宽带可重构数字射频发射机关键技术研究

发布时间：2018-09-03 12:30

【摘要】：随着软件无线电技术的快速发展,接收机技术在国内外领域已十分成熟,然而宽带可重构数字射频发射机的研究却比较少。宽带可重构数字射频发射机直接采用数字化的混频器和频率合成器,简化了使用模拟器件所带来的电路设计和调试的复杂度,使无线通信系统性能变得更加稳定。本文首先提出一种宽带可重构数字射频发射机实现的整体方案,并主要分析了该发射机中基于FPGA实现的数字信号合成的具体方案,该数字信号合成主要包括数字上变频与特定频率的信号合成,并对其涉及到的关键技术如低通增量求和调制、极坐标转换、DDS数字调相技术进行了详细的分析。本文学习研究的主要成果如下:1)对涉及到的低通增量求和调制技术进行研究设计,该调制技术具有降噪抗干扰能力。基于MATLAB分别对一阶、二阶增量求和调制器进行SIMULINK建模,过采样率OSR均设为128,1 bit量化,最后通过仿真分析得出二阶调制器的信噪比约为99 d B,而一阶的约为73 d B,均与直接用信噪比公式计算出的值相近,同时对比二者最终输出信号的频谱图得出二阶调制器的降噪效果明显优于一阶,信噪比也明显提高了约26 dB的结论。2)对涉及到的极坐标转换技术进行研究设计,实现已调I、Q信号的极坐标转换。首先设定I、Q信号分别为频率5 Hz的余弦与正弦波,然后用MATLAB编程仿真得出极坐标转换后的极径r为一个常数,极角q为周期性变化锯齿波的结论。3)对涉及到的DDS数字调相技术进行研究设计,用来合成所需频率并具有相位调制的信号。首先建立SIMULINK模型,设置参考源cf为125 MHz,相位累加器位数N为20,分别让频率控制字K取2~15、2~13、2~11进行仿真,得到对应信号的频谱图,由频谱图得到信号频率分别约为2.45*10~7 rad/s,6.14*10~6rad/s,1.53*10~6 rad/s,结果满足该系统合成信号频f_0=K·f_c/2~N的计算公式,也进一步说明变化K就能调节DDS系统最终合成信号的频率值;其次,对实现普通的2PSK调制技术的键控法与模拟法进行SIMULINK建模仿真,为DDS数字调相技术的仿真验证奠定基础;最后,对DDS数字调相技术建立SIMULINK模型,各参数设置与之前的DDS系统相同,仅以K取182为例进行仿真,通过设置固定周期的偏转相位信号,最后输出2PSK信号,从而验证DDS系统具有数字调相功能。4)对该发射机中数字上变频与信号合成的整个方案在FPGA中实现,最终下载至FPGA开发芯片上,并调用CHIPSCOPE软件观察各个关键模块输出信号波形,计算得出输出信号的频率约为21.4 MHz,这与起初设置的频率控制字K取764504178对应的频率是相近的,从而验证整个方案的合理性。
[Abstract]:With the rapid development of software radio technology, receiver technology has been very mature at home and abroad, but the research of broadband reconfigurable digital RF transmitter is less. Digital mixer and frequency synthesizer are used directly in broadband reconfigurable digital radio frequency transmitter, which simplifies the complexity of circuit design and debugging brought by using analog devices, and makes the performance of wireless communication system more stable. In this paper, a whole scheme of broadband reconfigurable digital radio frequency transmitter is put forward, and the concrete scheme of digital signal synthesis based on FPGA in this transmitter is analyzed. The digital signal synthesis mainly includes digital up-conversion and signal synthesis at specific frequencies. The key technologies involved in the synthesis are analyzed in detail, such as low pass increment summation modulation, polar coordinate conversion and DDS digital phase modulation. The main results of this study are as follows: 1) the low pass incremental summation modulation technique involved is studied and designed. The modulation technology has the ability of noise reduction and anti-jamming. The first and second order increment summation modulators are modeled by SIMULINK based on MATLAB. The over-sampling rate OSR is all set to 12881 bit quantization. Finally, the simulation results show that the signal-to-noise ratio of the second order modulator is about 99 dB, and that of the first order modulator is about 73 dB, which is close to the value calculated directly from the signal-to-noise ratio formula. At the same time, comparing the spectrum of the two final output signals, the results show that the noise reduction effect of the second order modulator is obviously better than that of the first order, and the signal-to-noise ratio (SNR) is significantly improved by about 26 dB. 2) the polar coordinate conversion technology involved is studied and designed. The polar coordinate transformation of the modulated IQ signal is realized. First, we set the IQs signal as cosine and sine wave of frequency 5 Hz, and then we use MATLAB to simulate the polar diameter r is a constant. Conclusion .3) the DDS digital phase modulation technique is studied and designed to synthesize the signals with phase modulation and required frequency. First, the SIMULINK model is established, and the reference source cf is set to 125 MHz, phase accumulator bit N is 20, and the frequency control word K is selected to be 2 / 15 / 2 / 1 / 13 / 2 / 11 respectively for simulation, and the corresponding signal spectrum is obtained. The signal frequency obtained from the spectrum diagram is about 2.45 ~ 10 ~ 7 rad/s,6.14*10~6rad/s,1.53*10~6 rad/s, respectively, which satisfies the calculation formula of the synthetic signal frequency f _ s _ 0 K f_c/2~N. It is further proved that changing K can adjust the frequency value of the final synthetic signal of the DDS system. Secondly, the frequency of the final synthetic signal of the DDS system can be adjusted when the signal frequency is changed. The SIMULINK modeling and simulation of common 2PSK modulation technology are carried out by keying method and analog method, which lays a foundation for the simulation and verification of DDS digital phase modulation technology. Finally, the SIMULINK model of DDS digital phase modulation technology is established, and each parameter setting is the same as that of the previous DDS system. Taking only K 182 as an example to simulate, the 2PSK signal is output by setting the deflection phase signal of fixed period. The whole scheme of digital up-conversion and signal synthesis in the transmitter is realized in FPGA, finally downloaded to the FPGA development chip, and the output waveform of every key module is observed by using CHIPSCOPE software. The frequency of the output signal is about 21.4 MHz, which is similar to the frequency corresponding to the frequency control word K of 764504178, which verifies the rationality of the whole scheme.
【学位授予单位】：杭州电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN838

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