OFDM for Underwater Acoustic Communications

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Design considerations and experimental results

Recent advances in high speed underwater acoustic communications. Sozer, E. Underwater acoustic networks. Kilfoyle, D. The state of the art in underwater acoustic telemetry.

  1. CI/OFDM Underwater Acoustic Communication System;
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Proakis, Sozer E. Shallow water acoustic networks. Chiu, L. Zhou, G. Adaptive transmission technique in underwater acoustic wireless communication. Kang, Y. Zeng Eds. Berlin: Springer. Parrish, N.

System design considerations for undersea networks: Link and multiple access protocols. Underwater acoustic communication channels: Propagation models and statistical characterization. Singer, A. Signal processing for underwater acoustic communications. Lin, C. Poncela, J. Wireless underwater communications. Wireless Personal Communications, 64, — Song, H. An overview of underwater time-reversal communication. Benson, B. Design of a low-cost underwater acoustic modem. Wu, L.

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  • Designing an adaptive acoustic modem for underwater sensor networks. Sendra, S. Underwater acoustic modems. Cheng, X. Cooperative OFDM underwater acoustic communications pp. Switzerland: Springer. Nam, H. Low-power based coherent acoustic modem for emerging underwater acoustic sensor networks. Wireless Personal Communications, 57, — Clemente, M.

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    • Adaptive turbo coded modulation for shallow underwater acoustic communications. Wireless Personal Communications, 78, — Diamant, R. Adaptive error-correction coding scheme for underwater acoustic communication networks. Qu, F. Differential orthogonal space-time block coding modulation for time-variant underwater acoustic channels. Dol, H. Konstantakos, D. Multicarrier code division multiple access MC-CDMA technique for underwater acoustic communication networks using short spreading sequences.

      Tsimenidis, C. Underwater acoustic receiver employing direct-sequence spread spectrum and spatial diversity combining for shallow-water multiaccess networking. He, C. A variable-rate spread-spectrum system for underwater acoustic communications. Direct mapping OVSF-based transmission scheme for underwater acoustic multimedia communication.

      Then, we give a description of network design and the method to determine the power consumption dependent transmission loss within the water medium in dependence on transmission distance and frequency by using a proper model. Phenomenological Model of Underwater Channels The attenuation coefficient is derived from a variety of factors. A fresh water case will be considered first and the more complicated saltwater case water mixture: freshwater, seawater and chemical products Magnesium sulfate MgSO 4 , the Sodium chloride, Boric acid BOH 3 and other molecular compound found in seawater will be built on from there, taking in to account both shear and bulk viscosity.

      A phenomenological underwater channel model based on the Wong method Wong, and Coppens method Coppens et al. This modified model represents accurately the sea layer by taking into account the majority of the underwater channel physics parameters.

      Ph.D. Candidate Specializes in Underwater Acoustic Communications - UConn Today

      Especially, the diffraction and diffusion effects are not considered in the other models. Under Fig. For the low frequencies from 1 to 20 KHz , the path loss is less than dB for a distance varying from 1 to 10 Km and do not exceed dB for a distance of 50 km. For thus, we limit to low frequencies. Figure 2 shows the absorption versus frequency for a few underwater channel models. Network Design and Power Consumption An underwater acoustic communication network is considered which consists of a large number of nodes operating in a shallow water environment at a depth of approximately m Proakis, The network is constrained by power consumption, because the acoustic modems are battery powered, as are the sensor processors.

      The goal of the network design is to achieve a good trade off between the quality of service and the power consumption. In particular, a good quality of service includes maximum information maximum available bandwidth through output at minimum delay with the desired transmission distance.

      One of the network design goals is to minimize the power consumption while providing reliable connectivity between the emitter and the receiver. To quantify the power consumption of the network, we investigate a simplified case in which emitter and receiver are arranged linearly. To determine the energy needed for transmission of a single data packet of duration T p from an emitter at distance d to the receiver, we assume that a required quality of reception is achieved if the received power level is P 0. To transmit a data packet from emitter to receiver over a distance d, the total consumed power from transmission is:.

