computational complexity with only linear additions and modifications. Theoretical analysis and simulation results show that the algorithm performs quite well in low SNR environment, and is much better than all the existing typical algorithms with a comprehensive consideration both in performance and computational complexity.
基金supported by Joint Foundation of and China Academy of Engineering Physical (10676006)
文摘To estimate the spreading sequence of the direct sequence spread spectrum (DSSS) signal, a fast algorithm based on maximum likelihood function is proposed, and the theoretical derivation of the algorithm is provided. By simplifying the objective function of maximum likelihood estimation, the algorithm can realize sequence synchronization and sequence estimation via adaptive iteration and sliding window. Since it avoids the correlation matrix computation, the algorithm significantly reduces the storage requirement and the computation complexity. Simulations show that it is a fast convergent algorithm, and can perform well in low signal to noise ratio (SNR).
文摘An approach based on discrete Karhunen-Loeve transformation of the DS/SS signals is proposed to estimate PN sequence in lower S/N ratio DS/SS signals. Characteristics of self-organization and principle components extraction of unsupervised neural networks are exploited adequately. Theoretical analysis and experimental results are provided to show that this approach can work well on the lower S/N ratio input signals.
基金supported by the National Natural Science Foundation of China (10776040 60602057)+4 种基金Program for New Century Excellent Talents in University (NCET)the Project of Key Laboratory of Signal and Information Processing of Chongqing (CSTC2009CA2003)the Natural Science Foundation of Chongqing Science and Technology Commission (CSTC2009BB2287)the Natural Science Foundation of Chongqing Municipal Education Commission (KJ060509 KJ080517)
文摘This paper presents an approach of singular value de- composition plus digital phase lock loop to solve the difficult problem of blind pseudo-noise （PN） sequence estimation in low signal to noise ratios （SNR） direct sequence spread spectrum （DS-SS） signals with residual carrier. This approach needs some given parameters, such as the period and code rate of PN sequence. The received signal is firstly sampled and divided into non-overlapping signal vectors according to a temporal window, whose duration is two periods of PN sequence. An autocorrelation matrix is then computed and accumulated by those signal vectors one by one. The PN sequence with residual carrier can be estimated by the principal eigenvector of the autocorrelation matrix. Further more, a digital phase lock loop is used to process the estimated PN sequence, it estimates and tracks the residual carrier and removes the residual carrier in the end. Theory analysis and computer simulation results show that this approach can effectively realize the PN sequence blind estimation from the input DS-SS signals with residual carrier in lower SNR.
文摘The key to narrow-band interference excision in frequency domain is to determine the excision thresh- old in direct-sequence spread-spectrum （DS-SS） systems. The excision threshold is a non-linear function related to the number and the power of interference, and attempting to get the exact relation of threshold related to the number and the power of interference is almost impossible. The N-sigma algorithm determines the excision threshold using subsection function; however, the excision threshold determined by this method is not exact. A new method to determine the threshold of N-sigma algorithm is proposed. The new method modifies the scale factor N by use of the membership function. The threshold determined by this method is consecutive and smooth, and it is closer to the fact than that of the initial N-sigma algorithm. The GPS signal and single-tone （CW） interference （that is, typical narrow-band interference） are implemented in the simulation, and the results are presented to demonstrate the validity of the new algorithm.
文摘短码扩频长码加扰的直扩信号可视为特殊的长码直扩信号,将其短扩频码和长扰码作为复合码。首先通过特征值分解和酉矩阵去位置模糊实现复合码的盲估计;然后利用m序列的三阶相关函数特性识别短扩频码的类型;最后根据识别结果采用三阶相关法或延迟三阶相关法实现长短伪码的盲估计。仿真表明,复合码估计在信噪比-7.5 d B以上可达到1%以下的误码率;当信噪比高于-6 d B时,三阶相关法估计长短伪码本原多项式的正确率可以达到90%以上;当信噪比高于-4 d B时,延迟三阶相关法估计长短伪码序列的误码率低于1%。
文摘正交时频空(Orthogonal Time Frequency Space,OTFS)调制技术因其在多普勒频偏和时延条件下的适应能力,正逐渐应用于高动态场景中。作为一种多载波调制方式,尽管OTFS技术在高速移动通信中表现出色,但其高峰均比(Peak-to-Average Power Ratio,PAPR)问题依然亟待解决。高峰均比问题容易导致OTFS信号出现非线性失真,降低信号质量,进而影响通信系统的整体性能。为了有效降低OTFS系统信号波形的峰均比并提升系统的整体传输性能,本文提出了一种基于扩频的OTFS系统峰均比抑制方案。具体而言,通过软扩频和直接序列扩频的方式在时延-多普勒域内对OTFS信息符号进行扩展,利用Zadoff-Chu(ZC)序列良好的自相关性和恒模特性以及m序列良好的自相关性,能够显著抑制系统信号的峰均比,从而减少信号非线性失真,提升系统传输能力。进一步通过理论推导,本文说明了在相移键控(Phase Shift Keying,PSK)调制条件下,当OTFS系统符号数大于扩频因子且为其2的整数次幂倍数时,发射信号波形的峰均比更高。仿真结果表明,相较于原始OTFS系统,提出的扩频OTFS系统在峰均比方面表现出显著改善,尤其基于ZC序列的软扩频OTFS系统,其发射信号呈现出恒模特性,极大降低了对功率放大器线性度的要求。同时,基于m序列的直接序列扩频方案亦在发射信号峰均比方面实现了约8.5 dB的改善。仿真结果验证了理论分析的正确性,并且表明提出的扩频OTFS系统具有更优的传输性能。
