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      Adaptive OFDM modulation for underwater acoustic communications: Design considerations and experimental results

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      Author(s)
      Radosevic, A.
      Ahmed, R.
      Duman, T. M.
      Proakis, J. G.
      Stojanovic, M.
      Date
      2014
      Source Title
      IEEE Journal of Oceanic Engineering
      Print ISSN
      0364-9059
      Publisher
      Institute of Electrical and Electronics Engineers Inc.
      Volume
      39
      Issue
      2
      Pages
      357 - 370
      Language
      English
      Type
      Article
      Item Usage Stats
      240
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      577
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      Abstract
      In this paper, we explore design aspects of adaptive modulation based on orthogonal frequency-division multiplexing (OFDM) for underwater acoustic (UWA) communications, and study its performance using real-time at-sea experiments. Our design criterion is to maximize the system throughput under a target average bit error rate (BER). We consider two different schemes based on the level of adaptivity: in the first scheme, only the modulation levels are adjusted while the power is allocated uniformly across the subcarriers, whereas in the second scheme, both the modulation levels and the power are adjusted adaptively. For both schemes we linearly predict the channel one travel time ahead so as to improve the performance in the presence of a long propagation delay. The system design assumes a feedback link from the receiver that is exploited in two forms: one that conveys the modulation alphabet and quantized power levels to be used for each subcarrier, and the other that conveys a quantized estimate of the sparse channel impulse response. The second approach is shown to be advantageous, as it requires significantly fewer feedback bits for the same system throughput. The effectiveness of the proposed adaptive schemes is demonstrated using computer simulations, real channel measurements recorded in shallow water off the western coast of Kauai, HI, USA, in June 2008, and real-time at-sea experiments conducted at the same location in July 2011. We note that this is the first paper that presents adaptive modulation results for UWA links with real-time at-sea experiments.
      Keywords
      Adaptive modulation
      Feedback
      Orthogonal frequency-division multiplexing (OFDM)
      Underwater acoustic (UWA) communication
      Computer simulation
      Experiments
      Feedback
      Orthogonal frequency division multiplexing
      Underwater acoustics
      At-sea experiment
      Average bit-error rates
      Channel measurements
      Design considerations
      Modulation levels
      Propagation delays
      Sparse channel impulse response
      Underwater acoustic communications
      Adaptive modulation
      Permalink
      http://hdl.handle.net/11693/26642
      Published Version (Please cite this version)
      http://dx.doi.org/10.1109/JOE.2013.2253212
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      • Department of Electrical and Electronics Engineering 3868
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