According to the signal-to-noise ratio （SNR） loss of average algorithms in direct P-code acquisition method, this paper analyzes the SNR performance of the overlap average algorithm quantitatively, and derives the r...According to the signal-to-noise ratio （SNR） loss of average algorithms in direct P-code acquisition method, this paper analyzes the SNR performance of the overlap average algorithm quantitatively, and derives the relationship of SNR loss with overlap shift value and initial average phase difference in the overlap average algorithm. On this basis, the bidirectional overlap average algorithm based on optimal correlation SNR is proposed. The algorithm maintains SNR consistent in the entire initial average phase difference space, and has a better SNR performance than the overlap average algorithm. The effectiveness of the algorithm is verified by both theoretical analysis and simulation results. The SNR performance of the bidirectional overlap average algorithm is 5 dB better than that of the direct average algorithm, and 2 dB better than that of the overlap average algorithm, which provides the support for direct P-code acquisition in low SNR.展开更多
P code direct acquisition is an important technology in satellite navigation system. As the P code has a long period, it is hard to directly acquire. The traditional average method can process multiple code phases in ...P code direct acquisition is an important technology in satellite navigation system. As the P code has a long period, it is hard to directly acquire. The traditional average method can process multiple code phases in a time to shorten the acquisition time. But with the increase of average phase error of the input signal and the local code, the correlation signal-to-noise ratio （SNR） loss increases. To reduce the SNR loss, an improved average method is introduced. A new sequence is generated with a summation of phase shifting sequences to decrease correlation peak loss. Simulation results show that compared with direct average method, the improved average method effectively increases correlation SNR.展开更多
According to the requirements of the high-sensitivity acquisition of Direct Sequence Spread Spectrum(DSSS) signals under ultrahigh dynamic environments in space communications, a three-dimensional joint search of the ...According to the requirements of the high-sensitivity acquisition of Direct Sequence Spread Spectrum(DSSS) signals under ultrahigh dynamic environments in space communications, a three-dimensional joint search of the phase of Pseudo-Noise-code(PN-code),Doppler frequency and its rate-of-change is presented to achieve high sensitivity in sensing high-frequency dynamics. By eliminating the correlation peak loss caused by ultrahigh Doppler frequency and its rate-of-change offset,the proposed method improves the acquisition sensitivity by increasing the non-coherent accumulation time. The validity of the algorithm is proved by theoretical analysis and simulation results. It is shown that signals with a carrier- to-noise ratio as low as 39 dBHz can be captured with high performance when the Doppler frequency is up to ±1 MHz and its rate-of-change is up to ±200 kHz/s.展开更多
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
Complement is a typical feature of Chinese grammar, and it seldom appears in other languages. Because of its complexity, it is very difficult for Chinese learners all over the world. The paper takes seven groups of si...Complement is a typical feature of Chinese grammar, and it seldom appears in other languages. Because of its complexity, it is very difficult for Chinese learners all over the world. The paper takes seven groups of simple directional complement （SDC）, ＂V-Shang＂, ＂V-Xia＂, ＂V-Jin＂, ＂V-Chu＂, ＂V-Kai＂, ＂V-Qi＂, and ＂V-Hui＂, as research goals. The investigation on second language acquisition （SLA） is carried out in terms of different native languages. The conclusion can be drawn that native language has a close relationship with SLA, because of their difference in Semantic Incorporation. In addition, the category of SDC is also an important factor influencing SLA.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
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
Recently, direct acquisition of GPS P-code has received considerable attention to enhance the anti-jamming and anti-spoofing capabilities of GPS receivers. This paper describes a P-code acquisition method that uses bl...Recently, direct acquisition of GPS P-code has received considerable attention to enhance the anti-jamming and anti-spoofing capabilities of GPS receivers. This paper describes a P-code acquisition method that uses block searches with large-scale FFT to search code phases and carrier frequency offsets in parallel. To limit memory use, especially when implemented in hardware, only the largest correlation result with its position information was preserved after searching a block of resolution cells in both the time and frequency domains. A second search was used to solve the code phase slip problem induced by the code frequency offset, Simulation results demonstrate that the probability of detection is above 0.99 for carrier-to-noise density ratios in excess of 40 dB. Hz when the predetection integration time is 0.8 ms and 6 non- coherent integrations are used in the analysis.展开更多
Focusing on the fast growth of BRICS＇ outward foreign direct investment （OFDI） and multinational companies during the crisis has left unheeded that some other emerging economies also grow much faster than average i...Focusing on the fast growth of BRICS＇ outward foreign direct investment （OFDI） and multinational companies during the crisis has left unheeded that some other emerging economies also grow much faster than average in the global economy and has become significant and fast-growing direct investors abroad. A sample of such （thirteen） new-wave emerging countries （NWECs） is gathered on the criterion of being ranked among the most significant foreign direct investors in the global economy. The literature review exhibits only very few articles existing on such a topic so far. Descriptive statistics enable tracing OFDI by NWECs-based multinational companies back to the 1970s, checking its geographical orientation and industrial structure, and assessing the relative importance of cross-border mergers and acquisitions. Econometric estimation exhibits that direct investment moving off the NWECs is explained by so-called push factors such as the home country＇s GDP, GDP per capita, GDP rate of growth, the share of high-technology exported products in overall export, the number of technological patents registered, and how much inward foreign direct investment discussed in the light of Dunning＇s investment development hypothesis. stock has previously been hosted. These results are path model and Matthews＇ linkage-leverage learning展开更多
基金supported by the National Natural Science Foundation of China(61102130)the Innovative Program of the Academy of Opto-Electtronics,Chinese Academy of Sciences(Y12414A01Y)
文摘According to the signal-to-noise ratio （SNR） loss of average algorithms in direct P-code acquisition method, this paper analyzes the SNR performance of the overlap average algorithm quantitatively, and derives the relationship of SNR loss with overlap shift value and initial average phase difference in the overlap average algorithm. On this basis, the bidirectional overlap average algorithm based on optimal correlation SNR is proposed. The algorithm maintains SNR consistent in the entire initial average phase difference space, and has a better SNR performance than the overlap average algorithm. The effectiveness of the algorithm is verified by both theoretical analysis and simulation results. The SNR performance of the bidirectional overlap average algorithm is 5 dB better than that of the direct average algorithm, and 2 dB better than that of the overlap average algorithm, which provides the support for direct P-code acquisition in low SNR.
