Performance of the bit-interleaved frequency domain turbo equalization over experimental underwater acoustic channels

Abstract

We investigate the performance of the bit-interleaved frequency-domain turbo equalization (Bi-FDTE) with spatial diversity over experimental underwater acoustic (UWA) channels. Our receiver combines the frequency domain minimum mean square error (MMSE) equalization with the soft interference cancellation with the bit-interleaved turbo equalization. Pilot symbols are periodically inserted and multiplexed with data symbols similar to that of the orthogonal frequency division multiplexing (OFDM). We test our transmission system over a real UWA channel environment conducted at Narragansett Bay, RI. We develop three different transmission scenarios to investigate performance/data rate tradeoff. Results from the experiment show that without spatial diversity the bit error rate (BER) reaches 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> at the 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> iteration when signal-to-noise ratio is equal to 18.3 dB at 3.71 kbps data rate. The BER performance is improved by exploiting the spatial diversity of the UWA channels by combining and equalizing data from multiple receive channels.