• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.10
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• pp.824-831
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• 2013

The delta driven GMSK is a modulation scheme to generate the gaussian pulse by the bipolar delta signal and to modulate the phase function with the differential gaussian pulse between $+T_b/2$ and $-T_b/2$. The demodulation of delta driven GMSK differs from conventional GMSK schemes. This paper proposed a demodulation with the differential phase detector at the end of each bit interval. A designed detector then finds the one of the possible region by hard decision, in which the phase difference lies. Finally the binary data can be recovered by state transition process. Through the BER simulation for AWGN channel, it was found that the proposed demodulation effected by the run length of binary data. The simulated BER degradation of about 2[dB] was analyzed, as compared to the theoretical coherent demodulation with $BT_b$=0.3.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.7
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• pp.581-588
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• 2013

In the basic GMSK, the modulated signals are generated by the preprocessing of NRZ pulse trains with the gaussian low pass filter. In this paper, we proposed the GMSK modulation system with the delta pulse trains. The proposed system constructed with the gaussian pulse generator triggered by the bipolar delta pulse, the differentiator between $+T_b/2$ and $-T_b/2$, and then a matched filter for frequency-modulation function. The spectrum of proposed system was found to be smaller than about 35[%] at 40[dB] attenuated bandwidth, and the center spectrum to be lower than the basic GMSK with zero-crossing property.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.1
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• pp.7-16
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• 2015

The transmitter of quadrature multiplexed GMSK (QM-GMSK) is composed of two quadrature multiplexed GMSK modulators. QM-GMSK has a slightly increased spectrum main lobe compared with $Q^2PSK$ or QMSK, but it has highly suppressed side lobes. As a result, practical spectrum efficiency of QM-GMSK is achieved. By replacing the baseband elementary pulses of QM-GMSK with their approximate, the squared sinusoid of half-period, offset-$Q^2PSK$($OQ^2PSK$) is obtained. The $OQ^2PSK$ signal has similar spectral properties to QM-GMSK. The transmitter of $OQ^2PSK$ can be simply implemented without the Gaussian lowpass filter, which is required in QM-GMSK transmitter. In this paper, we propose an overlapped pulse shaping in $OQ^2PSK$ with RC(raised-cosine) or SRC(squared raised-cosine) pulses of length longer than the symbol period. Power spectrum of the proposed modulation scheme exhibits further suppressed side lobes, hence enhanced spectrum efficiency is obtained. Simulation results indicate that BER performance of the proposed scheme is comparable to that of $OQ^2PSK$.