Interaction and Secrecy in Gaussian Diamond Relay Networks

In this thesis, the physical layer secrecy for several Gaussian network models are studied. We first establish the secure degrees of freedom (d.o.f.) of helper-assisted Gaussian wiretap channel with shared keys between the transmitter and the helpers. As a natural extension, we next consider the Gaussian diamond wiretap channel where the relays can obtain common randomness from the source node. Secure d.o.f. for the diamond wiretap channel is established and upper and lower bounds for the multi-relay case are also provided. We then study the diamond channel with conferencing links and investigate the effects of the conferencing links under Gaussian channel as well as binary adder MAC channel. Finally we discuss the artificial noise transmission for secrecy with constant-amplitude constraint for the beamforming vector. The effects of such constraint are examined and algorithms to solve for the beamforming vector are given.