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 frequency-selective 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.
Highlights
Everyday devices are evolving to have connectivity owing to the advancement of short-range wireless communication technology, such as near-field communication (NFC) [1] and Bluetooth low energy (BLE) [2]
Compatibility issues exist in NFC and BLE, since they require corresponding hardware transceiver modules, which are rarely embedded in most devices except recent smartphones or tablets
Considering the improved connectivity of short-range wireless communication, acoustic communication can be a suitable alternative to the conventional systems, since acoustic communication transmits and receives data through a speaker and a microphone, which are typically implemented or attached to most digital devices
Summary
Everyday devices are evolving to have connectivity owing to the advancement of short-range wireless communication technology, such as near-field communication (NFC) [1] and Bluetooth low energy (BLE) [2]. Owing to the attenuation of LFU through typical building barriers such as walls, doors, and windows, Google Tone can share URLs between devices located in the same room without manual exchange of password for connecting a common network through Wi-Fi or Bluetooth [10] Such connection between near devices can be vastly utilized for data sharing, and for home automation [10] or indoor positioning systems [11], if the LFU communication performance would be reliable according to various characteristics of COTS microphones and speakers as well as operating environments. The proposed system is based on a noncoherent communication framework without using the synchronization that often fails to perform under the highly frequency-selective channel [12] This is because the LFU channel is highly frequency-selective, caused by the limited performance of COTS microphones and speakers in realistic noisy environments.
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