Decision-directed Passive Phase Conjugation for underwater acoustic communication: experimental results

Passive Phase Conjugation is a method for coherent underwater acoustic communication that uses multiple receive-only hydrophones. The technique is essentially a space-time matched filter. Previous results from a field experiment demonstrating the method were reported by Rouseff et al. [IEEE J. Oceanic Eng. 26, pp. 821-831, 2001]. In this paper, performance results are presented for Decision-Directed Passive Phase Conjugation, an adaptive extension to the basic technique. Using decision directed estimates for the channel impulse response, the method requires training overhead of less than 2% for the 10000-symbol packets used in the experiment. Mean-Square-Error and Bit-Error-Rates are reported for various array configurations including a three-element horizontal array.