In this paper, we analyze the characteristics of pseudo-random code, by the case of m sequence. Depending on the description of coding theory, we introduce the jamming methods. We simulate the interference effect or probability model by the means of MATLAB to consolidate. In accordance with the length of decoding time the adversary spends, we find out the optimal formula and optimal coefficients based on machine learning, then we get the new optimal interference code. First, when it comes to the phase of recognition, this study judges the effect of interference by the way of simulating the length of time over the decoding period of laser seeker. Then, we use laser active deception jamming simulate interference process in the tracking phase in the next block. In this study we choose the method of laser active deception jamming. In order to improve the performance of the interference, this paper simulates the model by MATLAB software. We find out the least number of pulse intervals which must be received, then we can make the conclusion that the precise interval number of the laser pointer for m sequence encoding. In order to find the shortest space, we make the choice of the greatest common divisor method. Then, combining with the coding regularity that has been found before, we restore pulse interval of pseudo-random code, which has been already received. Finally, we can control the time period of laser interference, get the optimal interference code, and also increase the probability of interference as well.
Nowadays the technology of laser positioning based on four-quadrant detector has the wide scope of the study and application areas. The main principle of laser positioning is that by capturing the projection of the laser spot on the photosensitive surface of the detector, and then calculating the output signal from the detector to obtain the coordinates of the spot on the photosensitive surface of the detector, the coordinate information of the laser spot in the space with respect to detector system which reflects the spatial position of the target object is calculated effectively. Given the extensive application of FPGA technology and the pseudo-random sequence has the similar correlation of white noise, the measurement process of the interference, noise has little effect on the correlation peak. In order to improve anti-jamming capability of the guided missile in tracking process, when the laser pulse emission, the laser pulse period is pseudo-random encoded which maintains in the range of 40ms-65ms so that people of interfering can’t find the exact real laser pulse. Also, because the receiver knows the way to solve the pseudo-random code, when the receiver receives two consecutive laser pulses, the laser pulse period can be decoded successfully. In the FPGA hardware implementation process, around each laser pulse arrival time, the receiver can open a wave door to get location information contained the true signal. Taking into account the first two consecutive pulses received have been disturbed, so after receiving the first laser pulse, it receives all the laser pulse in the next 40ms-65ms to obtain the corresponding pseudo-random code.
Laser positioning technology in the world has a very broad application prospects. With the development of technology and enhancement of productivity, the technology of positioning accuracy and the detection region also need to improve. There are key factors for laser positioning system, including performance of photosensitive devices, localization algorithm and signal processing circuitry, which are important in determining the performance advantages and disadvantages. Therefore, we need to study in-depth research and improvement to enhance the overall performance of the detector. In this paper, after analyzing the principle of mainstream photo-sensitive induction device, we focus on the current and various positioning algorithms which are widely used. Then use simulation to compare the advantages and disadvantages of each method. Based detector probe in the actual working conditions, we analyze the reasons for the differences in the measurement detector sensitivity, linearity, etc., and provide noise and uniformity correction algorithm while improving on the previous probe calibration method. According to the distribution of the incident light energy, we improve the mathematical model of the original description of the received light energy in each quadrant. Based on the Gaussian distribution of light energy, light intensity correction algorithm is proposed in order to meet the needs of the actual probe. Based on the selected four-quadrant detector APD, we design and build a complete laser positioning system. At last, we design and build the experimental system which can be used to test the main parameters including measurement accuracy and response range of the four-quadrant detector, so the laser positioning system has been tested and verify the feasibility of the system. This paper has mainly innovation in the localization algorithm on the detector.
Crystal growth of KTiOPO<SUB>4</SUB>(KTP) family with flux method has been summarized. The results of defect observation with synchrotron radiation topography and other methods have been reported. It is shown that KTP crystal is of high-quality and there exist different kinds of defect such as growth striations, multiple domains in doped KTP and KTA crystals. The observation and discussion about the bicrystal of KTP family crystal have been mentioned in the paper. SHG and SFG measurements indicated that KTP family crystals investigated have excellent nonlinear optical properties.