Serveral methods for the pararrel acquisition of a PN sequence in a baseband direct sequence spread spectrum system are investigated. Four different kinds of schemes are considered: the optimal estimation scheme, the ...Serveral methods for the pararrel acquisition of a PN sequence in a baseband direct sequence spread spectrum system are investigated. Four different kinds of schemes are considered: the optimal estimation scheme, the locally optimal estimation scheme, the optimal testing searches and the locally optimal testing scheme. In the four kinds of parallel acquisition schemes, the expressions for the probability of error are given and compared with the actual error probabilities obtained via Monte Carlo simulation. We also outline a technique that can be suboptimal because of a large amount of hardware and computation when using the parallel acquisition schemes.展开更多
Aiming at improving acquisition performance for direct sequence spread spectrum (DSSS) signals, a new acquisition algorithm based on fast Fourier transform (FFT) is proposed. The code phases are parallel searched ...Aiming at improving acquisition performance for direct sequence spread spectrum (DSSS) signals, a new acquisition algorithm based on fast Fourier transform (FFT) is proposed. The code phases are parallel searched throughout the Doppler frequency domain. Since the influence of Doppler frequency errors on peak-to- average ratios of correlation power shows a pattern similar to the sinc function, it is our belief that by judging on peak-to-average ratios for different Doppler frequency errors false alarm probabilities should be lowered. Analyses have supported the underlying principle of this new algorithm. Simulation results have also indicated that the new algorithm can effectively improve the acquisition performance for DSSS signals.展开更多
With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based ...With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based underwater acoustic communication system using dual spread spectrum code is proposed. To solve the contradictions between the information data rate and the accuracy of Doppler estimation, channel estimation, and frame synchronization, a data frame structure based on dual spread spectrum code is designed. A long spread spectrum code is used as the training sequence, which can be used for data frame detection and synchronization, Doppler estimation, and channel estimation. A short spread spectrum code is used to modulate the effective information data. A delay cross-correlation algorithm is used for Doppler estimation, and a correlation algorithm is used for channel estimation. For underwater networking, each user is assigned a different pair of spread spectrum codes. Simulation results show that the system has a good anti-multipath, anti-interference, and anti-Doppler performance, the bit error rate can be smaller than 10^(-6) when the signal-to-noise ratio is larger than-10 dB, the data rate can be as high as 355 bits/s, and the system can be used in the downlink of CDMA based networks.展开更多
A novel direct sequence (DS) design method for suppressing the narrowband interference in DS spread spectrum ultra-wideband receivers is proposed. The method has low computational complexity and can be easily implem...A novel direct sequence (DS) design method for suppressing the narrowband interference in DS spread spectrum ultra-wideband receivers is proposed. The method has low computational complexity and can be easily implemented in practical systems. Simulation results prove that the proposed method is effective to suppress the narrowband interference. Therefore, the integrity of both the ultra-wide bandwidth and the narrowband systems can be highly enhanced.展开更多
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
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
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
In this paper, a new approach is proposed to estimate pseudo noise(PN) sequence in the lower SNR DS/SS signals blindly. This method utilizes the characteristics of self-organization, principal components analysis and ...In this paper, a new approach is proposed to estimate pseudo noise(PN) sequence in the lower SNR DS/SS signals blindly. This method utilizes the characteristics of self-organization, principal components analysis and extraction of unsupervised neural networks adequately, in addition to its higher-speed operation ability, successfully solve the difficult problem about PN sequence blind estimation. The theoretic analysis and experimental results show that this approach can work very well on lower SNR input signals.展开更多
