  This paper studies the intercept behavior of an industrial wireless sensor
network (WSN) consisting of a sink node and multiple sensors in the presence of
an eavesdropping attacker, where the sensors transmit their sensed information
to the sink node through wireless links. Due to the broadcast nature of radio
wave propagation, the wireless transmission from the sensors to the sink can be
readily overheard by the eavesdropper for interception purposes. In an
information-theoretic sense, the secrecy capacity of the wireless transmission
is the difference between the channel capacity of the main link (from sensor to
sink) and that of the wiretap link (from sensor to eavesdropper). If the
secrecy capacity becomes non-positive due to the wireless fading effect, the
sensor's data transmission could be successfully intercepted by the
eavesdropper and an intercept event occurs in this case. However, in industrial
environments, the presence of machinery obstacles, metallic frictions and
engine vibrations makes the wireless fading fluctuate drastically, resulting in
the degradation of the secrecy capacity. As a consequence, an optimal sensor
scheduling scheme is proposed in this paper to protect the legitimate wireless
transmission against the eavesdropping attack, where a sensor with the highest
secrecy capacity is scheduled to transmit its sensed information to the sink.
Closed-form expressions of the probability of occurrence of an intercept event
(called intercept probability) are derived for the conventional round-robin
scheduling and the proposed optimal scheduling schemes. Also, an asymptotic
intercept probability analysis is conducted to provide an insight into the
impact of the sensor scheduling on the wireless security. Numerical results
demonstrate that the proposed sensor scheduling scheme outperforms the
conventional round-robin scheduling in terms of the intercept probability.
