Low signal-to-noise-ratio underwater acoustic communications using direct-sequence spread-spectrum signals

Direct sequence spread spectrum (DSSS) uses a code sequence to spread the symbols at the transmitter and a de-spreader at the receiver to recover the transmitted symbols. The de-spreader via a correlator or a matched filter provides a processing gain (matched filter gain) which enhances the symbol energy over noise thus allowing communications at low input signal-to-noise ratio. This paper analyzes DSSS data collected during the TREX04 experiment and determine the bit error rate as a function of input SNR. The data analyzed cover a total of 1160 packets with input SNR ranging from 23 dB to as low as -15 dB.