Abstract
The current state‐of‐the‐art in high‐rate acoustic communications is represented by adaptive multi‐channel equalization of single‐carrier wideband signals. An alternative technique with significant potential for achieving high bit rates over multipath‐distorted (frequency selective) channels is multi‐carrier modulation (MCM). There are obvious technical advantages of MCM. Each frequency channel of MCM can be transmitted using a relatively narrow‐band, high‐efficiency transducer, and low‐power amplifier, which allows achieving a very broad bandwidth. Use of narrow‐band channels increases the tolerance for time synchronization errors in multipath array processing. Each frequency channel has a relatively low delay spread when measured in symbol units and can be equalized with low‐complexity algorithms and simplified array processing. The reduction of the ISI span in each sub‐channel allows for the application of soft decision decoders optimal for joint channel estimation and data recovery such as maximum‐likelihood sequence detectors (MLSDs) and adaptive BCJR MAP algorithm. The adaptive form of the MAP algorithm is considered. The combination of channel shortening equalization and a practical MLSD algorithm with dual loop feedback and pre‐survivor processing were tested in shallow water acoustic communications experiments and shown a very good performance. [Work supported by ONR Grant N00014‐07‐1‐0229.]
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