• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.3
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• pp.240-244
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• 2019

SOQPSK-TG which consists of differential precoder and CPM modulator was adopted as telemetry standard because of its high power and bandwidth efficiency. We proposed four-state Viterbi decoder for SOQPSK-TG. Reducing the trellis state to four was possible by simplifying frequency pulse of SOQPSK-TG to square pulse of symbol length 2 and combing this with differential precoder. Compared with conventional SOQPSK-TG receivers, computer simulation result shows about 1 dB performance improvement was achieved at BER of $10^{-5}$ in AWGN channel.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.3
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• pp.193-201
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• 2022

SOQPSK-TG is a modulated signal for aircraft telemetry with excellent frequency efficiency and power efficiency. In this paper, the phase waveform of the partial response SOQPSK-TG modulation is linearly approximated and modeled as a full response double duobinary SOQPSK (SOQPSK-DD) signal. And using the XTCQM method and the Laurent decomposition method, the SOQPSK-DD signal was approximated as OQPSK having linear pulse waveforms, and the results of the two methods were proved to be the same. In addition, it was confirmed that the Laurent decomposition waveform of the SOQPSK-DD signal approximates the Laurent decomposition waveform of the original SOQPSK-TG signal. And it was shown that the decision feedback IQ-detector, which applied the Laurent decomposition waveform of SOQPSK-DD to the detection filter, exhibits almost the same performance even with a simpler waveform than before.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.10
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• pp.879-882
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• 2021

The telemetry standard adopts SOQPSK-TG with excellent power and bandwidth efficiency as a modulation technique, and LDPC code with excellent performance as an error correction code. The SOQPSK-TG transmitter consists of a precoder and a CPM modulator. Rather than implementing each receiver separately, the reception performance is improved by combining the trellis and implementing it as a Viterbi decoder. In this paper, the reception performance of LDPC-encoded SOQPSK-TG was evaluated by replacing the Viterbi decoder with a max-log-map decoder capable of soft metric output. As a result of computer simulation in AWGN channel, there is an Eb/No performance gain of about more than 0.7~0.8dB compared to the conventional method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.11
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• pp.945-951
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• 2021

The SOQPSK-TG is a modulated signal for aeronautical telemetry with a very good bandwidth efficiency. In this paper, the frequency waveform filter of the SOQPSK-TG is linearly approximated and modeled with a duobinary precoder and a modified frequency waveform filter having a phase transition period of about 1T_b. In combination with the existing precoder, the SOQPSK-TG is modeled by a double duobinary MSK. Comparing the SOQPSK-TG signal and the newly modeled double duobinary MSK signal in time domain and frequency domain, it is confirmed that the two signals are almost identical and there is virtually no performance difference. Moreover, we can attain 0.1 dB BER performance improvement compared to the existing cosine filter when the filter of the IQ-detector is implemented with a cosine sum filter taking into account the change in the modulation index by the new double doubinary precoder.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.7
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• pp.589-592
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• 2021

SOQPSK-TG, which is composed of a precoder and a CPM modulator, adopts a differential precoder method with a differential encoder added to the transmitter as a telemetry standard to simplify the receiver structure. In this paper, we evaluated the effect of the differential encoder on receiver performance at low Eb/No. According to the results of computer simulation, the Eb/No performance in the AWGN channel without the differential encoder is about 2dB better when the BER is 10^-1 and about 1dB when the BER is 10^-2.