Effect of ambient noise on OFDM signals

Underwater sensor nodes find applications in oceanographic data collection, pollution monitoring, offshore exploration, disaster prevention, assisted navigation and tactical surveillance applications. Moreover, unmanned or autonomous underwater vehicles equipped with sensors enables the exploration of natural undersea resources and gathering of scientific data in collaborative monitoring missions. Underwater acoustic networking is the enabling technology for these applications. Underwater networks consist of a variable number of sensors and vehicles that are deployed to perform collaborative monitoring tasks over a given area, communicating with each other through acoustic signals. Electromagnetic waves as well as optical waves do not propagate over long distances. Current underwater transmission techniques utilize sound waves and the velocity of sound in water is approximately 1500m/s; the resultant communications have problems like multipath propagation, low bandwidth, ambient noise, etc.. This paper presents a study of the ambient noise,simulates underwater acoustic communication with OFDM using 16-QAM and compares it with that of an Additive White Gaussian Noise (AWGN) channel. For simulating underwater acoustic communication, Bellhop is used for generating channel impulse response which is convolved with the transmitted signal to model multipath propagation.