  A novel monostatic multiple-input multiple-output (MIMO) dual-function radar
communication (DFRC) system is proposed, that uses the available bandwidth
efficiently for both sensing and communication. The proposed system, referred
to as Shared-Subcarriers DFRC (SS-DFRC) transmits wideband, orthogonal
frequency division multiplexing (OFDM) waveforms and allows the transmit
antennas to use subcarriers in a shared fashion. A novel, low complexity target
estimation approach is proposed to overcome the coupling of radar target
parameters and transmitted symbols that arises in that case. When all
subcarriers are used in a shared fashion, the proposed system achieves high
communication rate but its sensing performance is limited by the size of the
receive array. We show that when some of the subcarriers are reserved for
exclusive use by one transmit antenna each (private subcarriers), the
communication rate can be traded off for improved sensing performance. The
latter can be achieved by using the private subcarriers to construct a larger
aperture virtual array that yields higher resolution angle estimates. The
system is endowed with beamforming capability, via waveform precoding, where
the precoding matrix is optimally designed to meet a joint
sensing-communication system performance metric.
