基于FFT和相干累积的DS/FH测控信号捕获算法

FFT-and-coherent-accumulation-based acquisition of DSFH TT&C signal

为解决相干跳频和直接序列扩频结合的抗干扰测控信号在大时差大多普勒条件下快速捕获的问题,采用基于FFT并行相关的分段码相关算法,实现积分时长为单个跳频段的快速码相位滑动相关;采用相位补偿算法,补偿各个跳频段间因时间差、跳频频率和多普勒导致的相位差,实现了较大多普勒频偏条件下跳频段之间的相干累加。与非相干累加相比,本算法消除了大时差大多普勒条件对信号长时间相干累积的影响,在某信号体制下检测性能提升9 d B,代价是算法复杂度随捕获时间分辨率的增加而线性增加10倍。本算法可改变搜索精度,能灵活适应不同应用背景下扩频应答机的计算资源限制,目前已经应用于某卫星系统的测控应答机。

To deal with the acquisition of a hybrid direct-sequence and fast-frequency-hopping（DSFH） spread spectrum signal under large Doppler and time delay, this paper used an FFT-based code correlator to perform the fast slide-correlation in each hop, a phase-compensation-based accumulator to compensate the phase errors between different hops and perform the coherent accumulation among several hops under large Doppler frequency. This paper analyzed the signal-to-noise ratio loss and the complexity of the proposed algorithm and verified the detection performance through simulations. Comparing to non-coherent accu-mulation, the algorithm improves the detection performance by 9 dB at the expense of a ten-time increase of computation complexity. This algorithm is currently running in a satellite TT＆C responder and the searching resolution can be changed to fit different application scenario.