On the zero forcing optimality for friendly jamming in MISO wiretap channels

Abstract

We study beamforming strategies for a friendly jammer (or helper) in a MISO wiretap channel. We characterize the beamforming strategy for the maximization of the secrecy rate and analyze the optimality of zero forcing. We show that zero forcing is optimal up to a small constant for high SNR. For low SNR, we derive optimal beamforming strategies for transmitter and helper in terms of minimum Eb/N0 and wideband slope.