In this paper, we estimate the upper limit of the transmission data rate in airborne ultrasonic communications, under condition of the optimal power allocation. The presented method is based on frequency response of a channel in case of single-path LOS propagation under different climatic conditions and AWGN background noise model, and it can be easily extended to the case of frequency-dependent noise. The obtained results go beyond the discrete distances for which experimental SNR values were available, and are more accurate than the previous calculations in the literature, due to the inclusion of the channel frequency response and its changes over the distance. The impact of air temperature, relative humidity and the atmospheric pressure on the channel capacity is also investigated. The presented results can serve as a reference during the design of airborne ultrasonic communication systems operating in the far-field region.
This paper proposed a new OFDM scheme called damped zero-pseudorandom noise orthogonal frequency division multiplexing (DZPN-OFDM) scheme. In the proposed scheme, ZPN-OFDM non-zero part is damped to reduce its energy, thus the mutual interference power in-between the data and training blocks with conservative the pseudo-noise conventional properties required for channel estimation or synchronization. The motivation of this paper is the OFDM long guard interval working in wide dispersion channels, whereas a significant energy is wasted when the conventional ZPN-OFDM is used as well as the BER performance is also degraded. Moreover, the proposed scheme doesn’t duplicate the guard interval to solve the ZPN-OFDM spectrum efficiency loss problem. Both detailed performance analysis and simulation results show that the proposed DZPNOFDM scheme can, indeed, offer significant bit error rate, spectrum efficiency and energy efficiency improvement.