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An effective method was recently proposed to increase secrecy capacity in MIMO wireless communication systems. By adding artificially generated noise signal into the information-bearing signal, this method can degrade the eavesdropper's receiving signal, but does not affect the desired receiver. This method, however, can only be used in systems where the transmit antenna has more elements than the receive antenna. In this paper, we present a novel noise signal generation approach to enable secure wireless communications in a transmit-receive diversity system. In this approach, we generate our jamming noise signal based on the null space of an equivalent channel of the system. The presented wireless security mechanism can be applied to systems with arbitrary antenna configurations, unlike existing methods that only work for specific array configurations. In addition, the eavesdropper cannot increase its information detection capability by employing more antenna elements. With this scheme, we also enable more degrees of freedom for selecting parameters for jamming noise signal generation, making the decoding at the eavesdropper even harder due to the increased search space. We performed Monte Carlo simulations to evaluate the proposed method in an urban macro cellular environment using the 3rd Generation Partnership Project (3GPP) spatial channel model. Our simulation results show that the proposed approach can significantly increase secrecy capacity, which is independent of the eavesdropper's position and the element number of its antenna.