文摘P code direct acquisition is an important technology in satellite navigation system. As the P code has a long period, it is hard to directly acquire. The traditional average method can process multiple code phases in a time to shorten the acquisition time. But with the increase of average phase error of the input signal and the local code, the correlation signal-to-noise ratio （SNR） loss increases. To reduce the SNR loss, an improved average method is introduced. A new sequence is generated with a summation of phase shifting sequences to decrease correlation peak loss. Simulation results show that compared with direct average method, the improved average method effectively increases correlation SNR.
基金supported by the Youth Science Fund,National Natural Science Foundation of China under Grant No.61102130
文摘According to the requirements of the high-sensitivity acquisition of Direct Sequence Spread Spectrum(DSSS) signals under ultrahigh dynamic environments in space communications, a three-dimensional joint search of the phase of Pseudo-Noise-code(PN-code),Doppler frequency and its rate-of-change is presented to achieve high sensitivity in sensing high-frequency dynamics. By eliminating the correlation peak loss caused by ultrahigh Doppler frequency and its rate-of-change offset,the proposed method improves the acquisition sensitivity by increasing the non-coherent accumulation time. The validity of the algorithm is proved by theoretical analysis and simulation results. It is shown that signals with a carrier- to-noise ratio as low as 39 dBHz can be captured with high performance when the Doppler frequency is up to ±1 MHz and its rate-of-change is up to ±200 kHz/s.
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.
文摘Complement is a typical feature of Chinese grammar, and it seldom appears in other languages. Because of its complexity, it is very difficult for Chinese learners all over the world. The paper takes seven groups of simple directional complement （SDC）, ＂V-Shang＂, ＂V-Xia＂, ＂V-Jin＂, ＂V-Chu＂, ＂V-Kai＂, ＂V-Qi＂, and ＂V-Hui＂, as research goals. The investigation on second language acquisition （SLA） is carried out in terms of different native languages. The conclusion can be drawn that native language has a close relationship with SLA, because of their difference in Semantic Incorporation. In addition, the category of SDC is also an important factor influencing SLA.
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Recently, direct acquisition of GPS P-code has received considerable attention to enhance the anti-jamming and anti-spoofing capabilities of GPS receivers. This paper describes a P-code acquisition method that uses block searches with large-scale FFT to search code phases and carrier frequency offsets in parallel. To limit memory use, especially when implemented in hardware, only the largest correlation result with its position information was preserved after searching a block of resolution cells in both the time and frequency domains. A second search was used to solve the code phase slip problem induced by the code frequency offset, Simulation results demonstrate that the probability of detection is above 0.99 for carrier-to-noise density ratios in excess of 40 dB. Hz when the predetection integration time is 0.8 ms and 6 non- coherent integrations are used in the analysis.
文摘Focusing on the fast growth of BRICS＇ outward foreign direct investment （OFDI） and multinational companies during the crisis has left unheeded that some other emerging economies also grow much faster than average in the global economy and has become significant and fast-growing direct investors abroad. A sample of such （thirteen） new-wave emerging countries （NWECs） is gathered on the criterion of being ranked among the most significant foreign direct investors in the global economy. The literature review exhibits only very few articles existing on such a topic so far. Descriptive statistics enable tracing OFDI by NWECs-based multinational companies back to the 1970s, checking its geographical orientation and industrial structure, and assessing the relative importance of cross-border mergers and acquisitions. Econometric estimation exhibits that direct investment moving off the NWECs is explained by so-called push factors such as the home country＇s GDP, GDP per capita, GDP rate of growth, the share of high-technology exported products in overall export, the number of technological patents registered, and how much inward foreign direct investment discussed in the light of Dunning＇s investment development hypothesis. stock has previously been hosted. These results are path model and Matthews＇ linkage-leverage learning
