4G Techniques For Underwater Acoustic Communications

As the backbone of the 4G wireless communication, the combination of Orthogonal Frequency Division Multiplexing(OFDM) and Multiple Input Multiple Output(MIMO) techniques has raised great popularity in marineacoustic communication these years. OFDM technique divides the original channel bandwidth into a bank of narrow-band sub channels so that in each sub carrier channel, the channel frequency response can be approximatelty treated as flat fading. By adding signal on each sub carrier and transmitting signal in parallel form, the problem of signal delay and dispersion, brought by frequency selective character of the original signal, can be eliminated to a great deal. As the sub carriers are orthogonal to each other, the bandwidth among each other can be overlapped, the channel bandwidth efficiency therefore is improved. As for MIMO system, the multiple transmission links it introduces decreases the possibility of channel deep fade to a large deal so that the channel capacity as well as data rate can be improved.In this report, we built a 2×2 MIMO system of high-capacity for the shallow area of underwater wireless communication. The model was established upon a typical commercial projector and hydrophone with refer to OFDM parallel transmission. To imitate the real underwater environment, we invited the Rayleigh fading and Added White Gaussian Noise(AWGN). The model is designed for the distance of a few kilo-meters. Simulation was then carried out on MATLAB with the marine transceivers. Frequencies varied from 10 to 100 kHz. OFDM subcarriers were set to 128 with QPSK modulation. Finally, the BER graph indicated that the channel performance with OFDM MIMO would be much superior to the Single Input Single Output(SISO) channel without OFDM.