An efficient demodulation algorithm for CSK modulated signals based on partial output FFT
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摘要: 为了实现精密星历数据的高速率播发，码移键控(CSK)调制技术将是下一代卫星导航系统的重要选项. CSK调制信号在解调时需要遍历计算各种码相位偏移的相关值，因此通常使用基于快速傅里叶变换(FFT)的频域解调算法. 根据CSK频域解调仅需FFT部分输出结果的特点，提出了基于部分输出FFT的CSK信号频域解调算法. 该算法对传统FFT的蝶形解算结构进行优化，通过定义计算节点以消除与输出结果无关的计算，从而降低解调的计算复杂度. 以码率为1.023 Mcps的CSK(4,1023)调制信号为例，所提算法可节省约45.6%的计算量，这对下一代卫星导航接收机的设计具有重要的意义.
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关键词:
- 卫星导航 /
- 码移键控(CSK)调制 /
- 信号解调 /
- 快速傅里叶变换(FFT) /
- 计算复杂度
Abstract: In order to broadcast precise ephemeris data with high speed, code shift keying (CSK) modulation is likely to be adopted in next generation satellite navigation system. The correlation values of various code phase offsets are needed during demodulation, so the frequency domain demodulation algorithm based on fast Fourier transform (FFT) is usually used. According to the characteristic that only partial output are needed in CSK frequency domain demodulation, an efficient demodulation algorithm for CSK signal based on partial output FFT is proposed in this paper. The algorithm optimizes the butterfly-shaped structure of traditional FFT, and reduces the computational complexity of demodulation by defining computing nodes to eliminate invalid computations irrelevant to the output results. Taking the CSK(4,1023) modulated signal with a code rate of 1.023 Mcps as an example, the algorithm proposed in this paper can reduce about 45.6% of the calculation, which is of great significance to the design of the next generation satellite navigation receiver. -
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