China Digital Radio (CDR) broadcasting is a new standard of digital audio broadcasting of FM frequency (87108 MHz) based on our research and development efforts. It is compatible with the frequency spectrum in analog FM radio and satisfies the requirements for smooth transition from analog to digital signal in FM broadcasting in China. This paper focuses on the signal characteristics and processing methods of radio-based passive radar. The signal characteristics and ambiguity function of a passive radar illumination source are analyzed. The adverse effects on the target detection of the side peaks owing to cyclic prefix, the Doppler ambiguity strips because of signal synchronization, and the range of side peaks resulting from the signal discontinuous spectrum are then studied. Finally, methods for suppressing these side peaks are proposed and their effectiveness is verified by simulations.
The bandwidth allocation bounds and admission control of a self-similar traffic input queue system are investigated. With the overflow probability of queue system, the analytic formulas about resource allocation are obtained. The results are succinct and effective. Because of the self-similarity in network traffic, the performance of queue system can be influenced greatly, which is different from that of Markov models in a long time and must be considered in network design.
Given the functions and performance advantages of passive radar, this paper first reviews the research history of passive radar for more than 80 years and then examines the research progress of related key technologies, including reference signal reconstruction, multipath clutter suppression, target detection, target tracking, and passive radar imaging. On this basis, the latest research results of typical experimental systems of passive radar abroad (particularly in European countries) are presented in terms of system structures, technical parameters, and performance indices. Then this paper focuses on the Multi-Illuminator-based PAssive Radar (MIPAR) series of Wuhan University in China. The target detection results of MIPAR in different frequency bands (HF/VHF/UHF/L) are given, that show the application potential of the MIPAR system in long-range early warning and close-range high-precision monitoring. Finally, the development trends of passive radar, including the integration of multiple illuminators, system network configuration, and intelligent signal processing, are discussed.
As it is an important development trend of passive radar by using multiple FM radio signals to improve detection performance, this paper presents a study on the phase compensation methods for high range resolution signal synthesis of multi-frequency passive radar. Firstly multi-FM radio received signal model is introduced and the impact of single-FM radio received signals phase on high range resolution signal synthesis is analyzed; then two phase compensation methods that are used to adaptively adjust the received signals phase are proposed to achieve the best signal synthesis effect. This paper not only elaborates in theory the internal mechanism of the methods, but also verifies multi-FM signal synthesis can distinguish adjacent targets based on the methods through simulation.
Flying birds and Unmanned Aerial Vehicles (UAVs) are typical “low, slow, and small” targets with low observability. The need for effective monitoring and identification of these two targets has become urgent and must be solved to ensure the safety of air routes and urban areas. There are many types of flying birds and UAVs that are characterized by low flying heights, strong maneuverability, small radar cross-sectional areas, and complicated detection environments, which are posing great challenges in target detection worldwide. “Visible (high detection ability) and clear-cut (high recognition probability)” methods and technologies must be developed that can finely describe and recognize UAVs, flying birds, and “low-slow-small” targets. This paper reviews the recent progress in research on detection and recognition technologies for rotor UAVs and flying birds in complex scenes and discusses effective detection and recognition methods for the detection of birds and drones, including echo modeling and recognition of fretting characteristics, the enhancement and extraction of maneuvering features in ubiquitous observation mode, distributed multi-view features fusion, differences in motion trajectories, and intelligent classification via deep learning. Lastly, the problems of existing research approaches are summarized, and we consider the future development prospects of target detection and recognition technologies for flying birds and UAVs in complex scenarios.
In this paper, the self-similar phenomenon in network traffic is analyzed. The modeling of self-similar traffic and its impact to the performance of network queue system is also discussed. Some useful results are obtained. Because of the character of long-range dependence in network traffic, the delay and jitter of queue system can be influenced greatly, which is different from that of Markov model in a long time and must be considered in network design.
While Wireless Fidelity (WiFi)-based passive radar can achieve high detection resolution in both the range and Doppler domain, it is difficult to extract the reference signal because of the complexities of its signal format and application scenarios. In this study, we analyze a typical application of WiFi-based passive radar and discuss different methods for reference signal extraction. Based on the format and features of WiFi signals, we propose a method for reference signal reconstruction, and analyze the influence of the reconstructed reference signal's performance on detection. The results show that higher reference SNRs generate lower decoding bit rate errors and better clutter suppression with the reconstructed reference signal. Moreover, we propose a method for removing irrelevant signals to avoid the impact on target detection of a non-direct path signal in the receiving signal. The experimental results validate the efficacy of the proposed signal processing method.
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