An indoor airborne ultrasonic wireless communication network

There is an increasing interest in the use of modulated airborne ultrasound as a means of indoor wireless communication. By using commercially available capacitive ultrasonic transducers at 50 kHz, this paper describes the successful practical implementation of a prototype airborne ultrasonic communication network with ceiling-mounted base stations (BSs) and a mobile transceiver unit. An asynchronous ultrasonic location technique using Gold code-modulated ranging signals was chosen to optimize the modulation schemes and data transfer and offered automatic handover between different cell regions on a switch ON and OFF basis as all BSs used the same frequency bands for data transmission. The 16-quadrature amplitude modulation (QAM) based on orthogonal frequency division multiplexing (OFDM) was used to achieve an uplink data transfer rate of 37.4 kb/s, whereas the range was extended by using quadrature phase-shift keying (QPSK)-OFDM with a data rate of 18.7 kb/s. For the uplink connection, the achieved data rates using 16-QAM-OFDM and QPSK-OFDM were 36.1 and 18.1 kb/s, respectively. A more robust handover technique using received signal strength with hysteresis was also proposed to improve system efficiency when multiple mobile receivers used the service.