• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.7
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• pp.39-44
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• 2009

It is well-known that the performance of turbo codes can be improved by allocating different energies per code symbol. In this paper, based on this observation, we propose a joint encoding and modulation scheme for quadrature amplitude modulated turbo code systems. In the proposed scheme, the amount of energy difference between the turbo coded symbols is optimized by optimizing the constellation of quadrature amplitude modulation (QAM). The proposed scheme offers better coding gain compared to the conventional combination of binary turbo code and QAM at the bit error rate of 10$^{-5}$. Also, the performance of binary turbo codes with the proposed QAM constellation for various code symbol mapping strategies are verified.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.3
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• pp.282-291
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• 2011

Adaptive modulation(AM) is an important technique to increase the system efficiency, in which transmitter selects the most suitable modulation mode adaptively according to channel state in the temporary and spatially varying communication environment. Fixed modulation on channels with varying signal-to-noise ratio(SNR) is that the bit-errorrate(BER) probability performance is changing with the channel quality. An adaptive modulation scheme can be designed to have a BER which is constant for all channel SNRs. The correct as well as fast and simple SNR estimation is required essentially for this adaptive modulation. In order to operate adaptive modulation system effectively, in this paper, we analyze the effect of SNR estimation performance to it through the average BER and data throughput. Applying SNR estimation based on auto-correlation of decision feedback signal and others to adaptive modulation system, we also confirm performance degradation or improvement of its which is decided by SNR estimation error at each transition point of modulation level. Since SNR estimation based on auto-correlation of decision feedback signal shows stable estimation performance for various quadrature amplitude modulation(QAM) comparatively, this can be reduced degradation than others at each transition point of modulation level.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.3
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• pp.3-10
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• 2016

To establish a network environment where multiple wireless personal area networks(WPAN) are simultaneously operating in the same area, we need to consider the effects of inter-device interference. The extent of interference effect from neighboring frequency channel interferer may be different depending on the modulation types that are used for constructing the wireless network. If a modulation scheme with high spectral side lobes is used, the spatial separation between devices plays a major role in determining the amount of interference from neighboring frequency channel interferer. In this paper, we investigate the effect of inter-device interference in the overlapped raised cosine offset quadrature-quadrature phase shift keying (ORC-$OQ^2PSK$) modulation based WPAN. By comparing the results with those of GFSK modulation based WPAN, we verify the feasibility of ORC-$OQ^2PSK$ based WPAN.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.3
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• pp.31-38
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• 2004

The wavelength variation of a scanned fiber laser is analyzed using quadrature sampling technique. By time delayed sampling of a phase modulated Mach-Zender interferometer, the wavelength information can be precisely determined regardless of the nonlinearity in the Fabry-Perot wavelength filter which scanned the fiber laser. A wavelength readout resolution of ～20 pm was obtained at 2 KHz M-Z modulation frequency, and it was shown that the resolution could be improved in case of using an electro-optic phase modulator.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.77-79
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• 2016

In this paper, we consider hierarchical modulation (HM), which has been widely exploited in digital broadcasting systems. In HM, each independent data stream is mapped to the modulation symbol with different transmission power and normalization factors of conventional M-QAM cannot be used. In this paper, we derive the method and formula for exact normalization factor of three-level hierarchical 64QAM.

• Proceedings of the IEEK Conference
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• 2001.06a
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• pp.5-8
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• 2001

SSB(Single Sideband) modulation scheme is high bandwidth efficient method in the mobile communication system compared with present DSB(Double Sideband) modulation scheme. Using the othogonality between inphase PN code and Hilbert transformed quadrature PN code, we propose phase estimation structure that enables coherent demodulation in the reverse link basestation receiver Several system characteristics, bit error rate and phase error variance, are simulated and compared with balanced QPSK DS/CDMA system. To verify system performance, SSB/BPSK-DS/CDMA test board is implemented using FPGA chips.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.1
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• pp.93-99
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• 2008

