Waveforms For Reducing Direct Blast Effects And Mutual Interference.

Abstract : In bistatic sonar, the direct blast transmission can hide target echos. The potential for hiding target echos is dramatically reduced by dividing the transmission into a wavetrain of noncontiguous pulses with appropriate interpulse spacing. The potential for mutual interference between targets is also reduced for both bistatic and monostatic sonar systems. Strategies for determining the appropriate interpulse spacings are discussed. One approach is based on the Optical Orthogonal Codes (OOC) concept from the communication literature. Code search methods are also discussed and an exhaustive list of codes given for wavetrains of up to 12 pulses. To increase the duty cycle, a closely-related family of codes, noncircular Optical Orthogonal Codes (NOOC), is developed assuming the pulse sequence is not retransmitted back to back. Properties of NOOC's are derived, methods of searching for the codes are discussed, and another exhaustive list of codes is given for wavetrains of up to 9 pulses. Finally, criteria for choosing a particular code in designing waveforms are discussed. (MM)