Adaptive artificial noise transmission against randomly distributed eavesdroppers

In this paper, we investigate the design of the artificial-noise-aided multi-antenna transmission in slow fading channels coexisting with randomly located eavesdroppers. Our objective is to maximize the outage-constrained secrecy throughput under an on-off transmission strategy in which when to start information exchange depends on the main channel´s quality. To achieve our goal, we propose to adjust all the transmission parameters, including the wiretap code rates, the transmission threshold of the on-off strategy, and the power allocation between the confidential signal and artificial noise, adaptively according to the main channel´s instantaneous channel state information. We formulate the optimization issue and provide explicit solutions on these transmission parameters. We further demonstrate numerical results to verify our theoretical analysis and show some insights into the secure transmission design.