An idea of estimating the direct sequence spread spectrum(DSSS) signal pseudo-noise(PN) sequence is presented. Without the apriority knowledge about the DSSS signal in the non-cooperation condition, we propose a s...An idea of estimating the direct sequence spread spectrum(DSSS) signal pseudo-noise(PN) sequence is presented. Without the apriority knowledge about the DSSS signal in the non-cooperation condition, we propose a self-organizing feature map(SOFM) neural network algorithm to detect and identify the PN sequence. A non-supervised learning algorithm is proposed according the Kohonen rule in SOFM. The blind algorithm can also estimate the PN sequence in a low signal-to-noise(SNR) and computer simulation demonstrates that the algorithm is effective. Compared with the traditional correlation algorithm based on slip-correlation, the proposed algorithm's bit error rate(BER) and complexity are lower.展开更多
Reconfigurable intelligent surface(RIS)-assisted symbiotic radio is a spectrum-and energy-efficient communication paradigm,in which an RIS performs passive beamforming to enhance active transmission,while using the el...Reconfigurable intelligent surface(RIS)-assisted symbiotic radio is a spectrum-and energy-efficient communication paradigm,in which an RIS performs passive beamforming to enhance active transmission,while using the electromagnetic waves from the active transmission for additional information transfer(i.e.,passive transmission).In this paper,a hybrid RIS-based modulation,termed hybrid phase and code modulation(HPCM),is proposed to improve the reliability of RIS-assisted symbiotic radio.In RIS-HPCM,the RIS simultaneously performs direct sequence spread spectrum and passive beamforming on incident signals.Moreover,both the spreading code and phase offset are exploited to carry the RIS’s own information.A low-complexity detector is designed,in which the receiver first detects the spreading codes and then demodulates the constellation symbols.We analyze the bit error rate(BER)performance of RIS-HPCM over Rician fading channels.BER upper bounds and approximate BER expressions are derived in closed-form for maximum-likelihood and low-complexity detectors,respectively.Simulation results in terms of BER verify the analysis and show the superiority of RIS-HPCM over the existing RIS-based modulation.展开更多
In hybrid Direct Sequence/Frequency Hopping Spread Spectrum (DS/FH SS) system, the fast acquisition is a key technique. A combined fast scanning and waiting method for FH acquisition is introduced, and a neural netw...In hybrid Direct Sequence/Frequency Hopping Spread Spectrum (DS/FH SS) system, the fast acquisition is a key technique. A combined fast scanning and waiting method for FH acquisition is introduced, and a neural network for DS acquisition is presented also. Using these two methods, the fast acquisition of the hybrid DS/FH SS system can be realized.展开更多
A novel algorithm is proposed to resolve the defects in the traditional linear frequency modulation(LFM)jamming suppression algorithm in the fractional Fourier transform(FRFT)domain.The traditional LFM jamming suppres...A novel algorithm is proposed to resolve the defects in the traditional linear frequency modulation(LFM)jamming suppression algorithm in the fractional Fourier transform(FRFT)domain.The traditional LFM jamming suppression algorithm in the FRFT domain has some defects.For example,the exact threshold is difficult to set and both the signal-to-noise ratio(SNR)loss and spectrum leakage are serious in strong jamming-to-signal ratio(JSR)situations.Windowing,overlapping and inverse windowing techniques are used in the FRFT domain to reduce the spectrum leakage and the SNR loss.Under the condition that only the direct sequence spread spectrum(DSSS)signal and white Gaussian noise are present,the amplitude of the received signal after FRFT is assumed to be Rayleigh distributed.Based on the distribution characteristic,hypothesis testing is used to suppress the jamming spectrum using the algorithm.Simulation results show that the performance of proposed algorithm is better than that of the conventional algorithms,especially in a strong jamming and multi component LFM jamming environment.展开更多
For direct sequence spread spectrum (DSSS) receivers, the capability of rejecting narrow-band interference can be significantly improved by a process of frequency-domain interference suppression (FDIS). The key is...For direct sequence spread spectrum (DSSS) receivers, the capability of rejecting narrow-band interference can be significantly improved by a process of frequency-domain interference suppression (FDIS). The key issue of this process is how to determine a threshold to eliminate interference in the frequency domain, which has been extensively studied. However, these previous methods are tedious or very complex. A simple and ef- ficient algorithm based on medians is proposed. The elimination threshold is only related to the median by a scale factor, which can be obtained by the numerical analysis. Simulation results show that the algorithm provides excellent narrow-band interfer- ence suppression while only slightly degrading the signal-to-noise ratio (SNR). A one-pass algorithm using logarithmic segmentation is further derived to estimate medians with low computational complexity. Finally, the FDIS is implemented in a field programmable gate array (FPGA) of Xilinx. Experiments are carried out by connecting the FDIS FPGA to a DSSS receiver, and the results show that the receiver has an effective countermeasure for a 60 dB interference-to-signal ratio (ISR).展开更多
