Non-orthogonal pilot pattern design and sparse channel estimation for underwater acoustic MIMO-OFDM systems

This paper proposes a novel non -orthogonal pilot pattern design method for underwater acoustic (UWA) multiple -input -multiple -output orthogonal frequency -division multiplexing (MIMO-OFDM) systems, leveraging compressive sensing (CS) channel estimation. This approach adopts the mutual incoherence property (MIP) and enhances pilot density without increasing pilot overhead. We conducted rigorous mathematical derivation to generate the explicit formula for the non -orthogonal pilot pattern with the mutual coherence of zero. In addition, we estimate multipath delay and amplitude by employing parallel orthogonal matching pursuit (OMP) channel estimation. The co -channel interference (CCI) is eliminated from the systems with the proposed non -orthogonal pilot pattern to estimate the channel coefficients from two transmitters without interference in a single iteration. Simulations and lake trial results demonstrate the superior performance of the proposed non -orthogonal pilot pattern over the orthogonal and existing non -orthogonal pilot patterns in terms of normalized mean square error (NMSE) of channel estimation and bit error rate (BER). The 2 x 8 UWA MIMO-OFDM system achieves a data rate of 78.11 kbps with a BER of 1.42x10-4 in the lake trial over the communication distance of 773 m.