      The carrier since multiple access with collision avoidance protocol appears efficient and adapted for underwater communication. We notice, when no activity is detected on the channel, the emitter waits for an inter-frame space and senses the medium again. And when the medium remains free, the emitter emits the data packet over the channel. If the medium is busy, the emitter waits for a random time before actuating the described above for transmitting the data packet. Figure 3 shows the attenuation graph according to the frequency and the distance of 1 Km.

      The emission power required to transmit a packet of data decrease to any great extend ratio of 10 -3 with many frequencies, for a distance of 1 km. For transmitting the packet of data from emitter to receiver, the total energy received and detected by the receiver after 1Km is 0,1mW for the emission power is 0,1 W. Figure 5 presents the normalized energy according to the distance with many frequencies. Figure 6 shows the consumed power from transmission with the desired distance and frequency. In Fig. Therefore the maximum value of the consumed power is 42 mW. For wireless underwater communication application, the frequency dependent attenuation links the maximum available bandwidth with the desired transmission distance.

      The available bandwidth of the underwater communication channel is limited and depends on both range and frequency. Within this limited bandwidth, the acoustic signals are subject to time varying multi-path, which may result in severe inter-symbol interference and a large Doppler shifts and spreads, relative to radio channels. Additional to the bandwidth and a range restriction due to frequency dependent transmission loss, multi-path spreading leads to inter-symbol interference, where subsequent transmitted symbols can overlap in time at the receiver position.

      Furthermore, deviations from the nominal carrier frequencies of the OFDM modulation, caused by Doppler, can lead to an over lap of the sub-bands of the OFDM signal which is called inter-carrier interference. Thus, modulation schemes for underwater communications must combat multi-path effects for optimum performance.

      Above all, we present the main considerations to choose the used OFDM structure. When combined with guard interval and cyclic prefix, OFDM eliminates inter symbol interference and inter carrier interference and overcame fading by using forward error correction coding. The channel estimate can be incorporated in to a soft decision Viterbi decoder in a bit-interleaved coded modulation fashion to get more coding gain and have the system operate in lower signal to noise ratio.

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      Another advantage of OFDM is its capability to capture multi-path energy with a simple fast Fourier Transform, where rake correlator fingers should be used to exploit multi-path diversity. On the subject of the Peak to Average Power Ratio PAPR of a multi-carrier signal, we emphasize that low values of the autocorrelation coefficients represent only a sufficient condition for a small value of the PAPR of the signal. Therefore, the autocorrelation coefficients of the generating sequences cannot serve as a basis for comparison of PAPR of the corresponding signals.

      The phenomena of the Inter-Carrier Interference ICI , caused by Doppler spreading in an OFDM system when the angle of arrival of the received signal is not uniformly distributed, can be taken into account. Average and differential Doppler compensation has not been studied in detail for single-carrier communication, but it will likely play an important role in underwater OFDM system.

      An approach based on simple ray propagation models will be used to predict the evolution of Doppler in each path and guide the tracking algorithm Gomes et al. Considering all the design considerations above-mentioned and in accordance with the simulation parameters results that can be used as initial values for this wireless communication , our proposed multi-band OFDM UWB wireless transceiver of underwater communication is shown in Fig. The proposed system will have: a scrambler to make data look random eliminating long runs of ones and zeros as well as repetitive patterns.

      A convolutional encoder to realize the error correction coding scheme. An interleaver to spread burst errors in time. A QPSK modulation mapper to achieve higher bit-per-symbol. Time frequency codes are utilized to interleave data sequences in different bands, there by achieving spread-spectrum communications.

