Underwater Communications Networks Model Library

The underwater communications networks (UCN) model library can be incorporated into QualNet, Exata, and NDT, adding support for underwater acoustic and optical communications.

The UCN Model will enable analysis of underwater network resiliency and self-healing performance and provide communications visualization and communications system simulations. It provides high-fidelity simulation of underwater acoustic and Free-Space Optical (FSO) communications.

Propagation Models

BELLHOP acoustic propagation model:

BELLHOP is a beam tracing model for predicting acoustic pressure fields in ocean environments. It allows for variations in the sound speed profile (SSP) that refract the beam away from the straight line path. Reflection of the ray from the ocean surface and seabed are also calculated. It also optionally includes the geometric spreading and Thorp absorption processes. Since the beam tracing is quite slow to run, the properties of the environment are calculated before running the simulation in EXata. The values obtained from beam tracing are loaded into the simulation to provide pathloss, arrival delay, and multi-path interference values.

Thorp acoustic pathloss model: 

Sound losses in the ocean are due to both spreading and absorption; both are modeled in UCN. In deep water the spreading will be spherical, and in shallow water the spreading will be cylindrical. In both cases, the loss will be in an inverse power of distance between source and receiver. Absorption is due to effects of molecules dissolved in the water. This is frequency dependent, and it results in an energy loss that is an exponential function of distance. The Thorp model of absorption includes terms for the most important modes of acoustic absorption and is valid for a range of frequencies between about 100 Hz and 50kHz.

Beer-Lambert optical pathloss model:

Light travelling through sea water is both scattered and absorbed. The coefficient of absorption and scattering are wavelength dependent and are also a strong function of the minerals dissolved in the water and particulate matter floating in it. These parameters are often referred to as the intrinsic optical parameters (IOPs) of the medium. 

Physical Layer Models

Acoustic PHY model:

This is based upon the abstract PHY model, which is described in the wireless model library. There are many sources of sound in the undersea environment. In the frequency range used for acoustic communications, the dominant sources of noise are wind and shipping. Other ambient noise sources include turbulence, rain, and thermal noise. Anthropogenic sources also include communications devices, sonar, and explosions dues to seismic exploration. Marine life, most notably whales and shrimp, can also contribute to noise. When a signal is being received at an underwater communications node, the receiver will also pick up the ambient noise. This noise, combined with signals from other transmitters and the inter-symbol interference, reduces the receiver’s ability to correctly discern the received signal.