ZoomFFT-Based Demodulation Algorithm for Underwater Acoustic OFDM Signals

doi:10.16182/j.issn1004731x.joss.20-0714

Abstract

Abstract:

The picket fence effect of fast Fourier transform (FFT) restricts the demodulation performance of the underwater acoustic(UWA) communication systemusing orthogonal frequency division multiplexing (OFDM). To solve this problem, we propose a demodulation algorithm based on ZoomFFT. Specifically, the received signal is processed by frequency shifting and downsampling forarefined spectrum, which improves the spectralresolution and weakens the picketfence effect.Meanwhile, the channel response is refined, and the channel equalization algorithm is constructed on the basis of the minimum mean square error (MMSE) principle to eliminate the channel influence. Simulations show that the performance of underwater acoustic OFDM demodulation algorithm based on ZoomFFT is better than that of traditional FFT, and the algorithm complexity is low. Increasing the downsampling coefficient can further enhance the algorithm performance. The proposed algorithm can meet the requirements of low complexity and high performance of a UWA communication system.

Key words: picket fenceeffect, ZoomFFT, orthogonal frequency division multiplexing (OFDM), underwater acoustic communication

CLC Number:

TN971.+1

Qing Guo, Angdi Li, Jing Wu, Haitao Su. ZoomFFT-Based Demodulation Algorithm for Underwater Acoustic OFDM Signals[J]. Journal of System Simulation, 2022, 34(2): 314-322.

Figures/Tables 10

Fig. 1

Table 1

Comparison of running time between ZoomFFT and FFT

不同分辨率条件	执行时间/ms
不同分辨率条件	ZoomFFT	FFT
$Δ f 1 = 23.44 D = 3$	$9.528 ? 045$	$9.722 ? 055$
$Δ f 2 = 17.58 D = 4$	$9.042 ? 610$	$17.521 ? 960$
$Δ f 3 = 11.72 D = 6$	$8.658 ? 230$	$22.209 ? 200$
$Δ f 4 = 5.86 D = 12$	$8.578 ? 310$	$32.603 ? 900$

Table 1

Fig. 2

Fig. 3

Table 2

Complexity of ZoomFFT algorithm

步骤	复杂度
串并转换	$Θ (N M)$
去CP	$Θ (N M)$
ZoomFFT	$Θ (N M / D + R N M / D + N 2 D l b (N / D))$
均衡器	$Θ (N M)$
总计	$Θ (N M / D + R N M / D + N 2 D l b (N / D))$

Table 2

Table 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

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仿真参数	参数值	仿真参数	参数值
DFT点数	2 048	细化倍数	[2,4,6]
子载波数	648	中心频率/kHz	29.1
采样率/kHz	144	凯瑟窗滤波器步长	45
频带/kHz	29.1~32.7	凯瑟窗滤波器系数	5