Comparison of the secrecy rates of two suboptimal transmission methods for the fading MIMO wiretap channel

Secure transmission in Multiple Input Multiple Output Multiple Eavesdropper (MIMOME) wiretap channels under quasi static Rayleigh fading is considered. Closed-form expression for the secrecy capacity of this type of channel is known only for some special cases. Therefore, we investigate the performance of two different suboptimal transmission methods under the assumption that the transmitter has full Channel State Information (CSI). In the first method the transmitter performs beamforming based on the Generalized Singular Value Decomposition (GSVD). In the second method the transmitter sends information along directions where there is gain to the legitimate receiver and artificial noise in all other directions. We determine the SNR regions where each of the methods outperforms the other.