This paper presents noncooperative and cooperative security transmission schemes for multiple-input multiple-output（MIMO） Gaussian wiretap channel with one helper for antenna configuration with arbitrary number. In these two schemes, the transmitter performs beamforming based on generalized singular value decomposition（GSVD）, where an appropriate power allocation algorithm is utilized. Meanwhile, the helper sends artificial noise for higher secrecy rate. However, the transmission strategies for the artificial noise are different in the two schemes. In the first scheme, the helper adopts GSVD-based beamforming. Nevertheless, in this scheme, the impact of the artificial noise on the information signal at the receiver is not considered. To solve the problem, the helper performs space projection（SP）-based beamforming in the second scheme. In this scheme, suboptimal weighting factors are introduced to reduce the computational complexity, which can be adapted to the change of the channel quality. Theoretical analysis for the performance of the two proposed schemes is then given. Furthermore, simulation results indicate that the two presented schemes perform better than the existed schemes without helper. They also show that in the second scheme the suboptimal parameter setting is better than equal parameter setting and quite close to optimal parameter setting.
