Design and Capacity Analysis of Cellular-Type Underwater Acoustic Networks

Abstract

The design of a cellular underwater network is addressed from the viewpoint of determining the cell size and the frequency reuse pattern needed to support a desired number of users operating over a given area within a given system bandwidth. By taking into account the basic laws of underwater acoustic propagation, it is shown that unlike in the terrestrial radio systems, both the cell radius R and the reuse number N must satisfy a set of constraints to constitute an admissible solution (which sometimes may not exist). The region of admissible (R,N) , which defines the possible network topologies, is determined by the user density and the system bandwidth (rho,B) , and by the required signal-to-interference ratio and per-user bandwidth (SIR₀,W ₀) . The system capacity is defined as the maximal user density rho_max that can be supported within a given bandwidth, and it is derived analytically. Numerical examples are used to illustrate the results. It is shown that capacity-achieving architectures are characterized by N, which grows with rho_max. The capacity, as well as the range of admissible solutions, is heavily influenced by the choice of frequency region to which the bandwidth is allocated. Moving to a higher frequency region than that dictated by signal-to-noise ratio (SNR) maximization improves the SIR and yields a greater capacity. Although higher frequencies demand greater transmission power to span the same distance, they also imply a reduction in the cell size, which, in turn, provides an overall reduction in the transmission power. While complex relationships are involved in system optimization, the analysis presented offers a simple tool for the design of future ocean observation systems based on cellular types of network architecture for wide area coverage.