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<p>Multi-Frequency Modulation (MFM) has been developed at NPS using both differential quadrature-phase-shift-keying (DQPSK) and differential-quadrature- amplitude-modulation (DQAM) encoding formats. Previous applications of these encoding formats were on industry standard computers (PC) over a 16-20 kHz channel. This report discusses the implementation of MFM to a voice frequency channel of 200-3400 Hz, for possible future use with high-speed modems over switched telephone networks. Research and testing for this report included the DQPSK and differential 16-quadrature-amplitude-modulation (D16-QAM) encoding formats implemented on PCs. Experimental results of the implemented MFM signal were comparable to theory with acceptable bit error rates for input signal-to-noise ratios (SNR) of 15 dB and higher.
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<br>Subjects: Communications; Multi-frequency modulation; High-speed modems</div>
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Salsman, Charles P.</div>
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