For decreasing the multiple access interference of weaker signal acquisition in direct sequence spread spectrum(DSSS) systems,a new single decision algorithm is presented.The maximum value of correlation results is ...For decreasing the multiple access interference of weaker signal acquisition in direct sequence spread spectrum(DSSS) systems,a new single decision algorithm is presented.The maximum value of correlation results is conventionally detected.However,there may be not only one strong peak among correlation results when the cross-correlation noise is strong enough to affect the correlation results.The proposed algorithm decreases the false alarm probability through the decision of the ratio of the maximum value and the second maximum value of the correlation results.Theoretical analysis and simulation results indicate that the proposed algorithm effectively suppresses the acquisition problem of multiple access interference in DSSS system.展开更多
A new method for the rejection of linear frequency modulation (LFM) interference in direct sequence spread spectrum (DSSS) system based on the fractional Fourier transform is proposed, and the configuration of the rec...A new method for the rejection of linear frequency modulation (LFM) interference in direct sequence spread spectrum (DSSS) system based on the fractional Fourier transform is proposed, and the configuration of the receiver with an interference exciser is also presented. Based on the property that the fractional Fourier transform of a signal is equivalent to rotating the signal in the time-frequency plane, the received signal is transform into a certain fractional Fourier domain, this transform will result in the least spectrum overlap between the signal and interference. Then, a narrowband filter is exploited to extract most of the interference energy. The performance analyses show that remarkable improvements in signal-to-noise ratio (SNR) and bit-error-ratio (BER) are obtained.展开更多
The direct sequence ultra-wideband (DS-UWB) is a promising technology for short-range wireless communications. The UWB signal is a stream of very low power density and ultra-short pulses, and the great potential of ...The direct sequence ultra-wideband (DS-UWB) is a promising technology for short-range wireless communications. The UWB signal is a stream of very low power density and ultra-short pulses, and the great potential of DS-UWB depends critically on the success of timing acquisition. A rapid acquisition algorithm for reducing the acquisition time of the coarse pseudo-noise (PN) sequences is proposed. The algorithm utilizes the auxiliary sequence and bisearch strategy based on the threshold comparison criterion. Both theoretical analysis and simulation tests show that with the proposed search strategy and simple operations over the symbol duration at the receiver, the proposed algorithm can considerably reduce the acquisition time even as it maintains the PN sequence acquisition probability in the DS-UWB system over the dense multipath environment.展开更多
The correlation matrix, which is widely used in eigenvalue decomposition (EVD) or singular value decomposition (SVD), usually can be denoted by R = E[yiy'i]. A novel method for constructing the correlation matrix...The correlation matrix, which is widely used in eigenvalue decomposition (EVD) or singular value decomposition (SVD), usually can be denoted by R = E[yiy'i]. A novel method for constructing the correlation matrix R is proposed. The proposed algorithm can improve the resolving power of the signal eigenvalues and overcomes the shortcomings of the traditional subspace methods, which cannot be applied to low SNR. Then the proposed method is applied to the direct sequence spread spectrum (DSSS) signal's signature sequence estimation. The performance of the proposed algorithm is analyzed, and some illustrative simulation results are presented.展开更多
