Frequency and code modulations for underwater acoustic spread spectrum communication

We compare two orthogonal modulation schemes for underwater acoustic sensor network using spread spectrum communication. The first which has been recently published, employs a frequency modulation signals spread by the same code. As an alternative, we propose to modulate the signals by using a different orthogonal code for each signal. Simulations and sea trial results demonstrate that the performance of both schemes is quite similar. In general, both schemes provide more flexibility of the system design. The first scheme is mainly suitable to a memory resources limited platform and a high number of network nodes, whereas, the second scheme has better utilization of the bandwidth and low computational complexity.