• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.7C
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• pp.706-714
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• 2009

In this paper, we proposed a burst mode AGC loop and preamble detector applicable for VDL(VHF Digital Link) mode-2 using D8PSK modulation scheme and the performance analysis of proposed schemes is described. Generally the AGC scheme can be divided into two types, continuos and burst mode AGC. The continuos mode is performed well only with an analog feedback AGC loop. But the analog feedback AGC loop is not suitable for burst mode since its gain lock time is more than preamble duration, which causes the preamble detector misses preamble. Hence a fast digital AGC loop is required for burst mode. Also the AGC loop has to be designed with full gain during idle time to detect bursts although the signal level is very low. If the time to acquire gain lock is slow, the preamble detector fail to detect burst due to saturation of a lot of preamble samples. The receiver performance might be down even if the burst was detected because the preamble is used to estimate several parameters need to demodulation at receiver. In this paper we analysed relationships between the AGC loop and preamble detector. we present an AGC loop and preamble detector in burst mode.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5C
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• pp.469-477
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• 2007

Most multimedia source coders exhibit unequal bit error sensitivity. Efficient transmission system design should therefore incorporate the use of matching unequal error protection (UEP). In this paper, we present and evaluate a flexible space-time coding system with unequal error protection. Multiple transmit and receive antennas and bit-interleaved coded modulation techniques are used combined with rate compatible punctured convolutional codes. A near optimum iterative receiver is employed with a multiple-in multiple-out inverse mapper and a MAP decoder as component decoders. We illustrate how the UEP system gain can be achieved either as a power or bandwidth gain compared to the equal error protection system (EEP) for the identical source and equal overall quality for both the UEP and EEP systems. An example with two/three transmit and two receive antennas using BPSK modulation is given for the block fading channel.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.9
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• pp.1654-1665
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• 2008

This paper presents bit splitting methods to apply multilevel modulation to iterative codes such as turbo code, low density parity check code and turbo product code. Log-likelihood ratio method splits multilevel symbols to soft decision symbols using the received in-phase and quadrature component based on Gaussian approximation. However it is too complicate to calculate and to implement hardware due to exponential and logarithm calculation. Therefore this paper presents Euclidean, MAX, sector and center focusing method to reduce the high complexity of LLR method. Also, this paper proposes optimal soft symbol split method for three kind of iterative codes. Futhermore, 16-APSK modulator method with double ring structure for applying DVB-S2 system and 16-QAM modulator method with lattice structure for T-DMB system are also analyzed.

• Journal of Broadcast Engineering
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• v.12 no.1 s.34
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• pp.2-10
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• 2007

We analyzed the receiving performance of the DVB-S2 transmission system in the BC(Backward Compatibility) mode. The transmitter employs the hierarchical modulation, and the receiver can be implemented by the direct demodulation or the hierarchical demodulation. The performance of each demodulation scheme is analyzed by a statistical method and a computer simulation for the AWGN and nonlinear channels. The ratio of the LP/HP streams which is proper in the domestic satellite broadcasting environments, is also suggested.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.8
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• pp.2900-2922
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• 2021

In this paper, the power spectral density(PSD) for Multilevel Minimum Shift Keyed signal with modulation index h = 1/2 (M-ary MSK) are derived using the mathematical method of the Markov Chain model. At first, according to an essential requirement of the phase continuity characteristics of MSK signals, a complete model of the whole process of signal generation is built. Then, the derivations for autocorrelation functions are carried out precisely. After that, we verified the correctness and accuracy of the theoretical derivation by comparing the derived results with numerical simulations using MATLAB. We also divided the spectrum into four components according to the derivation. By analyzing these figures in the graphic, each component determines the characteristics of the spectrum. It is vital for enhanced spectral characteristics. To more visually represent the energy concentration of the main flap and the roll-down speed of the side flap, the specific out-of-band power of M-ary MSK is given. OMLCD(Optimum Maximum Likelihood Coherent Detection) of M-ary MSK is adopted to compare the signal received with prepared in advance in a code element T to go for the best. And M-ary MSK BER(Bit Error Rate) is compared with the same ary PSK (Phase Shift Keying) with M=2,4,6,8. The results show the detection method could improve performance by increasing the length of L(memory inherent) in the phase continuity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.10A
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• pp.1147-1158
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• 2004

In this paper we design STBC-OFDM systems by applying several STBC schemes to the OFEM system and show their comparative analysis results obtained through computer simulations under Rayleigh fading environments, considering the effect of channel estimation error. We first consider the space-time coding algorithms of major STBC schemes, together with their demodulation algorithms. We then select the OFDMparameters considering mobile environments and design the STBC-OFDM systems by choosing one of digital modulation schemes such as QPSK, BPSK, 16QAM, 64QAM, and 256QAM according to the transmission rate, and describe the block diagrams of the demodulator and channel estimator. We finally compare and analyze the BER performances of the STBC-OFDM systems according to the transmission rate and the number of receive antennas.