In this paper, we examine the secrecy performance of two-way relaying betweena multiple antenna base station (BS) and a single antenna mobile user (MU) inthe presence of a multiple antenna friendly jammer (FJ). We consider theuntrusted relaying scenario where an amplify-and-forward relay is both anecessary helper and a potential eavesdropper. To maximize the instantaneoussecrecy sum rate, we derive new closed-form solutions for the optimal powerallocation (OPA) between the BS and MU under the scenario of relaying withfriendly jamming (WFJ). Based on the OPA solution, new closed-form expressionsare derived for the ergodic secrecy sum rate (ESSR) with Rayleigh fadingchannel. Furthermore, we explicitly determine the high signal-to-noise ratioslope and power offset of the ESSR to highlight the benefits of friendlyjamming. Numerical examples are provided to demonstrate the impact of the FJ'slocation and number of antennas on the secrecy performance.
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