  In this paper we address a sum secrecy rate maximization problem for a
multi-carrier and MIMO communication system. We consider the case that the
receiver is capable of full-duplex (FD) operation and simultaneously sends
jamming signal to a potential eavesdropper. In particular, we simultaneously
take advantage of the spatial and frequency diversity in the system in order to
obtain a higher level of security in the physical layer. Due to the non-convex
nature of the resulting mathematical problem, we propose an iterative solution
with a guaranteed convergence, based on block coordinate descent method, by
re-structuring our problem as a separately convex program. Moreover, for the
special case that the transmitter is equipped with a single antenna, an optimal
transmit power allocation strategy is obtained analytically, assuming a known
jamming strategy. We also study a FD bidirectional secure communication system,
where the jamming power can be reused to enhance the sum secrecy rate. The
performance of the proposed design is then numerically evaluated compared to
the other design strategies, and under different system assumptions.
