  Spectrum congestion and competition over frequency bandwidth could be
alleviated by deploying dual-function radar-communications systems, where the
radar platform presents itself as a system of opportunity to secondary
communication functions. In this paper, we propose a new technique for
communication information embedding into the emission of multiple-input
multiple-output (MIMO) radar using sparse antenna array configurations. The
phases induced by antenna displacements in a sensor array are unique, which
makes array configuration feasible for symbol embedding. We also exploit the
fact that in a MIMO radar system, the association of independent waveforms with
the transmit antennas can change over different pulse repetition periods
without impacting the radar functionality. We show that by reconfiguring sparse
transmit array through antenna selection and reordering waveform-antenna
paring, a data rate of megabits per second can be achieved for a moderate
number of transmit antennas. To counteract practical implementation issues, we
propose a regularized antenna selection based signaling scheme. The possible
data rate is analyzed and the symbol/bit error rates are derived. Simulation
examples are provided for performance evaluations and to demonstrate the
effectiveness of proposed DFRC techniques.
