Secrecy Rate Improvement Based on Joint Decoding in MIMO Wiretap Channels With a Helping Interferer

In a wiretap channel, a transmitter sends confidential messages to an intended legitimate receiver in the presence of an eaves-dropper. An external helper can assist secret communication by transmitting independent artificial interference to confuse the eavesdropper. We consider that the legitimate receiver jointly decodes messages from the transmitter and interference from the helper to boost the secrecy rate. In the discrete-memoryless wiretap channel with a helper, we characterize the achievable secrecy rates by comparing the strength of interference at the legitimate receiver and at the eavesdropper. Based on these secrecy rates, we formulate a secrecy rate maximization problem in Gaussian multiple-input multiple-output (MIMO) wiretap channels with a helping interferer, and present an alternating optimization algorithm. Numerical results show that the proposed joint decoding achieves higher secrecy rates than the conventional separate decoding.