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A Prototype Design and Experiment of Time Division Duplex (TDD) Underwater Small Area Acoustic Network (USAAN) System


Taisaku Suzuki, Atsushi Kinjo, Suguru Kuniyoshi, Rie Saotome, Tomohisa Wada


Vol. 17  No. 10  pp. 95-102


Underwater wireless acoustic networking is being demanded for many applications to reduce cable cost, impractical or too time consuming to deploy, as well as radio wireless technologies have enabled the information technology to spread over our real life such as high bandwidth data transfer between humans and machines. Because of the long propagation delays of the underwater acoustic channel, Media Access Control (MAC) design is challenging. Although many radio access MAC protocols are based on handshake type between the sender and the receiver such as IEEE 802.11, it is not efficient in underwater acoustic network and handshake-free MAC protocols are getting important. In this paper, we propose a TDD USAAN communication system, which uses SC-FDMA modulation. The target applications are 1) underwater civil engineering machine control and view monitoring, 2) marine aquaculture monitoring such as underwater environment data and fishes, 3) human monitoring and position tracking at marine leisure such as diving, 4) controlling a remotely operated vehicle (ROV) wirelessly to exterminate harmful creatures such as acanthaster in coral reef and so on. The proposed system assumes small service area less than 100 m diameter. Then USAAN system can avoid a hand-shake protocol and instead use TDD protocols. There is one base station and several user stations. Both Down Link (DL) communication from the base station to the user stations and Up Link (UL) communication from the user stations to the base station are supported as Time Division Duplex (TDD) method. To realize a stable TDD operation with assuming User Equipment movement, twice repeating chirp preamble signal is proposed. The prototype system uses 16-24 kHz ultrasonic channel and total of 169 subcarriers are used in 8 kHz bandwidth to deliver 10.35Kbps by QPSK modulation. The TDD operation has been confirmed by field experimentation using the prototype system at a Dam Lake in Shizuoka prefecture, Japan. The Lake experiment demonstrated vertical downward DL and upward UL two way TDD communication. The synchronization robustness has been confirmed by the experiment of User Equipment vertical up and down moving. The proposed chirp preamble method realized stable TDD synchronization in water with maximum moving speed of 0.7m/sec.


SC-FDMA, OFDM, TDD, Underwater Network, Digital Communication