UACE2017 Proceedings: Array Processing to Mitigate Channel Fluctuations in High-Speed Shallow Water Communication

• Session:
  Underwater Communications and Networking
• Paper:
  Array Processing to Mitigate Channel Fluctuations in High-Speed Shallow Water Communication
• Author(s):
  Jacob Rudander, Thor Husøy, Pål Orten, Paul Van Walree
• Abstract:
  Rapid time fluctuation of shallow water high frequency acoustic channels can be a major obstacle for reliable\nand persistent high-speed acoustic communication. Coherence times below 30ms and channel lengths exceeding 8ms may occur for a 250kHz carrier. To allow for high speed communication and real time processing of such a channel the coherence time must be increased in a cost efficient way.\nThis paper presents a method for slowing down the rapid time fluctuation of the channel. The method utilizes\nseveral antennas and can in some situations successfully increase the channel coherence time by several hundred\npercent. \nThe method which, builds upon traditional beamforming has been evaluated on real data from two different high frequency shallow water experiments, suffering from short coherence times. The experiments were conducted\nin August and November 2016 at two locations in the Oslofjord with depths of 18 and 200 meters. The horizontal ranges for the communication channel varied between 200 and 500 meters. The transmitter was located on the seabed transmitting a long burst (40 seconds) of repetitive m-sequences (2047 symbols long in August, respectively 1023 in November) using a 250kHz carrier and a high baudrate of 78.1255kBd. The receiver, a 64-element line array was located on a boat slowly drifting with the wind, mimicking a slanted seabed to surface communication channel.\n\nThe preliminary results shows that the increase in coherence time is much dependent upon the aperture of the array, rather than the number of active element.
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Contact details

• Contact person:
  Mr Jacob Rudander
• e-mail:
  
• Affiliation:
  Kongsberg Maritime/University of Oslo
• Country:
  Norway