• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.11
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• pp.1124-1131
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• 2014

The chirp spread spectrum (CSS) technique that transmits data signal by using a chirp signal is often used for maritime wireless communication systems such as sound detection radar systems for submarines. However, maritime multipath environment could reduce the data rate of the CSS system. To tackle the problem, an overlap-based CSS transmission scheme is proposed and analyzed in this paper: Based on the approximated Gaussian Q function, we derive a closed form expression of the bit error rate (BER) of the proposed overlap-based CSS system and investigate the mathematical relationship between the number of overlaps and the intersymbol interference (ISI).

• The Journal of the Acoustical Society of Korea
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• v.31 no.7
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• pp.441-448
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• 2012

Spread spectrum provides the minimized inter-symbol interference, the low probability of intercept and the multiple access capability. This paper presents a direct sequence spread spectrum with carrier/timing recovery and equalizer which compensates the delay spread caused by multipath transmission. When the sea trials were performed in Korean East Sea, the bit error rates of QPSK and direct sequence spread spectrum are $1.46{\times}10^{-2}$ and $5.17{\times}10^{-4}$ at 3 km source-receiver range, respectively.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.3
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• pp.653-660
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• 2000

In this paper, an adaptive interference excision scheme with multiple adaptive filter bank using an adaptive algorithm is proposed. This scheme suppresses interference in the wavelet packet transform domain for the direct spread spectrum communication systems. Using the Monte-Carlo simulation, we analyze the performance of the direct spread spectrum communication systems with this excision scheme using LMS and RLS adaptive algorithms in AWGN and interference channel.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.3
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• pp.517-526
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• 2000

In this paper, we propose the trellis coded spread spectrum communication system with one channel signal selection of the subset by the PN code. This paper proposes the Viterbi decoder that have the squared Euclidean distance of the order phase difference as well as 1st order phase difference as the branch metrics by using the multiple symbol detection method. TCM method was developed to overcome limited power and bandwidth efficiently in digital communication. we multiply one of convolution code's output data to PN code for applying TCM to the spread spectrum. We investigated the performance of the direct sequence/spread spectrum communication system with trellis coded modulation. In this system, we could improved the coding gain in the spread spectrum.

• Journal of Satellite, Information and Communications
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• v.12 no.2
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• pp.65-70
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• 2017

The structure of MMSE receiver front-ended by CMA(Constant Modulus Array) array working in CDMA forward link which is applicable to LEO spread spectrum satellite communication system is proposed. By using the despreaded pilot signal of forward link as a reference signal, the CMA array can capture multi-path signals securely even in severely faded LEO satellite channel. The remaining MAI (Multiple Access Interference) is cancelled by the cascaded MMSE receiver. Besides theoretical development, through relevant computer simulation, it is proved that the proposed system shows much better BER performance than any other possible candidate systems. As a spatio-temporal receiver mounted on a mobile vehicle, the proposed system also reduces implemental cost and complexity by adopting the simplest algorithm for its spatial and temporal domain processing.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.10
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• pp.12-21
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• 1998

A chaotic spread spectrum communication system using a polar quarternary method is designed and implemented. Four different chaotic signals in the relation of multiplication each other are generated through the use of a coupled synchronization method in the transmitter which is composed of four Chua's circuits. Information is retrieved at the receiver which is connected to the transmitter through the use of a drive synchronization method. Since spread spectrum of information signal is spread by chaotic signal, the configuration of the system is simpler than that of any other conventional system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.14 no.2
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• pp.164-176
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• 1989

With reference to the Spread Spectrum techniqeu diseussed and further extended by many investigators, the Peseudo-noise Code Polarity Modulation (PNCPM) technique has proposed in this paper. By using this new technique of PNCPM, some problems pertaining to the Spread Spectrum mode has been sloved. In addition by the PNCPM mode it is proposed that data shifting can be easily demodulated every clock(frame) by measn of simple hardware implementaton for the purpose of operating of the asynchroniged detection mode. And in this paper it is shown that PNCPM mode can be easily implemented by the CCD correlator, and is applicable to the Spread Spectrum Multiple Access.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5A
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• pp.440-446
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• 2010

Convergence of IT and BT is considered in many area, especially in medical care industry. The example of this trend is a capsule endoscope. But in a capsule endoscope, communication through human body has a few restrictions. At first, the transmit power should be limited not to have a bad effect on human organs and for the battery capacity. Second, the channel characteristic of human body has not been examined exactly. Third, general modulation / demodulation techniques which require a channel estimation cannot be used because of battery limit. There also may be a lot of interference signals because a capsule endoscope uses UWB bandwidth. In this paper, we introduce Chirp Spread Spectrum Differential Binary Phase Shift Keying(CSS-DBPSK) and propose Chirp Spread Spectrum On-Off Keying(CSS-OOK) which don't require a channel estimation and robust to interference signals. Using CSS-DBPSK or CSS-OOK, we can get 5 dB or 2~3 dB of Eb/N0 gain at 10-5 target BER. And if there are interference signals, those gains of CSS-DBPSK and CSS-OOK are increased.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.8
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• pp.1629-1637
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• 2003

In this paper, we analyzed the performance of a hybird DS/SFH(Direct­Sequency­Slow Frequency­Hopping) Spread Spectrum system with BFSK modulation over Nakagami­m fading channel with multitone jamming. The performance of the system was improved when a frequency bowing rate increased. In case that process gain of hybrid DS/SFH Spread Spectrum system to be fixed, the hybrid DS/SFH Spread Spectrum takes the low bit error probability than a DS Spread Spectrum system. Also, when the fading index m increases, the fading effect decrease, when the JSR(jamming to signal power ratio) increases ,the performance of a hybrid DS/SFH Spread Spectrum system improved than DS Spread Spectrum system. The result, we have been proved that performance of a hybrid DS/SFH Spread Spectrum was superior to DS Spend Spectrum system over Nakagami­m fading with tome jamming.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.8
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• pp.1422-1430
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• 2016

Researches for oceans are limited to military purpose such as underwater sound detection and tracking system. Underwater acoustic communications with low-probability-of-interception (LPI) covert characteristics were received much attention recently. Covert communications are conducted at a low received signal-to-noise ratio to prevent interception or detection by an eavesdropper. This paper proposed optimal covert communication model based on direct sequence spread spectrum for underwater environments. Spread spectrum signals may be used for data transmission on underwater acoustic channels to achieve reliable transmission by suppressing the detrimental effect of interference and self-interference due to jamming and multipath propagation. The characteristics of the underwater acoustic channel present special problems in the design of covert communication systems. To improve performance and probability of interception, we applied BCJR(Bahl, Cocke, Jelinek, Raviv) decoding method and the direct sequence spread spectrum technology in low SNR. Also, we compared the performance between conventional model and proposed model based on turbo equalization by simulation and lake experiment.