Tomato fruit are sensitive to chilling injury(CI)during cold storage.Several factors have been discovered to be involved in chilling injury of tomato fruit.Plant hormones play an important regulatory role,however,the ...Tomato fruit are sensitive to chilling injury(CI)during cold storage.Several factors have been discovered to be involved in chilling injury of tomato fruit.Plant hormones play an important regulatory role,however,the relationship between chilling injury and N6-methyladenosine(m^(6)A)methylation of transcripts in plant hormone pathways has not been reported yet.In order to clarify the complex regulatory mechanism of m^(6)A methylation on chilling injury in tomato fruit,Nanopore direct RNA sequencing was employed.A large number of enzymes and transcription factors were found to be involved in the regulation process of fruit chilling injury,which were associated with plant hormone,such as 1-aminocyclopropane 1-carboxylate synthase(ACS),aspartate aminotransferase(AST),auxin response factor(ARF2),ethylene response factor 2(ERF2),gibberellin 20-oxidase-3(GA20ox)and jasmonic acid(JA).By conjoint analysis of the differential expression transcripts related to chilling injury andm^(6)Amethylation differential expression transcripts 41 differential expression transcripts were identified involved in chilling injury including 1-aminocyclopropane-1-carboxylate oxidase(ACO)and pectinesterase(PE)were down-regulated and heat shock cognate 70 kD protein 2(cpHSC70),HSP70-binding protein(HspBP)and salicylic acid-binding protein 2(SABP2)were up-regulated.Our results will provide a deeper understanding for chilling injury regulatory mechanism and post-harvest cold storage of tomato fruit.展开更多
Transcriptome analysis based on high-throughput sequencing of a cDNA library has been widely applied to functional genomic studies.However,the cDNA dependence of most RNA sequencing techniques constrains their ability...Transcriptome analysis based on high-throughput sequencing of a cDNA library has been widely applied to functional genomic studies.However,the cDNA dependence of most RNA sequencing techniques constrains their ability to detect base modifications on RNA,which is an important element for the post-transcriptional regulation of gene expression.To comprehensively profile the N^(6)-methyladenosine(m^(6)A)and N^(5)-methylcytosine(m5 C)modifications on RNA,direct RNA sequencing(DRS)using the latest Oxford Nanopore Technology was applied to analyze the transcriptome of six tissues in rice.Approximately 94 million reads were generated,with an average length ranging from 619 nt to 1013 nt,and a total of 45,707 transcripts across 34,763 genes were detected.Expression profiles of transcripts at the isoform level were quantified among tissues.Transcriptome-wide mapping of m^(6)A and m5 C demonstrated that both modifications exhibited tissue-specific characteristics.The transcripts with m^(6)A modifications tended to be modified by m5 C,and the transcripts with modifications presented higher expression levels along with shorter poly(A)tails than transcripts without modifications,suggesting the complexity of gene expression regulation.Gene Ontology analysis demonstrated that m^(6)A-and m5 C-modified transcripts were involved in central metabolic pathways related to the life cycle,with modifications on the target genes selected in a tissue-specific manner.Furthermore,most modified sites were located within quantitative trait loci that control important agronomic traits,highlighting the value of cloning functional loci.The results provide new insights into the expression regulation complexity and data resource of the transcriptome and epitranscriptome,improving our understanding of the rice genome.展开更多
文摘Serveral methods for the pararrel acquisition of a PN sequence in a baseband direct sequence spread spectrum system are investigated. Four different kinds of schemes are considered: the optimal estimation scheme, the locally optimal estimation scheme, the optimal testing searches and the locally optimal testing scheme. In the four kinds of parallel acquisition schemes, the expressions for the probability of error are given and compared with the actual error probabilities obtained via Monte Carlo simulation. We also outline a technique that can be suboptimal because of a large amount of hardware and computation when using the parallel acquisition schemes.
基金Sponsored by the National "863" Program Project (1010021310XXX)
文摘Aiming at improving acquisition performance for direct sequence spread spectrum (DSSS) signals, a new acquisition algorithm based on fast Fourier transform (FFT) is proposed. The code phases are parallel searched throughout the Doppler frequency domain. Since the influence of Doppler frequency errors on peak-to- average ratios of correlation power shows a pattern similar to the sinc function, it is our belief that by judging on peak-to-average ratios for different Doppler frequency errors false alarm probabilities should be lowered. Analyses have supported the underlying principle of this new algorithm. Simulation results have also indicated that the new algorithm can effectively improve the acquisition performance for DSSS signals.
