• 한국통신학회논문지
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• 제40권10호
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• pp.1937-1939
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• 2015

Chirp 기반의 전송 기법에서 Cross-coherence는 전송 성능에 영향을 미치며, 전송 성능의 향상을 위해서는 Cross-coherence가 적은 Chirp 조합을 사용해야 한다. 이에 본 논문은 IEEE 802.15.4a CSS (Chirp Spread Spectrum)의 전송 성능을 향상시키기 위한 Chirp 조합으로 다중 선형 Chirp 기법을 제안한다. 모의실험 결과, 제안된 기법인 다중 선형 Chirp 기법이 단일 선형 Chirp 기법 보다 Cross-coherence가 적은 부분이 있음을 확인하였고, 이 조합을 이용하여 전송하였을 때 전송 성능이 향상됨을 확인하였다.

• ETRI Journal
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• 제33권6호
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• pp.841-848
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• 2011

A signal-to-noise ratio (SNR) enhancement algorithm using multiple chirp symbols with clock drift is proposed for accurate ranging. Improvement of the ranging performance can be achieved by using the multiple chirp symbols according to Cramer-Rao lower bound; however, distortion caused by clock drift is inevitable practically. The distortion induced by the clock drift is approximated as a linear phase term, caused by carrier frequency offset, sampling time offset, and symbol time offset. SNR of the averaged chirp symbol obtained from the proposed algorithm based on the phase derotation and the symbol averaging is enhanced. Hence, the ranging performance is improved. The mathematical analysis of the SNR enhancement agrees with the simulations.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(4)
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• pp.155-158
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• 2001

A new method for simultaneous multiple transmit focusing using orthogonal weighted FM chirp is proposed. Weighted chirp signals focused at different depths are transmitted at the same time. These chirp signals are mutually orthogonal in the approximate sense that the autocorrelation function of each signal has a narrow mainlobe width and low sidelobe levels, and the crosscorrellation function of any pair of the signals has smaller values than the sidelobe levels of each autocorrelation function. This means that each weighted chirp signal can be separately compressed into a short pulse, focused individually and combined with other focused beams to form a frame of image. Theoretically, any two chirp signals defined in two nonoverlapped frequency bands are mutually orthogonal. In the present work, however, a fractional overlap of adjacent frequency bands, by up to 25%, were permitted to design more chirp signals within a given transducer bandwidth. The crosscorrelation values due to the frequency overlap could be reduced by alternating the direction of frequency sweep of the adjacent chirp signals. The simulation results show that this method can improve the lateral resolution of image without sacrifice in the frame rate compared with the conventional pulse system.

• 한국통신학회논문지
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• 제41권11호
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• pp.1417-1419
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• 2016

처프 확산 대역 시스템의 전송 성능을 향상시키기 위해서는 처프 신호 사이의 상호 상관 계수를 반드시 고려해야 한다. 본 논문은 단일 사용자 전송을 위한 처프 신호의 상호 상관 계수를 수식적으로 도출하였으며, 이를 기반으로 전송 성능을 향상시킬 수 있는 처프율을 이론적으로 제안하였다. 모의실험 결과, 최적의 상호 상관 계수를 고려했을 때 전송 성능이 향상되었으며, 도출된 이론적인 성능이 모의실험 결과와 동일함을 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권2호
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• pp.253-270
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• 2013

To achieve accurate localization information, complex algorithms that have high computational complexity are usually implemented. In addition, many of these algorithms have been developed to overcome several limitations, e.g., obstruction interference in multi-path and non-line-of-sight (NLOS) environments. However, localization systems those have complex design experience latency when operating multiple mobile nodes occupying various channels and try to compensate for inaccurate distance values. To operate multiple mobile nodes concurrently, we propose a localization system with both low complexity and high accuracy and that is based on a chirp spread spectrum (CSS) radio. The proposed localization system is composed of accurate ranging values that are analyzed by simple linear regression that utilizes a Big-$O(n^2)$ of only a few data points and an algorithm with a self-calibration feature. The performance of the proposed localization system is verified by means of actual experiments. The results show a mean error of about 1 m and multiple mobile node operation in a $100{\times}35m^2$ environment under NLOS condition.