Key Techniques Of Digital Intermediate Frequency Receiver

Due to worse electromagnetic environments where modern electronic receiving devices often work,analog receiving systems with worse anti-jamming abilities and agility unable to adjust. After 1980's, in order to utilize fully the digital signal processing techniques with higher reliability, better anti-jamming ability and agility,analog receiving systems are digitized gradually. And at the beginning of 1990's, the software defined radio is proposed. However, it is a tradeoff project to develop digital intermediate frequency receivers because of the imitations of analog-to-digital converter, digital signal processing, etc. Therefore,it's significant to develop highly effective telemetry digital receivers, which can be used to digitize the telemetry communication receiving systems, improve the performance of the telemetry communication receiving systems, and implement the desired receiving systems based on software radio.At present, the existing telemetry communication receiver systems have following problems: there are many kinds of models and they are incompatible, the volume of receiver equipments are so big that it is convenient to work in fieldwork with them, there are different parameters for the receiver equipments of different models, the upgrading and updating of receiver equipments need replacing the hardware equipments with long time, high costs. The only approach to resolve those problems is to research and develop the new telemetry communication receiver equipments which can recognize the modulation modes and modulation parameters of telemetry signals and can accomplish the demodulation of multimode modulation signals. That is, a universal telemetry platform with openness, standardization and modularization is designed by means of digital techniques, software defined radio techniques, system on chip techniques, field programable gate array techniques and dynamic reconfiguration techniques in order to realize the new generation telemetry communication system with incorporate and intellectualized design. With the rapid development of the digital signal processing techniques, it is feasible to realize the new telemetry communication receiver equipments.Therefore, the research emphases in this dissertation are the key techniques of the digitalized reciving. That is, the universal telemetry platform with incorporate is designed by means of the research on the digital modulation automatic recognition techniques, the digital modulation parameter estimation techniques and the digital modulation signal noise ratio estimation techniques.Firstly, the different modes modulation signals received are needed to classify and recognize automatically in order to realize the telemetry digital receiver with the demodulation of multimode modulation signals. After analyzing the different modulation methods proposed in the literatures carefully, we propose the recognition algorithm based on decision-tree. Compared to traditional recognization algorithms, it is used to recognize modulation signals with higher recognization rates and lower computational complexity. As result, it will be used with applied cost. After analyzing the automatic recognization techniques based on wavelet transform, we put forward a recognization algorithm which is used to recognize digital telemetry modulation signals with the amptitude, frequency and phase informations. The simulation results show that the algorithm proposed in this paper may be used to recognize modulation signals with higher recognization rates under additive gauss white noise channel.Secondly, in view of engineering application, two carrier frequency estimation algorithms adapting to the hardware implemention with short datas are given in order to receive the telemetry digital modulation signals with unknown carrier parameters. On other words, one is based on the extention of the Prony's method, and the other is based on linear fitting. At the same conditions, the simulation results show that the linear fitting algorithm can work with better frequency estimation performance. As far as the hardware implementation is concerned, the extention of the Prony's method can work with little operand and better real-time.In order to receive the telemetry digital modulation signals with unknown carrier parameters, the symbol rate estimation algorithm based on harr wavelet is proposed, in which the characteristic signals is the optimum scale factors signals. Compared to traditional estimation algorithms, it is used to estimate symbol rate with better antinoise and precision, sampling frequency may be choosed arbitrarily, and the threshold is not need setting. Therefore, the influence of the threshold on the symbol rate estimation is removed. In addition, the symbol rate estimation algorithm based on templet matching is put forward. The new algorithm can estimate the symbol rate without transcendental information more accurately, and its computational complexity is between the one of classic delay multiplication algorithm and the one of cycle correlation algorithm.Then, after analyzing the signal noise ratio estimation carefully, we propose two non-data aided signal noise ratio estimation algorithms for the sake of the realization of the polarization diversity receiving. One is the modified algorithm based on eigenvalue decomposition and the principle of minimum description length,which is independent of the modulation mode of receiving signals. The simulation results show that it is used to estimate the signal noise ratio precisely in AWGN channel. The other is the algorithm based on Gibbs sampler. The new algorithm can estimate the signal noise ratio without transcendental information and with shorter datas. The simulation results show that it is used to estimate the signal noise ratio with better performance than traditional algorithms in AWGN channel.Lastly, after analyzing the traditional polarization diversity combing scheme carefully, a new modified polarization diversity combing scheme is proposed. Compared to the traditional two phases locked loop structure, it is better with simpler implemention and more flexiable control. Considering the available devices, we newly developed a PCM-FM telemetry digital diversity receiver system based on FPGAs. The test results of the practical system show that it can accomplish the telemetry communication receiving better, which is of great actual value.