• Journal of Positioning, Navigation, and Timing
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• 제11권3호
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• pp.147-156
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• 2022

In this paper, we propose Time-Division-Multiplexing Tertiary Offset Carrier (TDMTOC), a novel GNSS modulation based on Tertiary Offset Carrier (TOC) modulation. The TDMTOC modulation multiplexes two three-level signals (i.e., -1, 0, and 1) while crossing over time, and is a type of TOC modulation designed specifically for signal multiplexing. The proposed modulation generates TDMTOC subcarriers of two different phases by simply combining two Binary Offset Carrier (BOC) subcarriers by addition or subtraction. TDMTOC has better correlation and spectral properties than conventional BPSK, BOC, and MBOC modulation techniques, and has good power and spectral efficiency since it can multiplex signals without power loss similar to time division multiplexing. To prove this, we introduce the multiplexing process of TDMTOC, and compare TDMTOC with Binary Phase Shift Keying (BPSK), BOC, Composite BOC (CBOC), and Time Multiplexed BOC (TMBOC) that are currently serviced in GNSS by simulations of various aspects. Through the simulation results, we prove that TDMTOC has better correlation property than modulations currently used in GNSS, less intersystem interference due to its wide spectrum property, and robustness in multipath and noise channel environments.

• Journal of Positioning, Navigation, and Timing
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• 제13권1호
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• pp.1-13
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• 2024

In this paper, we investigate the signal design of six (USA, EU, Russia, China, Japan, and India) countries for Global Navigation Satellite Systems (GNSS). Recently, a navigation satellite system that is capable of high-precision and reliable Positioning, Navigation, Timing (PNT) services has been developed. Prior to system design, a survey of the signal design for other GNSS systems should precede to ensure compatibility and interoperability with other GNSS. The signal design includes carrier frequency, Pseudorandom Noise (PRN) code, modulation, navigation service, etc. Specifically, GNSS is allocated L1, L2, and L5 bands, with recent additions of the L6 and S bands. GNSS uses PRN code (such as Gold, Weil, etc) to distinguish satellites that transmit signals simultaneously on the same frequency band. For modulation, both Binary Phase Shift Keying (BPSK) and Binary Offset Carrier (BOC) have been widely used to avoid collision in the frequency spectrum, and alternating BOCs are adopted to distinguish pilot and data components. Through the survey of other GNSS' signal designs, we provide insights for guiding the design of new satellite navigation systems.

• Journal of Positioning, Navigation, and Timing
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• 제9권4호
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• pp.293-304
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• 2020

In this paper, various modulation techniques, including the legacy Global Navigation Satellite System (GNSS) signal modulation techniques, are introduced and the spectral characteristics and correlation characteristics of signals with various modulation techniques are analyzed based on numerical simulation. With the development of various GNSS services, the limited frequency band has become increasingly saturated, and issues of interoperability and compatibility have emerged in the new GNSS design. Since the efficient allocation of frequency resources is closely related to spectrum design, modulation techniques are one of the important signal design parameters of new signal design. Signal modulation techniques are closely related to various figure of merits (FoMs) as well as spectrum characteristic, and in some cases there is a complicated trade-off between FoMs. Thus, the FoMs associated with modulation technology should be analyzed and the best signal candidates should be chosen carefully via the trade-off analysis for FoMs. In this paper, we define the modulation technique based on Phase Shift Keying (PSK), Binary Offset Carrier (BOC) and Continuous Phase Modulation (CPM) for the design of KPS signals, and the FoMs of signals in terms of spectrum and correlation function are evaluated. Signals with various modulation techniques are implemented through a numerical simulation, and the relevant FoMs are analyzed.

• Journal of Positioning, Navigation, and Timing
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• 제6권3호
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• pp.87-94
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• 2017

GNSS modernization and development is in progress throughout the globe, and it is focused on the addition of a new navigation signal. Accordingly, for the next-generation GNSS signals that have been developed or are under development, various combinations that are different from the existing GNSS signal structures can be introduced. In this regard, to design an advanced signal, it is essential to clearly understand the effects of the signal structure and design variables. In the present study, the effects of the GNSS spreading code period and GNSS data bit duration (i.e., signal design variables) on the signal processing performance were analyzed when the data bit transition was considered, based on selected GNSS signal design scenarios. In addition, a method of utilizing the obtained result for the design of a new GNSS signal was investigated.

• Journal of Positioning, Navigation, and Timing
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• 제10권4호
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• pp.335-340
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• 2021

A constant envelope multiplexing via constellation tailoring scheme is proposed for flexible power allocation of Global Navigation Satellite System (GNSS) signals. The proposed scheme is compared with the coherent adaptive subcarrier modulation (CASM) adopted in the L1 band signals of the Global Positioning System (GPS) in terms of power difference and power loss. Analysis of the constellation optimization results on the power difference and power loss show that the proposed scheme outperforms the CASM of the GPS signals in the allowable power difference of less than 0.1 dB.

