Identification And Parameters Estimation For OFDM Signals

With the development of communication technique, various modulation types will increasingly be complicated. In order to command the use of radio spectrum, the radio spectrum management department and the security department must keep communication signals under surveillance. Identification and estimation of signal's parameters for communication signals are very important to radio monitor and non-cooperative communication. They will support the following demodulation, communication nets analysis, identification of the user and even the identification of the radio's fine features. Identification of the signals and estimation of signals'parameters will classify the signals and estimate their parameters and modulation type from complex electromagnetic environment.Recently, with the development of Cognitive Radio technology and modern signal processing, lots of research has been explored for different modulation type and estimation of signals, especially single carrier serial signals, and much theoretic and practical progress has been made. But research on multi-carriers modulation recognition especially OFDM was rare. Base on this reason, multi-carriers modulation classification and parameters estimation are studied in this dissertation. The main achievements of this thesis include:1. Analysis of OFDM signals' characteristics. OFDM is more advanced communication system. To research the technique of OFDM signals'identification and parameters'estimation, it's necessary to analyze its characteristics. Basic principle of OFDM is introduced and analyzed in this thesis. Typical spectral characteristics are abstracted from above analysis, and the characteristics establish the foundation for OFDM signals'identification. An example of actual communication system is showed to analyze OFDM system basic characteristics. And possible procedure for OFDM parameters'estimation based on the interval of OFDM sub-carriers, the number of OFDM sub-carriers, the start and end frequency of OFDM sub-carriers is introduced in this thesis. 2. Simulation for identification and estimation of OFDM signals'parameters. Based on actual OFDM systems'characteristics, hypothesis and environment for the following algorithms are given. Algorithm based on signal amplitude spectrum to classify OFDM signals and single carrier serial signals, algorithm based on amplitude spectrum and auto-correlation to blind estimate the parameters of OFDM signals' sub-carriers, algorithm based on sub-carriers' instantaneous amplitude to estimate the symbol rate of OFDM signals' sub-carriers, improved algorithm based on constellation statistics to identify the modulation type of OFDM signals'sub-carriers are introduced respectively. And all the algorithms are simulated. The result of the simulations shows that the algorithms satisfy the request of identification and parameters estimation for OFDM signals. The algorithms are visual and simple.3. The flow of the total algorithms and a program used to identify OFDM signals and estimate their parameters. To all the algorithms introduced in this thesis, a flow for the identification and parameters estimation for OFDM signals is present. A program based on the flow to identify OFDM signals and estimate their parameters is developed. Some details about the program are described, too. The program is tested by actual signals. The test result indicates that the algorithms and the program are effective and useful, and the program can be used to identify and estimate the parameters for actual OFDM signals.