MIMO means Multiple Inputs Multiple Outputs. Such systems have been developed at first for radar applications. MIMO recently have gained interest in the underwater acoustic community because of certain benefits over traditional systems such as increase resolution or increase in signal to clutter ratio to name a few. The MIMO concept relies on multiple transmitters (Nt) sending unique and orthogonal waveforms through the environment. Several receivers (Nr) then capture environment, targets or clutter echoes. At each receiver point the total signal is filtered to separate each transmitter signal. The stage at which MIMO systems separates from multi-static systems is the information processing, which is done centrally rather that separately at each receiver node. Accessing the Nt x Nr signals requires the orthogonality of the out-coming pulses. As purely orthogonal waveforms do not exist, different approaches were developed to minimise the waveform cross-correlation. Such methods include CDMA (code division multiple access) where waveforms share the same frequencies at the same time, TDMA (time division multiple access) where waveforms share the same frequency band, but at different times, or FDMA (frequency division multiple access) where waveforms occupy different frequencies at the same time. In this paper we review the three main classes of orthogonal waveforms and present preliminary results in a test tank and real environment.
|Publication status||Published - Jun 2015|
|Event||3rd Underwater Acoustics Conference and Exhibition - Crete, Greece|
Duration: 21 Jun 2015 → 26 Jun 2015
|Conference||3rd Underwater Acoustics Conference and Exhibition|
|Period||21/06/15 → 26/06/15|