  In this paper, we investigate opportunistic relaying and jamming techniques
and develop relay selection algorithms that maximize the secrecy rate for
multiuser buffer-aided relay networks. We develop an approach to maximize the
secrecy rate of relay systems that does not require the channel state
information (CSI) of the eavesdroppers. We also devise relaying and jamming
function selection (RJFS) algorithms to select multiple relay nodes as well as
multiple jamming nodes to assist the transmission. In the proposed RJFS
algorithms inter-relay interference cancellation (IC) is taken into account. IC
is first performed to improve the transmission rate to legitimate users and
then inter-relay IC is applied to amplify the jamming signal to the
eavesdroppers and enhance the secrecy rate. With the buffer-aided relays the
jamming signal can be stored at the relay nodes and a buffer-aided RJFS
(BF-RJFS) algorithm is proposed. Greedy RJFS and BF-RJFS algorithms are then
developed for relay selection with reduced complexity. Simulation results show
that the proposed RJFS and BF-RJFS algorithms can achieve a higher secrecy rate
performance than previously reported techniques even in the absence of CSI of
the eavesdroppers.