• Journal of Positioning, Navigation, and Timing
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• 제12권1호
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• pp.59-65
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• 2023

A GNSS receiver must perform signal acquisition to estimate the code phase and Doppler frequency of the incoming satellite signals, which are essential information for baseband signal processing. Modernized GNSS signals have different modulation schemes and long PRN code lengths from legacy signals, which makes it difficult to acquire the signals and increases the computational complexity and time. This paper proposes a novel FFT/Inverse-FFT with baseband resampling to resolve the aforementioned challenges. The suggested algorithm uses a single block only for the FFT and thereby requires less hardware resources than conventional structures such as Double Block Zero Padding (DBZP). Experimental results based on a MATLAB simulation show this algorithm can successfully acquire GPS L1C/A, GPS L2C, Galileo E1OS, and GPS L5.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.405-410
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• 2006

Future GNSS signal using BOC modulation brings the advantages of positioning accuracy and multipath rejection. However, the BOC signal has an ambiguous autocorrelation function that complicates the process of acquisition. Three techniques that solve the ambiguous problem are BPSK-like, Sub Carrier Phase Cancellation, and Bump Jumping. In this paper, these methods are implemented by means of a DSP/FPGA board. Moreover, an experiment is conducted to examine and compare the performance of these techniques.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.15-22
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• 2006

This paper presents a novel signal tracking algorithm for GNSS receivers using a MLE technique. In order to perform a robust signal tracking in severe signal environments, e.g., high dynamics for navigation vehicles or weak signals for indoor positioning, the MLE based signal tracking approach is adopted in the paper. With assuming white Gaussian additive noise, the cost function of MLE is expanded to the cost function of NLSE. Efficient and practical approach for Doppler frequency tracking by the MLE is derived based on the assumption of code-free signals, i.e., the cost function of the MLE for carrier Doppler tracking is used to derive a discriminator function to create error signals from incoming and reference signals. The use of the MLE method for carrier tracking makes it possible to generalize the MLE equation for arbitrary codes and modulation schemes. This is ideally suited for various GNSS signals with same structure of tracking module. This paper proposes two different types of MLE based tracking method, i.e., an iterative batch processing method and a non-iterative feed-forward processing method. The first method is derived without any limitation on time consumption, while the second method is proposed for a time limited case by using a 1st derivative of cost function, which is proportional to error signal from discriminators of conventional tracking methods. The second method can be implemented by a block diagram approach for tracking carrier phase, Doppler frequency and code phase with assuming no correlation of signal parameters. Finally, a state space form of FLL/PLL/DLL is adopted to the designed MLE based tracking algorithm for reducing noise on the estimated signal parameters.

• 한국통신학회논문지
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• 제37권6C호
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• pp.502-511
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• 2012

GNSS의 중요성이 점점 증가하면서, 독자적인 위성항법시스템의 구축에 대한 필요성이 제기되고 있다. 위성항법 시스템 구축 시 위성 신호 설계는 반드시 필요한 과정이며, 이를 위한 요구조건 규정이 필수적이다. 본 논문에서는 위성 항법 설계 요소에 대한 수신 성능 분석을 수행하며, 이를 이용한 신호 설계 방안에 대해 제시한다. 먼저 설계 요소에 따른 후보군 정의 후, 성능 평가 지표에 따라 신호 후보의 수신 성능을 분석한다. 이때 다양한 적용 분야에서의 신호 성능을 판단하기 위하여 성능 평가 지표가 갖는 가중치를 정의하였으며, 정규화된 성능 평가 지표와 가중치간의 연산을 통해 최종적으로 성능 비교값을 도출하였다. 위성 항법 신호 설계 요소로 코드, 변조 기법, 반송파를 고려하였으며, 성능을 평가하기 위한 평가 지표로는 상관폭, DLL 및 PLL 열잡음 지터, 주파수 대역폭, 사이드로브 피크율을 정의하였다. 또한 적용 분야로는 측위 성능, 잡음에 대한 강인성, 대역 효율성을 고려하였다. 제안한 설계 방안 적용 시 소프트웨어 기반의 시뮬레이터를 이용하여 성능 분석을 수행하였으며, 최종적으로 성능 분석 결과로부터 신호 후보의 성능을 객관적으로 판단하고 비교하였다.

• 한국항공우주학회지
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• 제37권9호
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• pp.855-862
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• 2009

본 논문은 Galileo E5 AltBOC 신호를 수신하는 알고리듬에 대해 연구하고, 이를 소프트웨어 수신기에 적용하여 구현, 검증하였다. 신호 수신 소프트웨어는 로깅된 IF 데이터 파일로부터 신호의 획득과 추적을 진행하여 항법해를 구하기 위해서 필요한 데이터를 추출하는 기능을 수행한다. 신호 획득 단계에서는 항법 데이터와 부 코드에 의한 반전을 고려하여 1ms 데이터와 0.25ms 지연된 1ms 데이터를 활용하도록 구현되었고, 신호 추적 단계에서는 AltBOC신호의 장점을 이용하고 BOC 변조로 인한 모호성을 해결하기 위한 방법으로 개략 신호 추적과 정밀 신호 추적 두 단계로 나누어 신호 추적을 진행하였다. 구현된 신호 수신 소프트웨어는 상용 시뮬레이터에서 얻은 데이터를 이용하여 검증하였다.