偽碼調(diào)相-線性調(diào)頻的低軌導(dǎo)航信號波形及捕獲性能

林紅磊; 耿敏嫣; 付棟; 歐鋼; 肖偉; 馬明

doi:10.11999/JEIT240650

偽碼調(diào)相-線性調(diào)頻的低軌導(dǎo)航信號波形及捕獲性能

doi: 10.11999/JEIT240650

1.
國防科技大學(xué)電子科學(xué)學(xué)院長沙 410073
2.
導(dǎo)航與時空技術(shù)國家級重點實驗室長沙 410073

基金項目: 國家自然科學(xué)基金(U20A20193)

詳細信息

作者簡介:
林紅磊：男，博士，副研究員，研究方向為星基導(dǎo)航定位技術(shù)

耿敏嫣：女，碩士生，研究方向為星基導(dǎo)航定位技術(shù)

付棟：男，博士生，研究方向為通信導(dǎo)航一體化

歐鋼：男，教授，研究方向為導(dǎo)航與時空技術(shù)、衛(wèi)星載荷與導(dǎo)航終端技術(shù)等

肖偉：男，講師，研究方向為衛(wèi)星導(dǎo)航信號體制設(shè)計

馬明：男，講師，研究方向為時間頻率技術(shù)

通訊作者:
耿敏嫣　gmy1585206743@163.com

中圖分類號: TN967.1
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- 文章訪問數(shù): 121
- HTML全文瀏覽量: 49
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- 被引次數(shù): 0
出版歷程
- 收稿日期: 2024-07-25
- 修回日期: 2024-12-04
- 網(wǎng)絡(luò)出版日期: 2024-12-12
- 刊出日期: 2025-01-31

A Code-phase Shift Key-Linear Frequency Modulated Low Earth Orbit Navigation Signal and Acquisition Performance Analysis

1.
College of Electronic Science, National University of Defense Technology, Changsha 410073, China
2.
State Key Laboratory for Position, Navigation and Time, Changsha 410073, China

Funds: The National Natural Science Foundation of China (U20A20193)

