The Research On Transient Detection Theory And Application Technology Of OFDM System

This paper mainly studies the transient detection theory which is expounded as a new method to detect signal by the transient characteristic difference between the base band digital signal symbol waveforms and the additive noise. It varies from the traditional statistical detection methods in strong noise, which is mainly use of differential equation method to perform signal detection. First, the interference differential equation is given out only containing the measured received mixed signal and interference function, which have eliminated the detected signal. Second, the solution of interference can be solved through the interference differential equation which is already gotten. Finally, the detected signal can be recovered by the received mixed signal subtracting the interference which has been gotten from the interference differential equation.The base band signal function must be eliminated in the differential equation based on transient detection theory, so the signal function should be selected to make its polynomial summation in the differential equations of polynomial equals zero, then, te"at is to be selected as signal function based on the analysis and study through differential equation deducing, and the solution which make use of numerical analysis is given out from the first-rank interference differential equation, the simulation software and hardware system is designed for digital signal processor and the correctness of the theory is verified through those experiments.The problems of adjacent channel interference and intersymbols interference must be solved in the process of transient detection theory which is applied in the practical communication. Because frequency in the signal function of te-αt is relatively rich, the waveform of signal is distorted when it is through sharp cutoff filter. That will cause high Pe rate in transient detection, it is very adverse for detection. According to the characteristics of selected symbol function, the method about spectrum truncation compensation is taken to eliminate the adjacent channel interference and recovery of signal spectrum which should be detected. First, using a single without any interference symbol will be processed in FFT, then a series of coefficients will be gotten through comparing the outside points and the inside points of truncation, these coefficients are stored in the memory of digital signal processor. Finally, the digital signal processor processes sample of the actual signal with FFT, truncation and the all detected signal spectrum can be recovered after calculating with stored coefficients and inner points which is kept after truncation, so the source signal containing no adjacent channel interference can be gotten from Inverse Fast Fouier Transform (IFFT).The method of transient detection is proved entirely correct based on those above, the experimental system to eliminate adjacent channel interference is established from what is expounded above.Quicker speed data transmission is one of the goals in data communication. A new method which improve transmission rate can be derived in virtue of coefficient comp-ensation calculation method to inhibit the interference of adjacent channel in a narrow band, the transmission rate can be improved about 4 times by the transient detection method and does not increase the bandwidth in the same Pe. The method has applied SSB in 725 wireless basestation on vehicles. The transient detection method plays an important role in high speed data transmission, anti strong same frequency interference and secure communication.OFDM is a communication technology which is also a communication technology used for 3G and 4G in the future. The performance of inhibition of adjacent channel interference in the sub-carrier channel of OFDM will be improved by aid of characters of transient detection method in determinate weak signal detection. Then, the purpose to improve the transmission efficiency and reduce Pe will be realized in the ODFM sub-channel.There is entirely difference principle between the transient detection theory and the traditional detection method. The transient detection theory has incomparable superiority in the fight against strong noise and interference in the same frequency, its principle can not be limited by Shannon channel capacity formula because the transient character is adopted based on interference differential equation. It is a breakthrough in digital signals detection area. It opens up a new field of study for weak known signal detection theory and high speed data transmission. Because the transient detection theory has unique characteristics in anti strong interference of the same frequency, it also can be used in secure communication and electronic countermeasure at the same time. It has extremely high academic and economic value.