The Research On Android Software Reliability Test

Underwater acoustic(UWA) communication is the most important tool for wireless information transmission in underwater. With mobile platforms such as the Autonomous Underwater Vehicle(AUV) more and more extensive application in exploration and exploitation of marine resources and the urgent need to construct data network of UWA communication, mobile UWA communication is becoming a necessary technology in them. Moreover, because the mobile craft is small and flexible, its speed is much higher than the general one. Therefore, high-speed mobile UWA communication becomes a hot research around the world now.However, due to the low propagation speed of sound in water, there is inevitably serious Doppler spread in high-speed mobile UWA communication. It makes the communication signal become distorted, affecting the correct demodulation of the receiver. Therefore, it is necessary to estimate the Doppler spread and make corresponding compensation before the receiver's demodulation. The existing Doppler estimation and compensation methods generally assume the Doppler factor of each path in multipath channel is equal or approximately equal. But when the underwater vehicle moves in high speed, the Doppler factor of each path is larger and no longer the same, which leads to poor or failing results using the current methods.To solve this problem, the paper conducts an intensive research on non-uniform Doppler estimation and compensation techniques based on high-speed mobile UWA communication as the application background. By scouting for the sparse characteristics of UWA channel, a sparse representation theory based non-uniform Doppler estimation method is proposed in the paper using the time-varying filter with additive noise as the channel model. The proposed method converts the Doppler estimation problem to the sparse signal reconstruction one by utilizing a pre-generated over-complete redundant dictionary. Thereby the Doppler factor of each path in multipath channel can be estimated indirectly from the reconstructed results.Simulation results show that the proposed method can estimate not only the quite different Doppler factors but also the large Doppler frequency offset.After the study of non-uniform Doppler estimation in UWA channel, the paper also focuses on how to achieve Doppler compensation for orthogonal frequency division multiplexing(OFDM) communication system using the results of non-uniform Doppler estimation. Because of the Doppler sensitivity of OFDM itself,achieving non-uniform Doppler compensation exactly is significantly important in high-speed mobile UWA communication. Based on the existing techniques, an OFDM Doppler compensation method is proposed through a detailed theoretical analysis. A compensation receiver is also designed according to the method. The proposed technique uses multiple interpolations combined with the fast Fourier transform(FFT)algorithm. After a single resampling preprocessing aiming to reduce the size of the Doppler factor, an equivalent channel parameter model is considered. Finally, the OFDM is demodulated using the channel statistics obtained by multiple interpolation and FFT from the equivalent channel. Numerical simulation results show that the proposed receiver has a high Doppler compensation performance in different channel status. Especially when the non-uniform Doppler spread is quite serious, the performance of the method is much better.