4aSC14. Improvement in quality of speech received by a mistuned receiver at Suppressed Carrier SSB.

Session: Thursday Morning, December 4


Author: Shin'ichiroh Kaneko
Location: Dept. of Information and Comput. Sci., Saitama Univ., shimo-okubo 255 Urawa, 338 Japan
Author: Jouji Suzuki
Location: Dept. of Information and Comput. Sci., Saitama Univ., shimo-okubo 255 Urawa, 338 Japan
Author: Tetsuya Sjimamura
Location: Dept. of Information and Comput. Sci., Saitama Univ., shimo-okubo 255 Urawa, 338 Japan

Abstract:

Single sideband modulation (SSB) is the most efficient speech transmission system from the viewpoint of power consumption and bandwidth occupation. It is widely used in amateur radio, mobile radio, and others. At suppressed carrier SSB(SCSSB), the receiver should tune to the carrier frequency accurately. Manual tuning, however, is very difficult due to the lack of the carrier signal. It fails in fine tuning at the reception and the quality of received speech degrades seriously owing to the shift of speech spectrum. This paper proposes a method to improve the quality of speech degraded at SCSSB. Received speech is transformed into the log spectrum and its autocorrelation function (ACLOS) is calculated. If tuning is carried out correctly, the log spectrum of voiced sound has a harmonic structure. Mistuning gives a spectrum shift on that frequency axis. On the other hand, ACLOS is always a periodic signal that corresponds to the harmonic structure. By calculating a cross-correlation function between ACLOS and the log spectrum, mistuning frequency can be easily estimated. This method is able to estimate the mistuning frequency within the accuracy of 10 Hz, even in noisy channels. After obtaining the mistuning frequency, the shifting spectrum of received speech is carried out and more natural speech is obtained.


ASA 134th Meeting - San Diego CA, December 1997