Abstract:

A preliminary error-rate performance of comparison was conducted between two promising signal architectures for underwater acoustic telemetry modem use. The first candidate signal is a convolutionally encoded and interleaved QPSK modulation. The second candidate signal is an 8PSK trellis coded modulation (TCM). In both cases, the convolutional encoder is the same, i.e., k=1, n=2, and const=7. A short test in April of this year was performed at the Atlantic Undersea Test and Evaluation Center (AUTEC) in approximately 1000 m of water. Signals were transmitted from a seabottom mounted UQC transducer and were received by a hull-mounted transducer on a drifting surface vessel. One-hundred telemetry packets from each signal type were transmitted and were adaptively equalized within the receiver prior to decoding. The QPSK signal outperformed the TCM signal with bit error rates of 5e-6 and 1.4e-5, respectively.