• Journal of Satellite, Information and Communications
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• v.2 no.2
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• pp.22-28
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• 2007

Spectrum spreading, in its general form, can be conceived as an artificial expansion of the signal bandwidth with respect to the minimum Nyquist band required to transmit the desired information. Spreading can be functional to several objectives, including resilience to interference and jammers and reduction of power spectral density levels. In the paper, signal spreading is manly used for increasing the received energy, thus satisfying link budget constraints, for terminals with low aperture antennas, without increasing the transmitted EIRP. As a matter of fact, in many mobile scenarios, even when MODCOD configurations with very low spectral efficiency (i.e. QPSK-1/4) in DVB-S2 standard, are used, the link budget cannot be closed. Spectrum spreading has been recently proposed as a technique to improve system performance without introducing additional MODCOD configurations under the constraint of fixed power spectrum density level at the transmitter side. To this aim, the design of spectrum spreading techniques shall keep into consideration requirements such as spectrum mask, physical layer performance, link budget, hardware reuse, robustness, complexity, and backward compliance with existing commercial equipments. The proposed implementation allows to fully reuse the standard DVB-S2 circuitry and is inserted as an 'inner layer' in the standard DVB-S2 chain.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.8
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• pp.1-9
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• 2009

In this paper, we describe DSSS transceiver development robust to jamming signals as an investigation of ECCM transceiver for UAV uplink. The jamming margin is 15dB or greater with the development target of transceiver because the jamming margin is more important than the transmission rate of data and the spreading code can be changeable. The rake receiver is applied to combine multipath components and turbo code which the coding gain is 7.2dB as a FEC. In this paper, the whole structure, design method and functional test result about the designed modem are described and a conclusion is made.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.9
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• pp.1884-1891
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• 2012

In this paper, we design the sliding correlator SS transceiver which supports short message service. We also analyze the PN code acquisition circuit that is essential for spread spectrum receiver. Using Maxplus II tool provided by altera Co., Ltd, we have designed PN code generator, and sliding correlator for PN code acquisition. Then, they have been made into FPGA by way of EPM7064SLC44-10 - a chip of Altera Co., Ltd. Additionally, we have designed delay clock circuit which is faster than the clock of Tx PN clock, designed switching circuit to control the clock rate and data demodulation circuit. The performance of the transceiver is evaluated from the experimental results. Especially, the performance of PN code acquisition accomplished by sliding correlator which is very important to evaluate spread spectrum receiver is evaluated with the comparison of the lock states.

• The Journal of the Acoustical Society of Korea
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• v.41 no.1
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• pp.16-29
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• 2022

This paper presents a Doppler shift estimation method and signal processing schemes for Direct Sequence Spread Spectrum (DSSS) transmission to overcome the Doppler shift due to the moving of the underwater communication unit. The proposed method estimates a Doppler shift via 2 step procedures using the preamble with the two 64-length Frank sequences which has a good self-correlation characteristic and is insensitive to the Doppler shift. Furthermore, a packet of DSSS underwater mobile communication and a RAKE receiver are designed using the proposed Doppler shift estimation method. Due to the modulation scheme of the designed DSSS underwater mobile communication using Differential-Quadrature Phase Shift Keying (DQPSK) for the data symbol transmission, the RAKE receiver dose not need a phase tracking and easily makes coherent signals among the combining RAKE branches. The designed RAKE receiving scheme including the proposed Doppler shift estimation method successfully decides information data using the DSSS signal transmitted from the pseudo-moving transmitter with velocity upto about 17.5 m/s.

• Proceedings of the Korea Multimedia Society Conference
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• 2002.11b
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• pp.242-245
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• 2002

최근 인터넷의 보편화로 인한 디지털 컨텐츠의 폭발적 요구 증가로 디지털 저작권 보호를 위한 여러 기술들이 연구되고 있다. 디지털 워터마킹은 디지털 컨텐츠의 저작자의 정보를 삽입하여 저작권을 보호하는 기술이다. 본 논문에서는 DCT 영역에서 대역확산을 이용하여 이미지 압축에 강인하고, 비 가시성이 뛰어난 워터마킹 기술을 제안한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1700-1706
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• 2016

To improve the number of simultaneous transmissions of machine-to-machine traffic in a spread spectrum ALOHA channel, we propose a new spreading technique called doubly truncated cyclic code shift keying (DTCCSK). By truncating the codeset of cyclic code shift keying, DTCCSK freely adjusts the spreading factor and the symbol length. As a result, DTCCSK exhibits both a high spectral efficiency of M-ary signaling and low implementation complexity of a direct sequence.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.772-775
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• 2005

This paper describes a study on the digital watermarking algorithm which is used to confirm the copyright protection of digital audio data. The digital audio watermarking algorithm based on psychoacoustic model is used for the inaudibility of the watermark data. The psychoacoustic model which is a key algorithm in MP3 audio compression is analyzed by MATLAB simulation, and is applied to digital audio watermark insertion.

• Journal of Satellite, Information and Communications
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• v.4 no.2
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• pp.39-45
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• 2009

This paper proposes the specific code synchronization technique for DS-SS(Direct Sequence-Spread Spectrum transmission in the DVB-RCS +M standard. DS-SS is better than multi-carrier transmission method under nonlinear channel but imposes a long acquisition time. To improve the synchronization aspect, the robust correlation structure is introduced for acquisition and the nonlinear delay lock loop is done for tracking. MAT(Mean Acquisition Time) performances is shown to validate its superiority. In addition, code tracking and jitter performances are done when code tracking algorithm based on 2 oversamples which is not influenced by sampling clock timing offset and carrier freq. offset is used.

• 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.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.