  The problem of jamming on multiple-input multiple-output (MIMO) Gaussian
channels is investigated in this paper. In the case of a single target
legitimate signal, we show that the existing result based on the simplification
of the system model by neglecting the jamming channel leads to losing important
insights regarding the effect of jamming power and jamming channel on the
jamming strategy. We find a closed-form optimal solution for the problem under
a positive semi-definite (PSD) condition without considering simplifications in
the model. If the condition is not satisfied and the optimal solution may not
exist in closed-form, we find the optimal solution using a numerical method and
also propose a suboptimal solution in closed-form as a close approximation of
the optimal solution. Then, the possibility of extending the results to solve
the problem of multi-target jamming is investigated for four scenarios, i.e.,
multiple access channel, broadcasting channel, multiple transceiver pairs with
orthogonal transmissions, and multiple transceiver pairs with interference,
respectively. It is shown that the proposed numerical method can be extended to
all scenarios while the proposed closed-form solutions for jamming may be
applied in the scenarios of the multiple access channel and multiple
transceiver pairs with orthogonal transmissions. Simulation results verify the
effectiveness of the proposed solutions.
