실시간 수중음향 통신 시스템의 구현 및 천해에서의 실험 결과에 관한 연구

Abstract

Underwater acoustic communication plays an important role for various underwater activities. The control of AUVs and voice communications between divers are their typical examples. Although there are many kinds of information types, visual images are used for valuable data, especially for search and identification activities. For this reason, KRISO/KORDI recently developed a real-time image transmission system based on underwater acoustic communications. For easy adaptation to complicated and time-varying environments of the ocean, all-digital transmitter and receiver systems were implemented. For frame synchronization the CAZAC sequence was used and QPSK was chosen as the modulation/demodulation method. In the modulation/demodulation a carrier frequency of 25kHz and a bandwidth of 5kHz were applied to generate 10kbps transmission rate including overhead. To improve transmission quality, we used several techniques and algorithms such as adaptive beamforming, fast RLS adaptive equalizer, and convolution coding/Viterbi decoding. Seven directional transducers are used for the transmitter and a vertical line array of eight transducers was used for the receiver. The receiver system was implemented using four DSPs and block data parallel architecture. For the verification of the system performance, measurement of BER has been done in a very shallow water: depth of 8m. During the experiment images were successfully transmitted up to about 1.2km.