基金Project supported by the National Natural Science Foundation of China(Nos.61431005,51409235,and 61401111)the Fundamental Research Funds for the Central Universities,China(No.201213004)
文摘With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based underwater acoustic communication system using dual spread spectrum code is proposed. To solve the contradictions between the information data rate and the accuracy of Doppler estimation, channel estimation, and frame synchronization, a data frame structure based on dual spread spectrum code is designed. A long spread spectrum code is used as the training sequence, which can be used for data frame detection and synchronization, Doppler estimation, and channel estimation. A short spread spectrum code is used to modulate the effective information data. A delay cross-correlation algorithm is used for Doppler estimation, and a correlation algorithm is used for channel estimation. For underwater networking, each user is assigned a different pair of spread spectrum codes. Simulation results show that the system has a good anti-multipath, anti-interference, and anti-Doppler performance, the bit error rate can be smaller than 10^(-6) when the signal-to-noise ratio is larger than-10 dB, the data rate can be as high as 355 bits/s, and the system can be used in the downlink of CDMA based networks.
文摘A novel direct sequence (DS) design method for suppressing the narrowband interference in DS spread spectrum ultra-wideband receivers is proposed. The method has low computational complexity and can be easily implemented in practical systems. Simulation results prove that the proposed method is effective to suppress the narrowband interference. Therefore, the integrity of both the ultra-wide bandwidth and the narrowband systems can be highly enhanced.
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 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.
文摘In this paper, a new approach is proposed to estimate pseudo noise(PN) sequence in the lower SNR DS/SS signals blindly. This method utilizes the characteristics of self-organization, principal components analysis and extraction of unsupervised neural networks adequately, in addition to its higher-speed operation ability, successfully solve the difficult problem about PN sequence blind estimation. The theoretic analysis and experimental results show that this approach can work very well on lower SNR input signals.
基金supported by the National Natural Science Foundation of China under Grant No.61271168
文摘An idea of estimating the direct sequence spread spectrum(DSSS) signal pseudo-noise(PN) sequence is presented. Without the apriority knowledge about the DSSS signal in the non-cooperation condition, we propose a self-organizing feature map(SOFM) neural network algorithm to detect and identify the PN sequence. A non-supervised learning algorithm is proposed according the Kohonen rule in SOFM. The blind algorithm can also estimate the PN sequence in a low signal-to-noise(SNR) and computer simulation demonstrates that the algorithm is effective. Compared with the traditional correlation algorithm based on slip-correlation, the proposed algorithm's bit error rate(BER) and complexity are lower.
基金supported in part by the National Natural Science Foundation of China under Grant 62201228 and Grant 62001190in part by the Science and Technology Major Project of Tibetan Autonomous Region of China under Grant No.XZ202201ZD0006G02.
文摘Reconfigurable intelligent surface(RIS)-assisted symbiotic radio is a spectrum-and energy-efficient communication paradigm,in which an RIS performs passive beamforming to enhance active transmission,while using the electromagnetic waves from the active transmission for additional information transfer(i.e.,passive transmission).In this paper,a hybrid RIS-based modulation,termed hybrid phase and code modulation(HPCM),is proposed to improve the reliability of RIS-assisted symbiotic radio.In RIS-HPCM,the RIS simultaneously performs direct sequence spread spectrum and passive beamforming on incident signals.Moreover,both the spreading code and phase offset are exploited to carry the RIS’s own information.A low-complexity detector is designed,in which the receiver first detects the spreading codes and then demodulates the constellation symbols.We analyze the bit error rate(BER)performance of RIS-HPCM over Rician fading channels.BER upper bounds and approximate BER expressions are derived in closed-form for maximum-likelihood and low-complexity detectors,respectively.Simulation results in terms of BER verify the analysis and show the superiority of RIS-HPCM over the existing RIS-based modulation.
文摘In hybrid Direct Sequence/Frequency Hopping Spread Spectrum (DS/FH SS) system, the fast acquisition is a key technique. A combined fast scanning and waiting method for FH acquisition is introduced, and a neural network for DS acquisition is presented also. Using these two methods, the fast acquisition of the hybrid DS/FH SS system can be realized.
