Diversity Schemes for a Large MIMO Acoustic Transmitter on a C2000 Micro-controller

Two diversity schemes are implemented for a small form-factor, large MIMO acoustic transmitter for an underwater IoT application with a high reliability requirement and target data rate of 20 kbps using a Texas Instruments C2000 microcontroller. The first is linear precoding scheme which can yield both diversity and multiplexing gain and may use channel state information at the transmitter (CSIT). The second is the Space-Time Block Code which provides optimal diversity at the cost of reduced rate and no need of CSIT. The digital processing of the transmitter design, such as channel coding, interleaving, phase-shift-keying (PSK) bit to symbol mapping, and the diversity schemes are implemented in the software via the C2000 CPU and TMU (Trigonometry Multiplier Unit). The passband modulation is achieved by multiple EPWM (enhanced Pulse width modulation) channels of the C2000. The transmitter can encode frames at 21.3 kbps in the worst case and will allow the streaming of data. The carrier-modulated BPSK, QPSK, and 8-PSK symbols are recovered and shown to have an MSE of 3% or less with the ideal constellation. The operation of the precoder and STBC diversity schemes are verified from the generated passband waveform.