摘要

摘要: 低軌導(dǎo)航星座衛(wèi)星數(shù)量多，信號多普勒頻偏大，接收機冷啟動搜索空間巨大，捕獲速度慢，該文提出一種偽碼調(diào)相-線性調(diào)頻(CSK-LFM)的導(dǎo)航信號波形，線性調(diào)頻提高信號的多普勒容限，不同偽碼相位實現(xiàn)不同衛(wèi)星的多址播發(fā)，可以極大壓縮衛(wèi)星號、時延、多普勒3維搜索空間，加快了捕獲信號捕獲速度。仿真和實驗結(jié)果表明，當(dāng)信號強度為40 dBHz時，采用CSK-LFM調(diào)制的導(dǎo)航信號，其捕獲性能比同等條件下的傳統(tǒng)直接擴頻序列(DSSS)調(diào)制的導(dǎo)航信號高1 dB左右，且信號搜索空間可降低為直接擴頻序列調(diào)制的1/10。
- 低軌導(dǎo)航信號 /
- 線性調(diào)頻 /
- CSK調(diào)制 /
- 信號捕獲
Abstract: Objective The provision of satellite navigation services through Low Earth Orbit (LEO) constellations has become a prominent topic in the Position, Navigation and Timing (PNT) system. Although LEO satellites offer low spatial propagation loss and high signal power at ground level. However, their high-speed movement results in significant dynamics in the signal, leading to considerable Doppler frequency shifts that affect signal reception on the ground. This dynamic environment increases the frequency search space required by receivers. Furthermore, LEO constellations typically comprise hundreds or even thousands of satellites to achieve global coverage, further expanding the search space for satellite signals at terminals. Consequently, during cold start conditions, the LEO satellite navigation system faces a substantial increase in the search range for navigation signals, presenting significant challenges for signal acquisition. Existing GPS, BDS, GALILEO, and other navigation signals primarily utilize BPSK-CDMA modulation, relying on spread spectrum sequences to differentiate various satellite signals. However, these existing signals exhibit limited resistance to Doppler frequency offsets. Therefore, research into signal waveforms that are more suitable for LEO satellite navigation systems is crucial. Such research aims to enhance the anti-Doppler frequency offset capability and multi-access performance under conditions involving numerous satellites, thereby improving the signal acquisition performance of LEO navigation terminals and enhancing the overall availability of LEO navigation systems. Methods This paper adopts a multi-faceted research approach including theoretical analysis, simulation experiments, and comparative analysis. Since the performance of the correlation function directly impacts signal acquisition performance, an initial theoretical analysis of the correlation function and the multiple access capabilities of the proposed signal is conducted. Following this, the corresponding capture detection metrics and decision-making methods are proposed based on the principles of signal capture. The investigation continues with a focus on optimizing capture parameters, followed by verification of the signal’s acquisition performance through simulations and experiments. Additionally, the performance of the proposed signal is compared to that of traditional navigation signals using both theoretical and simulation analyses. Results and Discussions The theoretical analysis outcomes reveal that the proposed Code-phase Shift Key-Linear Frequency Modulated (CSK-LFM) signal exhibits lower Doppler loss, delay loss, and multiple access loss when compared to the traditional Binary Phase Shift Keying–Code Division Multiple Access (BPSK-CDMA) signal. To minimize the loss of signal detection capacity, it is advisable to expand the signal bandwidth and reduce the spread spectrum ratio during the signal design phase. A satellite parallel search method is developed for the acquisition of the CSK-LFM signal, employing a Partial Match Filter-Fast Fourier Transformations (PMF-FFT) approach. A parameter optimization model has also been developed to enhance the acquisition performance of the CSK-LFM signal. Furthermore, the acquisition performance of CSK-LFM and BPSK-CDMA signals are compared. Under the same conditions, the acquisition and search space required for the BPSK-CDMA signal is larger than that of the CSK-LFM signal. It is noteworthy that, under equivalent dynamic conditions, the acquisition performance of the CSK-LFM signal is approximately 1 dB superior to that of the BPSK-CDMA signal. Lastly, experimental results confirm that the proposed satellite parallel search method based on the PMF-FFT acquisition algorithm is effective for the acquisition of CSK-LFM signals. Conclusions To address the challenge of achieving rapid signal acquisition in low-orbit satellite navigation systems, a hybrid modulation scheme, CSK-LFM is designed. The LFM modulation improves the signal’s Doppler tolerance, while the use of diverse pseudo-code phases enables multiple access broadcasts from different satellites. This design compresses the three-dimensional search space involving satellite count, time delay, and Doppler shift. Additionally, a satellite parallel search method is implemented based on a PMF-FFT acquisition algorithm for the CSK-LFM signal. An optimization model for acquisition parameters is also developed to enhance performance. Our comparative analysis of the acquisition performance between CSK-LFM and BPSK-CDMA signals demonstrates that at a signal intensity of 40 dBHz, the navigation signal using CSK-LFM modulation achieves an acquisition performance approximately 1 dB superior to that of the BPSK-CDMA modulation signal under identical conditions; furthermore, the signal search space can be reduced to one-tenth that of the BPSK-CDMA modulation signal.
- Low Earth Orbit (LEO) satellite /
- Linear Frequency Modulation (LFM) /
- Code-phase Shift Key(CSK) modulated /
- Signal acquisition

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圖 1 偽碼調(diào)相-線性調(diào)頻信號的載波頻率和擴頻碼對應(yīng)關(guān)系示意圖

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圖 2 CSK-LFM信號的自相關(guān)函數(shù)值

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圖 3 不同采樣率下引起的相關(guān)損耗對比

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圖 4 不同可見衛(wèi)星數(shù)量情況下引起的多址相關(guān)損耗

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圖 5 CSK-LFM信號的捕獲檢測量構(gòu)造示意圖

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圖 6 基于PMF-FFT結(jié)構(gòu)的CSK-LFM信號并行捕獲框圖

