  Cooperative communication has been widely used to provide spatial diversity
benefits for low-end user equipments, especially in ad hoc and wireless sensor
networks. However, the lack of strong authentication mechanisms in these
networks leaves them prone to eavesdropping relays. In this paper, we propose a
secure orthogonal frequency division multiplexing (OFDM) transmission scheme,
where the destination node transmits a jamming signal over the cyclic prefix
(CP) duration of the received signal. Simulation results verify that as long as
at least a part of the jamming signal falls to the actual data portion of the
eavesdropping relay, it spreads through all the data symbols due to the fast
Fourier transformation (FFT) operation, resulting in degraded interception at
the eavesdropper.
