Analysis of using OFDM for short-range, multı-user, underwater acoustic communication

Abstract

Acoustic waves are being used in several underwater applications, such as SONARs, underwater communication systems. Most of already developed and deployed underwater communication systems use narrow band communication and lacks layered communication approach. In this thesis, we propose a spread spectrum, layered architecture for underwater communication system, such as for SCUBA divers. The communication device shall be designed such that divers can communicate with each other in shallow water, short range in a multi-user fashion and provide not only voice communication but also data transmission as well. The device shall use Orthogonal Frequency Division Multiplexing (OFDM) as a spread spectrum technique. The OFDM technique is selected from other spread spectrum techniques due to it’s inherent ability to combat the channel impairments and flexibility of implementing the communication system using software defined radio (SDR). The spread spectrum system shall operate in 100 kHz to 300 kHz frequency band using wideband acoustic transducers. In this work, we studied a layered architecture for the communication device. We mainly studied the application layer, data link layer and physical layer in order to analyze the achievable data rate and performance. In this work, we tried to find the optimal communication parameters to achieve guaranteed communication performance for possible scenarios. The communication parameters are set in order to achieve best performance for the worst condition. Using the optimal parameters, the system shall occupy 5 users voice and data communication at the same time using the entire frequency band at the same time, however with certain Grade of Service (GOS) the capacity shall be increased. The capacity of the system shall further be increased if the system uses adaptive communication parameters that are adapted to changing channel and user conditions. The system using adaptive communication parameters shall provide at most 16 users’ voice and data communication using the entire frequency band at the same time.