• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.19 no.4
• /
• pp.729-739
• /
• 1994

In a centralized spread-spectrum packet radio network, a random assignment -transmitter-based spreading code protocol(RA-T) is proposed which permits the contention mode only in the trasmission of a preamble while avoiding collision during the data packet transmission by assigning near-orthogonal spreading codes to each user. Compared to the conventional transmitter-based code scheme, this scheme allows reduction in receiver complexity when only a small number of distinct spreading codes are employed for the preamble transmission. Throughout theoretical and simulation results, it is shown that the use of the RA-T scheme with just two or three distinct codes for the preamble packet achieves most of the performance gain.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.24 no.6A
• /
• pp.775-781
• /
• 1999

A multi-media variable processing gain DS/CDMA system are considered. Two types of information sources with different rates and transmitting powers are assumed to be stransmitted simultaneously in the same channel. Average signal-to-noise ratios at the correlation receiver outputs for each type of information sources are analytically derived as funtions of partial cross-correlations between spreading code sequences. As the difference of information rates between information sources increase, the difference between signal-to-noise ratio regarding random spreading code and that regarding pseudo random spreading code increases (maximum 1.3dB). The result can provide a analytical tools for use in multi-media DS/CDMA system design.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.11B
• /
• pp.1725-1731
• /
• 2010

In this paper, we proposed preamble structure and code acquisition method to improve code acquisition performance for DS-SS/TDMA packet communication systems. Proposed algorithm changes the short PN code position depending on the sub slot number. Proposed algorithm also saves position differences between short PN codes and position offsets between short PN codes and data starting position of the TDMA packet. By using the position difference table, proposed algorithm can find out exact data starting position even though some sub slots were defected. As a result of simulation, we concluded that proposed algorithm has at least 5dB gain compared to conventional method when same short PN code is used. Moreover, proposed algorithm shows same code acquisition performance only with 1/4 shortened short PN code compared to conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.12A
• /
• pp.1205-1213
• /
• 2006

In this paper, we analyze the IQ(In-phase/Quadrature) imbalance effects at both transmitter and receiver side of OFDM(Orthogonal Frequency Division Multiplexing) and show that IQ imbalance is the parameter to improve the performance using ML and OSIC scheme. Especially, we can archive the diversity gain due to the IQ imbalance in multipath fading environment. In addition, new preamble format is proposed, which enable estimation of the channel and IQ imbalance parameters to maximize the diversity gain. Significant performance improvement is achieved by using the ML(Maximum Likelihood)and OSIC(Ordered Successive Interference Cancellation) with compensation compared to a standard receiver with no compensation for IQ imbalance and proposed channel estimation scheme achieves the better performance improvement than conventional.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.11 no.3
• /
• pp.429-436
• /
• 2000

In this paper, the performance of a orthogonal noncoherent FH-BFSK communication system in the presence of partial band noise jamming is analyzed. Also bit error rate(BER) is studied when jamming bandwidth ratio to overall spread spectrum bandwidth,$\rho$, changes according to processing gain(PG). The performance is investigated by numerical analysis and computer simulation of SPW. Even if PG is high, required performance could not gain because error floor occurs when JSR is 10 dB and SNR is under 10 dB. PG can be obtained to acquire a required BER according to $\rho$ when SNR is above 12 dB.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.36D no.3
• /
• pp.41-47
• /
• 1999

Ion implanted GaAs MESFET with low resistive layer was fabricated using Si diffusion into GaAs from SiN. During the thermal annealing at 95$0^{\circ}C$ for 30s, Si diffused into ion implanted region of GaAs from SiN and they formed low resistive layer of 350$\AA$ thickness. The diffusion of Si decreased the sheet resistance of source and drain region from 1000$\Omega$/sq. to 400$\Omega$/sq. and the AuGe/Ni/Au ohmic contact resitivity from 2.5$\times$10sub -6$\Omega$-cmsup 2 to $1.5\times$10sup -6$\Omega$-cmsup 2. The fabricated lum gate length MESFET with Si diffused surface layer shows the transconductance of 360ms/mm, 8.5dB of associated gain and 3.57dB of minimum noise figure at 12GHz. These performances are better than that of MESFET without Si diffused layer.

