UACE2017 Proceedings: Performance assessment of underwater acoustic modems operating simultaneously at different frequencies in the presence of background impulsive noise emitted by a sparker
Session: Underwater Communications and Networking
Paper: Performance assessment of underwater acoustic modems operating simultaneously at different frequencies in the presence of background impulsive noise emitted by a sparker
Author(s): Konstantin Kebkal, Oleksiy Kebkal, Veronika Kebkal, Luís Sebastião, Antonio Pascoal, Jorge Ribeiro, Henrique Silva, Miguel Ribeiro, Elbert Kelholt, Sergio Jesus
Abstract: This paper describes work done in the scope of the EC WiMUST project towards the development of a joint positioning / data communication system for a group of AUVs towing streamers together and a companion support vessel carrying an acoustic sparker, with a view to geotechnical surveying applications. In particular, the paper summarizes modelling and experimental results of short range acoustic communications (under 1000 m) using simultaneously a middle frequency modem (18-34 kHz) for the delivery of payload data from the AUVs to the surface vessel and a high frequency modem (42-65 kHz) for the exchange of service and positioning data among the AUVs undergoing formation control. The particular characteristics of these tests consisted in the presence of strong background impulsive noise generated by means of a powerful sparker, typically used for seismic surveys.\nTwo acoustic modem types were selected for this particular application: one with a relatively slow bitrate for the task of AUV positioning, the other with a relatively high bitrate for the task of payload data exchange with the surface vessel. During experimental tests, each of the the two selected types (S2CR18/34 and S2CR42/65) showed similar performance when operating either separately or simultaneously with the other. \nThe measured effective bitrate (i.e. the bitrate at the user interface) of the high frequency modems was 3.5-5 kbit/s (about 30% of the measured nominal bitrate under real communication conditions). This bitrate is for example sufficient for the transmission of a block of data containing 1.25 kbyte information within a time slot of less than 3 s in shallow water conditions, over a distance of several hundred meters (up to 1 km). The measured packet loss of the high frequency modems was in the range from 5-15% in conditions that are of practical interest to the WiMUST project (e.g. to compute the relative positions of AUVs in an underwater formation).\nThe tests performed validated also the concept of simultaneous operation of two different acoustic modems during activity (in close vicinity) of a sparker at the surface emitting strong and broadband electric and acoustic pulses. No significant electromagnetic interference was observed on the electronics of the acoustic modems; furthermore, only a moderate decrease of the communication performance due to the disturbing acoustic pulses of the sparker was detected (the data rate decrease was less than 20%).\nThe final version of the paper will include various graphic materials, a discussion of the results obtained, and the main conclusions. This work was made possible by a collaborative research effort among several WiMUST project partners: the Interuniversity Center of Integrated Systems for the Marine Environment (ISME), The organization of Instituto Superior Técnico for Research and Development (IST-ID, Univ. Lisbon), the Centro de Investigação Tecnológica do Algarve (CINTAL), the School of Computer Science at the University of Hertfordshire, and the companies Evologics, CGG, Geo Marine Survey Systems, Geosurveys, and Graal Tech.