Reciprocity based channel compensation for wideband communications in a multipath environment

The effectiveness of spread spectrum techniques to achieve low probability of intercept (LPI) communications can be severely degraded in multipath environments which are common in underwater acoustics. The problem of LPI response to a non-LPI interrogation signal is considered. The underlying concept is to use the received interrogation signal to estimate the channel characteristics. The response signal is then precompensated for the estimated channel distortion on the return path so that improved coherent processing gain can be achieved by the interrogator. Several compensation techniques are compared. The sensitivity of channel characteristics to range changes in a typical undersea environment is found to be significant. Techniques for compensation for range changes are discussed.<>