On Optimal Artificial-Noise Assisted Secure Beamforming for Fading Eavesdropper Channel
Date Issued
2011
Date
2011
Author(s)
Lai, Szu-Hsiang
Abstract
In this thesis we consider the secure transmission in fading channels with only the statistics of the eavesdropper’s channel state information known at the transmitter. We optimize the celebrated artificial-noise (AN) assisted beamforming, which was studied by Goel and Negi using heuristically selected AN and beamforming directions. We find that Goel and Negi’s AN selection is strictly sub-optimal. On the contrary, one may inject AN to the beam direction of the message to improve the secrecy rate performance. We prove that for a multiple-input, single-output, single-eavesdropper antenna system, the optimal transmission scheme is a beamformer. With the selected beamformer in the direction of main channel, we then prove that for the AN projecting in the null space of the legitimate channel, uniformly allocating power is optimal. We also provide the necessary condition for the proposed AN selection to be optimal. Simulation results show that our AN selection outperforms Goel and Negi’s, especially when the legitimate channel is poor. In particular, the regime with non-zero secrecy rate is enlarged, which can significantly improve the connectivity of the secure network when the AN assisted beamforming is applied.
Subjects
eavesdropper
secure
artificial noise
communication
fast fading
beamforming
Type
thesis
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