Acoustic Communication in Air Using Differential Biphase Shift Keying with Influence of Impulse Response and Background Noise

Abstract

We describe short-range acoustic communication in air using differential biphase shift keying (DBPSK). In this system, a carrier recovery circuit is unnecessary, since the differential encoding is adopted, and the system configuration is simple. The acoustic transmission channel can be simply constructed of only a loudspeaker (SP) and a microphone (MIC). Acoustic communication in air has three problems that degrade the quality of communication. There are multipath fading by reflected waves, the influence of the impulse response of the SP and MIC and that of background noise. Even when multipath fading is disregarded, the performance is limited by the influence of the impulse response of the SP and MIC and that of the background noise. In this study, the performance limits are experimentally evaluated, and the design guidelines for the one-symbol time and signal-to-noise ratio are obtained for an acoustic DBPSK system. The period of a particularly intense influence of the impulse response of the acoustic system is 0.3 ms or more. If the one-symbol time is set at 0.8 ms, the communication quality becomes stable.