This letter presents the principles of Coded Orthogonal Frequency Division Multiplexing (COFDM) system and focuses on the effect of the Guard Interval (GI) on the systemperformance. The role of the GI parameter period...This letter presents the principles of Coded Orthogonal Frequency Division Multiplexing (COFDM) system and focuses on the effect of the Guard Interval (GI) on the systemperformance. The role of the GI parameter period to solve the problem of interferences that occur at the receiver is discussed. A new COFDM concept with a Variable GI (VGI) is proposed in order to improve the Bit Error Rate (BER) performance in the presence of multipaths with variable delays. A series of simulations have been carried out on the BER performance as a function of GI, maximum delay spread, and Signal-to-Noise Ratio (SNR), with QPSK as modulation scheme over multipath fading and Additive White Gaussian Noise (AWGN). The results show that the optimum values of the GI parameter approximately equal to the maximum delay spread, and the proposed system with VGI provides a better performance compared with the fixed length GI.展开更多
Provided the results of a research conducted to investigate the relationships between the empirical vibration attenuation equation of Peak Particle Velocity （PPV） and the Scaled Charge （SC） through testing the bla...Provided the results of a research conducted to investigate the relationships between the empirical vibration attenuation equation of Peak Particle Velocity （PPV） and the Scaled Charge （SC） through testing the blasting-induced vibrations on the spot of Wanshishan tunnel based on 96 vibration recordings. It is found that the maximum charge amount per delay in Wanshishan tunnel excavating is determined by the buildings on the surface and the constructed tunnel nearby. Considering that the repeated blast loading in tunnel blasting caused accumulative effects of damage on buildings, comfortable threshold damage limits of PPV to maintain buildings safety was given. Dynamic Stress Ratio （DSR） was adopted to study the stability of constructed tunnel on the action of blasting induced vibrations. The method to determine specific maximum charge amount per delay in Wanshishan tunnel excavation was given. It is proved that the findings in this study are very effective to control the negative effects of blasting-induced vibrations on buildings on the surface and constructed tunnel nearby.展开更多
文摘This letter presents the principles of Coded Orthogonal Frequency Division Multiplexing (COFDM) system and focuses on the effect of the Guard Interval (GI) on the systemperformance. The role of the GI parameter period to solve the problem of interferences that occur at the receiver is discussed. A new COFDM concept with a Variable GI (VGI) is proposed in order to improve the Bit Error Rate (BER) performance in the presence of multipaths with variable delays. A series of simulations have been carried out on the BER performance as a function of GI, maximum delay spread, and Signal-to-Noise Ratio (SNR), with QPSK as modulation scheme over multipath fading and Additive White Gaussian Noise (AWGN). The results show that the optimum values of the GI parameter approximately equal to the maximum delay spread, and the proposed system with VGI provides a better performance compared with the fixed length GI.
基金Supported by the National Natural Science Foundation of China（50974059）
文摘Provided the results of a research conducted to investigate the relationships between the empirical vibration attenuation equation of Peak Particle Velocity （PPV） and the Scaled Charge （SC） through testing the blasting-induced vibrations on the spot of Wanshishan tunnel based on 96 vibration recordings. It is found that the maximum charge amount per delay in Wanshishan tunnel excavating is determined by the buildings on the surface and the constructed tunnel nearby. Considering that the repeated blast loading in tunnel blasting caused accumulative effects of damage on buildings, comfortable threshold damage limits of PPV to maintain buildings safety was given. Dynamic Stress Ratio （DSR） was adopted to study the stability of constructed tunnel on the action of blasting induced vibrations. The method to determine specific maximum charge amount per delay in Wanshishan tunnel excavation was given. It is proved that the findings in this study are very effective to control the negative effects of blasting-induced vibrations on buildings on the surface and constructed tunnel nearby.
