• The Journal of the Acoustical Society of Korea
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• v.33 no.4
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• pp.255-261
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• 2014

This paper presents an underwater acoustic communication with nonlinear chirp modulation. The information is carried by the carrier amplitude, frequency or phase in the most common underwater acoustic communications. However, the proposed method includes the information within frequency variation of carrier wave for a symbol. Especially, as carrier wave the hyperbolic frequency modulated signal, one of the nonlinear chirp signal, is used and it is robust in the Doppler channel. The proposed method was analyzed and compared to conventional method by simulation. When the doppler shift existed, the error probability of the proposed method is reduced by 5~12 % than conventional method with linear frequency modulated signal. Sea trial was performed to analyze the performance of the proposed method.

• Journal of Satellite, Information and Communications
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• v.10 no.2
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• pp.109-114
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• 2015

Frame synchronization is achieved by correlation between received symbols and a preamble pattern which is periodically appended at a frame header. In this paper, we deal with a frame detection method complaint with satellite-based DVB-S2 system. In DVB-S2, frame synchronization is performed under the low signal-to-noise ratio(SNR), a large frequency offset which can be up to 20% of a symbol transmission rate and unknown modulation schemes ranging from QPSK to 32-APSK. In this environment, we propose a method combining differential correlation based on SOF and PLSC with an accumulated correlation method for the detection of frame structures. In addition, detection performances about mean acquisition time(MAT) and detection error probability are evaluated via computer simulations.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.4 s.334
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• pp.15-20
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• 2005

Multi-Input, Multi-Output system suffers for the spatial channel correlation due to lack of spatial diversity. To overcome this defect, the antenna selection and switching system is proposed which selects the adequate antenna subset with highest channel diversity gain and switches the trasmission techniques according to channel environments. However. its performance analysis is insufficient due to the difficulty of modeling the spatial channel correlation. In this paper, the theoretical upper bound of symbol error probability is derived by using the statistical properties of Frobenius norm and minimum eigen-value of channel matrix. By computer simulation, it is shown that the derived theoretical upper bound is similar to the simulation results.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.6
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• pp.1-8
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• 1999

Multi-carrier CDMA is a transmission scheme where data symbols are spread in the frequency domain with a spread code then transmitted using multiple carriers. It is robust against narrowband interference because of its long symbol duration. However, due to large sidebands of the rectangular window frequency response, subchannels spectrally overlap with neighboring subchannels, which leads to substantial intercarrier interference in a dispersive channel. In this paper, we consider a mult-carrier CDMA system where subchannel spectral containment is achiveved by M-band cosine modulated filter bank (CMFB). In CMFB based MC-CDMA, subchannel spectral containment is achieved using the filter bank of longer impulse response than that of conventional discrete Fourier transform (DFT) filter bank. We show that spectral containment feature of the CMFB based fading channel is analyzed using computer simulations.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.10
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• pp.2100-2112
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• 2011

An orthogonal code hopping multiplexing (OCHM) technique has been proposed for accommodating a large number of users with low channel activities than the number of orthogonal codewords through statistical multiplexing in downlink cellular systems. In this paper, a multiple input multiple output (MIMO) antenna based OCHM system is proposed to improve the performance. Each modulated symbol is repeated N times and the N repeated symbols are transmitted simultaneously using N transmit antennas. Through repetitions, the effect of perforations that the OCHM system experiences is decentralized among the repeated symbols and the full perforation probability is significantly reduced. Each receiver detect the transmitted signal using its pre-assigned code hopping pattern. Simulation results show that the proposed scheme saves the required energy for a given frame error rate (FER).