2FSK Communication System Demodulation Algorithm for Novel Acoustically Excited SLF Antennas
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摘要: 针对声波激励超低频天线发射功率较小, 低接收信噪比下传统二进制频移键控(2FSK)非相干解调中窄带滤波器设计难等问题, 提出了一种基于Duffing混沌振子的2FSK弱信号解调方法。由于Duffing振子本身对相位敏感, 首先设计了“粗同步+细同步”的相位同步方法, 其中粗同步通过短时傅里叶变换完成, 细同步则通过Duffing混沌振子实现; 然后, 利用混沌振子对同频周期信号敏感、对噪声信号免疫的特性, 将信号并行通过2个Duffing振子, 二者的内置信号频率与2个载频一致。在某一时刻必定有一个系统处于大尺度周期态, 另一个处于混沌态, 二者比较判决来实现信号解调。仿真结果表明, 文中提出的基于Duffing混沌振子的解调算法比非相干解调和相干解调算法, 分别有约5 dB和4 dB的性能提升。Abstract: There exist some problems for acoustically excited super low frequency(SLF) antennas, such as low transmission power and low received signal-to-noise ratio. In addition, it is difficult to design a narrow-band filter in traditional binary frequency-shift keying(2FSK) non-coherent demodulation. Therefore, a 2FSK weak signal demodulation method based on a Duffing chaotic oscillator was proposed. Because the Duffing oscillator itself was sensitive to the phase, a phase synchronization method of “coarse synchronization + fine synchronization” was designed. The coarse synchronization was accomplished through the short-time Fourier transform, while the fine synchronization was achieved through the Duffing chaotic oscillator. Then, the properties of the chaotic oscillator, such as being sensitive to the same-frequency periodic signal and being immune to noise signals, were utilized, and the signal passed through two Duffing oscillators in parallel, with the built-in signal frequency of the two being consistent with the two carrier frequencies. At a certain moment when one system must be in the large-scale periodic state and the other in the chaotic state, the two systems could be discriminated to realize signal demodulation. The simulation results show that the proposed Duffing oscillator demodulation algorithm outperforms the non-coherent and coherent demodulation algorithms by 5 dB and 4 dB in bit error rate, respectively.
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图 11 功率谱熵法与求和法BER比较图
Figure 11. BER comparison diagram between power spec- trum entropy method and sum method
图 12 不同解调算法BER比较图
Figure 12. Comparison of BER among different demodulation algorithms
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