Burst mode spread spectrum technology for covert underwater acoustic communication

Considering that conventional continuous spread spectrum communication can be intercepted by an energy detector, a burst mode hybrid spread spectrum technology for covert acoustic communications is proposed in this paper. This method randomly transmits pulse hybrid spread spectrum modulation signal in time to reduce the probability of interception. Different interception probabilities can be achieved by adjusting the average duty cycle. However, the data rate is sacrificed. Burst hybrid signal consists of BPSK, CSK, and MFSK spread spectrum modulated schemes. Self-synchronization and time-frequency two-dimensional search algorithm are used to synchronize the chip and carrier. The interception probability and bit-error-rate (BER) performance over multipath channel are analyzed in the simulation and validated by South Sea experiments. The experiment results showed that the data rate of one pulse can be up to 317 bps with BER under 10^-3 in the distance of 5 km, over the bandwidth of 4 kHz.