• ETRI Journal
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• 제37권1호
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• pp.1-10
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• 2015

A blind hopping phase estimator is proposed for the demodulation of received signals in frequency-hopping spread spectrum systems. The received signals are assumed to be bandwidth limited with a shaping filter, modulated as frequency modulation (FM) or binary frequency shift keying (BFSK), and hopped by predetermined random frequency sequences. In the demodulation procedure in this paper, the hopping frequency tracking is accomplished by choosing a frequency component with maximum amplitude after taking a discrete Fourier transform, and the hopping phase estimator performs the conjugated product of two consecutive signals and moving-average filtering. The probability density function and Cramer-Rao low bound (CRLB) of the proposed estimator are evaluated. The proposed scheme not only is very simple to implement but also performs close to the CRLB in demodulating hopped FM/BFSK signals.

• 융합신호처리학회 학술대회논문집
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• 한국신호처리시스템학회 2000년도 하계종합학술대회논문집
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• pp.45-48
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• 2000

In this paper algorithms of frequency hopping sequences generation such as Lempel-Greenberger, optimum Lempel-Greenberger and Kumar sequences for spread spectrum communications are described. Using the scalogram based on wavelet transform, time-frequency characteristics of frequency hopped signals corresponding to the considered hopping sequences are analyzed.

• 한국전자파학회논문지
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• 제30권3호
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• pp.215-222
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• 2019

주파수 도약신호는 전송시간 동안 반송파 주파수를 변경시켜 주파수 대역에서 확산 스펙트럼 특성을 가진다. 이러한 특성으로 주파수 도약신호는 무선채널환경에서 저피탐 및 항재밍 능력이 필요한 분야에 널리 활용된다. 본 논문에서는 미상의 주파수 도약신호에 대해 시작시간, 유지시간, 그리고 도약주파수를 포함하는 도약정보를 생성하는 기법을 제안한다. 제안한 블라인드 도약정보 생성 기법은 스펙트럼 데이터로부터 신호원에 대한 탐지정보를 생성하고, 이로부터 대상 주파수 도약신호의 출현, 유지, 그리고 종료 여부를 추정하는 동작 과정으로 도약정보를 추출한다. 또한, 시뮬레이션 결과를 통해 제안한 기법이 다양한 주파수 도약신호에 대하여 탐지 누락 없이 정확한 도약정보를 제공함을 확인하였다.

• 한국정보통신학회논문지
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• 제17권4호
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• pp.789-796
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• 2013

시간에 따라 중심주파수를 바꾸는 도약신호를 도약주기, 도약 주파수 등에 대한 정보 없이 검출하는 것은 대단히 어렵다고 알려져 있다. 본 논문에서는 도약 신호가 존재하는 광대역 샘플링 신호로부터 도약신호의 중심주파수, 도약 주기 등의 정보를 검출하는 알고리즘을 제안하였다. 도약 신호를 검출하기 위한 일반적인 방법으로는 다수의 협대역 필터가 필요하지만 이러한 구현은 비효율적이므로 본 논문에서는 다상 DFT 필터뱅크를 도입하였다. 또한 다상 DFT 필터뱅크의 출력으로부터 도약신호를 검출하는 알고리즘을 제안하였다. 제안하는 검출 알고리즘은 메모리 사이즈나 구현 복잡도를 줄이기 위해 이진 이미지 신호처리에 기반하여 개발되었다. 제안하는 알고리즘의 성능은 모의실험과 FPGA (field programmable gate array) 구현을 통하여 확인하였다.

• ETRI Journal
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• 제35권5호
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• pp.748-756
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• 2013

This paper addresses the problem of online hop timing detection and frequency estimation of multiple frequency-hopping (FH) signals with antenna arrays. The problem is deemed as a dynamic one, as no information about the hop timing, pattern, or rate is known in advance, and the hop rate may change during the observation time. The technique of particle filtering is introduced to solve this dynamic problem, and real-time frequency and direction of arrival estimates of the FH signals can be obtained directly, while the hop timing is detected online according to the temporal autoregressive moving average process. The problem of network sorting is also addressed in this paper. Numerical examples are carried out to show the performance of the proposed method.

