An off-line software modem for underwater acoustic communications and its field evaluation results

This paper proposes an off-line software modem for underwater acoustic communications (UWAC), and evaluates bit error rate (BER) performance of the proposal modem in actual field environment. The proposed modem employs commercial electronic acoustic equipments. Therefore, the proposed modem operates as off-line mode, but it has simple structure. In addition, this paper evaluates BER performance of single carrier differential QPSK / differential detection (DD) in actual shallow environment of Lake Biwa, assuming water depth of around 3m. In detail, this paper evaluates BER performance as a function of distances between transmit and receive transducers in the cases of single branch reception and 2-branch diversity reception. The field evaluation results confirm that the proposed UWAC system has BER of less than 1% in the environment that has several msec delay spread, assuming 10m distance and 2-branch diversity reception and symbol rate of 187.5sps.