In this paper, we propose new modulation schemes using the conventional CACB modulation with constant amplitude property. Also the proposed modulation schemes supports high transmission data rate by increasing the spectral efficiency. In order to obtain the high spectral efficiency, the $Q^2$PSK and CA-$Q^2$PSK are used. We explain the simplest combining modulation scheme of CACB and $Q^2$PSK (i.e., CACB-$Q^2$PSK). However, this modulation scheme cannot support the constant amplitude property. Hence the first CACB-CA-$Q^2$PSK (or CACB-CA-$Q^2$PSK I) modulation scheme is proposed for the constant amplitude property. In the modulation scheme, the redundant constant amplitude encoding (spectral efficiency decrease) is required. Therefore, the second CACB-CA-$Q^2$PSK (or CACB-CA-$Q^2$PSK II) modulation scheme is proposed retaining the constant amplitude and the spectral efficiency. Computer simulations show that the proposed CACB-CA-$Q^2$PSK II is the efficient modulation scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.6B
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• pp.1082-1091
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• 2000

In this paper, the efficient equalization method for OFDM(Orthogonal Frequency Division Multiflexing) System using the QAM(Quadrature Amplitude Modulation) in multipath fading channel is proposed in order to faster and more efficiently equalize the received signals that are sent over real channel. In generally, the one-tap linear equalizers have been used in the frequency-domain as the existing equalization method for OFDM system. In this technique, if characteristics of the channel are changed fast, the one-tap linear equalizers cannot compensate for the distortion due to time variant multipath channels. Therefore, in this paper, we use one-tap non-linear equalizers instead of using one-tap linear equalizers in the frequency-domain, and also use the linear equalizer in the time-domain to compensate the rapid performance reduction at the low SNR(Signal-to-Noise Ratio) that is the disadvantage of the non-linear equalizer. In the frequency-domain, when QAM signals, consisting of in-phase components and quadrature (out-phase) components, are sent over the complex channel, the only in-phase and quadrature components of signals distorted by the multipath fading are changed the same as signals distorted by the noise. So the cross components are canceled in the frequency-domain equalizer. The time-domain equalizer and the adaptive algorithm that has lower-error probability and fast convergence speed are applied to compensate for the error that is caused by canceling the cross components in the frequency-domain equalizer. In the time-domain, To compensate for the performance of frequency-domain equalizer the time-domain equalizes the distorted signals at a frame by using the Gold-code as a training sequence in the receiver after the Gold-codes are inserted into the guard signal in the transmitter. By using the proposed equalization method, we can achieve faster and more efficient equalization method that has the reduced computational complexity and improved performance.

• The Journal of the Acoustical Society of Korea
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• v.10 no.4
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• pp.19-26
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• 1991

$GQ^2PSK$ which is a novel digital mobile communication modulation scheme has been introduced and described. $GQ^2PSK$ is a modulation scheme that bandlimits NRZ digital data with Gaussian filter and modulates it by $Q^2PSK$ scheme which uses two shaping pulses and two carriers which are pairwise quadrature. Thus transmission bit rate can be enhanced and available signal space dimensions are more efficiently utilized, with comparison to the already-existing GMSK, QPSK and OQPSK modulation methods. Via the computer simulation, bit error rate of $GQ^2PSK$ scheme which is bandlimited by gaussian filter to be suitable for digital mobil communication, is lower than that of $Q^2PSK$ by 1.4[dB] in case that the signal-to-noise ration is 0[dB], but we have confirmed that $GQ^2PSK$ modulation scheme is approximately equivalent to the GMSK in the respect of power efficiency, and transmission efficiency of $GQ^2PSK$ is improved to 1.5 times than that of GMSK.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.2
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• pp.343-351
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• 2008

In this paper, we investigate the design of the QAM(Quadrature Amplitude Modulation) method for the CACB(Constant Amplitude Coded Multicode Biorthogonal) scheme. The modulation method fan improve the transmission data rate by increasing the BE(Bandwidth Efficiency). Additionally, we can improve the system performance by using the QAM SD(Soft Decision) method with the MDSA(Minimum Distance Selection Algorithm). Finally, the DFE(Decision Feedback Equalizer) for the CACB-QAM is simulated under the MPF(MultiPath Fading) channel for real implementation. The proposed scheme can be used for the PHY(PHYsical layer) standard of the WPAN(Wireless Personal Area Network) requiring high rate data transmission.