• 한국군사과학기술학회지
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• 제13권5호
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• pp.775-784
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• 2010

In this paper we propose a design method of X band frequency hopping synthesizer in terms of phase noise and settling time with DDS driven PLL architecture, which has the advantages of high frequency resolution, fast settling time and small size. In addition, a noble method is proposed to remove the synthesizer output spurious signals due to superposition effect of DDS. The spurious signal which depend on its normalized frequency of DDS, can be dominant if they occur within the PLL loop bandwidth. We verify that the sources of that spurious signals are quasi-amplitude modulation and superposition effect, and suggest that such signals can be eliminated by intentionally creating frequency errors in the developed synthesizer.

• 한국통신학회논문지
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• 제39C권7호
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• pp.573-581
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• 2014

본 논문에서는 주파수 도약 대역확산 시스템에서 도약에 대한 사전 정보 없이 수신신호를 복조 할 수 있는 도약 위상 추정기를 제안하였다. 복조 과정은 첫째 샘플링 된 수신 신호를 DFT(Discrete Fourier Transform)를 한 후 도약 대역 내에 존재하는 신호 중 가장 큰 크기를 갖는 주파수 성분을 선택한다. 둘째 검출된 신호는 차곱 과정과 다운샘플링을 통하여 기저대역신호로 변환된 후 도약위상 추정기에서 도약 주파수에 의해서 발생된 도약 위상을 추정한다. 제안된 위상 추정기의 수학적 모델에 대한 성능 분석을 위해 확률밀도함수 및 분산 성능을 구하고 모의실험 결과와 비교하여 잘 일치함을 확인하였다.

• Journal of electromagnetic engineering and science
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• 제18권4호
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• pp.254-260
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• 2018

In this study, we suggest an emulator for generating multiple heterogeneous interference signals in the Korean radio frequency identification/ubiquitous sensor network (RFID/USN) frequency band. The proposed emulator uses only one universal software radio peripheral to generate multiple heterogeneous interference signals more economically. Moreover, the physical and media access control parameters can be adjusted in real time using the LabVIEW program, thereby making it possible to create various time-varying interference environments easily. As an example showing the capability of the proposed emulator, multiple interference signals consisting of a frequency-hopping RFID signal and two LoRa signals with different spreading factors were generated. The generated signals were confirmed in both frequency and time domains. From the experimental results, we verified that our emulator could successfully generate multiple heterogeneous interference signals with different frequency and time domain characteristics.

• 한국군사과학기술학회지
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• 제14권1호
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• pp.69-73
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• 2011

In the defence wireless communications, conventional Anti-Jamming techniques(Frequency Hopping/Spread Spectrum or Direct Sequence/Spread Spectrum) are used to overcome a intentional interfering signals which are single/multitone or partial band jammer etc. DS/SS techniques is very strong on tone jamming signal but not to be on a partial band jammer. So FH/SS AJ performances are expected method of an substitution of DS/SS, however FH/SS could not have good performance on some BMTJ(Band Multi-tone Jammer). So this paper proposes FH-CSS (Frequency Hopped - Chirp Spread Spectrum) to get more robustness against jammers(BMTJ, PBNJ) and analyze the AJ performances.

• Journal of Electrical Engineering and Technology
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• 제9권2호
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• pp.771-776
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• 2014

In this paper, an agile programmable chirp spread spectrum generator for wideband frequency-jamming applications from 20 MHz to 3 GHz is proposed. A frequency-mixing architecture using two voltage-controlled oscillators is used to achieve a wideband operating frequency range, and the direct digital synthesizer (DDS)-based chirping method with a two-point modulation technique is employed to provide a programmable and consistent chirp bandwidth. The proposed signal generator provides the various programmable FM signals from 20 MHz to 3 GHz with a modulation bandwidth from 0 to 400 MHz. The prototype successfully demonstrates arbitrary sequential jamming operation with a fast band-to-band hopping time of < 10 ${\mu}sec$.