• The KIPS Transactions:PartC
• /
• v.8C no.6
• /
• pp.703-710
• /
• 2001

In this paper, we consider a multiple watermarking for image copyright protection. Multiple watermarking can be defined that two or more watermarks are inserted into the same content. Multiple watermarking using spread spectrum technique is able to extract the correct watermarks from the watermarked content when the orthogonality among keys should be guaranteed only. To keep the orthogonal property between keys, we perform the process of Gram-Schmidt on the random sequences. The orthogonalized sequences are used as keys to embed the watermarks. The proposed method can not only extract correctly the embedded watermarks but also show the robustness against various attacks such as Gaussian noise addition, histogram equalization, gamma correlation, sharpening and brightness/contrast adjustment.

• Journal of Communications and Networks
• /
• v.16 no.1
• /
• pp.36-44
• /
• 2014

Exploiting the energy-delay tradeoff for energy saving is critical for developing green wireless communication systems. In this paper, we investigate the delay-constrained energy-efficient packet transmission. We aim to minimize the energy consumption of multiple randomly arrived packets in an additive white Gaussian noise channel subject to individual packet delay constraints, by taking into account the practical on-off circuit power consumption at the transmitter. First, we consider the offline case, by assuming that the full packet arrival information is known a priori at the transmitter, and formulate the energy minimization problem as a non-convex optimization problem. By exploiting the specific problem structure, we propose an efficient scheduling algorithm to obtain the globally optimal solution. It is shown that the optimal solution consists of two types of scheduling intervals, namely "selected-off" and "always-on" intervals, which correspond to bits-per-joule energy efficiency maximization and "lazy scheduling" rate allocation, respectively. Next, we consider the practical online case where only causal packet arrival information is available. Inspired by the optimal offline solution, we propose a new online scheme. It is shown by simulations that the proposed online scheme has a comparable performance with the optimal offline one and outperforms the design without considering on-off circuit power as well as the other heuristically designed online schemes.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.11
• /
• pp.25-32
• /
• 2004

In this paper, we first analysed the ability of DSSS resistance against noises, which are main interferences to the four types in power line communications. Based on the characteristic of these noises, we made a noise source of power line which is similar with the result measured, in practice. We simulated and analysed the BER performance of BPSK with DSSS over this noise model and one without the DSSS, for comparison. Result showed that the BPSK with DSSS system has improved by 8 dB, as compared to those without the DSSS, as against power line noises.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.6 no.4
• /
• pp.539-544
• /
• 2011

Balanced binary sequences of period $2^n-1(n{\geq}1)$ having the two-valued autocorrelation function have many applications in spread-spectrum communications system. In this paper we propose new nonlinear binary sequences which are constructed from Legendre sequences with the same cross-correlation as the sequences proposed by Cho. These sequences include the m-sequences, GMW sequences, Kasami sequences and No sequences which are described in terms of the trace function over a finite field. Also the proposed sequences have more low cross-correlation distribution than the quadratic form sequences proposed by Klapper.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.11A
• /
• pp.1085-1090
• /
• 2010

Ultra wideband (UWB) technologies have been developed to exploit a new spectrum resource in substances and to realize ultra-high-speed communication, high precision geolocation, and other applications. The energy of UWB signal is extremely spread from near DC to a few GHz. This means that the interference between conventional narrowband systems and UWB systems is inevitable. However, the interference effects had not previously been studied from UWB wireless systems to conventional mobile wireless systems sharing the frequency bands such as Cellular CDMA and Korean PCS. This paper experimentally evaluates the interference from two kinds of UWB sources, namely a direct-sequence spread-spectrum UWB source and an impulse radio UWB source, to a Cellular CDMA and K-PCS digital transmission system. The average frame error rate degradation of each system arc presented. From these experimental results, we show that in all practical cases UWB system can coexist with Cellular CDMA and K-PCS terminal without causing any dangerous interference.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.7A
• /
• pp.554-561
• /
• 2009

In this paper, we propose a novel Vehicular Ad-hoc Network(VANET) which includes communication and ranging features, using Spread Spectrum(SS) multi-carrier modulation scheme. In existing methods, a spread spectrum technique was used to communicate with other vehicles and raging was possible by detecting phase difference between transmission/reception of the PN signal. However, the use of high-speed PN signals is mandatory to detect possible errors of phase difference and to increase the analysis capacity. In the proposed system, multi-carrier modulation scheme was used as solution of mentioned problem. The multi-carrier modulation scheme uses smaller PN signal and chip-rate than the single-carrier modulation, so it is possible to send multiple carrier waves using the same frequency range. This technique (multiple carrier waves) allows to have the Equal Gain Combing (EGC) diversity effect, providing better result in phase difference error detection and raging accuracy.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.23 no.8
• /
• pp.988-995
• /
• 2019

In this paper, we propose the Tile Based Frequency Hopping - Chirp Spread Spectrum(TBFH-CSS) technique, which has excellent Low Probability of Intercept(LPI)/Anti-Jamming(AJ) performance. Conventional Frequency Hopping - Chirp Spread Spectrum(FH-CSS) technique uses only single chirp signal, that makes the follower jammer easy to find and jam. However, proposed TBFH-CSS uses various kind of chirp signals which are generated according to the structure of basis tile, it is composed the basis time unit and the basis bandwidth unit. The TBFH-CSS signal has variety signal period and signal bandwidth. Therefore, the follower jammer hard to find and difficult to jam the TBFH-CSS signal. We analysis the LPI/AJ performance of the TBFH-CSS technique when the follow jamming attack exist and compared with the performance of the conventional FH-CSS technique. From the analysis, we can see the proposed TBFH-CSS technique has better LPI/AJ performance than conventional technique.

• Proceedings of the Korean Institute of Communication Sciences Conference
• /
• 1983.10a
• /
• pp.88-92
• /
• 1983

The performance of noncoherent fast frequency-hopped spread spectrum multiple access communication systems with square-law combining over fading channel is presented. The expression for the probalility of error as a performance measure is derived by means of momenting function of the dedecision variables, and the cross-covariance of the fading process the ambiguty function of the transmitted signals.

• Proceedings of the IEEK Conference
• /
• 2001.09a
• /
• pp.971-974
• /
• 2001

Multi-Carrier Spread Spectrum communications has shown the ability of transform domain excision using the wavelet transformation to improve system performance when transmitting signals in the presence of additive white Gaussian noise and interference. In such work, the transforms were implemented using FIR filters and IIR filter. Some well-known classes of sequences, such as Pseudo noise, Walsh, Cold sequences are evaluated with respect to the basic criteria. The main objective is to implement the wavelet transform using IIR filters. This filters are well known to have sharper transition regions leading to better performance. Numerical simulation of multi-carrier spread spectrum communication systems have shown that IIR filters are better in removing the sinusoidal jammer and subsequently yield better BER performance.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.33A no.11
• /
• pp.19-31
• /
• 1996

Spread spectrum method gurantees good performance in digital communication system under multi-path interference and jamming signals. The purpose of this paper is to develop the wireless modem using DS/SS techinque. The transceiver consists of a spread spectrum DQPSK transmitter and a mtching receiver. The system operates with the chipping rate set to 4 Mcps and the number of chips/symbol at 64, making the data rate 62.5 Kbps using QPSK modilation. The receiver section uses a digital matched filter for fast acquisition of burst signals and uses the comparing the BER of proposed system iwth that of narrow bnd system under various additive white gaussian noises. It is showen that the proposed sysem has better performance than narrow band system. When jamming signals is added to the suggested DS/SS system, we also show that the experimental performance (BER) of the suggested wireless modem is almost same as theroretical performance.