Secure transmission using an untrusted relay with scaled compute-and-forward

A two-hop channel is considered, in which the source wants to send information to the destination while keeping the information confidential from the relay. A novel lattice chain and compute-and-forward based scheme is proposed in which the destination provides cooperative jamming. Channel state information is used at the source and the destination to scale the encoding lattices for the message and the jamming signal according to the channel gains. We compare the achievable secrecy rate of our scheme with an upper bound and with the achievable secrecy rate of other schemes. It follows that our scheme outperforms all existing schemes except in the low power region.