基金National Natural Science Foundation of China(61175059)the Natural Science Foundation of Hebei Province(F2011205023)。
文摘A novel algorithm is proposed to resolve the defects in the traditional linear frequency modulation(LFM)jamming suppression algorithm in the fractional Fourier transform(FRFT)domain.The traditional LFM jamming suppression algorithm in the FRFT domain has some defects.For example,the exact threshold is difficult to set and both the signal-to-noise ratio(SNR)loss and spectrum leakage are serious in strong jamming-to-signal ratio(JSR)situations.Windowing,overlapping and inverse windowing techniques are used in the FRFT domain to reduce the spectrum leakage and the SNR loss.Under the condition that only the direct sequence spread spectrum(DSSS)signal and white Gaussian noise are present,the amplitude of the received signal after FRFT is assumed to be Rayleigh distributed.Based on the distribution characteristic,hypothesis testing is used to suppress the jamming spectrum using the algorithm.Simulation results show that the performance of proposed algorithm is better than that of the conventional algorithms,especially in a strong jamming and multi component LFM jamming environment.
基金supported by the National Natural Science Foundation of China(60904090)
文摘For direct sequence spread spectrum (DSSS) receivers, the capability of rejecting narrow-band interference can be significantly improved by a process of frequency-domain interference suppression (FDIS). The key issue of this process is how to determine a threshold to eliminate interference in the frequency domain, which has been extensively studied. However, these previous methods are tedious or very complex. A simple and ef- ficient algorithm based on medians is proposed. The elimination threshold is only related to the median by a scale factor, which can be obtained by the numerical analysis. Simulation results show that the algorithm provides excellent narrow-band interfer- ence suppression while only slightly degrading the signal-to-noise ratio (SNR). A one-pass algorithm using logarithmic segmentation is further derived to estimate medians with low computational complexity. Finally, the FDIS is implemented in a field programmable gate array (FPGA) of Xilinx. Experiments are carried out by connecting the FDIS FPGA to a DSSS receiver, and the results show that the receiver has an effective countermeasure for a 60 dB interference-to-signal ratio (ISR).
基金supported by the National High Technology ResearchDevelopment Program of China (863 Program) (2008AA0248)
文摘For decreasing the multiple access interference of weaker signal acquisition in direct sequence spread spectrum(DSSS) systems,a new single decision algorithm is presented.The maximum value of correlation results is conventionally detected.However,there may be not only one strong peak among correlation results when the cross-correlation noise is strong enough to affect the correlation results.The proposed algorithm decreases the false alarm probability through the decision of the ratio of the maximum value and the second maximum value of the correlation results.Theoretical analysis and simulation results indicate that the proposed algorithm effectively suppresses the acquisition problem of multiple access interference in DSSS system.
文摘A new method for the rejection of linear frequency modulation (LFM) interference in direct sequence spread spectrum (DSSS) system based on the fractional Fourier transform is proposed, and the configuration of the receiver with an interference exciser is also presented. Based on the property that the fractional Fourier transform of a signal is equivalent to rotating the signal in the time-frequency plane, the received signal is transform into a certain fractional Fourier domain, this transform will result in the least spectrum overlap between the signal and interference. Then, a narrowband filter is exploited to extract most of the interference energy. The performance analyses show that remarkable improvements in signal-to-noise ratio (SNR) and bit-error-ratio (BER) are obtained.
基金supported by the National Natural Science Foundation of China (60572024)the Doctoral Fund of the Ministry of Education of China (20050293003)the National Basic Research Program (2007CB310607)
文摘The direct sequence ultra-wideband (DS-UWB) is a promising technology for short-range wireless communications. The UWB signal is a stream of very low power density and ultra-short pulses, and the great potential of DS-UWB depends critically on the success of timing acquisition. A rapid acquisition algorithm for reducing the acquisition time of the coarse pseudo-noise (PN) sequences is proposed. The algorithm utilizes the auxiliary sequence and bisearch strategy based on the threshold comparison criterion. Both theoretical analysis and simulation tests show that with the proposed search strategy and simple operations over the symbol duration at the receiver, the proposed algorithm can considerably reduce the acquisition time even as it maintains the PN sequence acquisition probability in the DS-UWB system over the dense multipath environment.
