Passive phase-conjugate signaling using pulse-position modulation

Acoustic communication is an attractive option for networking distributed assets, such as UUVs, autonomous sensors, and other systems that must talk to one another in the ocean. The ocean is often a complex multipath channel and impressive progress has been made in developing equalization algorithms to overcome this. Unfortunately, many of these algorithms are computationally demanding and not as power-efficient as one would like; in many applications it is better to trade bit rate for longer operational life. For example, a wakeup function is intrinsically low rate but must be low power and highly reliable. We discuss a fundamentally different modulation scheme to address these requirements. An added benefit is that it leads to a receiver that is much less complex than an adaptive equalizer