Environmentally-adaptive secure routing protocol for satellite networks

In order to solve the security problem of data transmission in Low Earth Orbit(LEO) satellite networks, a novel secure routing protocol is designed. First, by considering two aspects of satellite behavior attribute and communication capability attribute, a multi-dimensional security evaluation model is established, and the model for evaluating the satellite security communication capability is dynamically adjusted with the network state. Then, combined with the on-demand routing protocol, the secure communication path is established by taking the quantitative evaluation of satellite security communication capability as the routing metric. Finally the forwarding behavior of nodes in the transmission path is monitored in real time, and the routing reconstruction is triggered as needed. Simulation results show that, compared with the existing protocol, the proposed protocol can significantly improve the performance of the packet delivery rate, average end-to-end delay and average hop than the existing protocol when malicious nodes exist in the network. The protocol can effectively improve the security of data transmission in LEO satellite networks.     

Design of a satellite communication phased array antenna in the S-band

The phased array antenna for satellite communication has a smaller beam-scanning angel and a lower gain at the low elevation angel at present. A circularly polarized (CP) antenna element with a wide beam-width in the S-band is proposed. To enhance the realized gain at a low elevation angel, this element is adopted with the dual-layer micro-strip structure and loads a circular metal cavity. Based on the element, a phased array antenna composed of 24 antenna units is designed, which has a water-drop form to reduce wind resistance. The simulated results show that over the transmitting and the receiving frequency band, the voltage standing wave ratio (VSWR) of this element is less than 1.3, that the axial ratio (AR) is less than 3dB, and that 3dB beam-width of the element is about 120° in the array; the realized gain of the array is declined about 4dB when the scanning angle is approaching 65°. Later, the measured results of the manufactured array antenna present a good consistency with the simulated results. It possesses a wide scanning angle and a high realized gain at low elevation angel, which satisfies the design requirement.     

Analysis of echo correlation in diversity MIMO radars

For the target echo correlation, the existing target model has a huge limitation which just represents the angle or frequency interval with respect to the station, but ignores the influence of target attitude. To solve this problem, this paper utilizes the four straight prism scattering model to better simulate the true target, and the research shows that the correlation coefficient is affected by the observed direction, target size, spatial and frequency interval at the same time in the diversity MIMO radar. The study focuses on the variation of the targets effective size with the observed direction and spatial size in the case that the radars stay at different positions, which influences the correlation coefficient severely.     

Cumulative distribution function based resource allocation in the uplink of the small cells network

In order to reduce co-channel interference and improve spectrum efficiency in the uplink of the small cells network, the joint cumulative distribution function based user scheduling and distributed power allocation are proposed. In the proposed scheduling, the small cell base station selects the user having the largest cumulative distribution function value. The selected user adjusts its transmit power to reduce the co-channel interference to other cells based on a pre-determined threshold. We then transform the original global optimization problem into a distributed problem and attain the optimal transmit powers through Lagrangian dual decomposition. Simulation results show that the simplified algorithm has the performance hearly identical to that of the conventional optimal power allocation algorithm.     

Technology of the improvement on the output accuracy of DDS

In today's widely used direct digital frequency synthesis technology, there is a slight difference between the actual output frequency and the frequency to be generated due to the rounding of the frequency control word. In this paper, the phase accumulation process in the direct digital frequency synthesizer is controlled to basically realize a direct digital frequency synthesis technique without the mantissa frequency. The design and control process is optimized by the phase difference variation characteristics between the actual output frequency and the theoretical frequency. Experimental results show that the technical scheme can effectively reduce the influence of the mantissa frequency in the direct digital frequency synthesis technology by nearly ten thousand times, and the control process has a little effect on the phase noise, frequency stability, and other indicators of the output signal.     

Method of array antenna DOA under strong interference presence

In order to solve the problem of DOA estimation for the array antenna under strong interference,the concept of preserving orthogonality and characteristic beam is defined. It is proved theoretically that the characteristic vector of the corresponding feature vector is guaranteed when the source power and the angle interval are both large. And a novel DOA estimation algorithm based on the interference source feature vector is proposed. Through the simulation and comparison of JJM algorithm it is shown that the proposed algorithm has a better statistical estimation performance than the JJM algorithm.     

Robust energy efficiency optimization for secrecy MIMO systems with SWIPT

This paper investigates the secrecy energy efficiency optimization for simultaneous wireless information and power transfer in the multiple-input-multiple-output wiretapping system which consists of multiple eavesdroppers (Eves). In the presence of imperfect channel estimation ,the beamforming matrix, the artificial noise covariance matrix and the power splitting ratio are jointly designed to maximize the worst-case secrecy energy efficiency under the maximum transmit power and the minimum harvested energy constraints. Due to the non-convexity of this problem, the objective function is recast into an equivalent parametric problem by exploiting the fractional programming theory, and then the non-convex equivalent problem is approximated as a convex optimization problem by means of the S-Procedure and first order Taylor series expansion. Furthermore, a two level optimization iterative algorithm is proposed based on the Dinkelbach method. Finally, simulation results are provided to show the effectiveness and convergence of the proposed algorithm.     

Research on data transmission and survivability technology of the GEO/LEO satellite network

Aiming at the problem that Low Earth Orbit satellites have a low real-time performance in transmitting data to the ground, a data transmission and survivability technology based on the double-layer satellite network is proposed. In the method, the Geosynchronous Earth Orbit satellite network is used as the communication backbone network, which is responsible for the relaying and forwarding of the data in the satellite network. The low-earth satellite layer is responsible for data collection and auxiliary routing. Combining the advantages of Geosynchronous Earth Orbit and Low Earth Orbit satellites can realize the real-time transmission of Low Earth Orbit satellite data. The multi-path transmission strategy improves the survivability of the satellite network. The performance of the proposed method is analyzed in terms of throughput, transmission delay, delay jitter and packet loss rate. Under the attack environment, the data delivery capability of the network is studied. The data transmission method based on the multi-layer satellite can solve the single-layer low-earth satellite network in data transmission, and satisfy the requirement of multi-service real-time transmission.     

Multiple convolutional neural networks for facial expression sequence recognition

As an important part of the human-computer interaction system, facial expression recognition has been a hot research field. The convolutional neural network cannot recognize expression sequence although it can train the classification features automatically for the reason that the direction of feature training need to be specified manually. In order to solve this problem, this paper improves the network structure, and proposes a multi convolutional network fusion method that can be used to identify the expression sequences containing multiple frames. First, we construct a number of convolutional neural networks, so that each network processes one frame, and then merge the results in the merge layer, and finally pass the softmax classifier to give the identity result. On the CK+facial expression database, experiments are carried out on the 3rd, 4th and 5th frames of expression sequences, and a high recognition rate is obtained for all experiments.     

Measurement matrix construction based on empirical mode decomposition

In order to maintain the integrity information on the signal in high probability, the measuremental matrix is designed to be a random one. But this randomness results in the fact that both useful information and useless information are near the equiprobably measured, which leads to a low sensing efficiency. To improve the sensing efficiency, this paper proposes a new method of measurement matrix construction based on Empirical Mode Decomposition of the reference signal. It uses the Intrinsic Mode Function to construct a cyclic matrix, which is proved to satisfy the restricted isometry property condition by the Gersgorin disc theorem. It simulates the signal denoising process and uses signal noise reduction as the measure. Simulation results show: (1)it has a better effect on reducing noise by adding noise to the reference signal; (2)when the noisy signal and the reference signal are dislocated in the time domain, the effect of noise reduction is significantly decreased compared with the ideal condition. However, the reconstructed signal maintains its frequency information well, which is helpful in practical applications.