• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.33A no.11
• /
• pp.10-18
• /
• 1996

In this paper, performance of a hybrid direct-sequency/slow-frequency-hopped (DS/SFH) spread-spectrum (SS) system with coherent BPSK modulation is analyzed. The bit error probability is derived over a frequency=-selective rician fading channel in the presence of multiple tone jamming. The fading channel is modeled as the wide-sense stationary uncorrelated scattering (WSSUS) model. Numerical evaluations are presented for some combinations of system parameters. The performance of a hybrid DS/SFH SS system is shown to be inferior to that of a ure DS SS system at low jamming-to-signal power ratio (JSR). At high JSR, the performance of a pure DS SS system is shown to be the smae as the worst case performance of a hybrid DS/SFH SS system.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.11 no.3
• /
• pp.19-29
• /
• 2008

Underwater acoustic(UWA) communication is one of the most difficult field in terms of severe channel environments such as multipath propagation, high temporal and spatial variability of channel conditions. Therefore, it is important to model and analyze the characteristics of underwater acoustic channel such as multipath propagation, transmission loss, reverberation, and ambient noise. In this paper, UWA communication channel is modeled with a ray tracing method and applied to image transmission. Quadrature phase shift keying(QPSK) and multichannel decision feedback equalizer(DFE) are utilized as phase-coherent modulation method and equalization technique, respectively. The objective is to improve the performance of the image transmission using vertical sensor array instead of single sensor in the viewpoint of bit error rate(BER), constellation diagram, and received image quality.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.12
• /
• pp.2047-2054
• /
• 1997

This paper describes a measuring method of vibration mode shapes by the Electronic Shearography. This method called the speckle interferometer has many merits in practical use, such as low sensitivity to environmental noise, low limit of coherent-length and simple optical configuration. In this study, we developed Michelson-type shearing interferometer provided with a phase stepping mirror and with a bias modulation mirror to quantify the vibration gradient fields. Results of application to a simple cantilever plate show that the vibration amplitude fields obtained are in good agreement with those of the electronic speckle pattern interferometry (ESPI).

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1994.10a
• /
• pp.432-438
• /
• 1994

This paper describes the measuring method of vibration mode shapes by the Electronic Shearography. Shearographic interferometer has many merits in practical use, that is low sensitive to the environmental noisy, liw limit of the coherent-length and simple optical configuration etc.. In this study, we developed Michelson-type shearing interferometer provided with a phase stepping mirror and with a bias modulation mirror to quantify the vibration gradient fields. As a results of application to a simple cantilever plate vibration amplitude fields were obtained by the proper integration technique, and their exprimental results were in good agreement with those of the ESPI experiment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.10 no.6
• /
• pp.951-958
• /
• 1999

Multicarrier modulation or orthogonal frequency division multiplexing(OFDM) is a promising technique for mobile communications systems, since it has a strong immunity to multipath fading without employing complicated adaptive equalization. In this paper, performance of MC DS-CDMA/MPSK(multi-carrier direct sequence-code division multiple access/mary phase shift keying) and DS-CDMA/MPSK(direct sequence-code division multiple access/mary phase shift keying) with coherent detection for a CDMA system over Nakagami fading channel analysis. For a given bandwidth, it is shown that MC DS-CDMA/MPSK eventually outperforms DS-CDMA MPSK with random sequences.

• Proceedings of the IEEK Conference
• /
• summer
• /
• pp.110-113
• /
• 2004

Underwater acoustic(UWA) communication is one of the most difficult field because of several factors such as multipath propagation, high temporal and spatial variability of channel conditions. Therefore, it is important to model and analyze the characteristics of underwater acoustic channel such as multipath propagation, transmission loss, reverberation, and ambient noise. In this paper, UWA communication channel is modeled with a ray tracing method and applied to image transmission. Quadrature phase shift keying(QPSK) and multichannel decision feedback equalizer(DFE) are utilized as phase-coherent modulation method and equalization technique, respectively. The objective is to improve the performance of vertical sensor array than that of single sensor in the viewpoint of bit error rate(BER), constellation output, and received image quality.

• Journal of Positioning, Navigation, and Timing
• /
• v.10 no.4
• /
• pp.335-340
• /
• 2021

A constant envelope multiplexing via constellation tailoring scheme is proposed for flexible power allocation of Global Navigation Satellite System (GNSS) signals. The proposed scheme is compared with the coherent adaptive subcarrier modulation (CASM) adopted in the L1 band signals of the Global Positioning System (GPS) in terms of power difference and power loss. Analysis of the constellation optimization results on the power difference and power loss show that the proposed scheme outperforms the CASM of the GPS signals in the allowable power difference of less than 0.1 dB.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.8 no.6
• /
• pp.88-97
• /
• 2009

As the development of wireless techniques, transmission technology of body area network plays an important role in realizing a welfare society by combining IT and BT when applying to vehicles. Off-body WBAN (Wireless Body Area Network) systems for video data transmission require low battery consumption and high data rate. To satisfy the requirement, UWB has been considered as a promising candidate for high rate WBAN. This paper introduces an antenna selection technique for ultra-wideband based off-body WBAN system with low complexity. In this paper, we propose an antenna selection scheme using non-coherent receiver for off-body high data rate WBAN system. The proposed receiver antenna selection method takes advantage of the characteristic of BPPM (Binary Pulse Position Modulation). With the property of BPPM, this scheme calculates the approximate SNR of the received signal with non-coherent receiver.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.7 no.1
• /
• pp.61-70
• /
• 1996

M-ary differential phase shift keying(DPSK)is a bandwidth efficient digital modulation technique and recently has attracted increased attention in mobile satellite communication application where the available radio bandwidth is limited. Coherent detection offers good BER performance in AWGN channel. However, it requires long acquisition times in fading environment. In this paper, we analyze the BER performance of M-ary DPSK signal using the Multiple Differ- ential Feedback Detection(MDFD) technique in Rician fading and shadowed Rician fading channel. MDFD is an efficient scheme to decrease the performance gap between differential and coherent reception by increasing the complexity of the conventional differential receiver to some extent. Compared to the multiple symbol maximum likelihood detection technique, the multiple differential feedback detection technique has a much simpler structure for hardware implementation. Espe- cially, this technique has application to land mobile satellite channel which can vary in time and space between AWGN and rapidly fading channel.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.12 no.5
• /
• pp.755-764
• /
• 2001

In this paper, we propose maximum likelihood (ML) decision feedback channel estimation (DFCE) for M-ary orthogonal modulation in direct sequence/code division multiple access (DS/CDMA) systems. The proposed DFCE uses the maximum combiner output in a RAKE receiver as decision feedback information, enabling M-ary orthogonal signals to be demodulated coherently and a RAKE receiver to use a em maximal ration combining (MRC) scheme. However, the performance of the proposed DFCE in the multiuser environment is severely degraded due to multiple access interference (MAI). To overcome this problem, a multistage parallel interference cancellation (PIC) scheme is combined with the proposed DFCE for multiuser environments. Accurate knowledge of the channel coefficient estimated by the proposed DFCE is used to regenerate the signal of each user for the multistage PIC scheme. According to the results of our simulations, the performance of coherent demodulation using the proposed system is significantly improved in comparison with conventional noncoherent demodulation.