文摘The correlation matrix, which is widely used in eigenvalue decomposition (EVD) or singular value decomposition (SVD), usually can be denoted by R = E[yiy'i]. A novel method for constructing the correlation matrix R is proposed. The proposed algorithm can improve the resolving power of the signal eigenvalues and overcomes the shortcomings of the traditional subspace methods, which cannot be applied to low SNR. Then the proposed method is applied to the direct sequence spread spectrum (DSSS) signal's signature sequence estimation. The performance of the proposed algorithm is analyzed, and some illustrative simulation results are presented.
基金supported by grants from the National Natural Science Foundation of China(Grant Nos.31772022,32072284 and 31501544)the Special Innovation Ability Construction Fund of Beijing Academy of Agricultural and Forestry Sciences(Grant Nos.20200427 and 20210437)+4 种基金Science and Technology Planning Project of Tianjin City(Grant No.19YFSLQY00100)the Beijing Municipal Science and Technology Commission(Grant Nos.Z191100008619004 and Z191100004019010)Supported by China Agriculture Research System of MOF and MARA,collaborative innovation center of Beijing Academy of Agricultural and Forestry Sciences(Grant No.201915)the Young Investigator Fund of Beijing Academy of Agricultural and Forestry Sciences(Grant No.202016)the key scientific research projects of colleges and universities in Henan Province(Grant No.20A550014)。
文摘Tomato fruit are sensitive to chilling injury(CI)during cold storage.Several factors have been discovered to be involved in chilling injury of tomato fruit.Plant hormones play an important regulatory role,however,the relationship between chilling injury and N6-methyladenosine(m^(6)A)methylation of transcripts in plant hormone pathways has not been reported yet.In order to clarify the complex regulatory mechanism of m^(6)A methylation on chilling injury in tomato fruit,Nanopore direct RNA sequencing was employed.A large number of enzymes and transcription factors were found to be involved in the regulation process of fruit chilling injury,which were associated with plant hormone,such as 1-aminocyclopropane 1-carboxylate synthase(ACS),aspartate aminotransferase(AST),auxin response factor(ARF2),ethylene response factor 2(ERF2),gibberellin 20-oxidase-3(GA20ox)and jasmonic acid(JA).By conjoint analysis of the differential expression transcripts related to chilling injury andm^(6)Amethylation differential expression transcripts 41 differential expression transcripts were identified involved in chilling injury including 1-aminocyclopropane-1-carboxylate oxidase(ACO)and pectinesterase(PE)were down-regulated and heat shock cognate 70 kD protein 2(cpHSC70),HSP70-binding protein(HspBP)and salicylic acid-binding protein 2(SABP2)were up-regulated.Our results will provide a deeper understanding for chilling injury regulatory mechanism and post-harvest cold storage of tomato fruit.
基金supported by the National Natural Science Foundation of China(Grant No.31671775).
文摘Transcriptome analysis based on high-throughput sequencing of a cDNA library has been widely applied to functional genomic studies.However,the cDNA dependence of most RNA sequencing techniques constrains their ability to detect base modifications on RNA,which is an important element for the post-transcriptional regulation of gene expression.To comprehensively profile the N^(6)-methyladenosine(m^(6)A)and N^(5)-methylcytosine(m5 C)modifications on RNA,direct RNA sequencing(DRS)using the latest Oxford Nanopore Technology was applied to analyze the transcriptome of six tissues in rice.Approximately 94 million reads were generated,with an average length ranging from 619 nt to 1013 nt,and a total of 45,707 transcripts across 34,763 genes were detected.Expression profiles of transcripts at the isoform level were quantified among tissues.Transcriptome-wide mapping of m^(6)A and m5 C demonstrated that both modifications exhibited tissue-specific characteristics.The transcripts with m^(6)A modifications tended to be modified by m5 C,and the transcripts with modifications presented higher expression levels along with shorter poly(A)tails than transcripts without modifications,suggesting the complexity of gene expression regulation.Gene Ontology analysis demonstrated that m^(6)A-and m5 C-modified transcripts were involved in central metabolic pathways related to the life cycle,with modifications on the target genes selected in a tissue-specific manner.Furthermore,most modified sites were located within quantitative trait loci that control important agronomic traits,highlighting the value of cloning functional loci.The results provide new insights into the expression regulation complexity and data resource of the transcriptome and epitranscriptome,improving our understanding of the rice genome.