• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1988.10a
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• pp.89-92
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• 1988

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1992.06a
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• pp.744-747
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• 1992

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.05a
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• pp.39-42
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• 1999

Adaptive array is using the array of antenna elements spatially and its output is the sum of each antenna elements output signal which is multiplied by the controlled weight coefficients corresponding to each elements. In this paper, for the BPSK and BFSK signals with S/I=2, S/N=10 is applied to the linear array antenna using the LMS & the Kalman filter algorithm. For the 4 elements equidistance linear array antenna system LMS and Kalman filter algorithm was used as the adaptive instruction principles and the application results to the constant amplitude envelope signals such as BPSK or BFSK can be seen that the computer simulation results are very fast in the convergence characteristics of directional patterns and the signal following characteristics.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1991.10a
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• pp.386-389
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• 1991

• Journal of Satellite, Information and Communications
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• v.8 no.2
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• pp.94-98
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• 2013

A report of security problems and simultaneous operation limits of Standard tone currently used for FTS introduces the development of a next generation FTS. In this paper, BER performance by modulations and channel coding methods for EFTS are compared. Simulation results show that coherent modulations have better BER performance than noncoherent modulations. However the environments of a lunching vehicle may cause serious problems in achieving and maintaining synchronization and the increasing complexity of coherent systems also increases reliability problems. Therefore noncoherent systems are suitable for FTS even though BER performace of noncoherent systems is lower than coherent systems. Noncoherent DPSK has better BER performance than noncoherent CPFSK. However the PEP of noncoherent DPSK is 0.8dB higher than noncoherent CPFSK. Therefore a transmitter of noncoherent DPSK has more output power than noncoherent CPFSK. Convoltional code has better BER performance than RS code. However RS code has a tendency of steeply decreasing BER near the wanted $E_b/N_0$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.7
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• pp.573-581
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• 2014

We proposed a hopping phase estimator to demodulate the received signals without any hopping information in frequency hopping spread spectrum systems. The demodulation process in this paper is as follows: hopped frequency tracking is accomplished by choosing a frequency component with maximum amplitude after taking discrete Fourier transform and a hopping frequency estimator which estimates the phase generated by hopped frequency is established through difference product and down-sampling. We obtained the probability density function and variance performance of the proposed estimator and confirmed that the analysis and the simulation results were agreed with each other.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.3
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• pp.268-273
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• 2015

Recently many countries are researching actively underwater sensor networks for securing ocean resources and changes of ocean environment in all over the world. Current the commercial modem are not suitable because it has characteristics of long distance, higher price, larger power consumption with the special object mainly. In this paper, a low power and compact underwater communication modem which is suitable for underwater sensor networks is implemented. It is comprised by using a simple analog circuit for non-coherent BFSK modulation method, ultra low power MCU and orthogonal codes with a less operation and a simple implementation. It was experimented an underwater communication using our modem in a water tank and open sea farms. It communicates fewer than $10^{-4}$ bit error rate.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.161-166
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• 1999

The global trends of mobile communication system is moving toward digitizing, high-speed and large-capacity. Also, to utilize the limited frequency-resource efficiently, spread spectrum system is a mainstream. In this study we are concerning with the fast frequency-hopping system. Instead of the PLL with many problems such as phase-noise, we used the DDS is popular in these days minimizes the disadvantage of PLL. In the case the FFH system is designed using the PLL, it is difficult to be satisfied of the design conditions such as RF badwidth and the settling time of PLL, and it has limitation because of complex circuit by using the balanced modulator. In this study, we evaluated the performance in order to design the FFH system using the DDS. The system that has the improvement of error rate, 1Mhps hopping rate and 5MHz RF bandwidth is designed and evaluated.

• Journal of the Korean Institute of Telematics and Electronics
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• v.20 no.3
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• pp.52-60
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• 1983

This paper presents a complete analysis for the derivation of the probability of error for a fast (or multiple-hops per bit) frequency hopping spread spectrum system employing binary FSK modulation and noncoherent reception in the presence of partial-band noise jamming and thermal noise. The worst-case error rate performances were obtained numerically and presented as a function of E /N with L as a parameter, where E /N and L are the signal bit energy-to-jamiming density ratio and the number of hops per bit, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.15 no.3
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• pp.260-268
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• 1990

This paper investigates the design of a frequency hopping FSK tranceiver system, where the system enhancements are made in the following three aspects: dual frequency synthesiszation for the increased hopping rate, linearization of VCO gain in PLL to improve BFSK modulation characteristics, and fast code synchronization by the matched filter method.