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In recent years, with the popularity of crime prevention system, which plays a positive role in the field of crime prevention. But a number of security facilities are wasted due to no risk optimization of crime prevention system. This paper firstly establishes a risk optimization model on crime prevention system. Secondly, combinatorial optimization technology is used to calculate this model. Finally, a concrete example is given out to verify the model reasonably. This optimization model can not only guide security facilities more rational allocation and scheduling scientifically and effectively but also fully utilizes the protection capability of crime prevention system. It has great theoretical significance to the planning and layout on crime prevention system in the future.

Carrier frequency synchronization is the critical technique in orthogonal frequency division multiplexing (OFDM) systems. In this paper, an improved carrier frequency offset (CFO) estimation method is proposed, which divides the Schmidl’s CFO estimation into coarse and fine estimation by using PN sequence iteration, the new method has higher estimation accuracy and larger estimation range than that of Schmidl’s method in presence of the same computational complexity. The theoretical low bound of CFO estimation is derived by two mathematical methods. The validity of the new algorithm is verified in AWGN and multipath fading channels.

With the rapid development of industrialization and urbanization, crime prevention issues become serious in China each day. Although various security facilities have played a positive role in the field of crime prevention, defects exist in poorly designed systems targeting detection, delay, and response. Due to the absence of theoretical methods and technical means for scientific evaluation on the effectiveness, it is difficult to support a complete and efficient deployment of a comprehensive prevention and control system. Therefore, it is a major strategic task to improve effectiveness evaluation techniques and promote the objective evaluation of the effectiveness in such area. In this paper, firstly, adversary sequence diagram and intrusion path analysis model are established to describe the facilities and all the intrusion path of crime prevention system. Secondly, the path prompt detection analysis method of crime prevention system is introduced to evaluate its effectiveness quantitatively according to the adversary sequence diagram. Lastly, quantitative analysis on three elements (detection, delay, and response) of crime prevention system is presented with an imaginary example in the museum crime prevention. The results indicates that the path prompt detection analysis method works effectively to find the weak point of the crime prevention system in the museum, and meanwhile we can also get the high cost-effectiveness improved measures. It is an effectiveness approach to evaluate the overall effectiveness of the system.