• Journal of KIISE:Software and Applications
• /
• v.37 no.10
• /
• pp.751-759
• /
• 2010

This paper is to propose a method to enhance the connectivity of the broken structures. The pixels to be connected are found by a decision rule which is based on the intensity and gradient information of the neighboring pixels. The intensity of the pixel, if it is decided to be filled, is increased so that the pixel together with its neighbors looks connected. The anisotropic diffusion follows to make the connected structural region look more natural. The same structure matrices have been used both to get gradient information and to decide the direction of diffusion to improve the computational speed. It has been shown by the experiments on the real ultrasound images that the broken structural regions can be connected by the proposed method.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.18 no.2
• /
• pp.207-217
• /
• 1993

In this paper, knowing a priori probability of phase offset between transmitted codes and reference codes in the receiver, we construct the state diagram of acquisition process of the direct sequence spread-spectrum communication system using the expanding window search. The scannings are performed from the cell with higher probability code epoch synchronization to that with lower one. We expand window size from initial value by r times of its previous size in each search, construct the corresponding the state diagrams, and derive average synchronization time using the Markov process and Mason's gain formula. Average synchronization times versus number of search n and detection probability $P_d$ are calculated.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.13 no.5
• /
• pp.492-499
• /
• 2002

Performance analysis and comparison of the hybrid DS-SFH spread-spectrum (SS) system using coherent MSK and QPSK modulation techniques over Rayleigh fading channel are considered in the presence of MTJ(multi-tone jamming). To analyze the BER performance of the hybrid systems with or without the Rake receiver, signal-to-noise plus interference ratio is derived as a function of the average signal-to-noise ratio, the jammer-to-signal ratio and other system parameters. Numerical results show that the performance difference between the two modulation schemes, MSK and QPSK, is negligible for low JSR, while it becomes significant with the increase of JSR. In multi-path Rayleigh fading channel without Rake receiver, the performances of the two modulation schemes are slightly improved as the DS spreading gain is increased when the total SS bandwidth is fixed. In particular, there is an optimum DS spreading gain for large JSR, in which a minimum BER is achieved, while only DS spreading gives the best performance for small JSR. For hybrid systems with Rake receiver, it is shown that the hybrid system of the MSK modulation scheme provides better anti-jamming performance and larger performance improvement with the increase of multi-path resolution capability of Rake receiver than that of QPSK modulation for all conditions.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.1
• /
• pp.13-22
• /
• 2004

This paper drives the exact expression of bit error rate(BER) performance for successive interference cancellation(SIC) algorithm against multipath interference components in a high-speed downlink packet access(HSDPA) system of W-CDMA downlink and the BER performance is evaluated by numerical analysis. Numerical results showed that the average BER performance is rapidly saturated in terms of increasing the number of multipath and is revealed significant improvement for improvement Processing gain(PG). For example, the average BER Performance of the SIC algorithm is superior to the performance of conventional scheme by more than 7dB and 1.4dB for processing gain PG=54 and 128 under the two-path channel and average BER=$1.0{\times}10^{-3}$, respectively. This results also indicated that the average BER saturation is occurred at nearly one weight factor which is assigned to pilot and data channels. Likewise, the average BER performance is greatly degraded due to increasing the interference power in proportional to the number of multipath with increasing multicode K. And the smaller multipath fading channel gain is arrived later, the more the average BER performance is improved. The results of performance analysis in this paper indicated that the multipath interference cancellation is required to improve the BER performance in a HSDPA system under multicode for high-speed packet transmission, low spreading factor, and multipath fading channel.