| Individual Transmitter Identification is a process to determine the transmitter individual of signal by measuring of the fine feature of transmitter signal with the existing prior knowledge. Fine feature extraction is the core technology of individual transmitter identification. Due to the same craft and model of different transmitter source individuals, the small differences of fine feature are hardly found by the current algorithms, which has a high requirement on the precision of the fine feature. In this paper, transmitter sources in satellite communication are studied, and the fine feature selection and high-precision extraction algorithms are proposed. Main content and innovations are summarized as follows:1. In this paper, the influencing factors of carrier frequency and symbol rate in Satellite communication link are particularly analyzed, the objective existence of differences in carrier frequency and symbol rate between different transmitter individuals is demonstrated, and the conclusion that the differences of symbol rate is less than the ones of carrier frequency is drawn. Firstly, the stability of carrier is tracked and counted by using CZT to extract carrier frequency and symbol rate. Secondly, in view of the CZT spectrum’s drawback in extraction precision, a symbol rate fine feature estimation algorithm is put forward based on timing estimation and piecewise precision. Specifically, on the basis the symbol rate estimated by CZT, the symbol rate estimation accuracy is further improved by estimating optimum sampling time and averaging timing estimation error to the long data segments. Due to the contradiction exists between symbol rate estimation precision and data length, the piecewise precision method is proposed based on iterative. By gradually increasing the data length used to estimate, the estimation precision is being improved until reach the estimated accuracy requirement. Finally, the detailed performance analysis and simulation verification are given.2. The paper points out that the I/Q imbalance parameter of quadrature modulator can be the fine feature of satellite communications transmitter sources. In the condition of the I/Q imbalance, the equivalent baseband signal is deduced from the input signal of quadrature modulator. Within the equivalent signal, the influence of the spectrum and constellation diagram made by quadrature modulator I/Q imbalance is analyzed in detail. At last, an algorithm to estimate the parameters of I/Q imbalance is put forward, which is based on geometry analysis of constellation.3. Hardware transmitter platform is designed, which can accurately control the generation of fine feature, to test the fine feature extraction algorithm proposed above. To make the platform accurately control the symbol rate subtle differences between generated signal, producing a certain range any symbol rate of baseband signal is needed under the condition of DAC sampling rate unchanged. What’s more, based on the take adjacent thought, a fixed sampling rate and any symbol rate baseband signal generation algorithm is put forward, which takes any multiple adjacent extraction from big integer times symbol rate baseband signal and equals deviation led by take adjacent to baseband signal SNR loss. In the end, theoretical derivation and simulation results show that little storage resource and computing resources can decrease the take adjacent deviation influence on baseband signal quality to little enough, which can meet the needs of the actual system, especially suitable for implementation in FPGA.4. The paper puts forward an any symbol rate frequency division multiplexed single channel DAC emission structure, which is based on the fixed sampling rate and any symbol rate baseband signal generation algorithm. This structure uses only one DAC channel, which can realize multiple different symbol rate signal transmit at the same time and overcome the wasting of resource problem led by traditional multi-channel DAC structure. |
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