OFDM kullanan su altı akustik modem

This thesis is about design, simulation and testing of an underwater acoustic modemusing OFDM. The thesis work combines a theoretical part, whose objective is to understandthe appropriate techniques to deal with the characteristics of the targeted channel, simulationsand a practical part regarding the system deployment and experimental tests. Therehas been a great growing interest in transmitting real-time data and video. Unmanned underwatervehicles (UUVs) for military and scientific applications have become important.Building distributed and scalable underwater wireless sensor networks (UWSN) that willbring significant advantages and benefits to underwater applications, such as ocean observationfor scientific exploration, commercial exploitation, coastline protection and targetdetection in military events has been in the scope of researchers. Based on these, designinga concrete system with high data rate will benefit many underwater acoustic (UWA) applications.The existing systems in literature use single carrier transmission and rely on linearor non-linear equalization techniques to suppress inter-symbol interference (ISI), howeverthis requires complex equalizers and results in low data rates. Therefore we concentrate onmulticarrier modulation. In this thesis ZP-OFDM (Zero Padded-Orthogonal Frequency DivisionMultiplexing) receiver is built, where CFO (Carrier Frequency Offset) compensation,pilot-tone based channel estimation, and data demodulation are carried out on the basisof each OFDM block. The implemented OFDM system has been developed in MATLAB.MATLAB scripts generate a data burst that contained OFDM blocks, and then they aretransmitted to the hardware from a laptop by using a Data Acquisition (DAQ) Card. Atthe other side of the system, the receiver laptop gets the data by using a DAQ Card. As thedata is received, MATLAB scripts are demodulated and data is detected. Simulations aimto provide correct implementation of all the algorithms by coupling the generated OFDMsignal to a channel using Bellhop underwater channel model and noise addition algorithm,that artificially introduces some of the real channel effects into the signal. The method istested in a shallow-water experiment at Bilkent Lake. Over a bandwidth of 12 kHz, thedata rate is 13.92 kb/s with QPSK modulation, when the number of subcarriers was 1024.Bit-error-rate (BER) is less than 9x10^-2 without any coding.