Applied Mechanics and Materials Vols. 511-512

Abstract: Underwater acoustic channel is the biggest obstacle which causes the underwater acoustic communication falling behind the wireless communication. Generally speaking, underwater acoustic channel will represent doubly spread, i.e. multipath spread and Doppler spread. Also the multipath spread will be quite long in the underwater acoustic channel. For example, the multipath spread will be several milliseconds in the shallow sea and several seconds in the deep sea. Multipath spread will lead to Inter-Symbol Interference (ISI), and Doppler spread will cause the channel to be rapidly time-varying. Although ISI can be suppressed by channel equalizer, but because of the long multipath spread, it increases the complexity about the design of the equalizer. In this paper, channel shortening will be used to reduce the ISI. We present two methods of channel shorting, which are Time Reversal (TR) filter and the Minimum Mean Squared Error (MMSE) filter. When the two filters are used in FH-FSK, we found that the performance of MMSE filter is better than TR filter. Taking into account the characteristics of sparse underwater acoustic channel, Compressive Sensing (CS) algorithm is used for channel estimation. Finally, We perform a series of numerical simulations and the experiments on the lake to show that MMSE filter outperformances the TR filter under the FH-FSK system using the bit error rate (BER) as an evaluation criterion.

Abstract: Workshop information collection is the indispensable link in enterprise production. In view of the low efficiency, high error rate characteristics existed in traditional workshop information collection. This paper puts forward the idea of applying barcode to the production management, including products, materials, personnel and equipment. This method can realize the whole management of workshop condition, reduce the cost of enterprise production and enhance the competitiveness of enterprise. The above research has been applied in the machining process, which proves that to use barcode in the workshop management is feasible. The real underlying data is provided as reliable data support to make the workshop production platform.

Abstract: Weak signal detection has attracted many researchers attention all over the world. Most of the methods focus on the single frequency signal. This paper introduces a new method to separate the weak double-frequency signal overwhelmed in heavy background noise. The cascaded stochastic resonance (SR) system (CSRS) is composed of a bistable SR model in the first stage and a tristable one in the second. Based on the characteristic of the SR system, we can amplify the useful signal of high frequency using twice sampling technic to make its parameters matching the requirements of the system. In our proposed cascade stochastic resonance system, we highlight the appointed frequency from high to low successfully with adjusting the twice sampling multiple and the high pass filter band. The signal composition of different frequency can be obtained from the systems two stage output. Simulated experiment validates the CSRSs availability in weak double-frequency signal separation and also its promising application in a more complex mixed signal.

Abstract: Capability assessment of satellite communication system (SCS) is necessary for figuring out at what degree the system capability is and advising on how to reconfigure the system to improve its performance on data transmission. A new method for SCS capability assessment based on multi-granular modeling is presented in this text. A capability index system of SCS was established. Integration models for indexes were proposed. And mathematical models for indexes at last layer were proposed to improve the incredibility of assessment by analyzing the technical system of SCS. It is proved that the new method is feasible by an example of America SCS capability assessment.

Abstract: We report an indoor visible light communication (VLC) system by using of on-off-keying (OOK). Firstly, the magnitude of the channels frequency response was measured. Based on the measured data, we introduced the pre-equalization technology into the system. Finally, the system operated up to 312.5 Mbit/s with bit-error-ratios below 10^-6. The results were achieved for illuminance levels recommended by lighting standards.

Abstract: The issue of food safety is increasingly becoming the focus of social concerns, and breakage of packaging film is the main threat to the safety of sealing packaging food. For the small damage that is difficult to see with the naked eyes, according to that the impedance of damaged position is different from that of other position, the discharge signals of sealing packaging food in different damaged conditions are different in high voltage dielectric barrier discharge circuit, and then they are collected and analyzed. In order to solve the problem that different discharge signals are similar and characteristics are confused, wavelet packet and the EEMD method are novelly used to analyze discharge signals and the characteristic parameters of sealing packaging food that is intact or has pinholes are successfully extracted. This method solves the problem that the tiny damage is difficult to identify and detect, and it also provides a new train of thought for online test of sealing packaging food.

Abstract: According to the structure of a solenoid actuator, transient field mathematic model of two-dimension is established. Based on model, relationship between transient current of the coil and the motion of the armature is analyzed. Compared to experimental results, simulated results are proved, which are able to provide theory basis for displacement detection of electromagnet valve and fault diagnosis of valve and system by inner parameters of solenoid actuator. The results show that the rising current characteristic has the change process of increase-decrease-increase, and separating motion time of the solenoid actuator could be estimated to be 20 ms (18 v). The solenoid actuator is pulled back approximately in 8 ms under the action of the spring.

Abstract: The integral velocity error at the head end and the tail end of wave movement of ships or offshore platforms are too great. By improving the forecasting technique based on frequency spectrum, the integral velocity errors are maximally corrected and the wave movement of ships or offshore platforms is successful forecasted longer time ahead of time. Measurement technique of ship wave movement based on accelerometers array will be practically used.

Abstract: In this paper, a frequency-hopping frequency-shift keying (FH-FSK) underwater acoustic control and communication system based on Low Density Parity Check Codes (LDPC) is proposed by combining with FH-FSK system and LDPC. The anti-jamming performance of the system in the condition of Gaussian white noise and coherent multi-path channel is simulated respectively. The simulation result shows that FH-FSK system based on LDPC has a better performance than that of convolutional code. Therefore, it is more applicable for the system to have a stable anti-jamming performance and better robustness.

Abstract: After studying the research status of monitoring system for plant growth information, a system is developed with Kingview, VB and C to monitor soil temperature, soil moisture, air temperature, air humidity, Illumination and carbon dioxide. The system realizes real time monitoring, remote access, trend analysis and many other functions. Transmission distance is estimated by channel transmission loss model. Theoretical transmission distances are 1691.99m outdoor and 480.84m indoor. The real transmission distance is measured in the production base. The experimental communication distances are 1680m and 1520m in sunny and rainy day.