適用於GPS導航接收機多重窄頻干擾源消除之頻域數位訊號處理

Frequency Domain Approach for Multiple Narrowband Interference Cancellation in GPS Receivers

陳基孝(Chi-Hsiao Chen)

指導教授 ： 曹恆偉

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.11202

摘要

GPS衛星導航系統現今已經普及運用於民生和各種電子產品。當GPS晶片和其他無線通訊系統整合時會產生諧波(Harmonic)干擾問題。因此我們需要額外的消除干擾機制來處理干擾源問題。
本論文的干擾消除機制是參考文獻提出的Consecutive Mean Excision (CME)演算法，提出一套在頻域上進行數位訊號處理的方法來處理多重窄頻干擾源問題。CME演算法利用GPS訊號在無干擾的情形下，訊號振幅頻譜呈現瑞利分布(Rayleigh Distribution)的特性來計算出干擾消除需要的臨界閥值，並且經過疊代運算下，此方法可以可適性地調整頻域上的臨界閥值來消除窄頻干擾源。最後論文中使用Overlap-and-Add的數位訊號處理架構將演算法實現，設計出一個抗干擾濾波器。同時也分析此抗干擾濾波器在GPS導航系統中對於後端的信號擷取和信號追蹤造成的影響。
我們也將本論文提出的抗干擾濾波器和前人研究比較。本論文的方法可以處理2倍以上的窄頻干擾源數目，至多有8個干擾強為JSR=25dB的干擾源。而且在多重窄頻干擾源的狀況下，抗干擾濾波器並不會對展頻碼擷取造成影響，也能維持信號擷取偵測率達90%以上。同時本論文的方法，在展頻碼相位追蹤可以得到更小的追蹤誤差(約10-3 chips)；也縮小載波頻率追蹤誤差，頻率誤差值約0.5Hz，並且改善了載波相位追蹤誤差量，約0.20的載波相位誤差。

關鍵字

GPS衛星導航系統 ； 頻域數位訊號處理 ； 多重窄頻干擾源 ； 瑞利分布 ； 抗干擾濾波器 ； 信號擷取 ； 信號追蹤

並列摘要

Nowadays, GPS (Global Positioning System) has been widely integrated into consumer electronics products. The harmonic frequencies caused by other components may interfere with the GPS receivers. Therefore, GPS receivers need to implement an interference excision mechanism to deal with the issue.
In this thesis, we propose using the consecutive mean excision (CME) algorithm, which is a frequency-domain-based digital signal processing (DSP) approach, to implement an anti-jamming filter. The CME algorithm leverages the fact that the magnitude spectrum of the un-jammed GPS signal should have a Rayleigh distribution to adaptively adjust an excision threshold. By excising all the frequency bins whose magnitudes are above the threshold, the resulting magnitude spectrum ideally becomes Rayleigh distribution again. Therefore, the narrow band jamming signals can be eliminated. Moreover, the impaction of the proposed anti-jamming filter on the acquisition and tracking loops in the GPS receiver is analyzed.
Finally, we compare the approach in this thesis with one related previous work. Our method can handle more than two times the number of interference and at most eight jamming signals with jamming-to-signal ratio (JSR) of 25 dB. In this case, the anti-jamming filter does not affect the acquisition of C/A code phase and the resulting detection probability is over 90%; the resulting tracking errors are 10-3 chips, 0.5 Hz, and 0.20, with respect to the code phase, carrier frequency, and carrier phase.

並列關鍵字

GPS(Global Positioning System) ； consecutive mean excision (CME) algorithm ； frequency domain approach ； multiple narrowband interference ； Anti-Jamming filter ； acquisition ； tracking

參考文獻

[1] R. Johannessen , S. J. Cole and M. J. A. Asbury ,"Potential Interference Sources to GPS and Solutions Appropriate for Applications to Civil Aviation", Aerospace and Electronic Systems Magazine, IEEE, Vol.5, pp.3-9, Jan 1990

[2] Elliott D. Kaplan, Christopher J. Hegarty, “Understanding GPS Principles and Applications”, 2nd ed., Artech House , 2006

[7] 李冠儀, ”Design of Automatic Gain Control Circuits for GPS Receiver”,

[8] 黃議徵, “Low complexity solution to GPS Narrowband Interference Cancellation”, 台大電信所碩士論文, 2009

[10] L. B. Milstein,"Interference Rejection Techniques in Spread Spectrum Communications", Proceedings of the IEEE, Vol. 76 , pp. 657-671 , Jun 1988