• The Journal of the Acoustical Society of Korea
• /
• v.13 no.2
• /
• pp.30-37
• /
• 1994

Since the morden targets are of high speed and getting quiet in both active and passive mode, the necessities of developing advanced SONAR system capable of performing target motion analysis (TMA) and target classification are evident. In order to develop such a system, the scattering mechanism of complex bodies needs to be, some extent, fully understood and modeled. In this paper, MOving Spread Target(MOST) signal simulation model is presented and discussed. The model is based on the highlight distribution method, and simulates pulse elongation of spread target, doppler effect due to kinematics of the target as well as SONAR platform, and distribution target strength of each highlight point (HL) with directivity. The model can be used in developing and evaluating advanced SONAR system through system simulation, and can also be used in the development of target state estimation algorithm.

• The Journal of the Acoustical Society of Korea
• /
• v.40 no.4
• /
• pp.370-381
• /
• 2021

This paper presented an efficient transceiver structure of multiband Frequency Shift Keying (FSK) signals with direct sequence spread spectrum for maintaining covertness and performance. In aspect to covertness, direct sequence spread spectrum method, which multiplying by Pseudo Noise (PN) codes whose rate is much higher than that of data sequence, is employed. In aspect to performance, in order to overcome performance degradation caused by multipath and Doppler spreading, we applied multiband, turbo equalization, and weighting algorithm are applied. Based on the simulation results, by applying 4 number of multiband and number of chips are 8 and 32, experiments were conducted in a lake with a distance of moving from 300 m to 500 m between the transceivers. we confirmed that the performance was improved as the number of bands and chips are increased. Furthermore, the performance of multiband was improved when the proposed weighting algorithm was applied.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.9C
• /
• pp.871-879
• /
• 2009

The performance variations of a spatio temporal smart antenna which is equipped at the basestation of CDMA cellular communication network due to the parametric change of multipath fading environment are studied in this paper. The smart antenna of interest employs space diversity based adaptive array structure in conjunction with rake receiver that has fingers the number of which is the same as that of multipath links. The beamforming is achieved via LMS(Least Mean Square) algorithm in which a reference signal is generated using decision directed formula. It has been shown by computer simulation that the performance of our smart antenna of interest depends significantly upon not only the degree of desired signal's DOA(Direction of Arrival)spread but the number of fingers of the rake receiver. The relative insensitivity of the smart antenna's performance on desired signal's delay spread has also been observed. Computer simulation has shown that the increase of the number of fingers brings in a nonlinear enhancement of the performance of our smart antenna. The renewal of weight vector in the beamforming procedure is taken place at post PN despread stage.

• International Journal of Fuzzy Logic and Intelligent Systems
• /
• v.15 no.1
• /
• pp.20-26
• /
• 2015

It is very difficult to design an underwater communication system because of multipath, Doppler effects, noise, and attenuation. These factors lead to errors in the communication performance and maximum propagation distance. In this study, we calculate the distance that can be realized using the direct-sequence code division multiple access (DS-CDMA) technique with direct-sequence spread spectrum (DSSS) in an underwater communication system considering only the attenuation and noise. We also compare the estimated and calculated propagation distances obtained for several different scenarios.

• Proceedings of the IEEK Conference
• /
• 1998.06a
• /
• pp.42-45
• /
• 1998

Adaptive array antenas have emerged as a useful technique to enhance the cell capacity of mobile communications. In this research, to analyze the noncoherent CDMA systems employing adaptive array antennas, we modeled the transmitting signal of CDMA systems using M-ary orthogonal modulation. And we induced the conditional probability density function about the decision variable, the output of 2D-RAKE receiver and mean symbol error prabability through statistical analysis about MAI(Multiple Access Interference), SI(Self Interference) and Noise. Also, we analyzed the charateristics of adaptive array antenna for noncoherent CDMA systems using M-ary orthogonal modulation according to the distance between the array elements, doppler frequency and AOS(Angle of Spread).

