Selective decision directed channel estimation for UWA OFDM systems

In this paper we explore the performance of a selective decision directed channel estimation (CE) method for underwater acoustic (UWA) orthogonal frequency division multiplexing (OFDM) based communications. The method is based on hard or soft selection of data sub-carriers that are used in the decision directed mode. Particularly, in the process of hard selection we choose those sub-carriers that have high signal-to- noise ratios (SNR), while in the process of soft selection we weight the data sub-carriers for reliable channel estimation. The latter approach is shown to be advantageous since the channel state information (CSI) from all data sub-carriers is exploited. We couple selective decision directed CE with different channel reconstruction methods such as least-squares (LS) with thresholding, orthogonal matching pursuit (OMP), and basis pursuit denoising (BPD). Our results indicate good performance improvements as compared to the block-by-block pilot-assisted CE with a uniform pilot grid for high spectral efficiency communications. Moreover, we explore the trade-offs resulting from using a varying number of pilots and/or decision directed data sub-carriers in terms of the overall system throughput and bit error rate (BER). Experimental results are obtained using real data measurements from the Mobile Acoustic Communication Experiment 2010 (MACE´10), conducted off the coast of Martha´s Vineyard.