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
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
目的:探究不同刺激模式的经颅直流电刺激(transcranial direct current stimulation,tDCS)干预初级运动皮层(primary motor cortex,M1)对篮球运动员运动疲劳后运动技能习得的影响。方法:招募29名篮球运动员(女性9名、男性20名;年龄19.79...目的:探究不同刺激模式的经颅直流电刺激(transcranial direct current stimulation,tDCS)干预初级运动皮层(primary motor cortex,M1)对篮球运动员运动疲劳后运动技能习得的影响。方法:招募29名篮球运动员(女性9名、男性20名;年龄19.79±0.77岁;训练年限3.40±2.16年)按照平衡抵消法的顺序参与tDCS双侧正极刺激M1、tDCS正极刺激左侧M1(负极刺激右侧M1)和伪刺激实验,3种实验干预间隔至少1周。tDCS电流强度为2 mA,真刺激持续干预10 min,伪刺激仅在开始时持续刺激30 s。篮球运动员先进行递增负荷功率自行车运动诱导运动疲劳,随后进行tDCS干预,最后依次进行序列反应时任务(serial reaction time task,SRTT)和投篮命中率测试对受试者的运动技能习得能力进行评估。结果:在投篮命中率方面,双侧正极刺激M1组显著高于伪刺激组(P=0.010);在SRTT方面,双侧正极刺激M1组的各个组块平均错误数(组块2、3、7)低于伪刺激组(均P<0.05)。结论:tDCS双侧正极干预M1能够有效改善篮球运动员运动疲劳后的运动技能习得能力。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 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.
文摘目的:探究不同刺激模式的经颅直流电刺激(transcranial direct current stimulation,tDCS)干预初级运动皮层(primary motor cortex,M1)对篮球运动员运动疲劳后运动技能习得的影响。方法:招募29名篮球运动员(女性9名、男性20名;年龄19.79±0.77岁;训练年限3.40±2.16年)按照平衡抵消法的顺序参与tDCS双侧正极刺激M1、tDCS正极刺激左侧M1(负极刺激右侧M1)和伪刺激实验,3种实验干预间隔至少1周。tDCS电流强度为2 mA,真刺激持续干预10 min,伪刺激仅在开始时持续刺激30 s。篮球运动员先进行递增负荷功率自行车运动诱导运动疲劳,随后进行tDCS干预,最后依次进行序列反应时任务(serial reaction time task,SRTT)和投篮命中率测试对受试者的运动技能习得能力进行评估。结果:在投篮命中率方面,双侧正极刺激M1组显著高于伪刺激组(P=0.010);在SRTT方面,双侧正极刺激M1组的各个组块平均错误数(组块2、3、7)低于伪刺激组(均P<0.05)。结论:tDCS双侧正极干预M1能够有效改善篮球运动员运动疲劳后的运动技能习得能力。
