Experimental Estimation of the Constant Envelope FM-OFDM Method Usage in Underwater Acoustic Communication Systems

Aleksandr Rodionov,Aleksandr Golov,Peter Unru,Yury Morgunov,Eugene Voitenko,Alexey Kiryanov,Lyubov Statsenko

doi:10.3390/app8030402

Aleksandr Rodionov, Aleksandr Golov + Show 5 more

Open Access

https://doi.org/10.3390/app8030402

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Abstract

Nowadays, more and more complex methods of signal modulating and processing are actively used for organizing underwater acoustic communication with and between submerged mobile vehicles due to harsh underwater conditions. In this research, the method that is based on multi-frequency signals forming (OFDM) with the constant envelope is applied to the problem. It is based on multi-frequency FM-OFDM signals forming with Quadrature Phase Shift Keying (QPSK) modulated subcarriers and FM spectrum spreading coefficients of 1, 2, 4, and 10. The proposed solution was modeled in a software simulator, which implements a noisy underwater acoustic multipath channel, changing the bit error rate (BER) from 0.15 to 10−3. In addition, it was tested during the full-scale data transmission experiments at 25 km distance using a low frequency (400 Hz) underwater acoustic apparatus under conditions of strong impulse noises and quasi-non-stationary channel. The results of in-situ experiments were similar to the ones that were obtained during the simulation.

Highlights

Multifrequency methods of signal modulation, such as OFDM, gained a lot of attention in the radiocommunications, but in underwater acoustic communications (UAC) as well
We present an underwater acoustic communication system exploiting frequency modulated multi-frequency signals (FM-OFDM) with Quadrature Phase Shift Keying (QPSK) modulation of sub-carriers
Results of decoding of FM-OFDM-QPSK signals that were received during in-situ experiments are presented

Summary

Introduction

Multifrequency methods of signal modulation, such as OFDM, gained a lot of attention in the radiocommunications, but in underwater acoustic communications (UAC) as well. The specified spectral efficiency of the system with working frequencies up to 60 kHz allows to create relatively high-speed underwater communication links (up to tens of Kbit/s), but this throughput is achievable only if the channel parameters are stable and the transmitter/receiver are tuned properly using up-to-date complex approaches. That goal requires solving problem of implementation of algorithms, operating without regular channel state estimation and multiple transmissions of test packets (signals) It is especially important for mobile communicating objects for saving time resource and increasing the total data rate. In the third part the results of full-scale experiments with the proposed method at 25 km distances using low frequency (400 Hz) underwater acoustic equipment are shown and are analyzed along with the additional numerical simulation with strong Doppler shift. Values of BER for FM-OFDM-QPSK (with spread spectrum coefficient of 1, 2, 4, and 10) are obtained and are similar to the ones that were obtained during simulation

The Features of FM-OFDM Communications Scheme

Figure

Numerical Experiments with FM-OFDM-QPSK in Multipath Channels

Results

Marine Experiments and Numerical Estimations of Doppler Shift Sustainability

Conclusions