| With the rapid development of domestic and foreign remote sensing satellites and payload technology, data obtained by remote sensing satellite leaps and bounds. Therefore, the mainstream modulation, BPSK or QPSK, in the current satellite data transmission system is increasingly unable to meet the requirements of the satellite high-speed data transmission. The 16-QAM modulation representing for the high-level modulation has gradually been applied in the satellite high-speed data transmission system. This paper faces the design requirements of high-speed modulator in satellite data transmission system, uses the modern digital signal processing technology and makes full use of programmable logic devices and various high-speed hardware resources, finally, achievly designs and implements high-speed digital pulse-shaping filter and digital predistorter for RF power amplifier linearization. These two kinds of technology have been used in the baseband signal processing part of 16-QAM high-speed modulator in satellite data transmission system. As a result, they have not only significantly improved the spectrum utilization ratio and power efficiency of satellite data transmission system, but also laid the foundation for digital satellite data transmission system realization in future.First of all, the thesis has completed design and implementation of 800Mbps 16-QAM high-speed digital pulse-shaping filter, and the main technical indicators have reached domestic advanced level. During design of digital pulse-shaping filter, basis and method of selecting the FIR main parameter have been provided. Various aspects including hardware system speed, computation complexity, quality of filtered signals, spectral characteristic and the system BER performance have been analyzed and validated by simulation. In order to solve the bottleneck of high-speed digital shaping filter implementation, multi-phase filter structure and parallel look-up table have been proposed. Filter coefficients and symbol mapping in modulation method have been combined to form look-up table. Thus, it saved hardware multiplication and improved the hardware computational speed. Finally the principle prototype of Abstract 800Mbps high speed digital 16-QAM pulse-shaping filter has been implemented through parallel circuit structure and high-speed circuit technology.Secondly, predistortion linearization technique on digital RF power amplifier has been detailed studied. The thesis proposes a look-up table algorithm of digital predistortion and builds simulation model to validate it. Digital predistorter has been implemented according to a 2.3 GHz SSPA high power amplifier which is just applied to satellite data transmission system. The XtremeDSP Development Kit-IV Development board is used as mainly platform on which VHDL programming language is downloaded to the core chip Virtex?-4 FPGA. Through verification the predistorter can reduce intermodulation distortion of two-tone signal to 11dB, and greatly improve the RF power amplifier linearization level.Finally, 16-QAM high-speed modulator design in satellite data transmission system is studied, and the two technologies of high-speed digital shaping filter and RF power amplifier digital predistortion have been comprehensively and systematically implemented into the system. The dynamic simulation tool MATLAB/ SIMULINK has been used to build simulation model. Through analyzing the time domain waveform, constellation chart and BER performance, system has been sufficiently demonstrated correct, effective and feasible. In addition, according to the realization structure of 16-QAM high-speed modulator, RF power amplifier digital predistorter based on orthogonal structure has been formulated and designed. Through simulation test this method can effectively simplyfy system design and correct power amplifier nonlinear distortion. The algorithm for nonlinear distortion of orthogonal structure modulation system design has important theoretical significance and practical value.
|
PDF Full Text Request