Noncoherent Low-Frequency Ultrasonic Communication System with Optimum Symbol Length

Abstract

A noncoherent low-frequency ultrasonic (LFU) communication system is proposed for near-field communication using commercial off-the-shelf (COTS) speakers and microphones. Since the LFU communication channel is known to be a frequencyselective characteristic, the proposed system is basically designed by differential phase-shift keying (DPSK) modulation with forward error correction. In addition, automatic gain control of the carrier frequency band over the LFU communication channel is proposed. Then, in order to optimize the symbol length of the proposed LFU communication system under a realistic aerial acoustic channel, a propagation model of the LFU communication channel is proposed by incorporating aerial acoustic attenuation. The performance of the proposed LFU communication system is demonstrated on two different tasks: bit error rate (BER) measurement and successful transmission rate (STR) comparison with Google Tone for various distances between the transmitter and the receiver. Consequently, the proposed method can operate without a bit error at a distance of 8 m under various noise conditions with sound pressure level of 80 dB. Moreover, the proposed method achieves higher STR than Google Tone on a task of URL transmission using two laptops.

User-Aware Audio Marker Using Low Frequency Ultrasonic Object Detection and Communication for Augmented Reality

“…Next, is then encoded by an FEC algorithm [19]; thus, additional error correction bits are attached. In particular, a perfect binary Golay code, , is used for FEC encoding [19] encoding is applied to , as in [15]:…”

“…In Equation (2), T b is the symbol length and is set to 96 because this is known as being the optimum by taking into account both the data transmission rate and communication robustness in noisy environments [15]. Moreover, f c and f s are a carrier frequency and a sampling frequency of the modulated signal, respectively.…”

“…As shown in the table, the conventional audio marker system had a markedly increased FPR outside the MTZ because it always transmitted LFU signals with a maximum scale (see Equation 3). On the other hand, the proposed system controlled the transmission range up to the MTZ, i.e., 2 m for this experiment, by adaptively scaling the modulated signal produced by the LFU-based objective detection (see Equation (15)). Thus, the proposed system is suitable to provide marker information only to the people of interest in each location, rather than to all the people in the room, as would be the case in a conventional audio marker system.…”

“…There were many benefits to this approach. Since the frequency response of the LFU-based audio marker ranged from 18 to 20 kHz, the transmitted signal was inaudible to human ears, and its transceivers could be made of the most commercial off-the-shelf (COTS) loudspeakers and microphones [15]. Thus, operating the LFU-based audio marker did not require any additional hardware other than a generic device equipped with an audio interface, e.g., a smart phone.…”

“…The remainder of this paper is organized as follows. Section 2 reviews the conventional LFU communication-based audio marker system [14,15], after which Section 3 proposes a user-aware audio marker system based on object detection using reflected LFU images and LFU communication for sending audio maker information. Section 4 evaluates the objective performance of the proposed The proposed audio marker system consists of an object detection module using received LFU images as well as an LFU communication module providing the audio marker.…”