Underwater acoustic channel simulator for broadband communication systems

Application of signals with orthogonal frequency division multiplexing in underwater communication systems allows efficient use of the information transfer channel bandwidth and thereby increase the carrying capacity of the system. Among the main distinguishing features of the underwater channel there are the relatively low speed of sound propagation in water, multiple reflections from the water surface and the bottom of the reservoir and the Doppler effect, which leads to compression / stretching of the signal in time. The model of the underwater acoustic channel was developed on the assumption that the signal at the receiver input is a superposition of the signals which are copies of the transmitted signal, but passed through different paths from the transmitter. Each signal has its own amplitude, time delay and degree of compression / stretching in time. For correct demodulation of the orthogonal frequency division of the channel-signal, the receiver must first perform time and frequency synchronization. Time synchronization is performed to determine the beginning of the packet and the symbols’ boundaries, and frequency synchronization is necessary for matching the receiver and transmitter sampling frequency to eliminate interchannel interference.For frequency synchronization in a hydroacoustic channel of orthogonal frequency division type, either the preambles invariant to Doppler effect or pilot components of the channel of the orthogonal frequency division type are used. The method based on the synchronization preamble and on a bank of matched filters uses a non-invariant to the Doppler effect preamble at the beginning of the packet. Each filter is matched with a preamble having compression / stretching in time. The autocorrelation method assumes that two identical symbols are included in the transmitted data block for signals with orthogonal frequency division multiplexing, which are used to estimate the scale of signal stretching / compression. The conclusions on the advantages of using orthogonal frequency division multiplexing in an underwater acoustic channel are given.

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Underwater Image Transmission Using Spatial Modulation Unequal Error Protection for Internet of Underwater Things

Sensors ◽

10.3390/s19235271 ◽

2019 ◽

Vol 19 (23) ◽

pp. 5271 ◽

Cited By ~ 3

Author(s):

Esmaiel ◽

Qasem ◽

Sun ◽

Wang ◽

Junejo

Keyword(s):

Communication Systems ◽

Image Transmission ◽

Unequal Error Protection ◽

Spectrum Efficiency ◽

Spatial Modulation ◽

Error Protection ◽

Underwater Acoustic Channel ◽

Underwater Acoustic ◽

Acoustic Channel ◽

Underwater Image

A spatial modulation (SM) scheme has been developed as a hopeful candidate for spectral and energy-efficient wireless communication systems, as it provides a great judgment for the system performance, data transmission rate, receiver complexity, and energy/spectrum efficiency. In SM, the data is conveyed by both habitual M-ary signal constellations and the transmit antennas indices. Therefore, the system data rate improvement due to the side information bits transmitted, encapsulated in indices of the transmit antennas, improves the SM transmission efficiency compared to the different MIMO players. The information bits transmitted over the antenna index and data symbol constellation using M-ary signal performance have different levels of bit error rate (BER) performance. This paper proposes unequal error protection (UEP) scheme for image transmission over the Internet of Underwater Things (IoUTs) using SM. The Set Partitioning in Hierarchical Trees (SPIHT) coders encode the underwater image and classify the encoded bits in two categories: critical and uncritical bits. The critical bits are transmitted over the SM index bits and have a low BER while the uncritical bits are transmitted over high order M-ary signal constellation to resolve the underwater acoustic channel bandwidth limitation problem. The proposed SM-UEP technique has been developed carefully with enough justification and evaluation over the measured underwater acoustic channel and the simulated channel. The simulation results show that the proposed SM-UEP can increase the average peak signal-to-noise ratio (PSNR) of the reconstructed received image considerably, and significantly.

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