In paper 'To Harvest and Jam: A Paradigm of Self-Sustaining Friendly Jammers for Secure AF Relaying', it mentioned that the robust transmit covariance design for the secrecy rate maximization in a multiple-input-single-output (MISO) channel overheard by multi-antenna eavesdroppers was considered, and the enhanced secrecy performance was further achieved by
introducing a friendly jammer in the same scenario in which a joint optimization of the robust transmit covariance and power allocation between the source and the helper was
studied via geometric programming. The enhancement is from another related paper that you've read. Provide the full name of that paper.
