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Optimum Pre-Emphasis for FM Transmission with Frequency-Domain Voice Scrambling
Yoshihiko AKAIWA Eiji OKAMOTO Yukitsuna FURUYA
IEICE TRANSACTIONS (1976-1990)
Publication Date: 1989/05/25
Print ISSN: 0000-0000
Type of Manuscript: Special Section PAPER (Special Issue on Information Theory and Its Applications)
Full Text: PDF>>
With popularity of radio communication, voice scrambling has received increased attention for communication privacy. It has been known that pre-emphasis at the transmit side and de-emphasis at the receive side improves the received signal to noise power ratio (SNR) both for scrambled and nonscrambled signals. In this paper, optimum pre- and de-emphasis are theoretically investigated for FM and PM transmission including frequency-domain scrambling for voice security. Using a linear system model, the optimum frequency-characteristics for pre- and de-emphasis filter are given as a function of a voice signal spectrum, demodulator output noise spectrum, and the scrambling method. Comparisons of the maximum attainable SNR are made for various case including plain voice (non scrambling) and secured voice scrambled by spectrum inversion, reverberation and FFT spectrum transformation, assuming simple voice and noise spectra.