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圖 7 CSK-LFM調(diào)制信號的捕獲參數(shù)優(yōu)化結(jié)果

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圖 8 兩種體制的捕獲性能仿真結(jié)果對比

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圖 9 BPSK-CDMA信號和CSK-LFM信號的捕獲仿真結(jié)果

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圖 11 CSK-LFM和BSPK-CDMA信號捕獲性能仿真結(jié)果

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圖 10 case 4-1下CSK-LFM信號時延-多普勒解模糊處理結(jié)果

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圖 12 CSK-LFM信號并行捕獲結(jié)果(衛(wèi)星號維度剖面圖)

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表 1 不同調(diào)制方式下抗多普勒頻偏能力和多址方式分析對比

調(diào)制方式	抗多普勒能力	信號多址方式	典型應(yīng)用
直接序列調(diào)制	弱	不同碼序列	GSP、北斗、伽利略等系統(tǒng)
頻分復(fù)用調(diào)制	弱	不同頻點	GLONASS系統(tǒng)
碼相位偏移調(diào)制	弱	不同碼相位	數(shù)據(jù)鏈、QZSS等系統(tǒng)中信息調(diào)制
線性調(diào)頻調(diào)制	強	不同調(diào)頻斜率、起始頻率等	雷達系統(tǒng)，Lora系統(tǒng)
偽碼-線性調(diào)頻調(diào)制	強	不同調(diào)頻斜率、起始頻率、碼序列	-

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表 2 不同帶寬和擴頻比下的頻率分格大小(kHz)

	N	31	63	127	255	511
CSK-LFM	B=4.092 MHz	79.20	38.97	19.33	9.63	4.80
	B=20.46 MHz	396.00	194.85	96.66	48.14	24.02
	B=40.92 MHz	792.00	389.71	193.32	96.28	48.05
BPSK-CDMA	T=1 ms	0.9

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1 基于PMF-FFT 結(jié)構(gòu)的CSK-LFM 捕獲算法

步驟1　生成本地復(fù)制的線性調(diào)頻載波s_l(k)
步驟2　生成本地復(fù)制偽碼c_l(n)，并進行FFT運算，求復(fù)共軛，得到參考序列C_l(j)^*
步驟3　在調(diào)頻周期內(nèi)將復(fù)制線性調(diào)頻載波與接收信號相關(guān)并分段累加，得到累加結(jié)果y(n)
步驟4　對一個調(diào)頻周期內(nèi)的N段累加結(jié)果進行FFT運算，得到序列Y(j)
步驟5　將FFT結(jié)果與參考序列相關(guān)，對相關(guān)后的結(jié)果逆FFT處理，得到N顆衛(wèi)星的捕獲量z(k,i)
步驟6　對P個調(diào)頻周期內(nèi)的捕獲量z(k,i)累加，得到Z(k,i)，并與門限比較，超過門限則捕獲成功，跳至步驟9
步驟7　移動接收信號一個采樣點，重復(fù)步驟3–步驟6，直至遍歷完成2個調(diào)頻周期
步驟8　移動一個頻率搜索格子，重復(fù)步驟1–步驟7，直至遍歷完成所有頻率格子的搜索
步驟9　在上調(diào)頻信號捕獲時延附近，搜索上調(diào)頻和下調(diào)頻信號，根據(jù)捕獲位置按式(29)計算捕獲時延和多普勒

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表 3 捕獲參數(shù)優(yōu)化求解的信號條件

B(MHz)	f_d(kHz)	CN0(dBHz)	T(ms)	N	P
4.092	40	40	1	63	5

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表 4 兩類信號的搜索空間比較

		多普勒范圍(kHz)	多普勒格子(kHz)	搜索空間		多普勒范圍(kHz)	多普勒格子(kHz)	搜索空間
BPSK-CDMA	case4	±5	0.5	8 184×20	case5	±40	0.5	8 184×160
CSK-LFM	case4-1		2.5	8 184×8	case5-1		2.5	8 184×64
CSK-LFM	case4-2		10.0	8 184×2	case5-2		10.0	8 184×16

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