• Proceedings of the IEEK Conference
• /
• 1999.06a
• /
• pp.130-133
• /
• 1999

In the view point of further reducing the inter-symbol interferences studied in our previous paper 〔1〕, a quadrature pair of wavelet-based filter banks that are composed of a pair of cosine and sine modulated filter banks is applied to MC-CDMA transmultiplexing. For that fact, the symbol duration gets twice longer than the one in , 〔1〕, the interference effects due to channel overlapping and Doppler spread can be effectively alleviated while increasing the channel utilization efficiency. Moreover, the well-known wavelet properties are exploited to design the prototype filter in such a way to maintain the size of sidelobes much smaller than those of the FFT, the interference reduction effect can be further obtained. To verify the behavior of our proposed quadrature filter bank based MC-CDMA system, the reverse-link bit error rates with respect to SNR under Rayleigh fading and additive white Gaussian noise channel environments are computed. The results show an improved system performance over the conventional MC-CDMA.

• Archives of Plastic Surgery
• /
• v.41 no.3
• /
• pp.225-230
• /
• 2014

The increased application of the da Vinci robotic platform (Intuitive Surgical Inc.) for microsurgery has led to the development of new adjunctive surgical instrumentation. In microsurgery, the robotic platform can provide high definition $12{\times}-15{\times}$ digital magnification, broader range of motion, fine instrument handling with decreased tremor, reduced surgeon fatigue, and improved surgical productivity. This paper presents novel adjunctive tools that provide enhanced optical magnification, micro-Doppler sensing of vessels down to a 1-mm size, vein mapping capabilities, hydro-dissection, micro-ablation technology (with minimal thermal spread-$CO_2$ laser technology), and confocal microscopy to provide imaging at a cellular level. Microsurgical outcomes from the use of these tools in the management of patients with infertility and chronic groin and testicular pain are reviewed. All these instruments have been adapted for the robotic console and enhance the robot-assisted microsurgery experience. As the popularity of robot-assisted microsurgery grows, so will its breadth of instrumentation.

• Ocean and Polar Research
• /
• v.25 no.4
• /
• pp.437-446
• /
• 2003

Field measurements of directional waves were carried out during the summer of 2002 at two coastal sites in water of finite depth. A couple of general purpose instruments were used employing acoustic Doppler technology. The aim of the study was to investigate the spatial behavior of the directional movement of waves as they come ashore. In total,74 tests were carried out during which sea states of low to moderate intensity were recorded. A great number of these runs displayed bimodal characteristics of the spreading function at high frequencies. It was found that in general, the frequency-integrated directional width tends to broaden as the water shoals and when refraction effects are negligible. This is attributed to wave-wave interactions that become pronounced in shallow water. The same directional width showed, also, a tendency to increase with increasing peak frequency of the sea state spectrum. The behavior of the kurtosis of the spreading function was also examined. It was found that for higher frequencies this index tends to increase in wave spectra above a certain sea severity threshold.

• ETRI Journal
• /
• v.29 no.1
• /
• pp.79-88
• /
• 2007

This paper proposes a novel concept of adjusting the hardware size in a multi-carrier code division multiple access (MC-CDMA) receiver in real time as per the channel parameters such as delay spread, signal-to-noise ratio, transmission rate, and Doppler frequency. The fast Fourier transform (FFT) or inverse FFT (IFFT) size in orthogonal frequency division multiplexing (OFDM)/MC-CDMA transceivers varies from 1024 points to 16 points. Two low-power reconfigurable radix-4 256-point FFT processor architectures are proposed that can also be dynamically configured as 64-point and 16-point as per the channel parameters to prove the concept. By tailoring the clock of the higher FFT stages for longer FFTs and switching to shorter FFTs from longer FFTs, significant power saving is achieved. In addition, two 256 sub-carrier MC-CDMA receiver architectures are proposed which can also be configured for 64 sub-carriers in real time to prove the feasibility of the concept over the whole receiver.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.9 no.1
• /
• pp.98-107
• /
• 1998

For implementation of FM-DS/SS system. This paper has analyzed SO(Synchronous Oscillator) being oscillated by the motivation of injected signal. Transmitter has adopted FM-DS/SS modulation method using RF output-signal of FM. Receiver is used SO to demodulation of FM-DS/SS and applied sliding correlator for synchronization of PN clock. As a result of the inspection, SO presented stable lock ability in spite of doppler apperance and proved the synchronous properties of it in the FM-DS/SS system.