  We consider the problem of secure communications in a MIMO setting in the
presence of an adversarial jammer equipped with $n_j$ transmit antennas and an
eavesdropper equipped with $n_e$ receive antennas. A multiantenna transmitter,
equipped with $n_t$ antennas, desires to secretly communicate a message to a
multiantenna receiver equipped with $n_r$ antennas. We propose a transmission
method based on artificial noise and linear precoding and a two-stage receiver
method employing beamforming. Under this strategy, we first characterize the
achievable secrecy rates of communication and prove that the achievable secure
degrees-of-freedom (SDoF) is given by $d_s = n_r - n_j$ in the perfect channel
state information (CSI) case. Second, we consider quantized CSI feedback using
Grassmannian quantization of a function of the direct channel matrix and derive
sufficient conditions for the quantization bit rate scaling as a function of
transmit power for maintaining the achievable SDoF $d_s$ with perfect CSI and
for having asymptotically zero secrecy rate loss due to quantization. Numerical
simulations are also provided to support the theory.
