Experimental research and measurement on mobile services using inaudible frequency

Abstract

Sound is one of many side channels used by apps and services. It has its benefits in that there is no need for any additional devices to be installed. The transmitter is a speaker which can be commonly found in buildings and the receiver is a mic that is integrated in almost every mobile devices. In addition, it also makes room by room detection possible. It is relatively suitable to provide room-based services because of the weak nature of passing through walls compared to other signals such as wi-fi and Bluetooth. Especially, sound in the inaudible frequency domain is utilized in lots of services due to its inaudibility to human while being detectable to other devices. In this thesis, we have conducted some experiments and measurements to determine if these inaudible sounds are suitable for providing shop-scale services and to find out how each factor that affects the sound propagation actually has an influence on the real life usage of sound for these services. In addition, we experimented only with existing equipment installed in a real shop and showed that these services can be immediately applied without adding or modifying existing hardware. As a result, it can be confirmed that the non-audible frequency is suitable for the room-based service on the mobile device. Also, the higher the frequency, the more suitable for distinguishing the room from the room, but the intensity of the sound itself is measured to be low because of the characteristics of the speaker and microphone. Moreover, it can be confirmed that existing authentication methods using sound distinguish the inside and outside of the desired service space.