Evaluation of multiple-channel OFDM based airborne ultrasonic communications

Area of Science:

• Acoustics
• Signal Processing
• Wireless Communication

Background:

• Orthogonal frequency division multiplexing (OFDM) is a key technology for high-spectral-efficiency data transmission in wired and wireless systems.
• Airborne ultrasonic communication offers a potential alternative for data transfer, particularly in environments where radio frequency (RF) communication is challenging.

Purpose of the Study:

• To investigate the application and performance of OFDM modulation schemes in an airborne ultrasonic communication system.
• To evaluate the effectiveness of different modulation techniques (BPSK, QAM) and the impact of channel characteristics on data transmission.

Main Methods:

• Utilized commercially available capacitive ultrasonic transducers operating at 50kHz for airborne data transmission.
• Implemented Binary Phase Shift Keying (BPSK) and 16-Quadrature Amplitude Modulation (16-QAM) for modulating OFDM sub-carrier signals.
• Developed an ultrasonic channel model incorporating diffraction, beam spread, and attenuation, and simulated performance.

Main Results:

• Achieved a line-of-sight (LOS) transmission range of 11m with BPSK at 45kb/s (1b/s/Hz spectral efficiency) with no errors.
• Increased data rate to 180kb/s (4b/s/Hz spectral efficiency) using 16-QAM over shorter distances (up to 6m).
• Successfully demodulated non-LOS signals and demonstrated significant improvement in bit error rate (BER) performance in multipath environments by adding a cyclic prefix (CP).

Conclusions:

• OFDM is a viable modulation technique for airborne ultrasonic communication, offering high spectral efficiency.
• The choice of modulation scheme (BPSK vs. 16-QAM) impacts the trade-off between data rate and transmission distance.
• Channel modeling and techniques like cyclic prefix are crucial for robust ultrasonic communication, especially in the presence of multipath interference.