      An important concern regarding the multi-band OFDM UWB wireless transceiver for the underwater communication is its requirement of a transducer at the transmitter side. This transducer allows to transform electrical waves into sound waves and inversely. It is directly connected to an AWGN channel added noise to the useful signal and multi-path Rayleigh fading channel. Simulation Results and Discussion After the determination of the transmission loss within the water medium in dependence on transmission distance and frequency by using a proper model.

      And by considering that the most important characteristic of UWB system is its capability of operating in power limited regime which his value is estimated and determined above mentioned. In addition to the transmission loss, we also defined a Rayleigh random variable that represents fading. When received power of a packet is calculated, two Gaussian random variables with zero mean and unit variance are generated and the Rayleigh fading coefficient is calculated. The resulting number is multiplied by the received power after loss. Since we make this calculation for the entire packet, this is equivalent to simulating a quasi-stationary channel.

      The background noise of the system is fixed throughout the simulations. As for that, the noise level is calculated to achieve 70 dB SNR at maximum range. And we consider, for a UWB wireless underwater communication, the bandwidth will likely be much higher than the data rate, so that the system can operate at very low Signal to Noise Ratio SNR. This means that a UWB wireless underwater communication network will be able to achieve high data rates with relatively low transmit power. A key point is that in this regime, the capacity increases almost linearly with power, whereas in the bandwidth limited regime high SNR , capacity increases only as the logarithm of signal power which means that a linear increases in data rate requires exponentially more power.

      This fact also highlights the importance of a power efficient modulation format in the design of a UWB system. The disadvantages of the approach that the power efficiency directly translates to a corresponding reduction in throughput. In addition, the use modulation improves BER performance under multi-path conditions using more robust techniques to combat fading and ISI. This modulation product to be a robust scheme for underwater data transmission.

      Adaptive OFDM modulation for underwater acoustic communications

      ISI is reduced only by providing a mechanism to avoid symbol overlap due to multi-path delay. Considering all the indications above mentioned, the results of OFDM underwater communication parameters, with the channel characteristics, are summarized in the Table 1. Single carrier central frequency is employed in each sub-band, as illustrated in the Fig. In OFDM modulation for wireless UWB underwater communication, the message stream is divided into many parallel lower rate streams that modulate a set of partially overlapping orthogonal carriers.

      This response represents a party of the transmission data, arrives along a many clearly defined ways different of one another. Figure 9c shows the constellation scope for QPSK modulation with the multi-path and the noise effects: instead of to have condensed points, we have a scatter of points. Our contribution consists in the determination of the important parameters to get better the wireless underwater communication by using a phenomenological underwater channel model. Subscribe Today. Science Alert. All Rights Reserved.

      Research Article. Similar Articles in this Journal. Search in Google Scholar. Trends in Applied Sciences Research, 1: DOI: Introduction As in each wireless communication systems, the bandwidth allocation is a significant factor to determine the system efficiency. Under Water Channel Simulations For the design of such communication systems, the transmission conditions of the underwater medium have to be taken into account.

      Normalized energy needed to transmit one packet of data with respect to the frequency. Received signal for 1 km transmission distance and constellation scope for QPSK modularion. Barroso, V. Doppler compensation in underwater channels using time-reversal arrays. Channel estimation for equalization and synchronization in OFDM underwater communication systems. Berkhovskikh, L.

      OFDM for Underwater Acoustic Communications OFDM for Underwater Acoustic Communications
      OFDM for Underwater Acoustic Communications OFDM for Underwater Acoustic Communications
      OFDM for Underwater Acoustic Communications OFDM for Underwater Acoustic Communications
      OFDM for Underwater Acoustic Communications OFDM for Underwater Acoustic Communications
      OFDM for Underwater Acoustic Communications OFDM for Underwater Acoustic Communications
      OFDM for Underwater Acoustic Communications OFDM for Underwater Acoustic Communications
      OFDM for Underwater Acoustic Communications OFDM for Underwater Acoustic Communications
      OFDM for Underwater Acoustic Communications OFDM for Underwater Acoustic Communications

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