  The Internet-of-Things (IoT) emerges as a paradigm to achieve ubiquitous
connectivity via wireless communications between kinds of physical objects. Due
to the wireless broadcasting nature and the energy constraint of physical
objects, concerns on IoT security have triggered research on cooperative
jamming based physical layer security. With the help of a cooperative jammer,
existing solutions can effectively fight against eavesdroppers. However, these
schemes are of high energy cost due to continuously transmitting jamming
signals. To reduce the energy consumption, we propose a new idea of
intermittent jamming and design five specific intermittent jamming schemes
(IJSs). By taking the transmit frame formate into account, we optimize these
IJSs from three aspects, including the jamming power, the jamming method, and
the jamming positions. Then we analyze the applicability of the proposed IJSs
according to different requirements on the synchronization, the available
jamming energy and the jamming power constraints. Extensive MATLAB experiments
are conducted on the basis of the WLAN Toolbox, which demonstrate the proposed
IJSs can effectively degrade the reception of the eavesdropper and outperform
the widespread continuous jamming scheme (CJS) when the available jamming
energy is limited.
